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MITSUBISHIELECTRIC

VOL. 81/DEC. 1997

New Frontiers of Mechatronics in Manufacturing Processes Edition

TECHNICAL REPORTSFOREWORD

The Character and Roles of Electrical Machining .................................. 1by Takahisa Masuzawa

Extending the Limits of Machining Technology ..................................... 2by Mitsuo Yonetani and Tamio Takawashi

The Latest Technologies for Die-Sinking EDMs ..................................... 5by Koji Akamatsu and Atsushi Taneda

An Electrical-Discharge Scanning Machine ............................................ 8by Masaru Shinkai and Toshio Suzuki

FX Series General-Purpose Wire-Cut Electrical-DischargeMachines ................................................................................................... 11by Makoto Tanaka and Seiji Sato

Machining Technologies for Highly Precise Wire-CutElectrical-Discharge Machines ................................................................ 14by Takeshi Yatomi and Yutaka Terada

The LXP Series CO 2 Laser Processing Machine .................................... 17by Mitsunobu Oshimura

A Short-Pulse CO 2 Laser Processor for PCB Manufacturing ............... 20by Masanori Mizuno and Tsukasa Fukushima

A High-Brightness Nd:YAG Laser Processing Machine ....................... 22by Akihiro Otani

An Electron-Beam Processing Machine for Micro-ScaleWelding and Joining Applications .......................................................... 25by Kyuzo Arakawa and Masao Kikuchi

Excimer Laser Processing System Using Holographic OpticalElements ................................................................................................... 27by Yasushi Minamitani and Tomohiro Sasagawa

MITSUBISHI ELECTRIC OVERSEAS NETWORK

Editor-in-Chief

Editorial Inquiries

●Vol. 81/Dec. 1997 Mitsubishi Electric ADVANCE

Mitsubishi Electric Advance is publishedquarterly (in March, June, September, andDecember) by Mitsubishi Electric Corporation.Copyright © 1997 by Mitsubishi ElectricCorporation; all rights reserved.Printed in Japan.

A Quarterly Survey of New Products, Systems, and TechnologyOur cover is a montage of representativemodels from our range of industrial process-ing equipment. They represent revolutionaryadvances in industrial processing at theborderline between mechanical and electronictechnology known as “mechatronics,” usingthe spectacular progress being made inelectronics to meet the increasingly severedemands for high precision, uniformly highquality and higher productivity in many sectorsof industry, including automotive engineering.

Note: DIAX is a trademark registered in Japan.

Product Inquiries

Shin Suzuki

Jozo NagataToshimasa UjiKazumi IwaizumiYasuo KobayashiMasao HatayaGunshiro SuzukiSeiya InoueHiroaki KawachiAkihiko NaitoNobuo YamamotoShingo MaedaToshikazu SaitaHiroshi TottoriKouji Kadota

Tamio Takawashi

Kouji KadotaCorporate TotalProductivity Management& Environmental ProgramsMitsubishi Electric Corporation2-2-3 Marunouchi Chiyoda-ku,

Tokyo 100-0005, JapanFax 03-3218-2465

Kazumi IwaizumiGlobal Strategic Planning Dept.Corporate Marketing GroupMitsubishi Electric Corporation2-2-3 Marunouchi Chiyoda-ku,

Tokyo 100-0005, JapanFax 03-3218-3455

Orders:Four issues: ¥6,000(postage and tax not included)Ohm-sha Co., Ltd.1 Kanda Nishiki-cho 3-chomeChiyoda-ku, Tokyo 101-0054, Japan

Editorial Advisors

New Frontiers of Mechatronics inManufacturing Processes Edition

CONTENTS

Vol. 81 Feature Articles Editor

TECHNICAL REPORTS

*Dr. Takahisa Masuzawa is a professor at the Institute of Industrial Science, Tokyo University.

ForewordThe Character and Roles of Electrical Machining

by Takahisa Masuzawa*

T he technologies of the milling and grinding machines that have been a familiar sight in factories eversince the industrial revolution are now being supplemented by non-traditional methods of processingbased on quite different principles and approaches developed in recent years. These methods were

developed specifically to perform processing impossible, either in principle or in practice, with conventionalmethods.

An example of this is the dies for die-cast molding, which are made of tempered steel. These dies couldnot be ground to shape using tools made of the same tempered steel, so they had to be machined before beingtempered. The deformations that occurred as a result of the tempering process had to be corrected in asubsequent process that was both difficult and time-consuming. Then came the innovation of electrical-discharge machining (EDM).

EDM uses the repeated generation of small electrical “spark” discharges to create instantaneous localizedhigh temperatures that melt and disperse the material being machined, independent of its degree of hard-ness. This enables the direct, high-precision processing of tempered steel. Again, because there is no need torotate the workpiece or the jigs and tools, complex three-dimensional shapes including sharp corners,virtually impossible to create with conventional machining, rapidly became possible. This method has beenwidely adopted in machine shops and is indispensable in producing dies, etc.

Many such non-traditional methods use electrical energy, for example laser-beam, electron-beam, ion-beam and electrolytic methods. Their operating principles are fundamentally different from conventionalmethods of milling, etc. that remove material by force, and this gives them an overwhelming advantage incertain applications. We have seen how this is so for EDM; laser-beam processing makes a similar use ofheat. Because it uses no force, it is readily used to cut thin sheets that have already been shaped withoutdeforming them, something impossible using conventional methods. While it may not provide quite thesame high precision as EDM, it is extremely fast, making it ideal for mass production.

Naturally, these electrical methods can also be used for normal materials and common shapes, an areawhere they come into competition with conventional methods. Which method will be selected in aparticular application generally depends upon technical issues and resources. Currently, a large proportionof such applications are handled by conventional milling and other machinery, but the inroads being madeby electrical methods are too large to be ignored.

Most important, however, are the large inherent advantages of these methods, and they alone offer theprospect of responding to the future needs of the factory shop floor. With current moves towards moresophisticated materials and more severe machining requirements, for instance in amorphous materials,fiber-reinforced materials, micro-processing, and in the high-speed production of small lots of multipleproduct variants, electrical methods are becoming increasingly important. As the technologies improve, theprocessing systems that employ them will also find wider applications in contention with conventionalmethods. ❑

December 1997 · 1

TECHNICAL REPORTS

by Mitsuo Yonetani and Tamio Takawashi*

This report reviews advances in three specialtymachining technologies: electrical-dischargemachining, laser processing and electron-beamprocessing. These methods have extended thelimits of manufacturing technology and arecontributing to dramatic innovations in prod-uct development and manufacturing capabili-ties.

Electrical-Discharge Machines (EDMs)Electrical-discharge processing has found exten-sive use in die-manufacturing for high-precisionforging, casting, molding and stamping appli-cations in the automotive, electric and electron-ics industries.

DIE-SINKING EDMs. A major advance in machin-ing quality has been achieved by suspendingfine silicon particles in the dielectric fluid. Thesilicon particles improve the dielectric perfor-mance, yielding hard die surfaces that resistabrasion and corrosion, and are free of the heat-induced surface cracks and arcing discolorationthat accompany the use of conventional dielec-trics. In addition, maximum tool area undermirror finishing has increased to 100cm2, andthis capacity increase can be utilized for pro-ductivity enhancement.

Other problems of die-sinking EDMs are thedelays and cost of manufacturing the speciallyshaped copper or graphite electrodes requiredto transfer a specific pattern to a workpiece.These factors are especially noted in dies forminiature electronic components, since thecomplicated electrode shapes and patterns re-quire numerous machining operations. Low-wear machining conditions spread the cost overa larger number of dies, but only at the expenseof somewhat lower machining speeds.

Mitsubishi Electric has developed a techniqueusing copper pipe electrodes to produce the samesorts of shapes as die-sinking EDMs withoutthe cost and trade-offs of specialty electrodemanufacture. An “electrical-discharge scan-ning” process controls the pipe electrode underhigh-wear conditions for faster machining. Ac-curacy is maintained by measuring and com-pensating for electrode wear in realtime, which

Extending the Limits ofMachining Technology

yields die quality comparable to die-sinkingEDMs (Fig. 1) and vastly superior to that achievedwith a simple copper rod.

WIRE-CUT EDMs. Better performance, function-ality and cost effectiveness are bringing wire-cut EDMs into competition with mechanicaldie-production processes, especially in the semi-conductor and electronic component industrieswith their demands for high-quality, high-pre-cision and short product development cycles.

Wire-cut EDMs can produce high-precisiondies for stamping IC lead frames with greaterconsistency than mechanical processing. Thecorporation has developed wire-cut EDM tech-nologies for this application including anantielectrolysis power supply that minimizessurface stress and reduces the thickness of thestressed layer in both first-cut and finish ma-chining, and an ultrasmooth surface finishingpower supply (FSII) that yields a surface finishcomparable to the best mechanical processes(Fig. 2).

The next generation of high-precision wire-cut EDMs is incorporating highly rigid struc-tural members, precise wire tension control,discharge monitoring and control, and otheradvanced technologies that promise even wideruse of wire-cut EDM processing in semicon-ductor and electronic component manufacture.We expect to see continued improvements in

Fig. 1 A tiny die used in electronic component manufacturing.

2 · Mitsubishi Electric ADVANCE

*Mitsuo Yonetani is with the Factory Automation Systems Group and Tamio Takawashi with the Nagoya Works.

TECHNICAL REPORTS

Fig. 2 An example of ultraprecise die machining by the FSII EDM power supply.

Fig. 3 Blind via hole processing by a short-pulse CO2 laser.

December 1997 · 3

precision, cost and processing speed in the fu-ture.

Laser Processing MachinesRecent increases in processing speed make la-ser processing machines increasingly practicalfor cutting shapes out of sheet metal. Laser pro-cessing machines are beginning to replace theseveral hundred thousand turret-head stamp-ing machines currently used in Japan, and canserve as the basis for a cost effective sheet-metalprocessing cell.

Internationally, demand for three-axis laserprocessing machines is high due to strong in-vestment in high-productivity equipment, par-ticularly in large-scale sheet-metal formingoperations where minimizing die productioncosts is essential.

Laser-based welding and surface treatmentprocesses are also being developed for the spe-cialty processing niche that accounts for about10% of the market.

The corporation is now producing CO2 lasers,high-output solid-state yttrium aluminum gar-net (YAG) lasers and excimer lasers that per-form cutting, welding and hole-drilling onmicromachining scales beyond the capabili-ties of mechanical processing. Developmentcontinues in the areas of laser oscillators, con-trol systems and peripheral technologies to sup-port even wider applications.

SHORT-PULSE CO2 LASER PROCESSING MACHINES.Advanced CO2 laser technology is being appliedto hole drilling in printed-circuit boards (PCBs).To help shrink the PCBs used in compact infor-mation equipment, 300µm-diameter throughholes and blind via holes are being introduced(Fig.3). The corporation has developed a high-speed laser drilling system for producing theseholes using a three-axis orthogonal CO2 laserwith high peak power and short pulse duration,a special optical system and a high-speed,ultraprecise table drive. The system can drillholes in conventional glass-epoxy PCB materi-als with minimal thermal effects. This solutionis more general than drilling by photochemicalreaction, which requires a special PCB mate-rial. Continued improvements in the laser drill-ing system are expected to lead to widerapplications and fine-pattern processing capa-bilities approaching the minimum hole diam-eter for the optical wavelength.

HIGH-OUTPUT SOLID-STATE LASER PROCESSINGMACHINES. YAG lasers are being applied to weld-ing applications previously performed by CO2

lasers. Conventional YAG lasers have a practi-cal output ceiling of about 100W. Higher out-puts cause thermal distortion to occur in theYAG rod, resulting in a large spot size that slowsdeep welding operations. The corporation hasbroken through this barrier by developing a

TECHNICAL REPORTS

200W YAG laser suitable for deep welding andcutting. The laser minimizes thermal effectsby more uniformly exciting the YAG rod andintroducing technology that eliminates focus-ing errors associated with thermal lensing ef-fects.

EXCIMER LASER PROCESSING MACHINES. Excimerlasers efficiently produce light in the ultravio-let region. Because of the high photon energyinvolved, excimer lasers can directly cut thechemical bonds of a polymer material in a pro-cedure known as ablation processing withoutthe thermal effects experienced when using aCO2 or YAG laser. The short wavelength alsoallows better focusing, with a minimum spotsize in the tens-of-microns range for fine-pat-tern processing. The promise of excimer lasersmust be balanced against the high running costper unit of energy output.

The corporation is currently studying the useof holograms with excimer lasers because ho-lograms can create patterns without maskingthe beam. By boosting the effective light utili-zation by a factor of five to fifty, this techniqueallows the use of much smaller laser equipmentfor the same application.

Electron-Beam Processing MachinesElectron-beam processing offers small spot di-ameter, high speed and high positioning accu-racy, and numerous potential applications inelectronic component and ceramic packagemanufacturing are currently under investiga-tion. Although the immediate goal of highproductivity is somewhat hampered by a re-quirement for processing under vacuum, ex-tremely low operation cycle times have beenachieved utilizing an electron-beam processingmachine fitted with a continuous evacuationsystem. Productivity has been enhanced bydeveloping a beam deflection system capable ofprocessing multiple workpieces in a single pass.Applications of electron-beam processing arepoised to expand from a strong automotive baseinto precision electronic components.

4· Mitsubishi Electric ADVANCE

Owing to technologies such as those listedabove, Mitsubishi Electric's line of advancedprocessing machines continue to receive highpraise for performance from various industries.❑

TECHNICAL REPORTS

Resistorless power supply

Total 8,000W

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

Pow

er c

onsu

mpt

ion

(W)

Internal dissipation 5,500W (100A x 55V)

Processing power 2,500W (100A x 25V)

Total 3,700W

Internal dissipation 1,200W

Total power consumption reduced by about 50%

Internal dissipation reduced by 20%

Previous power supply

The Latest Technologies forDie-Sinking EDMs

by Koji Akamatsu and Atsushi Taneda*

*Koji Akamatsu and Atsushi Taneda are with the Nagoya Works.

December 1997 · 5

Mitsubishi Electric has introduced several newtechnologies for its VX and EX series of die-sinking electrical-discharge machines (EDMs).The FP power supply for the EDMs uses solid-state power circuits for reduced size and powerdissipation. A silicon powder-mixed EDM sys-tem has been developed that yields a smoothfinish, and fuzzy-logic adaptive control tech-nology achieves stable, high-speed processing.

Resistorless Solid-State Power SupplyThe FP power supply features a Mitsubishi-developed low-loss switching control systemfor regulating the peak discharge current. Thesystem dramatically improves the power effi-ciency of the VX and EX die-sinking EDMs.Fig. 1 shows the efficiency improvement ofthe resistorless power supply circuit. Theresistorless circuit reduces the internal dissi-pation of conventional circuits by about 80%and reduces the total power consumption byhalf. In addition, current feedback control inthe power supply yields stable, reproduciblemachining performance. The power supply ishalf the size of previous units, and its lowerdissipation reduces thermal effects on the EDMequipment. Lower dissipation also allows theuse of indirect cooling, which gives the benefitof enhanced reliability.

Machining with a Silicon Powder SuspensionFig. 2 shows the VPX10 EDM which utilizesdielectric fluid with a silicon powder suspen-sion. Use of silicon powder in the dielectric fluidmakes it possible to perform rapid machiningto a surface roughness of better than 1µmRmax.This process requires a special machining tankfitted with an agitator and a special dielectricfluid supply unit. The agitator maintains astable concentration of silicon, which has aspecific gravity three times that of the dielec-tric fluid. The agitator sprays the dielectric fluidthrough small holes and uses the kinetic en-ergy of the fluid to carry the powder. CAE soft-ware was used to model the three-dimensionalfluid flow in the tank, and the nozzle place-ment and throughput were optimized to holdvariations in silicon powder concentration to

Fig. 1 Power consumption of EDM power supplies.

Fig. 2 The VPX10 EDM for silicon powder-mix machining.

half that of previous units.

Bridge Elimination CircuitSilicon powder can result in surface pitting ofcomplicated shapes during first-pass machin-ing when sludge trapped in the machining gapcauses a short circuit from the electrode to theworkpiece (Fig. 3a). Fig. 4 shows the magnetic

TECHNICAL REPORTS

Fig. 3 Short-circuited machining gap.

Fig. 4 Magnetic field created in the machininggap by a short circuit.

field that surrounds this current. The field tendsto move the sludge toward the central axis,maintaining the short circuit even as the toolseparates from the workpiece (Fig. 3b). This con-tinued concentrated discharge causes pitting.

The FP power supply has a function thatprevents sludge concentration during short-circuiting. When a short circuit continues for acertain period, a brief current pulse is appliedto blow out the sludge and clear the short cir-cuit. This function increases machining speedand improves the surface finish.

A Machining Application Using SuspendedSilicon PowderFig. 5 shows a cold-forging die produced by anEDM utilizing suspended silicon. Hand polish-ing is unnecessary, and the absence of cracks

Another sludge particle

Magnetic field direction

B

Sludge particle mass

Current direction

Workpiece

+

Machining stress sensor

MF sensor Machining area sensor

Fuzzy Pro power supply control functions


Electrode

Electrode

a) Initial short circuit

b) Short circuit is maintained as tool moves away

Short-circuit current

Short-circuit current

Tool motion Sludge Sludge

WorkpieceWorkpiece

Fig. 5 An SKD61 cold-forging die machined bythe VPX10 to a surface roughness of0.8µmRmax using a copper tool. Machiningtime is six hours with oil dielectric fluidand 3.7 hours with mixed silicon powder.

and pits extends die life.

“Fuzzy Pro” Adaptive Control SystemThis control systems consists of three new sens-ing functions and a digital control unit thatincorporates the know-how of a skilled opera-tor (Fig. 6).

The first function is a machining area sensorthat automatically detects the area of the sur-face under processing.

The second is a machining stress sensor. Pro-cessing depths are generally less than the tar-get value when the processing area is large,especially in finishing passes. This occurs as aresult of play that develops when the mecha-

Fig. 6 The “Fuzzy Pro” power supply.

TECHNICAL REPORTS

Fig. 7 A ribbed die and the graphite electrode

used to produce it.

nism executes a jump movement while thedielectric fluid is adhesively coupling the tooland workpiece. The control unit has a machin-ing stress sensor that detects and compensatesfor these forces.

The third function is an MF sensor that dis-tinguishes between “good” pulses that contrib-ute to processing and “bad” pulses that causearcing and surface discoloration by checking thepresence of harmonic components in the volt-age waveform of the discharge pulses.

Fig. 7 shows a die with a thin, deep rib pat-tern typical for molding lightweight plasticstructures and the graphite electrode used toform it. Graphite EDM tools can produce thin-ner ribs than any other method. The FP powersupply supports stable machining, achievingresults comparable to copper machining with-out bridging problems even in deep rib sections.

Improvements in EDM machining performancemake this technology an increasingly attrac-tive alternative to mechanical fabrication. ❑

December 1997 · 7

TECHNICAL REPORTS

An Electrical-DischargeScanning Machine

by Masaru Shinkai and Toshio Suzuki*

*Masaru Shinkai and Toshio Suzuki are with the Nagoya Works.

Electrical-discharge scanning is a new electrical-discharge machine (EDM) process in which asimple pipe-shaped electrode is used to formcomplicated shapes with high precision in ascanning process that resembles mechanicalprocessing. This technique dramatically reducesfabrication costs by eliminating all the stepsinvolved in the design and manufacture of spe-cially shaped electrodes. Electrical-dischargescanning is also better at forming intricateshapes than shaped tools. The technology issuitable for manufacturing dies for semiconduc-tor fabrication equipment, finely detailed diesand components for micromachine research.

Basic PrinciplesIn conventional electrical-discharge machining,the shape of the electrode is transferred to theworkpiece, requiring a substantial investment intool design and manufacture. The tool must bemanufactured to the same high accuracy desiredof the finished product and the cost of productionmay be as much as half the die manufacturingcost. The time required for tool manufacture alsoimpacts production scheduling.

Electrical-discharge scanning uses precisecontrol of simply shaped tools to generate thedesired profile, eliminating the cost of speciallyfabricated tools. Fig. 1 shows MitsubishiElectric’s electrical-discharge scanning ma-chine, ED-Scan 8E. Fig. 2a shows how the scan-ning process works. The bottom of a rotatingpipe is used to perform the machining, remov-ing material from the workpiece layer by layeruntil the desired shape is formed (Fig. 2b). Thescanning process removes 10~100µm per scanin first-pass mode and 1~10µm per scan in fin-ishing mode.

Fig. 2c shows the process for conventionalcontour machining using the side of a cylindricaltool. Low-wear machining conditions are usedto prolong the tool life, but wear causes round-ing of the bottom of the electrode. Electrical-discharge scanning, in contrast, uses high-wearmachining conditions, which speeds productionand maintains the tool’s sharp edge, while aZ-axis feed automatically advances the elec-trode as it wears for extremely accurate pro-

Fig. 1 ED-Scan 8E.

Fig. 2 Principles of electrical-discharge scanning.

cessing. The Z-axis feed is corrected by peri-odic depth measurements.


Rotation unitFeed control for wear compensation

Dielectric fluid

Processing contour

Scanning feed

a) Electrical-discharge scanning

c) Conventional contour machining.

b) Layer-by-layer material removal.

Electrode

Power supply

TECHNICAL REPORTS

Features of the Electrical-Discharge ScanningProcessElectrical-discharge scanning offers many ad-vantages over previous EDM processes. Table 1lists these advantages, along with weaknessesof the scanning process. The greatest merit ofthe process is that it eliminates the electrodefabrication step and can produce finer shapesthan are possible with a conventional tool. Mostof the weaknesses of the process can be elimi-nated through process improvement and ad-vances in CAM performance.

Table 1 Features of Electrical-Discharge ScanningAdvantages

Eliminates specialty tool design and production costs

Finer machining than conventional EDM shaping processes

No electrode wear considerations

Excellent bottom-surface flatness

Uniformly smooth finish over large areas

Processing time is easily estimated

CAD data for the die design can be converted directly to NC data

No dielectric fluid processing considerations

Disadvantages

Sometimes slower than shaped-electrode EDM processes

Not yet suitable for curved surfaces

Poor precision on side-wall angles more than 10° from vertical

Table 2 Applications of Electrical-DischargeScanning

Application area Practical examples

Die plate relief for IC frame punchand die, stripper plate relief for IC

Semiconductor manufacture frame punch and die, IC leadframe punch, other componentsfor semiconductor production

MicromoldsMolds for subminiatureconnectors, small gears, watchparts, switch components, etc.

Precision dies for stamping Micro punches, die plate relief

Dies for aluminum window Aluminum extrusion die reliefframes

Printing Lettering on molds and dies

Component production Precision component fabrication

Micromachines Components for micromachines

Table 2 lists applications. The technology isalready building a track record in die produc-tion for semiconductor manufacture.

Fig. 3 shows a test-manufactured mold for astepped microgear. The diameter is 1.2mm atthe outer teeth, 0.72mm at the inner teeth and0.1mm across the central shaft. The deepest partof the die is 270µm below the surface level. Inthe conventional approach, a wire-cut EDMwould be used to create the stepped structure,which would then be shaped in additional passesusing other tool shapes. In this case, however,the required electrodes are too small to fabri-cate reliably. The new process allows CAM datato be converted to the desired mold in a singlestep with processing accurate to 5µm.

Features of ED-Scan 8EThe ED-Scan 8E has an automatic changer forthe tool and a tool guide that supports differentelectrode diameters for optimum first-pass andfinish machining. These enable the system toautomatically perform first-pass machining athigh currents with a large-diameter tool andfinish machining at low currents with a small-diameter tool.

Another significant advance in the ED-Scan8E is the new SS power supply circuit, whichdoubles finishing speed, bringing it closer tothe finishing performance of shaped-electrodemachining. High-speed power switching de-

Fig. 3 A test-produced microgear mold.

December 1997 · 9

TECHNICAL REPORTS

Fig. 4 Shape simulation.

vices in the SS circuit speed finishing by reduc-ing the gap voltage rise time, while a short-cir-cuit suppression circuit improves the stabilityof the finishing process.

CAM SoftwareMitsubishi Electric has developed an ED-Scan/CAM package to convert die-shape informationand process parameters into numeric control-ler (NC) instructions for the scanning process.ED-Scan/CAM runs on a personal computerunder the Microsoft Windows 95 operating sys-tem. The shape data, supplied in DXF format,can be created using general-purpose CAD soft-ware. The NC data includes instructions forscanning, tool changes and electrode wearmeasurement. The software also offers a three-dimensional graphic simulation of the workpieceshape that the operator can use to visually verifythe NC data. Programming is faster since shapedata errors can be easily spotted and corrected.Fig. 4 shows a shape simulation.

By eliminating costly electrode fabricationsteps, electrical-discharge scanning brings newpossibilities to EDM processing, extending theadvantages of this technology over mechanicaldie-fabrication techniques. ❑


TECHNICAL REPORTS

FX Series General-Purpose Wire-CutElectrical-Discharge Machines

by Makoto Tanaka and Seiji Sato*

*Makoto Tanaka and Seiji Sato are with the Nagoya Works.

Mitsubishi Electric has developed the FX Seriesof wire-cut electrical-discharge machines (EDMs)for the expanding EDM market. The series fea-tures automated machining achieved throughincorporation of the low-wire-breakage “PM2”power-control system, a moving-column tooltransport mechanism for simpler more accurateoperation, improved aesthetic design and a num-ber of other innovations.

BackgroundWire-cut EDMs are extensively used in die-making and many other manufacturing fieldsbecause they can make fine cuts that are im-possible with other machine tools and theyrarely cause stress damage. The current EDMmarket is emphasizing cost-effective general-purpose equipment capable of fast, efficientcutting. Fig. 1 is a photograph of the FX20 wire-cut EDM, developed to meet these needs. Along-side basic performance, the FX Series providesautomated operation, simplified setup, an im-proved user interface, and enhanced aestheticdesign.

The PM2 Power Control SystemWire breakage is perhaps the largest factor in thereduction of EDM machining efficiency. It can beminimized by using the correct machining en-ergy to suit workpiece contours and thickness.The PM2 features an adaptive control system thatutilizes machining status and workpiece thick-ness information to dynamically optimize thefirst-cut machining power and other parametersas machining proceeds, thereby minimizing theincidence of wire breakage.

Poor electrolyte flow around step shapes and atworkpiece edges can also lead to unstable ma-chining and wire breakage. The control systemdetects concentrated discharge and short circuitsthat occur under these conditions and reducesthe machining power automatically.

Overall machining speed is improved since thepower control system selects maximum machin-ing speed whenever the electrolyte flow is suffi-ciently stable.

Fig. 2 shows a stair-shaped workpiece that canbe machined automatically by the PM2 power

Fig. 2 Issues in machining a stair-shapedworkpiece.

control system. The system automatically opti-mizes machining even at difficult locations; atthe stair section where workpiece thicknesschanges, at the workpiece edge and wherever thereis a long distance to the upper electrolyte nozzle.Fig. 3 shows the machining time improvementsusing the automated power control function.

User InterfaceThe FX20 has an easy-to-use user-interface moni-tor screen (Fig. 4) that allows the operator to auto-mate control of first-cut and finish machining.The operator simply selects first-cut or finishing

Fig. 1 A photograph of the FX20 wire-cut EDM.

(b) Where workpiece thickness changes

Electrode: 0.25mm dia. brass wireWorkpiece: SKD-11 with staircase shape

Upper nozzle clearance: 15mm

Lower nozzle clearance: 0.1mm

(c) Near the workpiece edge

50mm

45mm

12mm

(a) At the stair section

December 1997 · 11

TECHNICAL REPORTS

mode and specifies the final surface roughness.The system then automatically selects the num-ber of passes, offset values and other machiningconditions. All operations from NC program en-try and verification to calculating the machiningtime and monitoring and managing the machin-ing process are easily accomplished, allowing evena first-time user to create finely finished prod-ucts.

Operability ImprovementsThe most labor-intensive tasks in EDM use arepreparatory operations—attaching, aligning andremoving the workpiece. The corporation rede-signed the door to the machining tank for spacesavings, easy opening and the recovery of leakedelectrolyte. Larger models have a motorized

Mac

hini

ng ti

me

(min

)

0

20

40

60

FX10 FX1

Power management off

KeyPower management on

door, and all models have an automatic door-lock mechanism to prevent operator error. Amechanism for automatically cutting and re-covering the wire electrode assists operation andmaintenance.

ConstructionThe moving column mechanism facilitatesworkpiece setup and reduces the equipmentsize by eliminating the need for an XY tabledrive. The moving column moves the wire elec-trode tool along the X and Y axes relative to aworkpiece and table that are fixed in place.

The moving column mechanism eliminatestwo key factors responsible for static and dynamicpositioning errors: flexing of loaded structuralmembers and changes in the mass of the work-piece and electrolyte.

The flexing errors are predictable and com-pensated while the moving column mechanismand machining head are maintained at a con-stant mass, ensuring inherent immunity to theeffects that changing electrolyte and workpiecemass would have on table movement precision.

The frame members of FX Series wire-cutEDMs were designed using state-of-the-art CAEtechnology. The members were analyzed indi-

Fig. 3. Effect of power management on machiningtimes for a stair-shaped workpiece.

Fig. 5 A vibration mode analysis model.


Fig. 4 The power monitor screen.

TECHNICAL REPORTS

Gai

n (d

B)

Pha

se (

deg)

Frequency (Hz)

Key

:Measured

:Predicted

Fig. 6 Positioning loop dynamic analysis results.

vidually for local problems, and then the entirestructure was tested for static and dynamic prop-erties that could affect right-angle movementsand corner shapes.

We performed a dynamic analysis to deter-mine vibration modes of the structural mem-bers as the basis for servo-system resonancestudies. The simulations were conducted onworkstations with the structural member vibra-tion mode analysis model feeding the drive sys-tem model used in the servo-system analysis.Fig. 5 shows the analysis model and Fig. 6 thepredicted and measured results. Good match-ing was achieved in the low-frequency region,and these findings will be used to develop futuremechanisms with even better dynamic proper-ties.

Overall DesignBelieving that the good performance of our FXSeries wire-cut EDMs deserved a functional andaesthetically pleasing overall design, we devel-oped a simple, futuristic design with an ergo-nomic user interface and special unit cover thatprovides enhanced safety.

The performance and design of the FX Seriesare earning Mitsubishi Electric EDMs an ex-cellent reputation worldwide.❑

December 1997 · 13

TECHNICAL REPORTS

Machining Technologies forHighly Precise Wire-Cut Electrical-

Discharge Machines

*Takeshi Yatomi is with the FA Systems Planning & Administration Department and Yutaka Terada with the NagoyaWorks.

by Takeshi Yatomi and Yutaka Terada*

Mitsubishi Electric has developed the DWC90PAwire-cut electrical-discharge machine (EDM) tomeet the high-end die-machining requirementsof the semiconductor and precision electroniccomponent industries. DWC90PA, which useswater as the machining fluid, is ready to com-pete head-to-head with the grinding processesin the production of dies for stamping IC leadframes and other ultrahigh-precision machin-ing applications.

Trends in Dies for IC Lead FramesIC lead frame technology needs to keep pacewith increases in IC integration scale, pin count,pin pitch and smaller package sizes. Lead framesare produced by etching or stamping, withstamping widely used for mass production ofdevices with up to about 240 pins. Dies forstamping are generally formed in sections bygrinding in a time-consuming and labor-inten-sive process. The wire-cut EDM offers the ad-vantages of manufacturing dies as a single piece,more rapid production, increased automationand tighter lead pitches.

Mitsubishi Electric is leading these advanceswith the DWC90PA wire-cut EDM (Fig. 1),which features extraordinary machining accu-racy, surface finishing and highly automatedoperation.

FeaturesSURFACE FINISH TO 0.3µmRmax. Dies for IC leadframes require extremely high precision and asmooth surface finish for better longevity. Tocompete with grinding, wire-cut EDMs need toprovide a high-quality surface finish comparableto grinding without the surface cracking or heatdamage that often accompanies electrical-discharge machining.

The corporation has developed a high-frequency AC power supply capable of stablemachining at extremely low power levels, andwhich achieves extremely smooth and stress-free finishes with a surface roughness of0.3µmRmax. Fig. 2 shows the roughness mea-surements of surfaces finished using a wire-cutEDM and Fig. 3 a scanning electron micrograph


Fig. 1 The DWC90PA wire-cut EDM.

Fig. 2 Surface roughness measurement data.

of an EDM-finished surface. This finish is com-parable to grinding and provides the same longstamping life at blade portions of the die.

HIGH SHAPING PRECISION. The DWC90PA em-ploys an automated gap control system toachieve the high precision required for machin-ing lead frame dies. Digital gap control tech-nology yields more accurate shapes, bettercontrol response and wider safety margins.Small-radius corners and narrow slits are moreaccurate and are finished smoothly. Also sig-nificant, this EDM offers a stable very-low-power finishing mode. Unstable autoexpansionmachining and corner points have been im-proved through effective digital gap control.

0.1mm

0.5µm

TECHNICAL REPORTS

December 1997 · 15

FILTER1

DIV1

MAGN2000 X

NO RPM

D 4020 P

HIGHLY RIGID STRUCTURE. The table drive em-ploys a 0.1µm linear-scale drive closed-loop con-trol system that provides uniformly precisepositioning while highly rigid special castingsfor the structural members prevent thermalshocks from affecting accuracy. Fig. 4 shows anillustration of a circular sample machined tohighlight feed and structural errors. The 20mm-thick SKD-11 plate was machined into a 20mm

diameter cylinder with an accuracy of 1.5µm.A specially designed lower-arm assembly pro-

tects the inner arm from external pressure. Thelower arm, which runs from the column to theinterior of the machining tank, employs a dualstructure made of carbon-fiber reinforced plas-tic. The external arm receives the small forcesthat come through the feeder wire and from theflow of water in the machining tank, prevent-ing small displacements that would otherwiseaffect the inner arm and the lower guide it sup-ports.

UNSUPERVISED MACHINING WITH NARROW-GAUGE WIRE. The DWC90PA can automaticallythread wire gauges as small as 0.05mm. An au-tomatic fine-hole search function and a small-diameter jet nozzle can automatically feed theelectrode wire through starting holes as smallas 0.3mm.

Machining TestsWe used a DWC90PA equipped with these newtechnologies to test machine small slits typi-cal of an IC lead frame. We machined a 9mm-thick hard alloy workpiece using a 0.1mm dia.brass wire electrode. The high-precision gapcontrol system was used for the first throughsixth passes, and finish machining was per-formed in the seventh and eighth passes. Themachining time was 35 minutes, and the finalsurface roughness 0.5µmRmax. We produced0.16mm slits, which is close to the smallestresolution available using 0.1mm wire.

Fig. 5 shows the results of measuring parts of

Unit: µm

1,30

0

3,000

160

0.10.1

1.1

1.1 1.1

1.1

1.1

0.5

0.2

1.4

1.4

0.6 1.2

1.3

Fig. 4 Example of true circle machining. Fig. 5 Lead frame shape accuracy measurements.

Fig. 3 Electrolytic corrosion on workpiece surface.

1,000X magnification10µm

TECHNICAL REPORTS

an IC lead frame. Fig. 6 shows an enlarged im-age of the lead end. The shape error is within1.4µm with surface roughness under 0.5µmRmax

and no stress damage.

Advances in power control and the table drivesystem, combined with an improved structuraldesign, give the DWC90PA the ability to pro-duce dies for lead frame stamping with accu-racy and durability on a par with the bestgrinding processes, yet with substantial laborsavings and largely automated operation. ❑

0.2mm

Fig. 6 Detail of a lead frame.


TECHNICAL REPORTS

The LXP Series CO2 LaserProcessing Machine

by Mitsunobu Oshimura*

December 1997 · 17

through use of a digital laser oscillator controlsystem, and the laser optics have been upgraded.The LXP Series also has an alternating pallet loaderthat allows a workpiece to be mounted on onepallet while another workpiece on a second pal-let is being processed. Fig. 2 illustrates the LXPSeries productivity improvement in cutting 1000pieces from nine 1,220 x 2,440 x 1mm SECC (zinc-coated steel) sheets.

CO2 Laser OscillatorMitsubishi Electric’s CO2 laser oscillator fea-tures a silent-discharge, three-axis cross-flowresonator design; an output sensor and controlloop that keeps the output level within 1%; andgas-tight construction that lowers runningcosts. The newly developed D Series adds sev-

Demand for productivity improvements in CO2

laser processing machines is high now thatsteel-plate processing applications have ex-panded from specialty fabrication to quantityproduction. This article introduces MitsubishiElectric's newly developed LXP Series CO2 la-ser processing machine and reports on state-of-the-art laser processing technologies.

The LXP Series Laser Processing MachineInternational competition is forcing down pricesfor manufactured goods. High-precision machineshops using CO2 lasers stand to benefit from pro-ductivity enhancements supporting small-lotmanufacture of numerous product variants.Mitsubishi Electric has developed a flying opticalsystem with three-axis control for the LXP Se-

ries, the corporation’s newest line of CO2 laserprocessing machines for faster, more accurateprocessing. Fig. 1 is a photograph of a typicalmodel.

The LXP Series operates at a feed speed of60m/min, double the rate of previous Mitsubishilaser processing machines. It can also cut a 10mmdia. hole to within 50µm in 1mm plate at a rate of8m per minute—60% faster than its predecessor.

The LXP Series features an X-axis with twodriving units, each with a ball screw and rotatingnut, which are controlled simultaneously. Fasterprocessing was achieved using a CAE-optimizedmechanical system, a more powerful controlmicroprocessor and a new high-accuracy controlalgorithm. Faster laser response has been achieved

Fig. 1 The ML3015LXP-4030D CO2 laser processing machine.

90

Fixed laser system (5m/min)

Processing time: 31:02:30

Moving laser system ML2512LXP

(8m/min) Processing time: 25:37:50

Cutting time

Workpiece loading time

Chute open/close time

Pallet change time

Parts and scrap unloading time

Key

SECC t1.0(Unit:mm)

240

Fig. 2 Productivity comparison for 1,000 of the items shown in the inset photograph.

*Mitsunobu Oshimura is with the Nagoya Works.

TECHNICAL REPORTS

eral enhancements.First of all, the oscillator emits most of its

beam load in the low-order TEM01 component,providing a high output suitable for cutting mildsteel plate up to about 12mm thick. This beamload cuts more efficiently and operation is morestable due to a lower thermal load on the opti-cal components.

Second, an output response three times fasterthan previous laser oscillators was achieved bymatching the control program of the micro-processor-based controller to oscillator perfor-mance curves.

Third, the laser oscillator offers continuousoutput up to 3kW and peak output of 4kW, pro-viding power for high-speed piercing.

Fourth, a new system has been adopted toprevent heat from causing distortion in the

Burn-through occurs

1. Swelling at pierced section

Minimal swelling using new control system

3. Hole cutting

New

con

trol

sy

stem

Pre

viou

s co

ntro

l sy

stem

Pre

viou

s co

ntro

l sy

stem

Short processing time: only slight molten drop at hole end

Low-speed processing

High-speed processing

Long processing time: large amount of molten drop at hole end

All during low-speed processing

2. At change from low-speed to high-speed cutting at edge

New

con

trol

sy

stem

4. Edge processing

New

con

trol

sys

tem

Optimizes settings to suit plate thickness and angle

No burn-through

Fig. 4 Automatic control of processing conditions.

Cutting speed (m/min)

Acc

urac

y (µ

m)

02 4 6 8 10

50

100

150

200

250

300

350

400

1989 and before 1990 - 92 1993 1994 1995 and later

Key

Fig. 3 Improvements in accuracy vs. speed for 10mm dia. holes in a 1mm SPCC (mild steel) sheet.

oscillator’s internal optical components. Thisprevents variations in beam mode and shape,


TECHNICAL REPORTS

and improves beam pointing stability.Finally, the oscillator uses an internal gas flow

action to prevent oil mist and dust from adher-ing to the oscillator optics and degrading per-formance.

Cutting Speed and AccuracyWhen CO2 lasers were first applied to specialtymetal fabrication, the maximum processingspeeds were about 3m/min for cutting outlinesin 1.2mm mild steel sheet and 1.5m/min for a10mm dia. hole true to within 50µm. MitsubishiElectric has achieved a fivefold increase in pro-cessing speed with improved cutting accuracythrough developing lighter, more rigid movingparts and improved control technologies.

Fig. 3 illustrates this progress, showing cut-ting speed vs. accuracy curves for successivelydeveloped laser processing machines from 1989to 1995. The 1.5m/min for 50µm circle cuttingaccuracy in 1989 has been increased to 8m/min,while at lower speeds accuracy has been boostedto 20µm for high-precision applications.

Control of Processing Conditions for CuttingThick Steel PlateBurn-through is a vigorous oxidation reactioncaused by excessive local heating and insuffi-cient assist gas flow at the kurf. Burn-throughtypically occurs in cutting steel plate thickerthan 12mm at edges, corners, or locations wherecutting speed changes.

Fig. 4 shows the benefits of an improved con-trol system for processing conditions introducedfor thick plate cutting. This system preventsexcessive heating of burn-through-prone work-pieces by turning off the laser beam, applyingassist gas for cooling and then resuming pro-cessing, initially at low speed. This approachhas increased quality and reduced processingtime by about 15%.

Eight years of refinements to laser and position-ing control technologies have brought substan-tial productivity improvements to laser processingmachines, leading to a wider market for this equip-ment in quantity manufacturing applications. ❑

December 1997 · 19

TECHNICAL REPORTS

A Short-Pulse CO2 Laser Processor forPCB Manufacturing

by Masanori Mizuno and Tsukasa Fukushima*

*Masanori Mizuno and Tsukasa Fukushima are with the Nagoya Works.

Mitsubishi Electric has developed a commer-cial CO2 laser processor for rapid drilling ofsmall-diameter holes in high-density, multi-layer printed-circuit boards (PCBs). The proces-sor consists of a Mitsubishi-developed three-axiscross flow silent-discharge excited laser reso-nator with high peak power and short pulseduration, a high-speed laser positioning mecha-nism and an optical image-transfer system.

BackgroundSize and weight reductions in handheld com-puters, mobile phones and other modern infor-mation equipment demand densely mountedmultilayer PCB technology. In pursuit of addi-tional space savings, PCB designers are usingvia holes of 300µm and smaller. Mechanicallydrilling these holes suffers disadvantages of lowproductivity and drill bit wear and breakageproblems.

Laser processing offers a viable alternative.Mitsubishi Electric currently offers theML605GTX CO2 laser processor for PCB drill-ing and similar processing applications. Thissystem drills holes smaller than 300µm at a rateof 500 per second.

Overall DesignFig. 1 shows the basic design of the ML605GTX.The rotating Galvano mirrors and fθ lens scanthe beam at high speed for drilling over a 50 x50mm scanning area. When all the holes in thescanning area are completed, the XY tablemoves the next section of the PCB into the scan-ning area. Hole diameters between 50 and300µm can be selected by changing the maskin the optical image-transfer system. A visionsensor uses image processing technology to rec-ognize registration marks on the PCB, and thisinformation is used to compensate for XY tablepositioning errors. Each unit is controlled byMELDAS Magic, a personal-computer-basednumeric controller (NC).

Fig. 2 shows a photo of the system. The sys-tem features a space-saving design with allequipment contained in a single, fully enclosedunit that offers high safety and has an excellentdust precipitator for use in clean environments.

CO2 LaserPrevious CO2 lasers lacked a sufficient peakpower level to vaporize glass, and consequentlywere unsuitable for drilling via holes in glass-


Fig. 1 Basic design.

Laser beam

Mask

Collimation lens

Controller (PC with NC board)

CO2 laser

Galvano mirrors

Optical image-transfer system

XY tableX

Y

Workpiece

f- lense

TECHNICAL REPORTS

Fig. 2 The ML605GTX CO2 laser processing machine.

epoxy PCBs since they left rough edges thatinterferred with the subsequent copper platingprocess.

The corporation has developed a CO2 laserresonator employing a three-axis cross flowsilent-discharge excitation system that producessmooth-walled holes by delivering short pulsesat a power level sufficient to vaporize both glassand polymers.

Positioning TechnologyA single high-density PCB may contain thou-sands or tens of thousands of via holes. Massproduction of PCBs therefore requires sometype of high-speed processing. We developed anoriginal beam-positioning system for theML605GTX employing a Galvano scanner thatsupports processing speeds of up to 500 pointsper second and an image processing system thatcompensates for positioning errors, yielding anaccuracy of 20µm. This gives the laser proces-sor a maximum rate of 500 holes per second inthe scanning area. This system is combinedwith a high-speed extremely rigid XY table thatcan shift scanning areas in 0.3s.

ControllerWe employ a personal computer with an add-inNC board to control all aspects of the laserprocessor’s operation: the Galvano scanning sys-tem, drilling data conversion and positioningerror compensation. In addition to excellentperformance, the controller offers the advan-tages of a graphical user interface, easy opera-tion and a wide array of networking andcommunication options.

Processing QualityFig. 3 shows a cross section of copper-plated150µm blind via holes in a 100µm-thick FR4

glass-epoxy board. The laser removes the PCBmaterial and processing stops when the laserreaches the reflective copper layer below. Theglass and resin are vaporized almost simulta-neously, yielding smooth-walled holes thatplate well.

PCB QualityThe via hole walls require a slight taper for plat-ing fluid circulation to enhance plating effec-tiveness. Laser systems that achieve this taperby defocusing the beam are unsatisfactory be-cause hole roundness suffers.

We developed a new taper function that usesbeam modes to simultaneously control the drill-ing progress in the thickness and diameter di-rections without defocusing. The beam isfocused on the board surface so that the maxi-mum focal depth is available to absorb the ef-fects of thickness and positioning irregularities.

Fig. 4 shows 150µm blind via holes with tapersof 15 and 30° in 70µm-thick epoxy resin. Fig. 5shows a 50µm blind via hole in a 50µm epoxyfilm. The high-quality laser beam yields a per-fectly round hole.

Advanced laser and beam-positioning technolo-gies give this laser PCB processor the capabil-ity to accurately drill hundreds of holes inminimal time, thus improving PCB quality andreducing production time. ❑

Fig. 4 Taper drilling of epoxy resin PCB.

Fig. 3 Blind via hole processing of a glass-epoxy PCB.

Fig. 5 A 50µm blind via hole in an epoxy-resinPCB.

December 1997 · 21

TECHNICAL REPORTS

A High-Brightness Nd:YAG LaserProcessing Machine

by Akihiro Otani*

*Akihiro Otani is with the Nagoya Works.

Mitsubishi Electric is developing commercialsolid-state neodymium yttrium-aluminum-garnet (Nd:YAG) lasers superior to CO2 lasersfor many welding and cutting applications. Thisreport describes original technology for increas-ing the brightness of Nd:YAG rod lasers andintroduces the Mitsubishi product line.

High-Brightness TechnologySubstantial increases in Nd:YAG laser outputhave benefited processing applications; how-ever, laser outputs of 200W and more cause ther-mal distortion of the YAG rod, which disturbsthe laser light wavefront and degrades the beammode quality. As a result, convergence is poorerthan in CO2 lasers operating at ten times thewavelength.

Pulsed operation can be used to minimizethese effects, allowing greater penetration depthin laser welding applications. To support con-tinuous-wave applications, Mitsubishi Electrichas studied how thermal distortion of rod lasersaffects brightness, and developed a new high-brightness laser oscillator that we call a high-power polarization-dependent-erased resonator(HIPER). This design provides for uniformpumping of the crystalline rod and eliminatesthermal lens aberration caused by the polariza-tion components.

One of the chief advantages of rod lasers isthat the beam can be easily delivered throughoptical fiber. A new beam-delivery system usinggraded-index (GI) fiber has been developed tohandle the enhanced power of Mitsubishi rodlasers.

Commercial YAG Laser ProductsWe will now introduce the Mitsubishi ElectricYAG lasers incorporating these technologies. InJuly 1995, the corporation introduced theML0202SC with a high-brightness continuous-wave output of 250W. In April 1996, ML0606SC-K, with a high-brightness continuous-wave outputof 500W, and ML0606SC-S, with a continuous-wave output of 600W, were introduced. In May1997, ML1005SP, a 500W general-purpose pulsed-wave laser, was released. Fig. 1 shows an SCSeries continuous-wave laser and Fig. 2 the

ML1005SP pulsed laser. Table 1 lists the specifi-cations of these lasers.

The beam quality index (M2) is M2 ≤30 forML0202SC and M2 ≤60 for ML0606SC-K.ML1005SP delivers 100J per pulse with a peakpulse output of 10kW.

The excellent beam convergence of the

Fig. 1 An SC Series continuous-wave laser processing machine.

Fig. 2 The ML1005SP pulsed laser processing machine.


TECHNICAL REPORTS

Table 1 Laser Specifications Laser type ML0202SC ML0606SC-K ML0606SC-S ML1005SP

(high brightness) (high brightness) (high power) (high power)

Oscillation type Continuous wave Pulsed

Wavelength (µm) 1.06

Operation mode Continuous wave and pulse modulated Pulse

Rated power (W) 250 500 600 500

Peak power (kW) 0.4 1 1 10

Pulse energy (J/pulse) — — — 100

Beam quality (M2) ≤30 ≤60 — —

Power input (kVA) 25 35 28

Dimensions (W x D x H)(mm) 1,350 x 700 x 1,455 2,000 x 750 x 1,590

Construction Single unit containing laser oscillator, power supply and pure-water circulation unit

Weight (kg) 600 700 1,050

continuous-wave lasers (ML0202SC andML0606SC-K) supports high-quality cuttingand high-speed, high-quality seam welding.ML0606SC-S is suitable for low-aspect ratiowelding and surface-treatment applications.The pulsed-wave ML1005SP offers excellentgeneral-purpose performance for spot welding,low-heat welding, welding of highly reflectivematerials and many other welding applications.

Processing PerformanceWe next explain the processing performance andtypical applications of high-brightness continu-ous-wave lasers.

WELDING. Welding is the single largest applica-tion of YAG lasers. Continuous-wave lasers aresuperior to pulsed lasers in continuous weld-ing capability and quieter operation. They offerhigh-reliability welding at high welding speedswith fewer cracks and less spatter than pulsedlasers.

Fig. 3a shows the welding speeds and penetra-tion depths of ML0202SC and ML0606SC-K forbead-on-plate welding of SUS304 stainless steel.ML0202SC welds at 2m/min to a depth of 0.4mm,while ML0606SC-K welds at 3m/ min to 0.6mm.Fig. 4 shows bead width and penetration depthfor bead-on-plate welding of SUS304. This con-tinuous-wave laser yields a sharp bead cross sec-tion with a 1.0~1.6 aspect ratio. Fig. 3 SC Series processing characteristics.

December 1997 · 23

ML0202SC

Welding speed (m/min)0 2 4 6

ML0606SC-K

Pen

etra

tion

dept

h (m

m)

1.0

2.0

ML0202SC

Max. cutting speed (m/min)0 2 6 10 12

1

2

3

4 8

ML0606SC-K

Thi

ckne

ss (

mm

)

b) Cutting characteristics for SPC mild steel plate

a) Welding characteristics for SU304 bead on plate

TECHNICAL REPORTS

0

0

1

1

2

2

3

3

0

1

2

3

0.68

0.84

0.760.680.72

1.001.00

1.28

1.68

3.16

2.52

ConditionsBeam delivery GI600 fiberFocal length 80mmProcessing gas Ar, 15 liters/minMaterial SUS304

Pen

etra

tion

dept

h (m

m)

Penetration depth

Bea

d w

idth

(m

m)

Bead width

Welding speed (m/min)

Laser power 400WFrequency 200HzDuty 50%

0.88

Key

CUTTING. The speed and quality of cutting byprevious YAG lasers were inferior to that of CO2

lasers for plate thicker than 1mm due to thepoorer convergence of YAG lasers. YAG laserswith the high-brightness laser oscillator and thehigh-brightness beam-delivery system offersuperior performance for welding and thin steelplate cutting applications.

Fig. 3b shows the cutting speed and thick-ness relationships for models ML0202SC andML0606SC-K. ML0606SC-K cuts 3.2mm mildsteel plate at 1m/min, making it suitable forcutting sheet metal for most stamping applica-tions.

By addressing the largest weakness of YAG rodlasers—thermal distortion of the YAG rod—Mitsubishi Electric has developed products su-perior to CO2 lasers for many welding andcutting applications. ❑

Fig. 4 Welding characteristics of the ML0606SC-K.


TECHNICAL REPORTS

An Electron-Beam Processing Machinefor Micro-Scale Welding and Joining

Applications

*Kyuzo Arakawa is with the Transmission & Distribution, Transportation Systems Center and Masao Kikuchi withthe Manufacturing Engineering Center.

flection signal generator and dynamic focusingof an auxiliary lens. In addition, high-resistancematerials used in the vicinity of the deflectionsystem eliminate the distorting effects of eddycurrents otherwise induced by high-frequencydeflection signals.

Continuous-Duty Exhaust System and CassetteTransport MechanismThe system transports cassettes at the sametime that the vacuum system exhausts thechambers, permitting operating cycle times of13s in even high-vacuum applications. Fig. 3shows the electron-beam processing machine’scassette transport mechanism. The exhaust unithas a pipe-shaped cassette transfer tube withseveral vacuum chambers and multiple cylin-drical cassettes. The cassettes are transportedsequentially from the loader to a vacuum ante-chamber to the processing chamber. O-rings onthe cassettes prevent the introduction of airto the processing chamber. This reduces theload on the exhaust system, allowing the use ofsmall-capacity vacuum pumps and enhancingreliability.

by Kyuzo Arakawa and Masao Kikuchi*

Electron beam

DEFLECTION SIGNAL GENERATOR

Deflection error compensation

COMPENSATION SYSTEMCurvature-of-field aberration

Focusing lens

Dynamic focusing

Deflection system

Mitsubishi Electric has developed a commer-cial electron-beam processing machine that re-alizes operating cycle times under 1s throughthe use of a high-performance beam-deflectionsystem, cassettes carrying multiple workpiecesand a continuous-duty vacuum exhaust system.The machine can seal ceramic packages rap-idly with a much smaller thermal input thanconventional soldering and welding technolo-gies.

Beam Deflection SystemFig. 1 shows the configuration of the beam de-flection system. The system can sweep thebeam at rates exceeding 10,000m/min andmodulation rates nearing 100kHz for smallamplitudes. The beam diameter is 110µm±15%over a swept area of 60 x 60mm.

The beam speed can be changed instanta-neously from several meters per minute forwelding to 10,000m/min for traversing to thenext weld point. Beam switching is unneces-sary because at this high speed the thermal in-put to the workpiece is negligible (about 1/10,000 of the energy used for welding). Fast andaccurate beam deflection enables the system toprocess multiple workpieces in a cassette in asingle pass for outstanding throughput (Fig. 2).

Curvature-of-field aberrations, which increaseat high deflection angles, are reduced by thecombined effects of compensation in the de-

Fig. 1 The deflection system.

Workpiece

Electron beam

Deflection magnet

Fig. 2 High-throughput processing using beam deflection.

December 1997 · 25

TECHNICAL REPORTS

Cassette removal

Electron gun

Cassette tube

Cassette

Cassette return

Monitoring optics

Processing chamber exhaust

Antechamber exhaust

Cassette supply

Fig. 3 Equipment configuration.

Component Packaging ApplicationsSealed ceramic packages are used for ICs requir-ing reliability and long operating life. Ceramicpackages are sealed by a metal cap attached bya seam weld, solder or low-melting glass undera nitrogen atmosphere or vacuum. The heatassociated with these conventional processescan damage the IC and reduce yields, leadingmanufacturers to search for a low-power seal-ing process suitable for mass production.

Electron-beam processing offers a nearly idealsolution. The cassette transport and high-speedbeam deflection control realize short operatingcycle times. The welded joint resists moisturepenetration and corrosion. Furthermore, heat-ing is highly localized, reducing thermal stresseson the semiconductor device. The ceramic pack-age under the die reaches a peak temperature of110°C (383K) 0.5 seconds after sealing with theelectron-beam processor and returns to near am-bient temperature after 10s.

Table 1 Temperatures of Ceramic Package Sealing Processes

Electron-beam joining 110°C (383K) at substrate under die

Seam welding (Au joint) 250°C (523K) at substrate under die

Au-Su brazing Melts at 280°C (553K)

Solder Melts at 300°C (573K)

By using an electron beam to supply energy,ceramic packages can be sealed with minimalthermal effects on the die and higher yields asa result. The electron-beam processing machinedescribed here performs this operation atthroughput levels suitable for mass production.❑


TECHNICAL REPORTS

Excimer Laser Processing System UsingHolographic Optical Elements

by Yasushi Minamitani and Tomohiro Sasagawa*

*Yasushi Minamitani is with the Transmission & Distribution, Transportation Systems Center and Tomohiro Sasagawawith the Advanced Technology R&D Center.

Mitsubishi Electric has developed a commercialexcimer laser processing system using holographicoptical elements (HOEs). The holographic ele-ments are used to convert a single beam into sepa-rate beams of uniform energy and specific shape.The holographic method makes it possible to forma processing hole pattern with one mask withmuch less wastage than a conventional block-ing-type mask. This higher efficiency lowers la-ser equipment power requirements and runningcosts, and improves productivity.

Issues in Excimer Laser Processing MachinesPrevious excimer laser processing machinesoptically reduced and transferred a mask pat-tern to a workpiece, allowing processing in asingle step. However poor light utilization pre-sented a significant problem. A 1cm2 mask forforming 100, 100µm holes transmits only 0.8%of the incident light. When the losses of a beamhomogenizer and transfer lens are added, theefficiency falls to 0.6%. This corresponds tousage of less than 1W of a 100W laser’s output.This huge waste is especially significant be-cause excimer lasers have high running coststhat increase disproportionately with outputpower. The costs are high because laser gas mustbe resupplied to the laser’s discharge pumpingsystem and the laser light output window mustbe maintained regularly due to the corrosiveeffects of F2 and HCl discharge gas.

Better light utilization lowers laser capacityrequirements and makes lasers more economi-cal for manufacturing applications. A fivefoldincrease in light utilization would allow a 100Wlaser to be replaced by a 20W unit, reducinginitial investment and running costs. This logicled us to pursue technologies for highly efficientoptical processing and development of the cur-rent holographic laser system.

Principles of the Holographic SystemIn previous optical transfer systems, the loss oflight associated with the mask area was large.If the task at hand was to form a single hole,the beam could be focused through a conver-gent lens and 100% of the available light used.Now assume that the converging rays could be

Laser wavefront Hologram

Spatially modulated wavefront

1 order component

0 order component

-1 order component

Fig. 1 Principle of a holographic optical element.

separated and directed individually. This wouldeliminate the need for a mask entirely.

One way to control the beam would be throughintroducing numerous prisms. A similar effectcan be achieved through using diffraction grat-ings. A diffraction grating can be used to modu-late the laser wavefront forming a spatialfrequency distribution that produces the desiredbeam directions. A HOE, a type of diffraction grat-ing that creates periodic differences in light paths,can be used to provide the required spatial modu-lation function. Fig. 2 shows how an HOE wouldbe used with a lens in an optical transfer system.The system includes a simple aperture mask,transfer lens, HOE transfer mask and theworkpiece. The presence of the hologram distrib-utes the laser light, creating overlapping imagesat the points where processing is required. If theHOE is omitted, the light is focused into a singlepoint on the workpiece surface.

A Processing ApplicationWe will describe a typical application of the holo

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Workpiece

Laser beam

Simple aperture mask

Transfer lens

Hologram

Fig. 2 A hologram-based multiple imaging optical system.

December 1997 · 27

TECHNICAL REPORTS

graphic optical system to the processing of a 20µmpolyimide film. The hologram pattern, designedto form 95 holes, employs a pattern of 1,024 ×1,024 pixels of 1µm2 each and four phase levels.The transmission efficiency of the grating wascalculated at 72% with a maximum variation of1%. Fig. 3 shows a micrograph of the hologram,and Fig. 4 the processed film with a 1cm2 patternof 95, 100µm holes. Pulses from a laser with anenergy of 20mJ are attenuated to 3.9mJ at theworkpiece, an energy density of 514mJ/cm2 at an

30µm

Fig. 3 Micrograph showing the surface of theholographic element.

4mm

Fig. 4 Result of machining by the holographicimaging system.

��

Workpiece

Beam-forming optics

HOE

Convergent lens

Transfer mask

Transfer lens

Fig. 5 A processing system with a homogenizerfunction.

outstanding 19.4% efficiency. Energy utilizationefficiency is 20 times better than conventionalequipment since the pattern transmission ratiois less than 1%.

Using a Hologram as a HomogenizerAnother application of holograms is as homog-enizers. The optical intensity distribution of anexcimer laser generally has a top-hat distribu-tion in the axis defined by the length of thedischarge gap and a Gaussian distribution inthe direction of the discharge. Beam uniformityrequirements tighten for processing scales ofless than 100µm. Fig. 5 shows the design of asystem exploiting the ability of a hologram toseparate and superimpose, achieving a region ofuniform beam-energy distribution over the aper-ture of a transfer mask. This processing system iseffective when the openings are concentrated inseveral local areas. Since the homogenized beamilluminates only the transfer mask aperture, theoptical efficiency is five times better than previ-ous laser processing systems.

Use of holograms to control the transmissionof laser light has brought about a dramatic in-crease in efficiency because the hologram elimi-nates the need for masks that block a largeportion of the beam’s usable light. ❑


Country Address TelephoneU.S.A. Mitsubishi Electric America, Inc. 5665 Plaza Drive, P.O. Box 6007, Cypress, California 90630-0007 714-220-2500

Mitsubishi Electronics America, Inc. 5665 Plaza Drive, P.O. Box 6007, Cypress, California 90630-0007 714-220-2500Mitsubishi Consumer Electronics America, Inc. 2001 E. Carnegie Avenue, Santa Ana, California 92705 714-261-3200Mitsubishi Semiconductor America, Inc. Three Diamond Lane, Durham, North Carolina 27704 919-479-3333Horizon Research, Inc. 1432 Main Street, Waltham, Massachusetts 02154 617-466-8300Mitsubishi Electric Power Products Inc. Thorn Hill Industrial Park, 512 Keystone Drive, Warrendale, Pennsylvania 15086 412-772-25 55Mitsubishi Electric Manufacturing Cincinnati, Inc. 4773 Bethany Road, Mason, Ohio 45040 513-398-2220Astronet Corporation 37 Skyline Drive, Suite 4100, Lake Mary, Florida 32746-6214 407-333-4900Powerex, Inc. Hills Street, Youngwood, Pennsylvania 15697 412-925-7272Mitsubishi Electric Research Laboratories, Inc. 201 Broadway, Cambridge, Massachusetts 02139 617-621-7500

Canada Mitsubishi Electric Sales Canada Inc. 4299 14th Avenue, Markham, Ontario L3R 0J2 905-475-7728Mitsubishi Electronics Industries Canada Inc. 1000 Wye Valley Road, Midland, Ontario L4R 4L8 705-526-7871

Mexico Melco de Mexico S.A. de C.V. Mariano Escobedo No. 69, Tlalnepantla, Edo. de Mexico 5-565-6269

Brazil MELCO do Brazil, Com. e Rep. Ltda. Av. Rio Branco, 123, a 1507, 20040, Rio de Janeiro 21-221-8343MELCO-TEC Rep. Com. e Assessoria Tecnica Ltda. Av. Rio Branco, 123, a 1507, 20040, Rio de Janeiro 21-221-8343

Argentina MELCO Argentina S.R.L. Florida 890-20º-Piso, C.P. 1005, Buenos Aires 1-312-6982

Colombia MELCO de Colombia Ltda. Calle 35 No. 7-25, Oficinas No. 1201/02, Edificio, Caxdac, Apartado Aereo 1-287-927729653, Bogotá

U.K. Mitsubishi Electric U.K. Ltd. Travellers Lane, Hatfield, Herts. AL10 8XB, England 1707-276100Apricot Computers Ltd. 3500 Parkside, Birmingham Business Park, Birmingham, B37 7YS, England 21-717-7171Mitsubishi Electric Europe Coordination Center Centre Point (18th Floor), 103 New Oxford Street, London, WC1A 1EB 71-379-7160

France Mitsubishi Electric France S.A. 25 Boulevard des Bouvets, 92741 Nanterre Cedex 1-55-68-55-68

Netherlands Mitsubishi Electric Netherlands B.V. 3rd Floor, Parnassustoren, Locatellikade 1, 1076 AZ, Amsterdam 20-6790094

Germany Mitsubishi Electric Europe GmbH Gothaer Strasse 8, 40880 Ratingen 2102-4860Mitsubishi Semiconductor Europe GmbH Konrad Zuse Strasse 1, 52477 Alsdorf 2404-990

Spain MELCO Iberica S.A. Barcelona Office P olígono Industrial “Can Magi”, Calle Joan Buscallà 2-4, Apartado de Correos 3-589-3900420, 08190 Sant Cugat del Vallés, Barcelona

Italy Mitsubishi Electric Europe GmbH, Milano Office Centro Direzionale Colleoni, Palazzo Perseo-Ingresso 2, Via Paracelso 12, 39- 6053120041 Agrate Brianza, Milano

China Shanghai Mitsubishi Elevator Co., Ltd. 811 Jiang Chuan Rd., Minhang, Shanghai 21-4303030

Hong Kong Mitsubishi Electric (H.K.) Ltd. 41st Floor, Manulife Tower, 169 Electric Road, North Point 510-0555Ryoden Holdings Ltd. 10th Floor, Manulife Tower, 169 Electric Road, North Point 887-8870Ryoden Merchandising Co., Ltd. 32nd Floor, Manulife Tower, 169 Electric Road, North Point 510-0777

Korea KEFICO Corporation 410, Dangjung-Dong, Kunpo, Kyunggi-Do 343-51-1403

Taiwan MELCO Taiwan Co., Ltd. 2nd Floor, Chung-Ling Bldg., No. 363, Sec. 2, Fu-Hsing S. Road, Taipei 2-733-2383Shihlin Electric & Engineering Corp. No. 75, Sec. 6, Chung Shan N. Rd., Taipei 2-834-2662China Ryoden Co., Ltd. Chung-Ling Bldg., No. 363, Sec. 2, Fu-Hsing S. Road, Taipei 2-733-3424

Singapore Mitsubishi Electric Singapore Pte. Ltd. 152 Beach Road #11-06/08, Gateway East, Singapore 189721 295-5055Mitsubishi Electric Sales Singapore Pte. Ltd. 307 Alexandra Road #05-01/02, Mitsubishi Electric Building, Singapore 159943 473-23 08Mitsubishi Electronics Manufacturing Singapore Pte. Ltd. 3000, Marsiling Road, Singapore 739108 269-9711Mitsubishi Electric Asia Coordination Center 307 Alexandra Road #02-02, Mitsubishi Electric Building, Singapore 159943 479-9100

Malaysia Mitsubishi Electric (Malaysia) Sdn. Bhd. Plo 32, Kawasan Perindustrian Senai, 81400 Senai, Johor 7-5996060Antah MELCO Sales & Services Sdn. Bhd. 3 Jalan 13/1, 46860 Petaling Jaya, Selangor, P.O. Box 1036 3-756-8322Ryoden (Malaysia) Sdn. Bhd. 2nd Fl., Wisma Yan, Nos. 17 & 19, Jalan Selangor, 46050 Petaling Jaya 3-755-3277

Thailand Kang Yong W atana Co., Ltd. 15th Floor, Vanit Bldg., 1126/1, New Petchburi Road, Phayathai, Bangkok 10400 2-255-8550Kang Yong Electric Co., Ltd. 67 Moo 11, Bangna-Trad Highway, Km. 20 Bang Plee, Samutprakarn 10540 2-312-8151MELCO Manufacturing (Thailand) Co., Ltd. 86 Moo 4, Km. 23 Bangna-Trad, Bangplee, Semudparkarn 10540 2-312-8350~3Mitsubishi Elevator Asia Co., Ltd. Bangpakong Industrial Estate, 700/86~92, Moo 6 Tambon Don Hua Roh, 38-213-170

Muang District Chonburi 20000Mitsubishi Electric Asia Coordination Center 17th Floor, Bangna Tower, 2/3 Moo 14, Bangna-Trad Highway 6.5 Km, 2-312-0155~7(Thailand) Bangkawe, Bang Plee, Samutprakarn 10540

Philippines International Elevator & Equipment, Inc. Km. 23 West Service Road, South Superhighway, Cupang, Muntinlupa, 2-842-3161~ 5Metro Manila

Australia Mitsubishi Electric Australia Pty. Ltd. 348 Victoria Road, Postal Bag No. 2, Rydalmere, N.S.W. 2116 2-684-7200

New Zealand MELCO Sales (N.Z.) Ltd. 1 Parliament St., Lower Hutt, P.O. Box 30-772 Wellington 4-569-7350

Representatives

China Mitsubishi Electric Corp. Beijing Office SCITE Tower, Rm. 1609, Jianguo Menwai, Dajie 22, Beijing 1-512-3222Mitsubishi Electric Corp. Shanghai Office Room No. 1506-8, Shanghai Union Building 100, Yanan-East Street, Shanghai 21-320-2010

Korea Mitsubishi Electric Corp. Seoul Office Daehan Kyoyuk Insurance Bldg., Room No. 1204 #1, Chongno 1-ka, 2-732-1531~2Chongno-ku, Seoul

Viet Nam Mitsubishi Electric Corp. Ho Chi Minh City Office 8 B2, Han Nam Officetel 65, Nguyen Du St., 1st District, Ho Chi Minh C ity 8-243-984

MITSUBISHI ELECTRIC OVERSEAS NEMITSUBISHI ELECTRIC OVERSEAS NEMITSUBISHI ELECTRIC OVERSEAS NEMITSUBISHI ELECTRIC OVERSEAS NEMITSUBISHI ELECTRIC OVERSEAS NETTTTTWORKWORKWORKWORKWORK (Abridged)

MITSUBISHI ELECTRIC CORPORATIONHEAD OFFICE: MITSUBISHI DENKI BLDG., MARUNOUCHI, TOKYO 100-8310, FAX 03-3218-3455

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