Sandvik Santronic™

Handbook

2 Sandvik Santronic Handbook

The versatility of Sandvik Santronic makes it ideal for both contact springs and shielding parts in, for example, hard drives.

Contents

New surface technology for electronic components 4Higher productivity 4Better product performance 4

The coating process 5Why use precoated material? 5Continuos coating of full width strip 5Well suited for tailor-making 6Superior environmental properties 6

Coatings 8General properties of the coatings 8Excellent adhesion 9Low contact resistance 10Excellent soldering properties 11Very narrow tolerances 11Comparison to electrochemical coatings 11

Base materials 12Sandvik 15R10 (ASTM 301) 12Sandvik 12R11 12 Sandvik 11R51 13Sandvik 13RM19 13Sandvik 6LR10 (ASTM 304) 13Sandvik IC34 (ASTM 430) 13Mechanical properties 14Physical properties 15Excellent spring properties 16Surfaces 19Flatness 19Straightness 20Good corrosion properties 21Tolerances 21

Material selection guides 22

Mechanical and electrical properties of materials 24

Replacement of copper alloy springs with Santronic 27Typical weight reduction: 25% 27Difference in density 27Difference in Youngs modulus (E-modulus) 27

Basic electricity 28Units 28Ohms law 28Combination of resistors 29Resistivity, conductors, semi-conductors and insulators 29Conductivity 30Conductivity of coated strip 30

Sandvik Santronic Handbook 3

4 New surface technology

Sandvik has developed a new process for coating of metal strip for producing electronic components. It is a roll-to-roll process where very thin layers of metal coating are applied on stainless steel base materials with excellent adhesion and high coating purity. The result is Sandvik Santronic.

Thanks to the excellent adhesion Sandvik Santronic can be bent and formed without cracking. Another unique feature is that coating is possible on just one of the sides, or different coating materials on opposite sides. Both give tremendous advantages compared to conventional coating.

Sandvik offers a vast supply of coatings and base materials. Examples of applications are contact springs, tactile domes and various EMC shielding components.

HigHeR pRoduCTiviTySandvik Santronic offers many advantages for elec-tronic components producers, which all lead to higher productivity.

• Due to excellent stamping and forming properties the finished parts can be made directly in the stamp-ing operation. The cost for a separate coating proc-ess vanish and the through-put time will be shorter.

• Uniform coating properties and even thickness assure very good productivity in stamping opera-tions, where a minimum of adjustment is needed. The stamping operation will be faster.

• As Sandvik Santronic can be single-sided coated, and the coating is very thin, it will result in less wear of forming and blanking tools. Less wear means less costs.

• Sandvik Santronic is stiffer, stronger, lighter and more endurant. When replacing copper-based con-tact springs with Sandvik Santronic weight savings of 25% or more are normally achieved.

BeTTeR pRoduCT peRfoRMaNCeAs Sandviks coating process does not include any chemicals, the coating layers are extremely pure, and therefore as soft and ductile as the coating metal can be. This is one reason for Sandvik Santronic’s very good and consitent contact properties, which leads to longer life and less use of battery power. For the dome producer it means less final inspection.

Sandvik Santronic also has good corrosion resistance, due to the stainless steel substrate. Other properties that enhance product performance are good wear resistance of coated layers and excellent soldering properties.

New surface technology for electronic components

5The coating process

The coating process

WHy uSe pReCoaTed MaTeRial?In the conventional fabricating process of metal parts for electronic devices, there are a number of additional costs in relation to sending the parts for plating, in many cases at a subcontractor: packaging, quality assurance, transportation, reception of incoming goods, sorting and control etc. On top of this, financial costs will arise from capital tie-up, i.e. material in work, stocks of semi-manufactured parts and increased risk of obsolessence due to long through-put time.

With Sandvik Santronic the finished parts are made directly in the stamping operation, and as a conse-quence the costs are limited to the cost for the mate-rial and the stamping process. All the additional costs originating from a separate coating process vanish.

CoNTiNuouS CoaTiNg of full WidTH STRipSandvik Surface Technology has developed a large area coating concept with a continuos coating of full width stainless steel strip. The coating line consists of a pre-treatment of the strip surface immediately followed by the coating process. As the coating is based on evapo-ration and the pre-treatment ensures a clean metallic surface, an extremly good adhesion is obtained.

A normal PVD (Physical Vapor Deposition) process is carried out for batch scale coating. In the Sandvik Sur-face Technology process the coating is made on a strip in motion. This assures homogenous coating of the whole strip surface and repeated quality from batch to batch.

1. Cleaning/inspection Cleaning is very important in order to get good adhesion. The entire strip surface is then inspected – the whole area and both on the upper side and the down side, in order to avoid harmful defects.

2. Coating Coating of metal layers or colors by Sandvik Surface Technology continuous evaporation coating process.

3. TestingAutomatic X-ray and visual inspection devices measure thickness and quality of the coating.

4. Slitting/checking and packagingAfter the coating line follows inspection and testing, for exam-ple tensile testing and hardness testing, surface properties and adhesion. Finally slitting to required width, control of burr height, width and shape, followed by packaging and shipment.

4

3

2

1

Blanking Plating

Waste Plating rejects Low output of finished parts

Finishing

Conventional process

Blanking No plating

Waste No rejects High output of finished parts

Sandvik Santronic

As the fabricating process with Sandvik Santronic does not include any plating the customer saves both time and money. Productivity will be higher compared to a conventional coat-ing process.

6 The coating process

Well SuiTed foR TailoR-MakiNg The Sandvik Surface Technology process is better suited for tailor-making to meet customer requirements than other technologies. The deposition is made on one side at the time, for which reason it is possible to combine different coatings on opposite sides of the strip depending on the application. The process therfore gives customers the opportunity to create new combi-nations of coating and substrate which may be the basis for completely new applications.

Customers may for example choose an isolating layer on one side and tin on the other side to make soldering possible, or nickel on one side and tin on the other side. No other coating processes makes it possible to choose an isolating layer one one side, like Sandvik Santronic.

Sandvik flexible coating process gives unique possibilities to combine different coatings on both sides.

SupeRioR eNviRoNMeNTal pRopeRTieSlow energy consumptionSandvik Santronic is an ideal product for companies with high environmental ambitions. Stainless steel is among the materials with highest recycle rate and con-tains on average 70% recycled material. Also the pro-duction of stainless steel is economical with regard to energy. The energy consumption for primary stainless steel is much less than for both copper and aluminium.

No waste productsEven the coating process itself is very environmentally friendly. The process does not incorporate hazardous chemicals or use of water. Consequently the process does not produce any waste water, as is the case with electroplating.

High degree of recyclingAnother environmental advantage is the thin coating applied, i.e. the low quantity of coating metal used. For instance the electroplating of thick tin coatings will impair the possibility of recycling the coated material. However, the thin and single sided coated Sandvik Santronic can normally be recycled without problems.

There are several reasons behind the thin Sandvik Santronic coatings. Firstly the special coating technol-ogy assures complete coverage and excellent properties already at very thin layers. Secondly the narrow thickness tolerances minimize the need for excess thickness to assure a certain minimum layer thickness. And thirdly Sandvik Santronic will in most cases be coated on one side only.

Sandvik Santronic already meets the present RoHS directive, as well as an upcoming EU directive on toxic substances in electrical equipment. The actual coating process fulfils EU definitions of Clean Tech manufacturing.

Oxide

Substrate

Oxide

Metal

Substrate

Metal

Substrate

Metal A

Metal B

Substrate

Oxide

Metal

Substrate

Metal B

Metal A

Substrate

7The coating process

Sandvik´s surface technology products conform with the requirements of the EC Directive (2002/95/EC) on the restricted use of certain hazardous substances (RoHS) in electrical and electronic equipment – regarding lead, mercury, cadmium and hexavalent chromium, polybrominated diphenyls (PBB) or polybrominated diphenyl ethers (PBDE) – and the maximum concentration values for lead, mercury, cadmium and hexavalent chromium as further specifi ed in Commission Decision 2005/618/EC.

BULK MANUFACTURING

Stainless steel contains on average 70%

recycled material* (*Sandvik~85%).

COMPONENTMANUFACTURING

No surface treatment necessary.

No waste water treatment.

Process scrap recyclable.

COMPONENTUSAGE

Surface Technology fully complies

with RoHS.

PRODUCT RECYCLING

Surface Technologyproduct

fully recyclable.

Environmentally friendly coating concept with no

discharge to water or air. Process scrap

fully recyclable.

Optional single or double sided thin precise coating with narrow tolerances minimizes coating

material con-sumption.

Sandvik Santronic has very good environmental properties during its entire life cycle.

8 Coatings

Coatings

Typical coating thickness range and coating characteristics

Coating Typical coating Coating characteristics thickness range, μmNickel 0.1–1 Good corrosion resistance, medium contact resistance, good fatique properties. (Ni) Typical used for contact springs with moderate to high demands for contact resistance.

Also used for contacts with high number of contact cycles. Melting point 1455 °C.

Tin 0.3–2 Excellent soldering properties. Good contact properties for contacts with high contact(Sn) pressure and low number of contact cycles. Melting point 232 °C.

Silver 0.1–0.5 Excellent contact properties, low contact resistance, good fatique properties. (Ag) Typical use for contacts with demands for low contact resistance at low contact pressure.

Tarnish sensitive in chloride and sulphur containing atmosphere. Melting point 962 °C.

Copper 0.1–2 Very good conductivity. Moderate contact properties due to tarnishing in many environ-(Cu) ments. Can be used with Sn or Ni as toplayer for tarnish protection. Melting point 1084 °C.

Oxides 0.2–0.5 Insulating coating. For parts and surfaces that needs to be insulating in low voltage electronics. Can also be used in combination with other coatings.

A wide range of different metal coatings can be applied to a wide range of substrate strips for applications such as contact springs, domes etc, where properties like contact resistance and soldering need to be enhanced.

Standard coating materials are nickel, tin, silver and copper. However, most other metals can also be supplied. Alloys and conductive nitrides are under development and may be available on request. Also binary compounds, for example oxides such as alumini-um oxide, titanium oxide or nitrides, can be applied.

Maximum coating thickness

Strip Max coating Max coating Max coatingthickness thickness, μm thickness, μm thickness, μm(mm) Tin (Sn) Silver (ag) Nickel (Ni)

0.04–0.09 0.5 0.5 0.2

0.10–0.24 1 2 1

0.25–0.35 2 2 1

9Coatings

geNeRal pRopeRTieS of THe CoaTiNgSlow levels of impuritiesAs the Sandvik Santronic process does not involve the use of chemicals, the coating layers are kept extremly pure, and possess the properties of the pure coating metals.

Soft layersDue to the pure coatings the layers are typically as soft as the metal in question can be. This is very important in relation to contact resistance and is one of the reasons behind the very good electrical contact properties of Sandvik Santronic.

low internal stressesThe extremly thin coatings have very low levels of internal stresses, which in combination with excellent adhesion eliminates the rise of spallation or flaking.

Single-sided coatings increase productivity For hard coating materials such as nickel, single-sided coatings combined with excellent adhesion, result in less wear of forming and blanking equipment and also in less dusting from coating.

Consistent coating increases productivitySandvik Santronic has very uniform coating properties and thickness both along and across the strip. This assures very good productivity in stamping operations, where a minimum of adjustment is needed. Very contra-dictionary to electroplated strip where the so called dog-bone effect calls for frequent tool adjustments.

Sandvik Santronics thinner coating also means less burr and less smearing on the tools.

Dog-bone effect after electroplating coating.

The Sandvik Santronic coating is thinner and much more uniforn.

exCelleNT adHeSioN A specific high-strength adhesion test has shown that the Sandvik Santronic material has excellent adhesion properties. Adhesion is also consistent from batch to batch, delivery to delivery.

Excellent and consistent adhesion between base material and coating allows stamping, forming and bending so that high productivity and short supply chain can be obtained. In many casses forming that is impossible with electroplated strip can easily be done with Sandvik Santronic.

Tested and approved according to ASTM D3359-02, Method A – X-cut tape test. Standardardized qualita-tive adhesion test of all coated materials from Surface Technology. Recommended tape adhesion strength 500g/cm. Specific high-strength tape used Permacel P-162 in 25 mm width. Adhesion strength to steel 642g/cm.

Base material

Base material

Tape

Adhesive

Substrate

Coating

Up to 50% lower tool-wear rate for single-sided nickel coating compared to double-sided.

10 Coatings

loW CoNTaCT ReSiSTaNCe The low levels of impurities and surface oxides also result in lower contact resistance and higher contact consistency than comparable plated material. It greatly benefits the finished component.

For example in tactile domes, it means more consistent and reliable operation, which leads to longer life and less use of battery power. For the dome producer, improved and consistent surface conductivity means better production yield and less final inspection and checking of components.

10000

1000

100

10

1

Contact resistance, mΩ

20 40 60 80 100 120

Force, N

Uncoated Silver, AgNickel, Ni

Contact resistance of Sandvik Santronic nickel and Sandvik Santronic silver. Measured with 4-point contact resistance measurements with goldplated probe, tip-radius 2mm, performed according to ASTM B667-97.

11Coatings

exCelleNT SoldeRiNg pRopeRTieSSandvik Santronic has excellent soldering properties even at very thin coating thickness like 0.5µm. Tin coated Sandvik Santronic has been tested according to IPC/EIA/JEDEC J-STD-002B test method A, and also approved according to DIN IEC 60068-2-20 with very good results.

few and very short whiskersWhiskers are a phenomena observed on coatings mainly of tin. Under special conditions hair-like metal whiskers will grow on the surface even to a millimetre in length. There are reported cases where such ”metal-hair” has caused short circuiting and total failure of electronics.

Sandvik Santronic tin-coat has been whiskers tested with a very good result. There has only been found very few whiskers and no longer than 6–8 µm. Electroplated tin coatings that were tested simultaneously did grow

whiskers 35–40 µm long, i.e. 5 to 6 times longer than on Sandvik Santronic.

The test has been performed according to the testing standard JEDEC-JESD22A121 with both temperature cycling (–55°C to +85°C) as well as high temperature/humidity storage (60°C, 90% RH for 1500 hours). The conclusion is that Sandvik Santronic tin-coat fulfils the demands stated in the standard JEDEC-JESD201, Acceptance Requirements for Tin and Tin alloy Surface Finishes.

veRy NaRRoW ToleRaNCeS Sandvik's coating process has a variation of maximum ±10% of the coating thickness, i.e a nominal 0.5 µm layer will have its tolerance limits between 0.45–0.55 µm (+/– 0.00005 mm). These values are valid across the strip width as well as along the strip length. Electroplated materials may have up to ±50% in thickness variation.

Sandvik Santronic• Excellent stamping and forming properties• Excellent adhesion• Narrow tolerances, typically +/– 10%• Very good coverage of thin coatings• Environmentally friendly production

No waste water• High purity of coatings• Even thickness, no thickness deviation at edges• Single sided coating standard• Duplex coating standard

electroplated coatings• Limited stamping and forming properties• Flaking can be a problem• Coarse tolerances, typically +/– 50%• Thicker coatings needed to achieve full coverage• Aggressive and poisonous chemicals used

in production• Chemicals from baths often incorporated in coatings• Material build-up B at edges (dog bone effect)• Single sided only with masking• Duplex coatings needs complex masking procedure

CoMpaRiSoN To eleCTRoCHeMiCal CoaTiNgS

12 Base materials

Sandvik Santronic can be stamped and formed in the same way as the base materials, and should also be handled likewise.

The following range of thicknesses and widths can be supplied as standard. On request Sandvik can deliver widths up to 800mm, but not for all base material or coatings.

SaNdvik 15R10 (aSTM 301) Standard base material according to EN 1.4310 (ASTM 301). General purpose stainless spring steel for springs and bent parts. It is very well suited for electrical contact springs and similar applications. Sandvik 15R10 is a standard austenitic stainless steel with good spring properties that in most cases fulfil demands regarding corrosion resistance, mechanical strength, fatigue and relaxation properties. Sandvik 15R10 can be delivered in Tension Annealed condition as well as in widths up to 800 mm.

SaNdvik 12R11 Base material according to EN 1.4310 (ASTM 301) like 15R10 but with tighter tolerance on composition for more homogenous properties. Sandvik 12R11 has similar good properties to 15R10 and can be offered with tighter tolerances for more demanding applica-tions. Sandvik 12R11 can be delivered in a wide range of customized thicknesses and tensile strenghts.

Base materials

Chemical composition and characteristics for popular base materials

Substrate Characteristics

Sandvik 15R10 0.10 C, 17 Cr, 7 Ni Standard stainless spring steel for general spring applications. (ASTM 301)

Sandvik 12R11 0.10 C, 1.2 Si, Equivalent to Sandvik 15R10; but with tighter tolerance on composition 16.5 Cr, 7 Ni for more homogenous properties.

Sandvik 11R51 0.09 C, 16.5 Cr, Improved 301-type spring material with molybdenum additive. 7.5 Ni, 0.7 Mo Superior stainless spring steel with higher tensile and fatigue strength for high performance springs.

Sandvik 13RM19 0.11 C, 6 Mn, Non-magnetic stainless spring steel. 18.5 Cr, 7 Ni, 0.25 N

Sandvik 6LR10 0.05 C, 18 Cr, 8 Ni Stainless strip steel for formed and bent parts.(ASTM 304)

Sandvik 1C34 0.05 C, 17 Cr Magnetic stainless steel for stamped parts with moderate forming.(ASTM 430)

Thickness range Width mm inch mm inch

0.04–0.8 0.0016–0.0315 6–370 0.24–14.5

Any steel grade that is available in the standard Sandvik program is available for the Sandvik Santronic line. Other materials such as high-alloyed steel or nickel-based alloys can be delivered on request. A wide range of versions and dimensions are available. Sandvik

works closely with customers to understand and meet their specific needs and ensure the success of their products. The most common base materials are Sandvik 15R10, Sandvik 12R11, Sandvik 11R51 and Sandvik 13RM19, as well as ASTM 304 and ASTM 430.

13Base materials

SaNdvik 11R51Sandvik 11R51 is an improved 301-type spring material with molybdenum additive. Compared with standard grade Sandvik 15R10, Sandvik 11R51 offers:

• Higher tensile strength and tempering effect • Higher relaxation resistance, especially at

elevated temperatures • Higher fatigue strength • Better corrosion resistance, due to the addition

of molybdenum

SaNdvik 13RM19Sandvik 13RM19 combines high mechanical strength with a non-magnetic structure. This combination of properties has previously been found mainly in expen-sive Co-Ni-base or Cu-Be-alloys. Corrosion resistance is comparable to Sandvik 12R11. Sandvik 13RM19 also possesses good fatigue properties and excellent ductility, which makes it a most suitable choice for

springs and other high strength applications where ferromagnetic materials cannot be used.

SaNdvik 6lR10 (aSTM 304)ASTM 304 is the most common austenitic stainless steel, and is very well-suited for bent and formed parts for general use. ASTM 304 has very good corrosion resistance in normal environments. The mechanical properties are good and the formability is excellent. ASTM 304 can be delivered in annealed condition as well as in coldrolled tempers. It is not suited for heavy loaded springs.

SaNdvik 1C34 (aSTM 430)ASTM 430 is a ferritic stainless steel with good mechanical properties. It is magnetic due to the ferritic structure. In most environments, the corrosion proper-ties are in line with ASTM 304. ASTM 430 can be an alternative to ASTM 304 for stamped parts with moderate demands to bending and forming.

14 Base materials

MeCHaNiCal pRopeRTieS The strength data presented here is based on compre-hensive tests conducted at the Sandvik R&D Centre. The tables show data for material as delivered.

HaRdNeSSThere is no direct relationship between tensile strength and hardness. However, higher tensile strength corrensponds with higher hardness. The curve below is approximate and the shaded area denotes its deviation. Thin materials (approx < 0.1 mm) must be expected to have a wider deviation, indicated by continous lines.

Sandvik 15R10/Sandvik 12R11

Condi- Tensile proof strength elonga- e- tion strength, Rm Rp0,2 tion, a11,3 modulus

Mpa ksi Mpa ksi % Mpa

A* 850 116 300 44 50 185000

C* 1300 189 1150 167 15 185000

C* 1500 218 1375 199 8 182000

C* 1700 247 1625 236 1.5 180000

C* 1900 276 1825 265 1 183000

Sandvik 11R51

Condi- Tensile proof strength elonga- e- tion strength, Rm Rp0,2 tion, a11,3 modulus

Mpa ksi Mpa ksi % Mpa

C* 1700 247 1600 232 1 180000

C* 1900 276 1850 268 0.8 183000

C* 2050 297 1975 286 0.5 186000

Sandvik 13RM19

Condi- Tensile proof strength elonga- e- tion strength, Rm Rp0,2 tion, a11,3 modulus

Mpa ksi Mpa ksi % Mpa

A* 850 123 470 68 45 185000

C* 1100 160 975 142 12 190000

C* 1300 189 1150 167 10 190000

C* 1500 218 1350 196 3 190000

C* 1600 232 1440 209 2 190000

2200

1900

1600

1300

1000

Tensile strength, MPa

300 350 400 450 500 550 600 650 700

Hardness, HV

Conversion from tensile strength to hardness (Vickers).

*A= Annealed*C= Cold rolled

15Base materials

pHySiCal pRopeRTieS For information on physical properties of the base materials, please see www.smt.sandvik.com, Technical center, Material datasheets.

RelaxationIf a spring is loaded heavily for an extended period, the material will yield slightly, and the stresses in the material as well as the spring force will be reduced. This phenomenon is referred to as relaxation or setting. The heavier the spring is loaded, i.e. the higher the stresses, the more it will relax. If the temperature is increased, the relaxation will be more severe.

In general stainless spring steels have excellent relaxation properties due to their high yield strength and good mechanical properties at elevated tempera-tures, better than carbon steel and much better than copperbased spring materials. Particularly at elevated temperatures, the stainless grades are significantly better than both carbon steel and copper alloys.

By adding a tin coating on one side, Sandvik Santronic offers excellent soldering properties for shielding cages.

16 Base materials

exCelleNT SpRiNg pRopeRTieS The base materials’ excellent mechanical properties assure good spring properties and long lasting service.

fatigueThe following data refer to 20°C (68°F) in a normal dry atmosphere. They are not guaranteed values but are to be taken as recommenedations concerning the choice of size, stress level, etc. The fatigue limit is defined as the stress at which 50% of the specimens withstand a minimum of 2 million load cycles.

The fatigue strength increases with increasing tensile strength, and remains unchanged up to about 200°C beyond which point it starts to diminish.

Bending fatigue testingBending fatigue is tested by reversed bending stress. The test pieces are fixed at one end and the other end is bent first in one direction (upwards) then in the other direction (downwards). This procedure creates alternat-ing tensile stresses in both surfaces. The bending is controlled so that the stresses in the surfaces are equal and the average stress is zero. The bending is done transversal to the rolling direction.

Sandvik 12R11

Tensile fatigue limit, Tensile fatigue limit, ksistrength, Mpa strength,Rm Rm Thickness, mm Thickness, inchMpa 0.50 0.75 ksi 0.020 0.030

1500 ± 555 ± 525 218 ± 80.5 ± 76.2

1700 ± 560 ± 545 247 ± 81.3 ± 79.1

1900 ± 570 ± 560 276 ± 82.7 ± 81.3

2000 ± 600 ± 580 290 ± 87.1 ± 84.2

Sandvik 11R51

Tensile fatigue limit, Tensile fatigue limit, ksistrength, Mpa strength,Rm Rm Thickness, mm Thickness, inchMpa 0.25 0.50 ksi 0.010 0.020

1700 ± 580 247 ± 84.2

1900 ± 590 276 ± 85.6

2100 ± 775 ± 630 305 ± 113 ± 91.4

2300 ± 780 334 ± 113

Sandvik 13RM19

Tensile fatigue limit, Tensile fatigue limit, ksistrength, Mpa strength,Rm Rm Thickness, mm Thickness, inchMpa 0.20 0.40 ksi 0.008 0.016

1600 ± 605 232 ± 88

1800 ± 680 261 ± 99

1800 ± 635 261 ± 92

17Base materials

Sandvik 13RM19

Tensile fatigue limit, Tensile fatigue limit, ksistrength, Mpa strength,Rm Rm

Thickness, mm Thickness, inchMpa 0.40 ksi 0.016

1600 500 ± 500 232 73 ± 73

1800 535 ± 535 261 78 ± 78

Sandvik 11R51

Tensile fatigue limit, Mpa Tensile fatigue limit, ksistrength, strength,Rm Rm

Thickness, mm Thickness, inchMpa 0.25 0.50 ksi 0.010 0.020

1700 495 ± 495 425 ± 425 247 71.8 ± 71.8 61.7 ± 61.7

1900 510 ± 510 455 ± 455 276 74.0 ± 74.0 66.0 ± 66.0

2100 525 ± 525 500 ± 500 305 76.2 ± 76.2 72.6 ± 72.6

2300 540 ± 540 334 78.4 ± 78.4

Sandvik 12R11

Tensile fatigue limit, Mpa Tensile fatigue limit, ksistrength, strength,Rm Rm

Thickness, mm Thickness, inchMpa 0.25 0.50 ksi 0.010 0.020

1500 420 ± 420 405 ± 405 218 60.9 ± 60.9 58.8 ± 58.8

1700 460 ± 460 425 ± 425 247 66.8 ± 66.8 61.7 ± 61.7

1900 475 ± 475 445 ± 445 276 68.9 ± 68.9 64.6 ± 64.6

2000 480 ± 480 460 ± 460 290 69.7 ± 69.7 66.8 ± 66.8

Tensile fatigue testingTensile fatigue is tested by fluctuating tensile stress ranging from zero (no load) to the chosen maximum test load. The result is reported as the average load, for example 420 +/– 420 MPa, meaning that the load has been fluctuating from 420–420 = 0 MPa to 420+420=840 MPa. Specimens are tested parallel to the rolling direction.

For components used in radio base stations for mobile telephony, where reliability and performance are of the essence, Sandvik Santronic is the natural choice.

18 Base materials

Sandvik 15R10/Sandvik 12R11

Nominal tensile Thickness, Min. bending radius strength, Rm t as function of thicknessMpa mm ^ //

1300 0.25 0.5 t 1 t

1300 0.50 0.5 t 2.5 t

1300 0.75 1 t 3 t

1300 1.0 1 t 3.5 t

1500 0.25 1 t 3.5 t

1500 0.50 1 t 5 t

1500 0.75 1.5 t 5.5 t

1500 1.0 2 t 6 t

1700 0.25 1.5 t 6.5 t

1700 0.50 2 t 9 t

1700 0.75 2.5 t 9.5 t

1700 1.0 3 t 9.5 t

1900 0.25 2 t 10 t

1900 0.50 3.5 t 11 t

1900 0.75 5 t 12 t

Sandvik 11R51

Nominal tensile Thickness, Min. bending radius strength, Rm t as function of thicknessMpa mm ^ //

1700 0.25 1.5 t 6.5 t

1700 0.50 2 t 9 t

1700 0.75 2.5 t 9.5 t

1700 1.0 3 t 9.5 t

1900 0.25 2 t 10 t

1900 0.50 3.5 t 11 t

1900 0.75 5 t 12 t

2050 0.25 2.5 t 14 t

Sandvik 13RM19

Nominal tensile Thickness, Min. bending radius strength, Rm t as function of thicknessMpa mm ^ //

1300 0.25 0.5 t t

1300 0.50 0.5 t 4 t

1500 0.25 1.5 t 3.5 t

1500 0.50 1.5 t 6 t

^ Bend transverse to the rolling direction

// Bend parallel to the rolling direction

BendabilityThe values given below have been obtained by bending according to Swedish standard SS 11 26 26 method 3. They can be used as guidance for the smallest recom-mended bending radius.

Sandvik Santronic offers new solution opportunities with its excellent bending and forming properties.

19Base materials

Surface roughness Class Class limit Class mean Ra, μm (μin.) Ra μm (μin.)

Y2 3.2–8 (126–315) 5.0 (197)

Y3 1.6–4 (63–157) 2.5 (98)

Y4 0.8–2 (31–79) 1.25 (49)

Y5 0.4–1 (16–39) 0.63 (25)

Y6 0.2–0.5 (8–20) 0.32 (13)

Y7 0.1–0.25 (4–10) 0.16 (6)

Y8 0.05–0.125 (2–5) 0.08 (3)

Tolerance Width < 20 mm (0.8 in.) Width 20–≤50 mm (0.8–≤2 in.) Width >50 mm (>2 in.)Class Cross bow Coil set Cross bow Coil set Cross bow Coil set % of width mm/300 mm % of width mm/300 mm % of width mm/300 mm (in./11.8 in.) (in./11.8 in.) (in./11.8 in.)

P1 0.6 35 (1.38) 0.8 35 (1.38) – 35 (1.38)

P2 0.4 20 (0.79) 0.6 20 (0.79) – 20 (0.79)

P3 0.3 10 (0.39) 0.4 10 (0.39) – 10 (0.39)

Cold rolled condition in tensile strengths of 1100 MPa and above. Maximum values.

flaTNeSSTo ensure the dimensional accuracy of products, Sandviks cold rolling mills are equipped with automatic gauge control and roll gap symmetry systems. Any deviations in shape characteristics are measured to guarantee the dimensions of the products delivered. The important characteristics for strip products are,

typically, thickness, flatness and straightness. Deviations from flatness could be in the form of

waviness (like edge waves or internal buckles), coil set and cross bow. Standards for deviations in coil set and cross bow according to different tolerance classes are given in the tables.

SuRfaCeS Sandvik Santronic is delivered with a bright, coldrolled surface. Typical surface roughness (Ra-value) for thicknesses above 0.10 mm is 0.10–0.25 µm. For thicknesses 0.10 mm and below, typical roughness is 0.05 to 0.12 µm. For critical applications, specific requirements for surface roughness, brightness and/or texture can be met.

Waviness Coil set Cross bow

20 Base materials

Width Max out-of-straightness, mm (in.). length 1 m (3 feet). Tolerance class1)

mm (in.) R1 R2 R3 R4

Cold rolled conditionTensile strength < 1100 Mpa8 – < 20 (0.31–0.79) 5 (0.2) 2 (0.079) 1.5 (0.059) 1 (0.039)

20 – < 50 (0.79–1.97) 3.5 (0.14) 1.5 (0.059) 1 (0.039) 0.7 (0.028)

50 – < 125 (1.97–4.92) 2.5 (0.098) 1.25 (0.049) 0.8 (0.031) 0.5 (0.02)

125 – (4.92) 2 (0.079) 1 (0.039) 0.5 (0.02) 0.3 (0.02)

Tensile strength 1100−1800 Mpa– < 8 (– 0.31) 7 (0.28) 4 (0.16) 2.5 (0.098) –

8 – < 20 (0.31–0.79) 5 (0.2) 3 (0.12) 2 (0.079) –

20 – < 50 (0.79–1.97) 4 (0.16) 2.5 (0.098) 1.5 (0.059) –

50 – < 125 (1.97–4.92) 2.5 (0.098) 1.5 (0.06) 1.25 (0.049) –

125 – (4.92) 2 (0.079) 1 (0.039) 1 (0.039) –

Tensile strength >1800 Mpa– < 8 (– 0.31) 8 (0.31) 5 (0.2) 3 (0.12) –

8 – < 20 (0.31–0.79) 6 (0.24) 4 (0.16) 2.5 (0.098) –

20 – < 50 (0.79–1.97) 5 (0.2) 3 (0.12) 2 (0.079) –

50 – < 125 (1.97–4.92) 3 (0.12) 2 (0.079) 1.5 (0.059) –

125 – (4.92) 2 (0.079) 1.5 (0.059) 1 (0.039) –

1)R0 = no requirements

R9 = according to customer’s specification

STRaigHTNeSSThe figure below shows how deviation from straight-ness is defined.The values in the table give the deviation from straightness for the length of 1 metre. Deviations from straightness can be determined for other lengths using the formula:

a=bxL2, wherea=the required deviation from straightness in mm for a given length, in m.b=deviation from straightness according to the table.Conversion between two lengths, L1 and L2

Different coatings for different needs – finger stocks and spring fingers made from Sandvik Santronic.

21Base materials

Thickness tolerances

Thickness Tolerance, mmmm Normal fine precision Special

0.04 - <0.05 ± 0.006 ± 0.004 ± 0.002

0.05 - <0.10 ± 0.010 ± 0.006 ± 0.004 ± 0.003

0.10 - <0.15 ± 0.010 ± 0.008 ± 0.006 ± 0.004

0.15 - <0.20 ± 0.015 ± 0.010 ± 0.008 ± 0.005

0.20 - <0.25 ± 0.015 ± 0.012 ± 0.008 ± 0.006

0.25 - <0.30 ± 0.017 ± 0.012 ± 0.009 ± 0.006

0.30 - <0.40 ± 0.020 ± 0.015 ± 0.010 ± 0.008

0.40 - <0.50 ± 0.025 ± 0.020 ± 0.012 ± 0.008

0.50 - <0.60 ± 0.030 ± 0.020 ± 0.014 ± 0.009

0.60 - <0.80 ± 0.030 ± 0.025 ± 0.015 ± 0.010

Width tolerances

Thickness Width Width tolerance ±, mmmm mm B1 B2 B3 B4

< 0.25 < 20 0.07 0.05 0.03 0.02

20 -< 50 0.10 0.07 0.05 0.035

50 -<125 0.15 0.11 0.07 0.05

125 -< 250 0.20 0.15 0.10 0.07

250 -< 400 0.30 0.20 0.15 0.10

0.25 - 0.40 < 20 0.10 0.07 0.05 0.03

20 -< 50 0.15 0.11 0.07 0.05

50 -<125 0.20 0.15 0.10 0.07

125 -< 250 0.25 0.20 0.15 0.10

250 -< 400 0.35 0.30 0.20 0.15

ToleRaNCeS

good CoRRoSioN pRopeRTieS A common problem with spring applications is leakage from batteries. This may cause corrosion, which in turn often leads to contact failure.

The good corrosion resistance of stainless steel is due to the very thin and highly insoluble passive film which will form on the surface of a steel containing about 12 per cent chromium.

Corrosion resistance is futher improved by increased chromium content and when a steel is alloyed with

molybdenum. Nickel also enhances resistance to certain types of corrosion.

All three standard base materials have a comparable corrosion resistance, hence good resistance to aggres-sive environments. The high nitrogen content is known to be beneficial to resistance to pitting and crevice corrosion. However, all austenitic steels of this type are susceptible to stress corrosion cracking when in contact with chloride solutions at elevated temperatures.

Tested according to ASTM B117. Saltspray test.

22 Material selection guides

The following guides are aimed at giving a simple indication of the best choice of base material and coating for particular requirements. The higher the column, the better the property.

The blue guide refers to base materials and illus-

trates how characteristic properties can be improved compared to Sandvik 12R11 by selecting other base materials from among our wide assortment.

The green guide shows how a selected coating improves characteristic properties compared to an uncoated material.

Material selection guides

13RM19

3R12

SAF 2205

9RU10

11R51

Fatigue strength

Non-magnetic

3R127C27Mo2 9RU10 30411R51

11R5111R51

430 11R51

7C27Mo2

9RU10 316

SAF2205

SAF2507

Relaxation

Corrosionresistance

Ferro- (soft)magnetic

Ferro- (hard)magnetic

Tensile strenght

Formability15R10/12R11

BaSe MaTeRial SeleCTioN guide

23Material selection guides

Tin[Sn]

Nickel[Ni]

Tin[Sn]

Silver[Ag]

Static contact

Soldering

Nickel[Ni]

Silver[Ag]

Cupper[Cu]

Copper[Cu]

Tin[Sn]

Silver[Ag]

Nickel[Ni]

Nickel[Ni]

Silver[Ag]

Silver[Ag]

Nickel[Ni]

Nickel[Ni]

Silver[Ag]

Tin[Sn]

Copper[Cu]

Silver[Ag]Fretting

resistance

Betterconductivity

Elevatedtemperature

Dynamic contact

Lesstarnishing

Lower contact resistance

SuRfaCe CoaTiNg SeleCTioN guide

24 Mechanical and electrical properties

Mechanical and electrical properties of alloys

alloy grade Composition density1 Modulus Thermal exp ansion electrical Recom. Max. Tensile yield elong. of elasticity2 coefficient conductivity service temp.°C strength3 strength Sandvik eN aSTM/uNS g/cm3 Mpa 20–300°C % iaCS for springs Mpa Mpa % x10-6

Stainless steel 1C34 1.4016 430 Cr 17, Fe rem. 7.8 200000 10.5 2.8 600 300 20

6LR10 1.4301 304 Cr 18, Ni 9, Fe rem. 7.9 185000 16.5 2.4 600 250 40

15R10/12R11 1.4310 301 Cr 17, Ni 7, C 0.08, 7.9 185000 16.5 2.4 250 1400 1250 12 Fe rem.

11R51 (1.4310) (301) Cr 16.5, Ni 7.5, 7.9 185000 16.5 2.4 300 2050 1950 2 Mo 0.7, C 0.09, F rem.

9RU10 1.4368 631 Cr 17, Ni 7, Al 1.0, 7.9 190000 14 2.0 350 1500 1400 6 Fe rem.

13RM19 1.4369 – Cr 18, Ni 7, Mn 6, 7.9 190000 18 2.4 250 1600 1440 3 N 0.25, Fe rem.

7C27Mo2 Cr 13.5, Mo 1.0, 7.7 210000 11.4 2.8 250 1800 1450 2 C 0.38, Fe rem.

Carbon steel 15LM 1.1248 1074 C 0.75, Mn 0.75, 7.85 210000 12.4 8 120 1700 1300 6 Fe rem.

Brass – CuZn30 C26000 Zn 30, Cu rem. 8.5 110000 20 28 90 650 450 3

Phosphor bronze – CuSn6 C51900 Sn 6.0, P 0.2, 8.85 110000 18 14 80 700 620 10 Cu rem.

Nickel silver – CuNi18Zn20 C75200 Ni 18, Zn 19, 8.75 124000 16.2 6 510 430 8 Cu rem.

Copper beryllium – CuBe2 C17200 Be 2.0 , Cu rem. 8.25 128000 17.8 22 150 1350 1200 3

The table contains typical values. The grades can be delivered in other tempers with properties

that deviated from those listed.

The grades listed are popular examples from each alloy type. Numerous other grades

with deviating composition and properties exist.

1) Density. Sandvik Santronic has 10% lower density than for example nickel silver. This means

that a Sandvik Santronic strip is 10% lighter and the customer can buy 10% less material.

2) Modulus of elasticity. Sandvik Santronic has higher modulus of elasticity than copper alloys.

Consequently a Sandvik Santronic spring can be made thinner and still give the same spring force.

Together with Sandvik Santronics lower density this amounts to 25% lighter spring compared

to nickel silver.

3) Tensile strength. The difference in tensile strength means that a Sandvik Santronic spring

can be loaded to 65% higher stress. By redesigning the spring it can be made much thinner.

25Mechanical and electrical properties

alloy grade Composition density1 Modulus Thermal exp ansion electrical Recom. Max. Tensile yield elong. of elasticity2 coefficient conductivity service temp.°C strength3 strength Sandvik eN aSTM/uNS g/cm3 Mpa 20–300°C % iaCS for springs Mpa Mpa % x10-6

Stainless steel 1C34 1.4016 430 Cr 17, Fe rem. 7.8 200000 10.5 2.8 600 300 20

6LR10 1.4301 304 Cr 18, Ni 9, Fe rem. 7.9 185000 16.5 2.4 600 250 40

15R10/12R11 1.4310 301 Cr 17, Ni 7, C 0.08, 7.9 185000 16.5 2.4 250 1400 1250 12 Fe rem.

11R51 (1.4310) (301) Cr 16.5, Ni 7.5, 7.9 185000 16.5 2.4 300 2050 1950 2 Mo 0.7, C 0.09, F rem.

9RU10 1.4368 631 Cr 17, Ni 7, Al 1.0, 7.9 190000 14 2.0 350 1500 1400 6 Fe rem.

13RM19 1.4369 – Cr 18, Ni 7, Mn 6, 7.9 190000 18 2.4 250 1600 1440 3 N 0.25, Fe rem.

7C27Mo2 Cr 13.5, Mo 1.0, 7.7 210000 11.4 2.8 250 1800 1450 2 C 0.38, Fe rem.

Carbon steel 15LM 1.1248 1074 C 0.75, Mn 0.75, 7.85 210000 12.4 8 120 1700 1300 6 Fe rem.

Brass – CuZn30 C26000 Zn 30, Cu rem. 8.5 110000 20 28 90 650 450 3

Phosphor bronze – CuSn6 C51900 Sn 6.0, P 0.2, 8.85 110000 18 14 80 700 620 10 Cu rem.

Nickel silver – CuNi18Zn20 C75200 Ni 18, Zn 19, 8.75 124000 16.2 6 510 430 8 Cu rem.

Copper beryllium – CuBe2 C17200 Be 2.0 , Cu rem. 8.25 128000 17.8 22 150 1350 1200 3

26 Replacement of copper alloy springs

Being the optimum choice for battery springs, contact springs, shielding cages, etc, Sandvik Santronic plays a vital role in people's everyday lives.

27Replacement of copper alloy springs

TypiCal WeigHT ReduCTioN: 25%Replacing copper alloy springs with Sandvik Santronic will result in substantial weight reduction. Simply by utilizing the advantages in physical and mechanical properties that Sandvik Santronic offers, weight reductions of 25% are normally achieved.

diffeReNCe iN deNSiTyThe density of Sandvik Santronic is 7.85g/cm3, which is significantly lower than the density of for instance phosphor bronze of 8.85g/cm3. This means that 1m2 of Sandvik Santronic strip weighs 11% less than 1m2 of phosphor bronze strip in the same thickness.

diffeReNCe iN youNg’S ModuluS (e-ModuluS)Sandvik Santronic has an E-modulus of 185000 MPa which is much higher spring force than the E-modulus of phosphor bronze of 110000 MPa. This has the consequence that Sandvik Santronic is significantly stiffer than phosphor bronze, and a spring in Sandvik Santronic will offer much higher spring force than a similar spring made in phosphor bronze. So when an

existing spring in phosphor bronze is replace with Sandvik Santronic, it is necessary to reduce the thick-ness of the spring in order to achieve the same spring force. The thickness reduction needed to balance out the difference in E-modulus is 16%.

an exampleA spring in phosphor bronze is made in 0.30 mm thick strip, and for each spring 25x40 mm of strip is used.

To produce 1000 springs is needed:0.025 • 0.040 • 0.30 • 8.85 • 1000=2.65kg of phosphor bronze strip

The spring is replaced with Sandvik Santronic. In order to have the same spring force and spring characteristic, the thickness is reduced by 16% from 0.30 mm to 0.25 mm. To produce 1000 springs requires:0.025 • 0.040 • 0.25 • 7.85 • 1000 = 1.96kg of Sandvik Santronic strip

Weight saving: 26%

Replacement of copper alloy springs with Santronic

A spring in Cu-alloy will deliver a certain spring force when it is deflected.

Cu-alloy

Sandvik Santronic 301

Sandvik Santronic 301

kg

kg

kg

As stainless steel is stiffer (higher E-modulus) than copper, a spring in stainless steel will deliver higher spring force than the spring in Cu-alloy.

As stainless steel is stiffer, a spring in Cu-alloy can be replaced by a thinner spring in stainless steel that still delivers the same spring force.

I.e. less material is used.

28 Basic electricity

uNiTSThe electrical units used to express and calculate electrical circuits are the following:

Electrical voltage, V: Volt [V]Electrical current, I: Ampere [A]Electrical resistance, R: Ohm [Ω]Electrical power, P: Watt [W]

Ampere is an SI base unit. The other units are derived units in the SI system. The units are used all over the world.

The SI system is the international system of units and it has been officially adopted by all nations in the world with the exception of Myanmar, Liberia and USA. Link: http://www.bipm.org/en/si

electrical circuitsIn an electrical device, the different components are connected by leads to form circuits that can provide us with lighting, heat, information or power. A very simple example of an electrical circuit is the following consisting of a battery, a light bulb and switch:

In the curcuit diagram to the right, the battery is presented as a voltage source and the bulb as a resistor.

oHMS laWIn an electrical curcuit the current is proportional to voltage and inversely proportional to the resistance between them. This is expressed in Ohms law:

With this equation the current can be calculated from the voltage and the resistance etc.

eleCTRiC poWeR – eNeRgy loSS iN ReSiSToRThe electric power flowing in an electric circuit does work for us in many useful forms, such as heat (electrical heaters), light (light bulbs), motion (electric motors) and sound (loudspeaker). Electric power is represented by the letter P in electrical equations and it is calculated by multiplying the voltage and the current, also referred to as Joules law:

In cases where the resistor is the resistance in a lead or the contact resistance in a switch, the power is calcu-lated the same way; but is then an expression of the loss in the lead or switch.

It is also possible to combine Joules law and Ohms law, in order to express the power (or the loss) by the resistance and the current:

The energy loss in a resistor will generate heat, and if the current is high the temperature of the resistor can rise dramatically, as the energy loss is equivalent to the current squared. In most electronics this is hardly a problem, but the energy loss and temperature rise needs to be considered carefully for connectors and contact-springs carrying high currents.

V

R

I

Basic electricity

I = or V = R • I or R =R

V

I

V

P = V • I

P = V • I and V = R• I P = R• I2

29Basic electricity

CoMBiNaTioN of ReSiSToRSWhen resistors are combined in curcuits, the total resistance is calculated depending on the way the resistors are combined. In series it is easy. Here the resistance is simply added, expressing that the current needs to flow through all resistors:

In parallel it is a bit more complicated. Here the current can flow through either of the resistors and the total resistance is calculated the following way:

ReSiSTiviTy, CoNduCToRS, SeMi-CoNduCToRS aNd iNSulaToRSResistivity is a material property and expresses how strongly the material opposes the flow of electric current. Low resistivity indicates that the material readily allows the movement of electrical charge. Materials with low resistivity are referred to as conduc-tors, and that includes most metals. Materials with medium resistivity are called semiconductors and these materials are used in production of different electronic components. Materials with high resistivity are insulators and include most oxides, polymers and many compounds. Some examples:

Resistivity is normally expressed by the greek letter ρ (rho). From the resistivity, the resistance of a uniform specimen can be calculated by this formula:

R Resistance in Ohms (Ω)ρ Resistivity in Ohm-metres (Ωm)l Length in metres (m)A Cross section ares in metres squared (m2)

If, for instance, you think of a wire, the formula expresses that the longer the wire (l), the larger the resistance, and the thicker the wire (A), the less the resistance, which is quite logical and consistent with the formulae for combined resistors.

R1 R2 R3

R1

R2

R3

R = ρ • Al

Rtotal = R1 + R2 + R3

Rtotal R1 R2 R3

1 1 1 1= + +

Resistivity

ohm-meters

Conductors Copper 1.7•10-8

Iron 1.0 •10-7

Semiconductors Graphite 10-5

Silicon 105

Insulators Paraffin 1015

Porcelain 1020

30 Basic electricity

CoNduCTiviTyConductivity and conductance express the same physical phenomena as resistivity and resistance, but from another point of view:

Resistivity expresses how strongly the material opposes the flow of electric current and conductivity expresses how easily the electrical current flows through the material.

The unit for conductance is Siemens (S) and:

A common unit of conductivity of metals is % IACS and is the materials conductivity relative to standard annealed copper. IACS stands for International Annealed Copper Standard.

CoNduCTiviTy of CoaTed STRipAs conductance is reciprocal to resistance, the calcula-tion of resistors in parallel becomes easy if done by conductance:

This is very helpful when calculating conductance (or conductivity) of coated strip as the strip can be considered as two parallel resistors where we can add the conductance of the different layers:

Conductivity

pure metals % iaCS

Cu 100

Al 65

Sn 15

Ag 109

Au 78

Ni 25

Fe 18

R1

R2

R3

t1

t2t

R1

R2

Conductance (G) is reciprocal to resistance (R)and Conductivity (σ) is reciprocal to resistivity (ρ)

100% IACS = 58 MS/m

Rtotal R1 R2 R31 1 1 1= + +

Resistance

Gtotal = G1 + G2 + G3

Conductance

Gtotal = G1 + G2

1 Siemens (S) =1

Ohm

Conductivity

alloys % iaCS

CuBe 15–22

Brass 19

Nickelsilver 6–9

Steel 10–15

304 2.4

301 2.4

430 2.8

31Basic electricity

σSandvik Santronic = σ1 • + σ2 •t

t1

t

t2

an example

0.10mm 304 with 1µm Cu on one side.

σSandvik Santronic = 2.4% IACS • + 100% IACS •

σSandvik Santronic = 3.4% IACS

I.e. 1µm Cu improves the conductivity by more than 40%.

0.101

0.1

0.101

0.001

Also, if we calculate on the basis of conductivity, this is done in the same way, but each layer needs to be weighted with the ratio of thickness:

In an increasingly complex electronics industry, Sandvik Santronic will help you find your way.

S-SY

016-

B-EN

G. 1

0.20

08. P

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Sandvik Materials TechnologySE-811 81 Sandviken, Sweden, Phone: +46 26-26 00 00, Fax +46 26-26 02 71

www.smt.sandvik .com