mil-s-46844c ing mil-s-o046844b(mi)...

MIL-S-46844C15 October 1976

INGMIL-S-O046844B(MI)15 November 1975MIL-S-46844A2 May 1969

MILITARY SPECIFICATION

SOLDER BATH SOLDERING OF PRINTED WIRING ASSEMBLIES

This specification is approved for use by all Departmentsand Agencies of the Department of Defense.

1. Sco e.---$--

This specification covers machine soldering processesfor printe board assemblies used in eletrical and electronic equipment.

2. APPLICABLE DOCUMENTS

2.1 The followinq caovernwmt documents of the issue in effect onthe date of invitatio~ ?or bids orof this speclfjcation to the extent

SPECIFICATIONS

Federal

QQ-S-571

Military

MIL-F-14256

MIL-P-28809

MIL-S-45743

MIL-P-46843

STANDARDS

Military

request for proposal form a partspecified herein.

Solder, Tin Alloy, Tin-Lead Alloyand Lead Alloy

Flux, Soldering, Liquid (Rosin Base)

Printed Uiring Assemblies

Soldering, Manual Type, High Reliability,Electrical and Electronic Equipment

Printed Hiring Assemblies

MIL-STD-202 Test Methods Yor Electronic and ElectricalComponent Parts

MIL-STD-429 Printed Wiring and Printed CircuitsTerms and Definitions FSC THJM

~ Beneficial comments (recommendations, additions,—

deletions) and any pertinent data ‘

which may be of use in improving this document should be addressed to: Commander,

U.S. Army Missile C~

L-

d, An’N: DRSMI-RCS, Redstone Arsenal, AL 35809 by using

the self-addressed Standardization Document Improvement Proposal (DD Fomn 1426)appearing at the end of this document or by letter.

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(Copie: gf specifications, standaras, drawings, and publications~equired b, suppliers in ccnnec~ Ion with specif~c procurement functionsn,ajfbe obtained from the procuring activity or as directed by thecontracting officer. )

2.2 Other publications. The following documents form a partof this speclflcatlon to the extent specified herein.

IPC-S-801 (Dee 1970) Edge Dip Solderability Test forPrinted Wiring Boards

(Application for copies should be addressed to Institute of PrintedCircuits, 1716 Howard Street, Evanston, IL 60202).

2.3 Conflict of documents. In case of conflict between any requirementspecified herein, and any c=ained in the engineering documentation(including other specifications or standards referenced therein) therequirements of the engineering documentation shall prevail.

3. REQUIREMENTS

3.1 Applicability. These requirements are applicable to machinesoldering operations and application of solder only.

3.2 Materials, Except when otherwise specified on detailed drawings,the materials utilized in soldering operations shall conform to therequirements.

3.2.1 Solder. An Sn 60 or Sn 63 tin lead solder, types conformingto QQ-S-571~1 be used.

3.2.2 Flux. Rosin based fluxes conforming to QQ-S-571 andMIL-F-14256–s~l be utilized. Type RA flux shall not be used excepton printed board assemblies without stranded wires.

3.2.3 Cleaning solvent. Solvents to be used for the removal ofprocess ccntarinants and residues from parts and solder joints shallnot degrade or damage the materials in the parts being cleaned.

3.3 ~acil ities, equipment and tools.

3.3.1 The soldering area. The soldering area and machinesshall be clean and orderly. Contaminants shall be precluded fromthe area.

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3,.?.1.2?vapors shall

3.3.1.3

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Exhaust for volatile and toxic vapors. Toxic or volatilebe exhausted ]n accordance with the OStiA standards.

Work S~. Working surface lighting ofsoldering stations shall be 00 foot-candles minimum (1077 lm/m2).Supplemental lighting may be used as required. “ - ‘

3.3.2 Soldering equipment. The soldering machines usedshall heat the printed board assemblies uniformly and have thecapacity to maintain the temperature during repetitive solder operationswith a maximum temperature variation of : 10”F (5.6”C) of the nominalsoldering temperature.

3.3. Cutting and forminq tools for conductor and component leads.Cutting and forming tools shall be as spticified in the applicableparagraphs of MIL-S-45743.

3.3.1 Insulation strippers. Insulation strippers shall be asspecified in the appllcabl e paragraphs of MIL-S-45743.

3.4 General soldering requirements.

3,4,? The solder machine and work station maintenance. Work areasand tools shall be maintained in a clean and orderlv condition. All dirt,grease, flux, solder spatter, chips, and other cont~minating foreign -matter shall be promptly removed. Smoking, eating and drinking at thesoldering work station shall not be permitted.

3.4.1.1 Dross cmtrol. Dross shall be periodically removed fromthe solder bath to assure that dross does not mix with the liquid solder.Automatic or manual methods are acceptable provided that the dross doesnot come in contact with the printed wiring assembly during any portionof the soldering process.

3.4.1,2 Dross control materials. Special oils formulated for drosscontrol shall have a flash point higher than the maximum temperature ofthe solder bath. Such oils shall be compatible with liquid solder andthe solder process and shall have an auto ignition point a minimum of10*F (5.6°C) higher than the maximum temperature of the solder bath.Other materials, a nitrogen blanket or glass balls, may be used providingprior approval is obtained from the procuring agency.


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“.P -~-,L ~r(~ess hand? ins an(.~stordge.Li’!-1 The p!inted buarcs...... -—‘.(J:>(.’ller,l.‘., ‘ailaU:\(A.Iml-~~_SShafl-Fe-‘p;”o~eytecifrom contamination anddai:.a~erlu~-,njhanflli~!$,asser;b?y, and storage operctjons. Soldered~uL.:~semblies aftci~s’:.emblicsshall, subsequent to cleaning operationsand prior to any encapsulation processing, be handled to precludecontamination,

NOTE : Printed board assemblies should be handled only by their edgesGr with lint-free gloves that are also free of oils, solventresidue, soil, or other contaminants that could be transferredto the assemblies.

3.4.3 SQ]derabi~it .+

All surfaces to be soldered that do not conformto the requlnywnts o MIL-5T&20Z, T~st Method ?08, and all printedwiri-.g:circuits that do not conform to IPC-S-801 shall he retinned orreplated t.oprovide solderability conforming to the MIL-STD-202 orIPC-L-801 requirements, as applicable. To prevent gold embrittlement,those dress of gold plated parts to be soldered shall be subjected to akuble tinning operation or the gold removed and a single tinningoperation performed, More active fluxes than those specified in 3.2.2may be used, provided all ionic and non-ionic contaminants are removedwithin one hour from the time that the item was ,retinned.

3.4.4 Documenta~ion. The contractor shall have written operatingprocedures fiscribingfie soldering pi-ocess and the prcper operation ofthe automtic soldering machine and associated equipment. For thesoldering ~achin[’, these procedures, as a minimum, shall define theprehepc temperature, solder temperature, rate of tr~vel, frequency~}f~~eretum ~erific;ation measurements, frequency of solder batharldl’fsis,maskinq and cleanina F_@LjL:irE?mentS. If any of the abG:emenk-io!iedcharac;tiristics mus~ be adjusted <board assemblies, the procedure shall identassembly drawing number, or other positivesetting to be utilized for each assembly.

3.5 Operations prior to soldering_.

3.5.”to startassembly

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or different printedfy bv printed boarddent~fication means, the

%wi- Printed board assemblies shall be clean priorof t e so derlng operations. Cleanliness of the printed wiringshall be sufficient to insure solderability.

Printed circuit boards that have been stored may haveabsorbed moisture and shouid be baked prior (within 8hours) to soldering to prevent corrosion or otherdegradat~on.

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3.5.2 Maskine

Areas of printed board assemblies not to besoldered sha e masked prior to the application of solder flux.The materials used must be compatible with the flux/solder processand shall not cause fire or create fire or health hazards.

3.5.3 The preparation of leads and terminals. The preparation ofleads and terminals shall be in accordance with the applicable paragraphsof MIL-S-45743.

3.6 Machine soldering.

3.6.1 Machine soldering shall be performed using an integralsystem having the follwing characteristics:

(a) All operations shall be performed semi-automatical?yor automatically.

(b) Controlled fluxing unit. The fluxing unit can be a separate, non-integral, operation if the solder is applied within two minutes from theapplication of the flux.

(c) Controlled preheating.

(d) Temperature controlled solder.

(e) Cooling areas.

(f) Controlled conveyor speed.

3.6.2 Flux application. The flux shall be applied by thedip, spray, brush, wave, foam, or other method which will produce aneven coated surface. Any thinner used shall be a product from theflux manufacturer recommended for the specific flux being utilized.

3.6.3 Preheatin4

The boards shall be preheated to a temperaturecompatible wlt t e UX, conveyor speed, solder temperature, and timeof solder contact.

3.6.4 Application of solder. The temperature of the solderbath in the area of contact with the printed wiring board shallbe held at 500” ~25°F (260°C ~14°C).

3.6.5 The solder contact. The printed board thickness andjoint density are critical factors in setting the solder contact. Thewave height or other contact method shall be adjusted to assure full solderflow and effective contact with the printed board across the full widthof the board. The time of contact between printed board assemblies

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,~l~dt-? LLIldeY sn~~l be pre~electec, deper)dent upon preheating, thicknessC? board, number of cantact~ or cGn:ductors, and the type of components.The length of time at temperature shall not cause damage to heatsensitive componer,ts or the structure of the board. Components shall beconstr~ined to assure lmdr do not move during the solder cycle.

3.6.6 Solder bath surfac~. Adequate means shall be taken to maintainthe solder bath clea~iness during the soldering processes.

3.6.7 C3nveyor. The conveyor shall transport printed boardassemblies through the fluxer (optional), preheater, solder, and cooling areThe selected conveyor speed shall be adjusted to assure compliancewith 3.6.5. The speed shall not vary more than one inch per minute.

3.6.8 Coolirr~. The printed board assemblies shall not be lifted— ---.~r’ulllLile~onveyor, nur shdll there be any method of forced cooling,until the solder has solidified after the completion of contact withthe solder bath.

3.6,9 Solder bath contamination limits. To maintain the properpurity of the solder bath, the amount of contaminants shall not exceedthe percentage specified in Table I.

TABLE I

AntimonyArsenicCopperIronGoldCadmi urnZincAluminum

SOLDER BATH CONTAMINATION LIMITS

Contaminant

Maximum Accumulative Impurities

Percentage(Maximum)

0.75%0.05%0.5%o.02%0.2%0.01%O.008%o.008%

1.5%

,.

Maximum Gold-Copper Combination o.40%


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MIL-:-46844C

3,7 ~ost solder-~erations..—

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3.7.1 Cleanin~ +“

Cleaning of soldered printed board assembliesshall be ~nltlate as soon as solder has solidified but no more than1 hour after the board assembly has been soldered. As soon as theboard has cooled to the cleaning temperature, solder masks shall beremoved . Excess solder shall be removed so that the connection isclean. Mechanical methods such as fil~ng, grinding, or scrapingshall net be used. All residual flux and soils shall be removed usingsolvents or combinations of solvents which will remove contaminants.After final cleaning, finished products shall not be contaminatedby handling or environment.

3.7.2 Touch up or rework. Any touch up or rework by manualsoldering shall be in accordance with MIL-S-45743.

3.8 Resistivity of solvent extract. When uncoated printedboard assemblies are tested as specif ied in 4.3.2 the resistivity shallbe not less than 2,000,000 ohm-centimeter for each unit of 10 sqfiareinches (64.5 C%) of board surface (counting both sides but not countingthe surface areas of the components).

3.9 Solder “ofnt. The solder joint shail have a br{ght metallic~adherence.appearance wlt goo Solder shall cover the wire, conductor,

or component lead, and the solder shall form a smooth fillet betweenthe terminal area and each side of the wire or component lead. Thecontour of the wire or component lead shall be visible after soldering,although individual strands of stranded wire may be obscured. Thereshall be no defects as noted In the applicable paragraphs of NIL-S-45743.

3.10 Qualification of soldering personnel. The qualification ofsolder operators and soldering inspectors will be by certificate oftrainin per MIL-S-45743 and the manufacturers (of the soldering

Ymachine operating procedures.

3.?1 Workmanship. The workmanship, utilized in accomplishmentof the processes specified herein, shall be of a level of qualityadequate to assure that the processed products shall meet the performancerequirements of the applicable product drawings and specifications,relative to these processes. The solder connections shall have asmooth, bright appearance with metallic luster and sha’ilnot have achalky, gritty, or irregular surface, nor exhibit points (peaks). Pits,scars, fractures, trapped flux, foreign materials, or have holes whichexpose base metal (where the bottom is not visible, exposed base metalwill be assumed). The connections shall be completely covered by solder


MIL-S-46844C

to the extent tfiat.no base metal is visible, including the copper endsof cut wire or leads, Sclder beads shall not project from terminals,nor shall solder spatter exist on adjacent components or surfaces.

NOTE : The visual standards provided as figures in !411-S-45743are intended as aids in determining acceptabil~ty ofprocessed products. It is expected that strict adherenceto the specified requirements should result in a generalquallty of workmanship eq~al to the applicable upperIllustratiolls. The applicable center Illustrationsrepresent minimum acceptable standards which are undesirableas a general condition but are acceptable. The applicablebottom illustration represents unacceptable conditions.Corrective action should be taken when general qualitycf wrk!nansh+p Is oot in accordance with the applicableupper illustration.

4, QUALITY ASSURANCE PROVISIONS

4.1 Responsibility for inspection. Unless otherwise specified inthe contract, or purchase order, the supplier is responsible for theperformance of all inspection requirements as specified herein. Exceptas otherwise specified in the contract or purchase order the suppliermay use his own or any other facilities suitable for the performance ofthe inspection requirements specified herein unless disapproved by thegovernment. The government reserves the right to perform any of theinspections set forth in the specification where such inspections aredeemed necessary to assure that suppliers and services conform toprescribed ~equirements.

4.2 Quality conformance inspection.

4.2.1 One hundred percent inspection. Each soldered connection andits associ~wlrlng or leads shaTT~visually inspected to determineconformance to the requirements specified. MIL-S-45743 provides a listof defects with reference to the applicable requirements. Any defectshall be cause for rejection.

4.2.2 Sampling inspection. Sampling for cleanliness of uncoatedprinted wiring assemb lies, utilizing the resistivity of solvent extractmethod, shall be in accordance with the applicable provisions ofM?L-P-46843 0!” MIL-P-28809.

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MJL-S-46844CL

4.2.2 Proce:s~l:pection, Surveillance shall be ~o~d:jctedOn a con’ti~s~asis tc a~ur~ that the requirements fnr tools,materials, handling, equipment, facilities, and processes specifiedare stricrly adhered to. Any noncompliance shall be grounds forrejection of the material processed,

4.3 Inspection methods.

4.3.1 Visual Inspection. Visual inspection shall be performedutillzing a minimum of magnification. Lighting shall equal orexceed the requirement af 3.3.1,3. A clear incandescent light shouldbe used for detection of uncovered copper. When solder connectionsare suspected as defective, magnification conunensurate with the sizeof th~ connection shall be used to aid the visual inspection. As aguideline, magnification for visual inspection of connections inmicrcm+niature, miniature, and standard assemblies may be limitedto 70X, 30X and 10X respectively,

4,3.2 Cleanliness test. The resistivity of solvent extractmethod for cleanliness testing of uncoated printed wiring assembliesshall be in accordance with the applicable provisions of NIL-P-46843or MIL-P-28809.

4,4 Inspection standard. The applicable figures of MIL-S-45743and any zdd ?tlonal provis~ons provided or approved by the ~rocuring activity,

L shall be utilized in determining compliance with the requirements ofthis specification,

~m~ ~ua?ificaticn and ce?tificaticn. prioi” to performance of thereqti<rewnts of ++is’~e7W’3_&E’i3~solderi ng personnel qualificationanticertif!catio~ sha?l be verified to 5C in accordance with 3.10.

5. PREPARATION FOR DELIVERY

This section is not applicable to this specification.

6. NOTES

6.1 Intended use. It is intended that the soldering p;’ocedurescovered in this specification are to be utilized for the sslder<ng ofhfgh reliability electrical connections in critical electrical andelectronic equipment of military weapons systems. This specificationoutllnes the basic solder~ng procedures and prccess requirements wbicF


MIL-S-46844C

are tc be emp?oyed. It is recognized that soldering connections existother than those dealtthat these connectionsof this specification.

6.2 Ordering data.

with in ~his specification, ~nd it is intendedshall be handled under the general provisions

a. Title, number and date of this specification.

b. If certification of operators is not required (see 3,10 and 4.5).

6.3 Cleaning solvents. Cleaning solvents as listed in MIL-S-45743have been found suitable for the removal of contaminants and residuesfrom parts, assp~hlies and solder connections.

6.4 Terms and definitions. Definitions applicable to thisspecification shall comply with MIL-STD-429 and MIL-S-45743.

Custodian: Preparinq Activity:Army - MI Army - M?

!’iavy- kSAir Force - 11 Project No. WJM-0069

Review Interest:Army - !4R, PA, ML, SC, ELNavy - 0SAir Force - 9g

User Interest:Army - AV, WC

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NOTE: lhis form my notbewed tokuwet rxwiaof doeument& nor to nqu-t usiw% deviAiolBe, or Clerifwdionof

epedicstion requi?emal to on current coatmctt. CammenU 4xnitted on thii fosm do tbot cxxwtitute or imply su~tion

to waiw sny portion of the refemncd document(s) or to remendcontmct~requiremeo-.

(FoId dew thk U-)

(Fold alms thb tine)

DEPARTMENTOF THE ARMY

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nNO ●OSTAGE

NEcEss4mv

IF MAILCO

IN THEUNITED -ATES

OFPOCIAL ●USINE=?ENALTV Son ●RIVATE USE S200 BUSINESS REPL’Y MAIL

FIRST CLASS PERMIT NO 120S2 WASHINGTON O CbPOflAGE WILL BE PAID BY THE DEPARTMENT OF THE ARMY

CommanderUS Army Missile CommandATTN : DRSMI-RSDSRedstone Arsenal , AL 35898

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STANDARDIZATION DOCUMENTIMPROVEMENTPR~L(i% instructions - Rcvcnc Side)

. DOCUMENT N’JMBER 2. OOCUMENT TITLE

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U.commwnd.d W ordlne:

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IDD fj”::R1426 ●REVIOUS EOITION IS O#SOLETE.

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