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ASTM B488-2011

Designation:B488–11

Standard Speci?cation for

Electrodeposited Coatings of Gold for Engineering Uses 1

This standard is issued under the ?xed designation B488;the number immediately following the designation indicates the year of original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.A superscript epsilon (′)indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.

1.Scope

1.1This speci?cation covers requirements for electrodepos-ited gold coatings that contain not less than 99.00mass %gold and that are used for engineering applications.

1.2Speci?cally excluded from this speci?cation are auto-catalytic,immersion,and vapor deposited gold coatings.

1.3Gold coatings conforming to this speci?cation are em-ployed for their corrosion and tarnish resistance (including resistance to fretting corrosion and catalytic polymerization),bondability,low and stable contact resistance,solderability,and infrared re?ectivity.Several types of coatings,differing in gold purity and hardness,are covered by this speci?cation.1.4The values stated in SI units are to be regarded as the standard.Values provided in parentheses are for information only.

1.5The following hazards caveat pertains only to the test methods section,Section 9,of this speci?cation:This standard does not purport to address all of the safety concerns,if any,associated with its use.It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

2.Referenced Documents 2.1ASTM Standards:2

B183Practice for Preparation of Low-Carbon Steel for Electroplating

B242Guide for Preparation of High-Carbon Steel for Elec-troplating

B253Guide for Preparation of Aluminum Alloys for Elec-troplating

B254Practice for Preparation of and Electroplating on Stainless Steel

B281Practice for Preparation of Copper and Copper-Base Alloys for Electroplating and Conversion Coatings B322Guide for Cleaning Metals Prior to Electroplating B343Practice for Preparation of Nickel for Electroplating with Nickel

B374Terminology Relating to Electroplating

B481Practice for Preparation of Titanium and Titanium Alloys for Electroplating

B482Practice for Preparation of Tungsten and Tungsten Alloys for Electroplating

B487Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of Cross Section

B489Practice for Bend Test for Ductility of Electrodepos-ited and Autocatalytically Deposited Metal Coatings on Metals

B499Test Method for Measurement of Coating Thick-nesses by the Magnetic Method:Nonmagnetic Coatings on Magnetic Basis Metals

B504Test Method for Measurement of Thickness of Me-tallic Coatings by the Coulometric Method

B507Practice for Design of Articles to Be Electroplated on Racks

B542Terminology Relating to Electrical Contacts and Their Use

B558Practice for Preparation of Nickel Alloys for Electro-plating

B567Test Method for Measurement of Coating Thickness by the Beta Backscatter Method

B568Test Method for Measurement of Coating Thickness by X-Ray Spectrometry

B571Practice for Qualitative Adhesion Testing of Metallic Coatings

B578Test Method for Microhardness of Electroplated Coatings

B602Test Method for Attribute Sampling of Metallic and Inorganic Coatings

B678Test Method for Solderability of Metallic-Coated Products

This speci?cation is under the jurisdiction of ASTM Committee B08on Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee B08.08.02on Precious Metal Coatings.

Current edition approved Oct.1,2011.Published November 2010.Originally approved in https://www.wendangku.net/doc/6b7708571.html,st previous edition approved in 2010as B488–01(2010)e01.DOI:10.1520/B0488-11.2

For referenced ASTM standards,visit the ASTM website,https://www.wendangku.net/doc/6b7708571.html,,or contact ASTM Customer Service at service@https://www.wendangku.net/doc/6b7708571.html,.For Annual Book of ASTM Standards volume information,refer to the standard’s Document Summary page on the ASTM website.

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B697Guide for Selection of Sampling Plans for Inspection of Electrodeposited Metallic and Inorganic Coatings

B735Test Method for Porosity in Gold Coatings on Metal Substrates by Nitric Acid Vapor

B741Test Method for Porosity In Gold Coatings On Metal Substrates By Paper Electrography 3

B748Test Method for Measurement of Thickness of Me-tallic Coatings by Measurement of Cross Section with a Scanning Electron Microscope

B762Test Method of Variables Sampling of Metallic and Inorganic Coatings

B765Guide for Selection of Porosity and Gross Defect Tests for Electrodeposits and Related Metallic Coatings B799Test Method for Porosity in Gold and Palladium Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor

B809Test Method for Porosity in Metallic Coatings by Humid Sulfur Vapor (“Flowers-of-Sulfur”)

D1125Test Methods for Electrical Conductivity and Resis-tivity of Water

D3951Practice for Commercial Packaging

F390Test Method for Sheet Resistance of Thin Metallic Films With a Collinear Four-Probe Array https://www.wendangku.net/doc/6b7708571.html,ernment Standards:4

MIL-DTL-45204Gold Plating,Electrodeposited

MIL-STD-1916DOD Preferred Methods for Acceptance of Product

2.3ANSI/ASQC Standard:5

ANSI/ASQC Z1.4Sampling Procedures and Tables for Inspection by Attributes

3.Terminology

3.1De?nitions —For de?nitions of terms used in this speci-?cation refer to Terminologies B374or B542,B374,and B542.3.2De?nitions of Terms Speci?c to This Standard:

3.2.1signi?cant surfaces —de?ned as those normally vis-ible (directly or by re?ection)or essential to the serviceability or function of the article.Can be the source of corrosion products or tarnish ?lms that interfere with the function or desirable appearance of the article.The signi?cant surfaces shall be indicated on the drawings of the parts or by the provision of suitably marked samples.

3.2.2underplating —a metallic coating layer between the basis metal or substrate and the topmost metallic coating.The thickness of an underplating is usually greater than 1μm (40μin.),in contrast to a strike or ?ash,which is thinner.

4.Classi?cation

4.1Types of Coatings —A coating shall be speci?ed by a combination of the following:

4.1.1Type,characterizing minimum purity in accordance with 4.2.1,

4.1.2Code,designating Knoop hardness in accordance with 4.2.3,and

4.1.3a numeral designating thickness in micrometres in accordance with 4.3.

4.2Purity and Hardness :

4.2.1Purity —The issue of this standard establishes a new ASTM Type designation,which is identical to the original standard (MIL-G-45204,which is now MIL-DTL-45204),established for electrodeposited gold and is outlined in the following table.

Mass Percent Gold,Minimum,Excluding Potassium,Carbon &

Nitrogen New ASTM Type

MIL-DTL-45204Type

Old ASTM Type

99.70I I 299.00II II 399.90

III

N OTE 1—It is commonly accepted that a gold purity of 99.7%is de?ned as no more than 0.3%of total codeposited metallic components,excluding potassium and sodium.Likewise,99.9%purity is recognized to mean no more than 0.1%of total codeposited metal impurities,excluding potassium and sodium.Almost all gold electrodeposits will contain potassium,carbon and nitrogen that are occluded or precipitated in the deposit.In the case of Type I gold,the occluded potassium has been shown to improve durability and is desirable for that reason.6,7

4.2.2Gold purity is calculated by subtraction of the sum of all non-gold metals in mass %,excluding potassium (K)and sodium (Na),from 100%.The presence of Carbon (C),Nitrogen (N),Hydrogen (H),Na,and K contained in the electrodeposit are not included in the calculation.

4.2.3Hardness —Hardness values shall be speci?ed by ASTM Code.The military standard designation of Grade is included for reference.

Knoop Hardness Range

ASTM Code MIL-DTL-45204Grade

90HK 25maximum A A 91–129HK 25B

B 90–200HK 25(see Note 2)

...130–200HK 25C C >200HK 25

N OTE 2—ASTM Code B has previously been speci?ed for hardness grade 90–200.This hardness grade has been eliminated and replaced with hardness grade 91–129in accordance with MIL-DTL-45204.

4.2.4Relationship Between Purity and Hardness —The fol-lowing combinations of purity and hardness ranges are repre-sentative of good commercial practice:

New ASTM Type

Old ASTM Type

Code I 2A,B and C II 3B,C and D III

A only

4.3Thickness —Thickness shall be speci?ed by an Arabic numeral that designates the minimum linear thickness in micrometres.Examples of commonly speci?ed thicknesses are shown in Table 1.

4.3.1See 7.4.2for thickness tolerances.

4.3.2Instead of specifying the thickness in micrometres,the purchaser may specify the mass of gold per unit area (coating

Withdrawn.The last approved version of this historical standard is referenced on https://www.wendangku.net/doc/6b7708571.html,.4

Available from Standardization Documents Order Desk,DODSSP,Bldg.4,Section D,700Robbins Ave.,Philadelphia,PA 19111-5098,https://www.wendangku.net/doc/6b7708571.html,.5

Available from American National Standards Institute (ANSI),25W.43rd St.,4th Floor,New York,NY 10036,https://www.wendangku.net/doc/6b7708571.html,.

Whitlaw,K.J.,Souter,J.W.,Trans.Inst.Metal Fin.,“The Role of Codeposited Elements in Gold Plated Contacts,”1984,62(1),pp.29–31.7

Whitlaw,K.J.,Souter,J.,Wright,I.S.,Nottingham,M.,Electrical Contacts ,“Wear Properties of High Speed Gold Electrodeposits,”(1984),30th.pp.

33–45.

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weight)in milligrams per square centimeter.Unless otherwise speci?ed,the density of gold is assumed to be 19.3g/cm 3for Type III and 17.5g/cm 3for Type I and Type II.

N OTE 3—The density of Type III gold coatings will be less than or equal to 19.3g/cm 3,but not less than 18.5g/cm 3.

N OTE 4—When signi?cant surfaces are involved on which the speci?ed thickness of deposit cannot readily be controlled,such as threads,holes,deep recesses,bases of angles,and similar areas,the purchaser and the supplier should recognize the necessity for either thicker deposits on the more accessible surfaces or for special racking.Special racks may involve the use of conforming,auxiliary,bipolar electrodes,or nonconducting shields.

5.Ordering Information

5.1To make the application of this standard complete,the purchaser needs to supply the following information to the supplier in the purchase order or other governing document.5.1.1The name,designation,and date of issue of this speci?cation.

5.1.2Classi?cation:Type,Code,and thickness (or mass per unit area)(see Section 4).

5.1.3Presence and thickness of underplating,if required (see 3.2.2).

5.1.4Signi?cant surfaces shall be speci?ed (see 3.2.1).5.1.5Requirement,if any,for performance testing such as porosity testing (see 9.6),solderability testing (see Appendix X4),ductility testing (see 9.7),etc.

5.1.6If the substrate is one that requires a nickel underplat-ing (see

6.5.1and Appendix X6).

5.1.7Whether or not stress relief has been or is to be done (steel parts only).

5.1.8Sampling plan employed (see Section 8).

6.Manufacture

6.1Any process that provides an electrodeposit capable of meeting the speci?ed requirements is acceptable.6.2Substrate :

6.2.1The surface condition of the basis metal should be speci?ed and should meet this speci?cation prior to the plating of the parts.

6.2.2Defects in the surface of the basis metal such as scratches,porosity,pits,inclusions,roll and die marks,laps,cracks,burrs,cold shuts,and roughness may adversely affect the appearance and performance of the deposit,despite the observance of the best plating practice.Any such defects on signi?cant surfaces shall be brought to the attention of the purchaser.

6.2.3The basis metal shall be subject to such cleaning procedures as are necessary to ensure a satisfactory surface for

subsequent electroplating (see Practices B183,B242,Guide B253,Practices B254,B281,B322,B343,B481,B482,and B558).

6.2.4Proper preparatory procedures and thorough cleaning of the basis metal are essential for satisfactory adhesion and performance of these coatings.The surface must be chemically clean and continuously conductive,that is,without inclusions or other contaminants.They must be smooth and as free of scratches,gouges,nicks,and similar imperfections as possible.

N OTE 5—A metal ?nisher can often remove defects through special treatments such as grinding,polishing,abrasive blasting,chemical treat-ments,and electropolishing.However,these may not be normal in the treatment steps preceding the plating and a special agreement is indicated.

6.3If required (see 5.1.7),steel parts with a hardness greater than 31HRC shall be given a suitable stress relief heat treatment prior to plating.Such stress relief shall not reduce the hardness to a value below the speci?ed minimum.Acid pickling of high strength steels shall be avoided.

6.3.1The coating shall be applied after all basis metal heat treatments and mechanical operations on signi?cant surfaces have been completed.

6.4Racking —Parts should be positioned so as to allow free circulation of solution over all surfaces.The location of rack or wire marks in the coating shall be agreed upon between the purchaser and the supplier.6.5Plating Process :

6.5.1Nickel Underplating —For thickness Classes except 5.0,a nickel underplating shall be applied before the gold coating when the product is made from copper or copper alloy.Nickel underplatings are also applied for other reasons (see Appendix X6).

N OTE 6—When the thickness of the nickel underplate has a detrimental impact on the mechanical properties or bondability of the substrate,the nickel thickness may be reduced to a non-detrimental level as speci?ed by the purchaser.

N OTE 7—In certain instances in which high-frequency analog signals are employed,such as in wave guides,the magnetic properties of nickel may attenuate the signal.

N OTE 8—In applications in which forming or ?aring operations are to be applied to the plated component,a ductile nickel electrodeposit should be speci?ed.

6.5.2Strikes —It is recommended to apply a gold strike to the underplate or substrate,except if the latter is silver or platinum,prior to applying the gold top coating.

6.5.3Plating —Good practice calls for parts to be electri-cally connected when entering the gold plating solution.A minimum of 0.5V is suggested.

N OTE 9—For rack and barrel plating processing,residual plating salts can be removed from the articles by a clean,hot (50to 100°C)water rinse.A minimum rinse time of 2.5min (rack)or 5min (barrel)is suggested.Best practice calls for a minimum of three dragout rinses and one running rinse with dwell times of 40s in each station when rack plating and 80s when barrel plating.Modern,high-velocity impingement-type rinses can reduce this time to a few seconds.This is particularly useful in automatic reel-to-reel applications in which dwell times are signi?cantly reduced.

7.Coating Requirements Coating Requirements

7.1Nature of Coating —The gold deposit shall meet the appropriate purity requirements as put forth in the following:

TABLE 1Coating Thickness

Class Minimum Thickness,μm

0.250.250.500.500.750.751.0 1.01.25 1.252.5 2.55.0

5.0

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7.1.1Type I coatings shall contain at least 99.70mass %gold,excluding potassium,sodium,carbon and nitrogen.For Type I Code A (“soft”)coatings only,metallic hardening agents such as nickel,cobalt or iron combined,shall be less than 0.05mass %and none of these three elements shall be present in an amount greater than 0.03mass %.All other metals excluding potassium and sodium are considered impurities and shall not be present in amounts greater than 0.05mass %combined.For Type I Code B and C coatings,metallic hardening agents such as nickel,cobalt or iron combined shall be equal to or less than 0.3mass %.All other metals are considered impurities and shall not be present in amounts greater than 0.05mass %each,0.1%combined.The gold purity shall be calculated by determining the content of all non-gold metals in mass %(except potassium and sodium)and subtracting this value from 100%.

7.1.2Type II coatings shall contain at least 99.00mass %gold,excluding potassium,sodium,carbon and nitrogen.Type II coatings may contain metallic hardening agents,such as nickel,cobalt or iron,which may be present in amounts greater than 0.3mass %.All other metals,excluding potassium and nitrogen,shall be considered impurities and shall not be present in amounts greater than 0.1mass %each.The gold purity shall be calculated by determining the content of all non-gold metals in mass %(except potassium and sodium)and subtracting this value from 100%.

7.1.3Type III coatings shall contain at least 99.90mass %gold,excluding potassium,sodium,carbon and nitrogen.Individual metal impurities shall not be present in a quantity greater than 0.04mass %.Iron,nickel and cobalt combined shall be less than 0.05mass %,and none of these three elements shall be present in an amount greater than 0.03mass %.All non-gold metals,excluding potassium and sodium,are considered impurities and shall not be present in amounts greater than 0.1mass %combined.The gold purity shall be calculated by determining the content of all non-gold metals in mass %(except potassium and sodium)and subtracting this value from 100%.

7.2Hardness —The gold coating shall have a Knoop hard-ness within the speci?ed range as shown in 4.2.3when tested in accordance with 9.2.

7.3Appearance —Gold coatings shall be coherent,continu-ous,and have a uniform appearance to the extent that the nature of the basis metal and good commercial practices permit.

7.4Thickness :

7.4.1The gold coating shall have a thickness on the signi?cant surfaces in accordance with 4.3unless otherwise speci?ed.

N OTE 10—Where Type I (Code B or C)or Type II (Code B or C)gold is speci?ed,improved protection of the underlying metals can be obtained by applying a duplex gold composite coating consisting of an underlying layer of Type III (Code A)gold.Typical thicknesses of the Type III gold underlayer are 10to 30%of the total speci?ed thickness.However,care must be taken to ensure that the thickness of the Type I or Type II gold topcoat is sufficient so as not to compromise wear properties.When measuring the total gold thickness of duplex composite coatings,a density of 17.5g/cm 3should be employed (see 9.4).

7.4.2The thickness of the gold coating shall be equal to or exceed the speci?ed thickness throughout the signi?cant sur-face (see 3.2.1).When plated parts are used in mating applications,the maximum thickness shall not exceed the tolerance speci?ed for the part on its engineering drawing.It is customary that allowance for plated coatings be included within the part tolerance.

N OTE 11—The coating thickness requirement of this speci?cation is a minimum requirement:that is,the coating thickness is required to equal or exceed the speci?ed thickness throughout the signi?cant surfaces,while conforming to all maximum allowed thicknesses created by part dimen-sional tolerances given in the engineering drawing.Variation in the coating thickness from point to point on a coated article is an inherent characteristic of electroplating processes.Therefore,the coating thickness at any single point on the signi?cant surface will sometimes have to exceed the speci?ed value in order to ensure that the thickness equals or exceeds the speci?ed value at all points.Hence,most average coating thicknesses will be greater than the speci?ed value;how much greater is largely determined by the shape of the article (see Practice B507)and the characteristics of the plating process.In addition,the average coating thickness on articles will vary from article to article within a production lot.Therefore,if all the articles in a production lot are to meet the thickness requirement,the average coating thickness for the production lot as a whole will be greater than the average necessary to ensure that any single article meets the requirement (see 8.1).

7.5Adhesion —The gold coatings shall be adherent to the substrate when tested by one of the procedures summarized in 9.5.

7.6Integrity of the Coating :

7.6.1Gross Defects/Mechanical Damage —The coatings shall be free of visible mechanical damage and similar gross defects when viewed at magni?cations up to 103.For some applications this requirement may be relaxed to allow for a small number of such defects (per unit area),especially if they are outside or on the periphery of the signi?cant surfaces (see 7.6.2).

7.6.2Porosity —Almost all as-plated electrodeposits contain some porosity.The tolerable amount of porosity in the coating depends on the severity of the environment that the article is likely to encounter during service or storage.If the pores are few in number or away from the signi?cant surfaces,their presence can often be tolerated.Such acceptance (or pass-fail)criteria,if required,shall be part of the product speci?cation for the particular article or coating requiring the porosity test (see 9.6for porosity testing).

8.Sampling

8.1The supplier is urged to employ statistical process control in the coating process.Properly performed,this process will ensure coated products of satisfactory quality and will reduce the amount of acceptance inspection.The sampling plan used for the inspection of the quality of the coated articles shall be as agreed upon between the purchaser and the supplier.

N OTE 12—Usually,with a collection of coated articles,the inspection lot (see 8.2)is examined for compliance with the requirements placed on the articles,a relatively small number of the articles,the sample,is selected at random and is inspected.The inspection lot is then classi?ed as complying with the requirements based on the results of the inspection of the sample.The size of the sample and the criteria of compliance are determined by the application of statistics.The procedure is known as sampling inspection.Test Method B602,Guide B697,and Test

Method

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B762contain sampling plans that are designed for the sampling inspection of coatings.Test Method B602contains four sampling plans,three for use with tests that are nondestructive and one with those that are destructive.The purchaser and supplier may agree on the plan or plans to be used.If they do not,Test Method B602identi?es the plan to be used.Guide B697provides a large number of plans and also gives guidance in the selection of a plan.When Guide B697is speci?ed,the purchaser and supplier need to agree on the plan to be used.Test Method B762can be used only for coating requirements that have a numerical limit,such as coating thickness.The test must yield a numerical value and certain statistical requirements must be met.Test Method B762contains several plans and also gives instructions for calculating plans to meet special needs.The purchaser and supplier may agree on the plan or plans to be used.If they do not,Test Method B762identi?es the plan to be used.

8.2An inspection lot shall be de?ned as a collection of coated articles that are of the same kind;that have been produced to the same speci?cations;that have been coated by a single supplier at one time,or at approximately the same time;under essentially identical conditions;and that are submitted for acceptance or rejection as a group.9.Test Methods

9.1Deposit Purity —Use any recognized method to deter-mine quantitatively the metallic impurities present.Atomic absorption spectrophotometry (or any methods with demon-strated uncertainty less than 10%)may be used to determine the metallic impurities.Initial scanning should be carried out for all elements in order to detect any unknown or unexpected metallic impurities.Determine deposit purity by subtracting total impurities in mass from 100%.Deposit purity should be determined on samples at plating conditions representative of actual production.

9.2Hardness —Measure hardness in accordance with Test Method B578.Deposit hardness should be determined on samples at plating conditions representative of actual produc-tion.

9.3Appearance —The coating shall be examined at magni-?cations up to 103for conformance to the requirements of appearance.

9.4Thickness and Mass per Unit Area —Measure thickness by methods outlined in Test Methods B487,B567,B568,or B748.The method chosen shall be such as to give an uncertainty of less than 10%on the particular coating being measured.

9.4.1Thickness —The beta backscatter,X-ray ?uorescence spectrometry,and coulometric methods measure the mass of gold per unit area that is present over the measured area.The cross-sectioning and magnetic methods measure the geometri-cal thickness of the gold present.Since many gold coatings have a density lower than the theoretical density of gold (19.3g/cm 3),instruments utilizing the measuring principles in Test Methods B504,B567,and B568will often give lower readings than the microscopical cross-section method.To convert mass of gold per unit area that is present over the measured area to a geometrical thickness,it is necessary to use standards having a density identical to that of the coatings to be measured,or to multiply the reading obtained by factor,f .

f 519.3d

(1)

where:

d =density of gold coating,g/cm 3.

9.4.1.1The density of gold coatings depends not only on the type of gold coating but also on the gold content and the composition and purity of the electroplating solution.The density ?gure,when the above methods are used for measure-ments of thickness,shall be considered to be 19.3g/cm 3for Type III coatings and 17.5g/cm 3for Type I and Type II coatings,unless:

(1)the density is supplied by the plating process vendor,or (2)the density has been measured.

9.4.2Mass Per Unit Area —Test Methods B504,B567,and B568measure the mass of gold per unit area (coating weight)directly and independently of the density of gold.

N OTE 13—The calibration standards available from the National Insti-tute of Standards and Technology (NIST)8are certi?ed in units of mass of gold per unit area.Other calibration standards for gold are generally certi?ed in thickness units that can be converted to mass per unit area units by multiplying by the density of pure gold.

Mass per unit area ~or coating weight !in mg/cm 2519.33thickness ~μm !/10

(2)

This conversion should be veri?ed by the supplier of the calibration standards.

9.5Adhesion —Determine adhesion by one of the following procedures (see Practice B571for full details).

9.5.1Bend Test —Bend the electroplated article repeatedly through an angle of 180°on a diameter equal to the thickness of the article until fracture of the basis metal occurs.Examine the fracture at a magni?cation of 103.Cracking without separation does not indicate poor adhesion unless the coating can be peeled back with a sharp instrument.

9.5.2Heat Test —No ?aking,blistering,or peeling shall be apparent at a magni?cation of 103after the gold electroplated parts are heated to 300to 350°C (570to 660°F)for 30min and allowed to cool.

9.5.3Cutting Test —Make a cut with a sharp instrument and then probe with a sharp point and examine at a magni?cation of 103.No separation of the coating from the substrate shall occur.

9.6Plating Integrity —Porosity shall be determined prefer-ably by either Test Method B735,B741,B799,or B809unless otherwise speci?ed.See Guide B765for guidelines for select-ing the appropriate test method.

N OTE 14—The test to be selected will depend upon the gold thickness,the nature of the basis metal,the nature and thickness of any intermediate layers or underplate,the shape of the gold-coated part,and its intended service environment.

9.7Ductility —When required,determine ductility in accor-dance with Practice B489.

10.Special Government Requirements

10.1The following special requirements shall apply when the ultimate purchaser is the https://www.wendangku.net/doc/6b7708571.html,ernment or an agent of the https://www.wendangku.net/doc/6b7708571.html,ernment.

Available from National Institute of Standards and Technology (NIST),100Bureau Dr.,Stop 1070,Gaithersburg,MD 20899-1070,

https://www.wendangku.net/doc/6b7708571.html,.

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10.1.1Sampling —For government acceptance,the sam-pling plans speci?ed in MIL-STD-1916or ANSI/ASQC Z1.4are to be used instead of the ASTM standards speci?ed in 8.1.10.1.2Thickness Testing :

10.1.2.1In addition to the nondestructive method outlined in Test Methods B499,B567,and B568,a cross-sectioning method,such as that speci?ed by Test Method B487or B748,can also be used as a referee method to con?rm the precision and bias of the particular non-destructive technique when thicknesses of 0.75μm or above are used.

10.1.2.2The part shall be covered with gold.The gold thickness on signi?cant surfaces shall be at least 1.25μm (50

μin.),unless otherwise speci?ed in the drawings or contract.Any speci?c requirement for thicknesses on non-signi?cant surfaces shall be agreed on between purchaser and supplier.10.1.3Packaging —Parts plated for the https://www.wendangku.net/doc/6b7708571.html,ernment and Military,including as subcontracts,shall be packaged in accordance with Practice D3951.11.Keywords

11.1engineering coatings;engineering gold;gold;gold coatings;gold electrodeposits;gold platings;underplate

APPENDIXES

(Nonmandatory Information)

X1.TYPICAL USES

X1.1The conditions of exposure and the uses of gold coatings are so varied that it is often not possible to predict the life of a coating of a given thickness and hardness.Some typical uses of gold coatings are enumerated below,but the list is not complete and is intended for general guidance only.

X1.1.1Type III,Code A Gold —For semiconductor compo-nents,nuclear engineering,thermocompression bonding,ther-mosonic bonding,ultrasonic bonding,solderability,and high-temperature applications.

X1.1.2Type I —For general-purpose,high-reliability electri-cal contacts,and wire wrap connections.

X1.1.3Type II,General-Purpose Wear Resistant Gold —Will not withstand high-temperature applications because the hardening agents in the gold coating will oxidize.

X1.1.4Solderability —Type III golds are preferred for solder applications.Oxidation of co-deposited metals can make sol-dering more difficult.It is strongly recommended that gold

coating thicknesses not exceed 0.5μm for solder applications.There is evidence to show that when the gold content in the tin-lead solder joint exceeds about 3%by weight,embrittle-ment occurs leading to potential solder joint failure.9

X1.1.5Printed Wiring Boards —Boards that will be sheared or cropped should not be electroplated with a heavy thickness of a hard gold because of possible cracking of the gold.Coatings with purities of 99.0to 99.7%are used with B or C hardness and at thicknesses generally not in excess of 2.5μm.X1.1.6Static Separable Connectors —Coatings at any of the listed purities and with hardnesses A,B,or C are used to any thickness up to 5μm.Selection of the type and thickness of the gold coating is determined by the desired life in the operating environment of the electroplated component.

X2.RESISTIVITY

X2.1When electrodeposited gold coatings are used as electrical conductor paths,the electroplating process can be expected to produce coatings having maximum resistivities as speci?ed in Table X2.1.

X2.2Use any reliable four-point probe method for deter-mining resistivity of gold coatings.A suggested four-point method is detailed in Test Method F390.

Glazer,J.,Kramer,P.A.,and Morris,J.W.,Jr.,“Effect of Au on the Reliability of Fine Pitch Surface Mount Solder Joints,”Proceedings from Surface Mount International Conference and Exposition ,August 25–29,pp.629–639.

TABLE X2.1Maximum Electrical Sheet Resistivity by the Four

Point Probe Method A

Gold Finishes Ohm per Square

A and

B C

0.030.10

When the electroplated coatings are used as electrical conductor paths,the sheet resistance in ohms per square should be speci?ed and not the coating

thickness.

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X3.RESIDUAL SALTS

X3.1Electroplated parts are placed in water of known conductivity and agitated for a speci?c time.The conductivity of the water extract is measured,and the increase in conduc-tivity due to residual salts and other conducting impurities is calculated.A suggested water extract conductivity test method uses a procedure in accordance with Test Methods D1125,Method A.

X3.2Conductivity of water for extract test shall be 1μS/cm or less (resistivity 1M V ·cm or more).

X3.2.1A sample of the coated parts having a total surface area of 30cm 3shall ordinarily be used and extracted in 100cm 3of equilibrated water.To prepare equilibrated water,?ll a clean polyethylene bottle half-way with high-purity water (X3.1),replace the bottle cap,and shake the bottle vigorously for 2min to equilibrate the water with the carbon dioxide (CO 2)in the air.CO 2is a component of air.It is soluble in water and forms carbonic acid that ionizes and is at equilibrium at 0.8

μS/cm.Slowly agitate the solution for 10min before determin-ing the conductivity of the extract.In a closed polyethylene bottle,the equilibrated water will remain in the range from 0.8to 1μS/cm for at least 1week.Place the specimen in the bottle in accordance with X3.1.

X3.3Inspection under a source of ultraviolet light is often employed to determine whether electroplating salts have been removed by the rinsing following gold electroplating.The presence of salts is evidenced by a characteristic ?uorescence and should not be confused with ?uorescing dirt or dirt particles.

X3.4Water or purging stains,resulting from blind holes or from parts that were assembled before electroplating,as normally obtained in good commercial practice,are permis-sible,except where they occur on surfaces to which electrical contact is to be made or on which subsequent soldering operations are performed.

X4.SOLDERABILITY

X4.1Where solderability requirements are speci?ed,sol-derability testing shall be done in accordance with Test Method B678.

X5.MANUFACTURE

X5.1Substrate Preparation:

X5.1.1Practices B183,B242,B253,B254,B281,B322,B343,B481,and B482should be used where appropriate for the preparation of the applicable basis metal.

X5.1.2When electroplated materials are used for electrical contacts,cleaning alone may not properly prepare the surface for gold electroplating.If the basis metal is scratched or rough,it may be necessary to level the surface by processes such as electropolishing,chemical polishing,or the application of a self-leveling nickel or copper undercoating before gold elec-troplating.However,the use of these undercoatings requires the approval of the purchaser.X5.2Underplatings:

X5.2.1Silver shall not be used as an underplating unless speci?ed by the purchaser.

X5.2.2Copper alloys containing zinc,beryllium,tellurium,or lead should be precoated to prevent adhesion problems.If copper or nickel underplatings are used,they should have a nominal thickness of at least 1.2μm.Thickness of the underplating should be consistent with end-use requirements.With cyanide-sensitive copper alloys,such as those containing beryllium or tellurium,an acid copper strike is recommended.

X5.2.3Gold coatings on zinc,aluminum,steel,and other metals normally require underplatings such as copper or nickel of sufficient thickness to impact adequate corrosion protection to the basis metal.

X5.2.4To minimize diffusion,a nickel underplating with a nominal thickness of at least 1.2μm should be applied before depositing any of these gold ?nishes on copper and copper alloy parts that can be subjected to elevated temperatures.The thickness of the underplating should be consistent with end-use requirements (see 6.5.1).

X5.2.5A gold strike is often used to precede the ?nal gold coating,to improve adhesion,and to prevent contamination of the main gold electroplating solution with metallic impurities.X5.3Gold Electrolytes —Most gold electroplating solu-tions used for producing these coatings are proprietary.Any bath that produces coatings meeting the requirements of the speci?cation may be used.

X5.3.1Solution Contamination —Care should be exercised to prevent contamination of gold electroplating solutions with organic or metallic impurities.Copper,zinc,cadmium (from racking materials,bus bars,etc.),iron (from insoluble anodes),lead and tin (from solder parts),and silver (from impurities in the electroplating bath makeup salts)are some of the

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common contaminants,which,if present in the coating in more than trace quantities,can have harmful effects on such prop-erties as hardness,solderability,and porosity.

X5.3.2Activated Carbon Treatment —Periodic treatment of the solution with activated carbon is recommended to control the buildup of organic impurities.This contamination can have the effect of producing discoloration of the deposit.Thus,the appearance of test coupons may serve as an indication of an approaching need for the activated carbon treatment.(Warning—Do not store activated carbon in areas in which vapors from solvents and other chemicals may contaminate the carbon.)

X5.3.3Control of the Gold Electroplating Bath —Under continuous operations,when control of bath composition can

be readily established by scheduled additions,analyses of the electroplating bath constituents should be made on a regularly scheduled basis.When the work load is erratic,each addition should be based on bath analyses.

X5.3.4Control of the Gold Deposit —The adhesion,hard-ness,and composition of the gold deposit should be determined on a regularly scheduled basis.Once it has been established that the co-deposited metallic impurity limitations are being continuously met in production,frequency of determination can be reduced.Appearance,porosity,and thickness should be determined often enough to ensure compliance with speci?c requirements.

X6.SOME REASONS FOR USING A NICKEL UNDERPLATE

X6.1Diffusion Barrier:

X6.1.1To inhibit diffusion of copper from the basis metal (and of zinc from brass)to the surface of the precious metal plating.

X6.1.2To inhibit interdiffusion between the basis metal and the gold top coat (for example,silver and copper),which might produce a weak alloy or intermetallic compound at the inter-face.

X6.2Levelling Layer —To produce a smoother surface than the basis metal in order to ensure a lower porosity gold top plate (for example,levelling nickel over a rough substrate).X6.3Pore Corrosion Inhibitor —A nickel underplate under

the gold top coat will form passive oxides at the base of pores in humid air,provided the environment does not contain signi?cant amounts of acidic pollutants (such as sulfur dioxide (SO 2)or hydrogen chloride (HCl)).

X6.4Tarnish Creepage Inhibitor for Gold —Non-copper base metals will inhibit creepage of copper tarnish ?lms over the gold—where the tarnish originates from pores and bare copper edges.

X6.5Load-Bearing Underlayer for Contacting Surfaces —A hard nickel underplate can serve as a load-bearing foundation for the gold top coat to prevent cracking of hard golds and reduce the wear of the precious metal during sliding of the contacting surfaces.

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