technically speaking · 2013. 5. 2. · speaking by rob mason, cef, margo neidbalson, ... public...

Update on Alternatives forCadmium Coatings on Military

Electrical Connectors

The metal finishing industry hasbeen impacted by numerous reg-

ulatory actions related to the haz-ardous materials that are used in dec-orative and functional coatingprocesses. These environmental regu-lations are applicable to both com-mercial and government facilities. Inaddition, Executive Order (EO)13423, Strengthening FederalEnvironmental, Energy, andTransportation Management, and EO13514, Federal Leadership inEnvironmental, Energy, and EconomicPerformance, were recently enacted.These EOs require government agen-cies to reduce the quantity of toxicand hazardous chemicals and materi-als acquired, used, or disposed.

Cadmium and hexavalent chromi-um are very toxic and carcinogenicmaterials heavily regulated by theEnvironmental Protection Agency(EPA) and the Occupational Safetyand Health Administration (OSHA).In addition, hexavalent chromium isamong the three hazardous materi-als that the Department of Defense(DoD) has targeted for reduction tomeet the requirements of the EO13423. Due to the toxicity and car-cinogenicity, as well as the numerousregulatory actions related to thesematerials, the U.S. Army Tank-auto-motive Research Development andEngineering Center (TARDEC) hasbeen working to eliminate or reducethe use of cadmium and hexavalentchromium in ground vehicles and

related systems. The NationalDefense Center for Energy andEnvironment (NDCEE), operated byConcurrent TechnologiesCorporation (CTC), has been taskedto support TARDEC’s activities inthis area.

Specifically, theprotective shells ofelectrical connec-tors currently usedin military groundsystems are cadmi-um plated and thenchromated withchromate conver-sion coatings(CCCs) to provideadditional corro-sion protection.The aforemen-tioned regulatoryconcerns under-score a need to findalternatives to thecurrently used coat-ing processes toreduce environmen-tal and safety risks.

However, thereplacement of cad-mium for anyapplication is not atrivial task.Cadmium has beenused as a protectivecoating for electri-cal connectors formany years becauseof the numerous

properties that it imparts to theoverall component. Key propertiesthat cadmium coatings impart toelectrical connector shells include: 1,2

• Ease of manufacturing• Ease of repair• Electrical conductivity• Electromagnetic compatibility (EMC)/electromagnetic interfer-ence (EMI) effectiveness

• Environmental resistance, particu-larly corrosion resistance

• Galvanic coupling

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BY ROB MASON, CEF, MARGO NEIDBALSON, AND MELISSA KLINGENBERG,PHD, CONCURRENT TECHNOLOGIES CORPORATION (CTC), JOHNSTOWN,PA., AND LARGO, FLA., AND PARMINDER KHABRA AND CARL HANDSY,UNITED STATES ARMY TANK-AUTOMOTIVE RESEARCH DEVELOPMENT ANDENGINEERING CENTER (TARDEC), WARREN, MICH.

Figure 1. Galvanic series, showing position of cadmium and viable alter-native metals. (Circled area: materials providing sacrificial protection.) 1

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failures) when induced by suddensurge currents (such as a lightningstrike). Cadmium-plated connectorsmeet this requirement throughoutthe life of the connector (i.e., the cor-rosion products of cadmium aregenerally non-insulating). Otherplated coatings, such as electrolessnickel (EN), meet this requirementinitially, but lose effectiveness overtime due to the resistances that aregenerated by corrosion products.

VIABLE ALTERNATIVES TO CADMIUMThe DoD has been interested incadmium replacement for manyyears, and numerous potentialreplacements have been identifiedand explored in past work conduct-ed by Brooman2,3,4, Gaydos5,Klingenberg3, 4, 6, Legg1; and Shahin7,among many others. It is the intentof this paper to summarize pastwork that has been accomplished inthis area, with the intent of provid-ing a rationale for the selection ofthe most promising candidates forfurther study under future phasesof this current effort.

Based on the many previous stud-ies related to cadmium replacement,and the available data on candidatetechnologies, a number of promisingcandidates for cadmium replace-ment were identified. Due to the par-ticular focus of this project, candi-dates were limited to commerciallyavailable or near-commercial tech-nologies. These include:

• Advanced materials• Alloys deposited by chemical vapor deposition (CVD)

• Alloys deposited by molten salt bath processes

• Alloys deposited by ionic liquid processes

• Electrodeposited aluminum and alloys

• Electroless nickel technologies• Electroplated tin alloys• Electroplated zinc-cobalt• Electroplated zinc-nickel• Ion vapor deposited (IVD) aluminum and alloys

• Metal-filled paints and ceramics• Sputtered aluminum and alloys

• Inhibition of algae growth• Low cost• Lubricity (meets established torque/tension requirements)

• Shock resistance• Solderability• Temperature resistance• Vibration resistance

CCCs are applied over cadmiumcoatings to provide additional proper-ties, the most important of which are:

• Enhanced corrosion resistance• Paintability (meets requirements for paint adhesion to coating)

• Color

As seen above, the synergistic bene-fits provided by this coating systemhave made its replacement challeng-ing. One example of the unique pro-tective properties that are impartedby cadmium and hexavalent chromi-um is corrosion resistance.Cadmium coatings provide galvaniccorrosion protection to electricalconnector shells, and very few metalscan provide a similar level of corro-sion protection in this application.This is demonstrated by the positionof cadmium in the galvanic series,shown in Figure 1. 1

Figure 1 demonstrates that zincand zinc alloys, beryllium, magne-sium, and aluminum alloys are gen-erally the most active metals in cor-rosive environments and, therefore,are the only materials that can pro-vide sacrificial corrosion protectionsimilar to cadmium in this applica-tion. However, beryllium is morehazardous than cadmium, and mag-nesium and pure zinc both corrodetoo rapidly for many engineeringapplications.

Other examples of the uniqueproperties that are imparted by cad-mium to connector shells involveelectrical properties, specificallyEMC and EMI effectiveness.Connector mating resistances mustbe kept to a minimum (e.g. less than2.5 milliohms) for EMC, becausegreater mating resistances can leadto high voltages (and subsequent

The viability of each of theseprocesses in the context of the specif-ic application—electrical connectorshells—is discussed herein. Wheredata is available, issues such as com-patibility of the alternatives withexisting cadmium-plated connectorswill be addressed.

ADVANCED MATERIALSThe use of advanced materials as areplacement for cadmium-platedparts has been considered mostlyfor larger aerospace components.Stainless steel is the most likely can-didate to replace cadmium on larg-er, non-electric components. A cor-rosion-resistant stainless steel, S53,was developed under a project fund-ed by the Strategic EnvironmentResearch and DevelopmentProgram (SERDP). This effort1, 5, 8

focused on providing corrosion pro-tection and resistance to stress cor-rosion cracking on aircraft landinggear. Stainless steel alloys wouldprovide many of the necessary prop-erties needed for electrical connec-tor shells and may be acceptable forsome applications. However, thesematerials generally exhibit a highmating resistance and also may notbe cost-effective. Likewise, titaniumalloys and Inconel® have beenfound to be adequate as substratesubstitutes for cadmium plated fas-teners5, but these may also be costprohibitive for use in electrical con-nectors. Polymer composite materi-als (such as polyetheretherketone)are already in use in some commer-cial applications. However, militaryusage appears to be minimal (atleast for ground vehicle applica-tions), and consideration of thismaterial introduces issues related tocost, conductivity, and mechanicalwear for some applications. Overall,it is evident that additional researchand development is required to useadvanced materials to replace thestandard shells in newer models ofelectrical connectors.

ALLOYS DEPOSITED BY CHEMICALVAPOR DEPOSITIONThe Air Force Research Laboratory(AFRL) evaluated aluminum coat-

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anions and large organic cations).These liquid salts have unique prop-erties that allow easy dissolution ofnormally insoluble chemicals, suchas cellulose. Ionic liquids enable elec-trochemical plating of metals likealuminum; deposition rates of onemicron per minute at low tempera-tures (60 to 100°C) have been report-ed.11 These deposition rates are sig-nificantly superior to other low-tem-perature aluminum coating meth-ods. While this process is not yetmature enough to enable the platingof commodity items such as electri-cal connector shells, work is pro-gressing rapidly and promisingresults will be forthcoming.

ELECTRODEPOSITED ALUMINUMAND ALLOYSAlumiPlate® is a proprietary processin which a pure aluminum coating iselectrolytically deposited onto a sub-strate that has been immersed into anon-aqueous, fully enclosed solu-tion in an inert atmosphere. Theresulting coating is highly versatile.It can be anodized or topcoated withthe standard CCC post treatment,trivalent chromium post-treatments(TCPs), or non-chrome post-treat-ments (NCPs). TCPs are much lesshazardous than CCCs and meetrequirements under the EuropeanUnion’s Reduction of HazardousSubstances (RoHS) Directive—although this substance is still regu-lated under U.S. requirements.Additionally, the AlumiPlate®process does not appear to imparthydrogen embrittlement—a concernwith cadmium plating.5

AlumiPlate® is one of the morepromising new processes for cadmi-um replacement on electrical connec-tors. Researchers at the Naval AirSystems Command (NAVAIR) con-ducted 2,000 hours of salt spray cor-rosion testing on electroplated alu-minum electrical connectors withTCP12,13, in accordance with ASTMB117.14. NAVAIR found that all con-nectors performed equal to or betterthan the cadmium-plated controlswith respect to visual appearance ofcorrosion. A plated connector isshown after 2,000 hours of B117

ings applied through AtmosphericPressure Chemical Vapor Deposition(APCVD).9 Environmentally benignCVD processes using triethylalu-minum as a precursor for producinghigh-quality aluminum coatings wasexplored. While promising, thisprocess involves special high-cost,equipment. Considerable furtherdevelopment from a process stand-point would likely be necessary toimplement this process for high-vol-ume applications such as electricalconnector shells.

ALLOYS DEPOSITED BY MOLTENSALT BATH PROCESSESAn aluminum-manganese moltensalt plating process was exploredunder funding from theEnvironmental Security TechnologyCertification Program (ESTCP), butthe process was plagued by inconsis-tent bath composition, visible fumes,and excessive crust formation [Ref.10]. In addition, this process operat-ed at a very high temperature, whichis likely to affect the properties ofaluminum shells. While this technol-ogy is promising, considerable fur-ther development from a processstandpoint would be necessary toimplement this process for electricalconnector shells.

ALLOYS DEPOSITED BY IONIC LIQUID PROCESSESAs an alternative to the molten saltbath process mentioned above, theuse of ionic liquids as an electrolyteto plate aluminum is under investi-gation. 5,11 Ionic liquids are salts witha low melting point, which originatesin their chemical structure (a mix of

exposure in Figure 2.12.From a functionality standpoint,

all tested connectors met the require-ment for shell-to-shell conductivity,with the exception of the AA6061AlumiPlate® coating with TCP at25% concentration (the most dilute).The AA6061 AlumiPlate® coatingwith Class III post-treatment was thetop performer.

Other projects involving thisprocess include a partnershipbetween Lockheed, Alcoa, and theU.S. Air Force, which is evaluatingseveral coatings, includingAlumiPlate®, to replace cadmiumfor military and commercial fasten-ers.15 Based on the results from boththe NAVAIR testing and this partner-ship, the AlumiPlate® coating is cur-rently being qualified for electricalconnectors under MIL-DTL-38999Las well as relevant internal manufac-turers’ specifications. Specifically,qualification and approval of theAlumiPlate® coating is anticipatedfor Model 38999 electrical connec-tors with spring fingers, which willbe used on the Lockheed Martin F-35 Lightning II (also known as theJoint Strike Fighter) program.

Despite the good performance ofthis candidate and its recent qualifi-cation, several drawbacks remainwith the use of AlumiPlate®. Due tothe use of the non-aqueous elec-trolyte, it is unlikely that this processcould meet the environmentalrequirements that would allow itsuse in a DoD facility.1 Furthermore,the process requires the use of highlyspecialized equipment (e.g. highstart-up cost). Finally, there are ques-tions regarding whether the platedcoating can be repaired, althoughinitial work has found that it may bepossible to use brush-plated tin-zincto repair this coating.1,5

ELECTROLESS NICKEL TECHNOLOGIESA number of new EN-based coatingsystems continue to be consideredfor electrical connector shells.However, as mentioned previously,the corrosion properties of nickel—and subsequent electrical proper-ties—are considerably different than

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Figure 2. AlumiPlate-coated electrical connec-tor, After 2,000 hours B117exposure.12



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speakingTestDescriptions

Baseline Coatings Alternative Coatings

LHECadmium

LHECadmium

TitaniumCadmium

TitaniumCadmium

IVDAluminum

IVDAluminum

AcidZincNickel

AcidZincNickel

AlkalineZincNickel

AlkalineZincNickel

Tin Zinc Tin Zinc

PostTreatmentà

None CCC(1) None CCC None CCC None CCC None CCC None CCC

Thickness P P P P P P P P P P P P

BendAdhesion

P P P P P P P P P P P P

Paint,Adhesion,Wet Tape

P P P P F P F P F P P P

CyclicCorrosionUnscribed

P P P P F F F F F F F F

CyclicCorrosionScribed

F P F P F F F F F F F F

HydrogenEmbrittlement

P P P P P P P P P P P P

EIC, Wet P P P F F F F P F F F F

EIC, Cooked P P P F F F P P P P P P

(1) CCC Chromate Conversion Coatingn= PASSES OR FAILS WITH INCONSISTENT RESULTSn = FAIL PER ACCEPTANCE CRITERIAn = PASS PER ACCEPTANCE CRITERIA

Table 1: Summary of Coating Performance from NDCEE Study


ing composition (and, hence, suffi-cient corrosion resistance) for theharsh environments to which mili-tary electrical connectors are rou-tinely submitted. Promising resultsunder past studies imply that thiscandidate could provide comparableperformance to cadmium if thedeposit composition could be mademore consistent.

It is noted that other tin alloys,specifically tin-indium coatings, arebeing considered for both commer-cial and military applications, butthese would take considerable devel-opment to be considered for electri-cal connector shells.

ELECTROPLATED ZINC-COBALTZinc-cobalt plating is typically usedto finish relatively inexpensive partsthat require a high level of abrasionand corrosion resistance. This coat-ing is reported to demonstrate par-ticularly high resistance to corrosionin sulfur dioxide environments.Several suppliers of commercial elec-trical connectors offer connectorshells coated with zinc-cobalt as areplacement for cadmium to meetRoHS criteria. Zinc-cobalt alloys arenot commonly used in applicationsrequiring heat treatment becausethese alloys have been reported todemonstrate reduced corrosionresistance when exposed to high tem-peratures. In one study20, after saltspray corrosion testing in accordancewith ASTM B11714, zinc-cobalt-plat-ed sleeves showed considerably lesscorrosion resistance after one hourheat treatment at 250°F as com-pared to the as-plated condition.While this process was initially con-sidered as being a worthy cadmiumreplacement, the questionable char-acteristics under high-temperatureenvironments excluded its considera-tion under further review.

ELECTROPLATED ZINC-NICKELZinc-nickel electroplating processes

are mature, commercially availablesystems that can deposit alloys of5–15% nickel (balance zinc) from anaqueous solution. Zinc-nickel alloyscan be deposited from both acid andalkaline processes. Boeing has found

those of cadmium.2 Further testingwould be required to fully assessthis candidate for military electricalconnector shells. Despite these con-cerns, at least one leading manufac-turer of electrical connectors isinvestigating the use of EN withoccluded particles (polytetrafluo-roethylene, or PTFE) as a cadmiumreplacement.16 While the inclusionof these particles will provide lubric-ity, the corrosion characteristics andelectrical properties imparted to theconnector shell must be consideredand are being evaluated.

ELECTROPLATED TIN ALLOYSAmong the most mature and prom-ising tin alloy coatings for electricalconnector shells are tin-zinc coat-ings. Tin-zinc electroplatingprocesses are mature, commerciallyavailable systems that can depositalloys of 20–30% zinc (balance tin)from an aqueous solution. Tin-zinccoatings have been consideredpromising for cadmium replace-ment 2,7,17, and this finish was foundto be a top performer in past studies.18 However, more recent studies havederived less positive results. Anextensive study on potential cadmi-um replacements conducted by theNDCEE19 found that a proprietarytin-zinc coating failed both cycliccorrosion and wet notch environ-mentally influenced cracking (EIC)tests yet passed hydrogen embrittle-ment and cooked EIC. A summaryof test results from this effort can befound in Table 1.19

In this study, it was noted that thedeposited tin-zinc coating wasfound to have an insufficientamount of zinc in the deposit toprovide adequate corrosion protec-tion (less than 1% zinc, versus theanticipated >20% zinc concentrationfound in more corrosion-resistantcoatings that had been tested underrelated projects). This implies that,while tin-zinc does show promise forsome applications, some bathchemistries may not be robustenough to provide a consistent coat-

that the alkaline process is easier tomaintain and provides a more con-sistent coating composition.5 From aperformance standpoint, theNDCEE found that a proprietaryacid zinc-nickel coating with CCCpassed bend adhesion, paint adhe-sion, and hydrogen embrittlementtests, but displayed only marginalEIC performance19 (see Table 1). Thecorrosion resistance was significant-ly less than the cadmium baselines,but increased coating thickness andselecting a suitable conversion coat-ing may improve those results—although the implications of thesechanges to the form, fit, and func-tion of the electrical connectorwould need to be identified. The pro-prietary alkaline zinc-nickel coatingwith a CCC performed similarly tothe acid zinc-nickel in this study19

(see Table 1). Previous TARDECwork also found alkaline zinc-nickelcoatings with a CCC to be promisingfor some electrical connectordesigns, particularly on MIL-C-83513 microminiature D-subminia-ture connectors, but less promisingon other connector designs.

Based on these promising results,zinc-nickel has seen implementa-tion as a cadmium replacementprocess in several areas. TheNDCEE work19 provided informa-tion that assisted Rolls RoyceDefense Aerospace in qualifyingzinc-nickel as an acceptable alterna-tive to cadmium on the T56 enginesystem. Boeing also found that zinc-nickel plating is an acceptable coat-ing to replace cadmium on compo-nent parts made of low strengthsteel (less than 200 ksi), stainlesssteel, aluminum, and copper alloys.1

Other ongoing projects involvingthis process include the aforemen-tioned partnership betweenLockheed-Martin, Alcoa, and theU.S. Air Force, which is evaluatingseveral coatings, including bothacid and alkaline zinc-nickel, toreplace cadmium for military andcommercial fasteners.15

It is recognized that both acid andalkaline zinc-nickel processes mayprovide an acceptable alternativecoating for cadmium in many appli-

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num also demonstrated improvedpassivation over pure aluminum.6

As mentioned previously, Boeinghas qualified IVD aluminum toreplace cadmium on componentparts made of low strength steel(less than 200 ksi), stainless steel,aluminum, and copper alloys. In apast TARDEC study, IVD alu-minum demonstrated the best over-all performance on aluminum con-nectors. Specifically, on MIL-C-38999 circular connectors, IVD alu-minum performed similar to or bet-ter than cadmium, with lower shell-to-shell resistance, but slightly lesscorrosion resistance. It was notedthat, on MIL-PRF-24308 D-sub-miniature connectors, cadmiumdemonstrated the best overall per-formance, with IVD aluminumbeing the best performing alterna-tive. It was also noted that on MIL-C-83513 microminiature D-sub-miniature connectors, IVD alu-minum was reported to have a sig-nificant drawback for use on theseconnectors. During the IVDprocess, aluminum coated theentire connector surface (includingthe phenolic material), causing thepins to be electrically continuouswith each other and the connectorshell, resulting in shorts and eventu-al connector failure.

As seen above, there are numerousdrawbacks to using IVD aluminumfor electrical connector shells. Theseinclude the aforementioned over-coating issues, as well as high start-up and operations costs because theequipment that is used to apply thisfinish is expensive. Also, while IVDaluminum is not completely limitedto line-of-sight coverage, the conven-tional process cannot “throw” intodeep recesses on some parts—partic-ularly holes.1, 5 There are some coat-ing performance concerns as well.IVD aluminum coatings display acolumnar structure with a highdegree of porosity. As a result, thecoatings must usually be glass-beadpeened to densify the coating andalleviate porosity and corrosion con-cerns. The NDCEE found that IVDaluminum coatings, even with CCC,provide only marginal cyclic corro-

cations. Acid zinc-nickel processeshave traditionally been used; howev-er, some embrittlement issues havebeen related to this process.1 Forthis reason, Boeing restricts the useof acid zinc-nickel to steels withultimate tensile strength of 220 ksior less. While these issues may notbe relevant for electrical connectors,a post-process bake has been foundto both relieve hydrogen embrittle-ment and enhance corrosion prop-erties.2 In any case, alkaline zinc-nickel appears to be the strongercandidate for this application, dueto the reduction in required mainte-nance of the bath and the aforemen-tioned current interest in the prop-erties of this coating.

ION VAPOR DEPOSITED ALUMINUM AND ALLOYSIon vapor deposited (IVD) alu-minum is a physical vapor deposi-tion (PVD) process in which a part isplaced in a vacuum chamber andglow discharge cleaned. Pure alu-minum is then melted in heatedceramic boats until it evaporates andcondenses on the part to form a coat-ing. Concurrently, ions from the dis-charge bombard the forming coatingto enhance its density.

IVD aluminum is a mature processthat has been used successfully todeposit a variety of coatings formany years, and has traditionallybeen one of the most promisingtechnologies for cadmium replace-ment. It is non-embrittling and gal-vanically compatible with aluminumsubstrates. In addition, it has excel-lent high temperature properties andcan be conversion coated. Corrosionresistance has been reported to becomparable to, or better than, cadmi-um in some environments.2,21

Alloying the IVD aluminum coatingis reported to provide even better cor-rosion protection; IVD aluminum-magnesium alloys with 10% magne-sium have demonstrated significantpitting corrosion protection.17 PastNDCEE work found that aluminum-tungsten and aluminum-molybde-

sion results19 (see Table 1), under-scoring the importance of a densealuminum coating. Also, like manypure aluminum coatings, IVD alu-minum has also been reported tohave poor wear resistance, and hasdemonstrated galling issues. The lat-ter is a particular concern for electri-cal connectors; an aluminum-to-alu-minum interface could result inexcessive mating forces, or evenunmateable connectors1 (the incor-poration of dry film lubricants havebeen proposed to resolve this issue,but this would have an adverse effecton electrical connectivity).

In summary, while IVD aluminummay be viable to replace cadmium inmany applications, it is not antici-pated to be a direct replacement forelectrical connectors. In fact, an AirForce study has recognized that IVDaluminum will not easily replacemore than about 50% of cadmiumplating requirements.17

METAL-FILLED PAINTS ANDCERAMICSOrganic paint systems that areloaded with sacrificial metals (gener-ally aluminum and zinc metal pow-ders) have demonstrated significantcorrosion resistance in several appli-cations. However, they are generallynot considered for cadmium replace-ment due to poor galvanic corrosionperformance and poor adhesion(compared to electroplating).5

Metal-filled ceramic coatings arebeing considered for some cadmi-um-replacement efforts. One sup-plier offers a coating that incorpo-rates aluminum flakes in a ceramicmatrix. The coating can be appliedvia brush or spray. It is used prima-rily for larger components in air-craft such as landing gear (specifi-cally the F-22), as well as for high-temperature applications.Drawbacks to this candidateinclude sole source (only one sup-plier provides the coating, and theyonly license to major users), highcost, limited available data, and therequirement to heat-treat the coat-ing before use.1,5 Also, coating con-ductivity has apparently not beendetermined. As such, this candidate

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ily deposited with thermal sprayprocesses, such as flame spray, butthese coatings are usually verythick—typically 76 to 127 microns(0.003'' to 0.005'')—and exhibit highroughness and porosity in the as-deposited state. The process alsoimparts a high degree of heat to thesubstrate. The latter issue can bepartly alleviated by utilizing “coldspray” processes; however, the formerissues restrict the use of this technol-ogy for electrical connectors.

As mentioned previously, the useof ionic liquids (salt mixtures thatmelt below room temperature) as anelectrolyte to plate aluminum is cur-rently under investigation. This tech-nology is a relatively new develop-ment, and while some information isavailable5,10, the ability to adapt thisprocess to coat electrical connectorshells in mass quantities has yet to bedetermined.

VIABLE ALTERNATIVES TO HEX CHROME TOPCOATSThe most promising alternatives tostandard CCCs at this time are TCPs.Specific applicability for electricalconnectors, when used in conjunc-tion with the AlumiPlate® process,has been promising.5,12,13 Furtherwork is necessary to fully qualifyTCPs as a replacement for CCCs.

NCPs are also becoming available,but these have been far less studiedin this application. NAVAIR is cur-rently continuing studies on theeffectiveness of their NCPs, andAlumiPlate® offers a proprietarynon-chromated topcoat over its coat-ing system. An NDCEE Task is cur-rently being conducted with theobjective of evaluating NCPs forTARDEC.

SUMMARY The most promising candidate coat-ing processes to replace cadmiumand hexavalent chromium in electri-cal connector applications are tech-nologies that are already being usedon electrical connectors to someextent, or demonstrate both consid-erable promise for the applicationand sufficient maturity. Theseinclude:

is likely not feasible for electricalconnectors.

SPUTTERED ALUMINUM ANDALLOYSSputtering, or magnetron sputter-ing, is another PVD process. In thisprocess, a part is placed in a vacu-um chamber, where it is glow dis-charge cleaned after the system isevacuated. The ionized gas (typical-ly argon) is attracted to the biasedaluminum target, and aluminumatoms are ejected from the targetand condense on the substrate toform a coating. The “Plug andCoat” method of sputtering allowsboth inner diameters (IDs) andouter diameters (ODs) to be coatedwithin the same chamber.

Recent work conducted by Boeing 1,

5 found that sputtering provides a bet-ter quality aluminum coating thanIVD, with lower porosity. Throughthe “Plug and Coat” process, partscan be 100% PVD aluminum-coated(IVD Al on OD, sputter Al on ID). Inaddition, the process is non-haz-ardous as compared to cadmiumplating (no air emissions, water emis-sions, or solid waste).

Sputtered aluminum alloys havealso showed promise to replace cad-mium. They include aluminummagnesium, aluminum-molybde-num, aluminum-tungsten, alu-minum-manganese, aluminum-zinc, and aluminum-magnesium-zinc.5, 6

While promising, magnetronsputtered aluminum is still underdevelopment for coating aircraftparts. Susceptibility to environ-mental embrittlement has yet to bedetermined, and more recent workhas generated mixed results.22 Also,while technically acceptable, thisprocess involves high start-up andoperational costs, and may not becost-effective for smaller parts suchas electrical connector shells.5, 22

OTHER DEPOSITION TECHNOLOGIESAluminum and its alloys can be read-

• Electroplated aluminum (AlumiPlate®)

• Electroplated alkaline zinc-nickel (5-15% nickel in the deposit)

• Electroplated tin-zinc (at least 20% zinc in the deposit)

Future efforts will focus on thesethree most promising candidates. Inaddition, to support efforts beingundertaken by electrical connectormanufacturers, two EN-based tech-nologies, both incorporating occlud-ed particles, will also be evaluated.Coatings with both CCCs and TCPswill be considered, as available, andcadmium with CCC will be used asthe control.

The most promising candidatecoating processes from emergingalternatives were also identified.These are technologies that showpromise for electrical connectorapplications, but require furtherdevelopment for the electrical con-nectors employed by TARDEC.These include:

• Alloys deposited from ionic liquids• Magnetron sputtered aluminum alloys

• Tin-indium alloys

Future efforts may consider thesecandidates as the technologymatures and becomes more feasiblefor electrical connectors.

REFERENCES1. K. Legg, “Cadmium Replacement

Options,” presentation to TheWelding Institute, Cambridge,UK, October 2003.

2. E. Brooman, “Alternatives toCadmium Coatings forElectrical/ElectronicApplications,” Plating and SurfaceFinishing Journal, AmericanElectroplaters and SurfaceFinishers Society, Orlando, FL,February 1993.

3. E. Brooman, D. Schario, M.Klingenberg, “EnvironmentallyPreferred Alternatives toCadmium Coatings forElectrical/ElectronicApplications,” ElectrochemicalSociety Proceedings 96-21,Electrochemical Society,

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Coated Electrical Connectorswith Trivalent Cr Post-Treatment,” presentation to theJoint Cadmium AlternativesTeam, New Orleans, January2007.

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ABOUT THE AUTHORS Rob Mason is a Senior Technical StaffMember at Concurrent TechnologiesCorporation (CTC) in Largo, Fla. In thisrole, he provides technical support toCTC’s clients in government and com-mercial industry. His current workincludes providing support to inorganiccoating activities under the NDCEE.Mason has more than 20 years cumula-tive experience in surface engineering,coatings R&D, and testing and evalua-tion methodology development, and hasco-authored upwards of 40 technical pub-lications and presentations on these sub-jects. He earned his B.S. in Chemistryfrom Fairleigh-Dickinson University, N.J.Prior to joining CTC, Mason spent sixyears at OMG-Fidelity, where he washeavily involved in product formulationand development, as well as technical serv-ice engineering. He is a member of theNational Association for SurfaceFinishing (NASF), ASM International,NACE International, and ToastmastersInternational.

Margo Neidbalson is CTC’s ProgramDeputy for the National Defense Centerfor Energy and Environment (NDCEE).In this role, she supports NDCEEProgram management and operationactivities. Her past technical efforts havebeen concentrated on evaluating haz-ardous plating chemistry alternatives onseveral NDCEE projects (non-cyanide sil-ver plating, non-line-of-sight hard chromi-um alternatives, and removal of cyanide-bearing chemistries at Corpus ChristiArmy Depot), where she provided labora-

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Technologies Discipline with particularemphasis in the laser decoating and inor-ganic finishing areas. Her primary inor-ganic finishing responsibilities lie in inno-vative coating and surface finishingprocesses, with her areas of expertise beingadvanced vacuum deposition/surface fin-ishing technologies and plating processes.Dr. Klingenberg received a B.S. inChemistry and engaged in post-baccalau-reate studies in Biology at the University ofPittsburgh at Johnstown. She received anM.S. in Manufacturing SystemsEngineering at the University of Pittsburgh

tory support in the evaluation and analy-sis of alternatives to various inorganic fin-ishing chemistries. Neidbalson holds a B.S.in Biology from Indiana University ofPennsylvania and a M.S. inManufacturing Systems Engineeringfrom the University of Pittsburgh.

Dr. Melissa Klingenberg is a PrincipalTechnical Advisor at CTC, providing over-all support to the Environmental

and a Ph.D. in Materials Engineering atthe Pennsylvania State University. Dr.Klingenberg has been an active member ofNASF since 1994, and has presentedand/or written numerous papers forNASF and AESF events and publications.In 2008, Dr. Klingenberg organized andco-chaired the first ASMInternational/NASF Surface Engineeringfor Defense and Aerospace Applicationsconference. In recognition of her contribu-tions to the industry, Dr. Klingenbergrecently received the Award of Merit fromNASF.

Pam Khabra holds a B.S. degree inChemical Engineering and a M.S. inEnvironmental Engineering from WayneState University. She is the SeniorEngineer for the Environmental Team atthe U.S. Army Tank and AutomotiveResearch, Development and EngineeringCenter in Warren, Mich. Her responsibili-ties include providing support to ProgramManagement Offices for elimination ofhazardous materials from tactical sys-tems, and compliance with environmen-tal requirements. Khabra is the TechnicalMonitor for NDCEE Task 0470,“Cadmium and Hexavalent ChromiumFree Electrical Connectors.”

Carl Handsy holds a B.S. degree inChemistry from Wayne State Universityand a Mechanical Engineering degree fromLawrence Technological University. Heworked as research engineer on theDeLorean car at W.R. Grace andCompany, and as a Development and TestEngineer at Gulf and WesternManufacturing, where he was involved inthe development of electrical propulsion forautomotive vehicles and load-leveling bat-teries for the Detroit Edison company.Handsy also worked as a Research Chemistfor Occidental Petroleum in metal platingat the Udylite Corporation prior to joiningthe U.S. Army Tank and AutomotiveResearch, Development and EngineeringCenter in Warren, Mich., where he is aSenior Materials and Corrosion Engineer.

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