III. Adhesion Quality of Tin Plating on Aluminum: Thermal Shock and Adhesion Tests

Transcription

1 Dt Bulletin Therml Aging Study of Tin Plting on Aluminum 0108DB /2007 Cedr Rpids, IA, USA Bell Chudnovsky* Vinent Pvgeu + Mihel Rpeux + Ali Zolfghri* Pierre Brdollet + *) Shneider Eletri North Ameri / Squre D, West Chester, OH USA + ) Shneider Eletri SA, Mteril Reserh Lortory, Grenole Cedex, Frne Astrt This pper presents therml study of luminum with tin plting deposited on Al y mens of three different types of tin plting using vrious ynide nd nonynide proesses. We determined the qulity of plting efore nd fter it ws exposed to the temperture of 150 C in ir for up to eight weeks using multiple testing tehniques, suh s n dhesion test, therml shok test, SEM tehniques, EDS X-ry nlysis, nd thikness mesurements. We determined tht fter ging, test tin plting shows ging relted rks, voids, nd seprtion ppering t the plting interfes; lthough in different onentrtion nd progression rtes depending on the plting tehnique used. All types of plting demonstrted deteriorted plting dhesion. Aelerted therml ging tests t 150 C disriminte plting types. Aged smples exhiit medium to poor dhesion hrteristis, nd these results re likely relted to the plting proess itself. At the origin of this ehvior, we might suggest therml-indued mehnisms, inluding formtion of intermetllis nd diffusion, presene of impurities t the plting-r interfe, defet propgtion nd stress relxtion t the interfe. I. Introdution Tin is one of the most ommon ommeril plting pplitions for luminum to improve the stility nd derese the glvni orrosion of luminum-to-opper onnetion 1. Tin-plted luminum us rs re lso often used in eletril pplition s ost-effetive replement of more expensive tin-plted opper. In ny eletril pplition where tin is used s protetive plting for luminum, it is importnt to determine wht kinds of hnges of the plting qulity n e produed y the ging proess nd how it my ffet the properties of the plting. The possile mehnisms of plting ging re not lwys fully understood nd explined, though numerous proesses, suh s oxidtion, stress relxtion, differentil therml expnsion, nd glvni nd fretting orrosion re ttriuted to irreversile hnges of ontting interfe nd orresponding hnge in ontt resistne 2, 3. In other ses, for exmple for tin plting over opper, highresistnt lyers of tin-opper intermetllis re usully formed; prtiulrly if the eletril ontt is exposed to high tempertures. Degrdtion of tin nd tin lloy plting on opper ws studied in mny spets due to the formtion of CuSn intermetlli ompounds 4, 5. The gol of the following study is to determine the possile ging mehnisms of tin plting on luminum due to exposure to elevted tempertures for n extended period of time. This study is foused solely on the qulity of tin plting on Al in s-plted onditions, nd fter exposure to elevted tempertures. The hoie of mient temperture (150 C) in n elerted ging study is sed on Interntionl Stndrd ISO 2819:1980 Metlli otings on metlli sustrtes. Eletrodeposited nd hemilly deposited otings. Review of methods ville for testing dhesion tht reommends 150 C s the temperture for the testing of tin plting on Al, Cu, nd Zn lloys nd steel sustrtes. The qulity nd ging ehviors hve een studied for three different trditionl tin plting tehniques on luminum. II. Tehniques nd Applitions of Tin Plting on Al To provide good dherene of the plting lyer to luminum, vrious tehniques re developed nd re urrently used y multiple mnufturers of luminum us rs to protet luminum from oxidtion. One of the tehniques is using ynide-sed solution for tivtion of n luminum surfe. Another tivtion tehnique is using non-ynide hemils, whih re onsidered more environmentllyfriendly. Either with or without ynide-ontining solutions, these proesses prepre the surfe of luminum us rs for tin plting through multiple-step proedures, inluding underplting of thin lyer of ronze or opper. To study the qulity of tin luminum plting for eletril ontt pplitions, three sets of luminum us rs hve een plted with tin, using three different tehniques of plting most often used in the eletril industry. Two of them re sed on two different versions of the proess with proprietry solutions, inluding ynideontining hemils, Type 1 (Alstn 80) nd Type 2 (Alstn 88). Both tehniques re supposed to provide tin plting on luminum with low surfe-to-surfe ontt resistne, nd to minimize surfe orrosion. The first set of luminum us rs ws plted with tin using the proess onsisting of n immersion or eletrolyti tivtion step in the proprietry solutions followed immeditely y tin ronze strike without n intermedite wter rinse. Tin plting is following this proessing sequene nd susequent pproprite id dip nd wter rinse. 1

2 Therml Aging Study of Tin Plting on Aluminum 0108DB0602 Dt Bulletin 02/2007 The primry dvntge of the Type 1 proess is tht it is supposed to improve orrosion resistne of the plted prt. The seond set of the Al us rs ws plted using the Type 2 proess, whih is similr to the Type 1 proess, ut uses different proprietry solutions. Aluminum surfe is tivted nd pre-plted with opper ronze strike, followed y tin plte. Non-ynide plting tehnique Type 3 (Bondl ), pplied to the third set of smples, uses surfe tivtion proedure with ynide-free zinte solution nd opper strike prior to tin plte. Smple Preprtion. The plting proess my ffet the qulity of the plting, depending on the ge of the plting th or position of the luminum r in the th. To determine if this influene is signifint, the us rs were plted in three different periods in the life yle of the th solution. The smples were prepred during two different life yles. SEM testing of the smples in these thes ould define how well the qulity of plting is reprodued in regrds to th ge. To investigte how the position in the th influenes the qulity of the plting, eh th onsisted of two rs plted in the sme th ut in different position on the rk, the totl numer of rs equls eing 12. Eh of the 12 rs ws ut in three prts, 50 m long, one prt in the middle of the r, nd two t eh edge of the r. Totl numer of the smples for eh type of plting ws 36. Non-ged (s-reeived) smples. Plting dhesion of s reeived tin-plted luminum ws tested for smples plted using ll three plting tehniques. Indeed, if the plting fils the dhesion test t non-ged sttus, further tests re no longer neessry nd the plting tehnique is onsidered not meeting the speifitions. In this study, ll of the plting tehniques sueeded sriing tests for non-ged smples. Originl plting qulity is good for oth Alstn tehniques nd ynide-free zinte tehniques. Aged smples. Adhesion testing ws performed on the smples of Al us rs plted using ll three different tin plting tehniques fter ging tests. Type 1 smples filed dhesion tests fter one week of therml ging (Figure 1), nd Type 2 smples filed dhesion tests fter four weeks of therml ging (Figure 2). Type 3 smples sueeded dhesion tests fter four weeks of therml ging. Figure 1: Adhesion Test on Type 1 Aged Smple III. Adhesion Qulity of Tin Plting on Aluminum: Therml Shok nd Adhesion Tests Aelerted Aging Test. To determine the originl qulity of tin plting on luminum the us r, nd ompre it with the plting qulity of ged smples, the smples hve een exposed to elevted tempertures. The elerted ging test onsisted of the exposure of plted us rs in lssil oven t the temperture of mient ir stilized t 150 C for the period from one to eight weeks. After the speified period, rndomly seleted r ws removed from the oven nd the smples were ut nd prepred for further testing. Aging test for Type 1 plting lsted for 8 weeks nd the rs hve een removed onsequently fter 1, 4 nd 8 weeks of therml exposure. For two other types of plting (Type 2 nd 3) more detiled ging proess ws studied, with the rs removed from the hmer fter eh week of exposure during totl four weeks. 1. Adhesion tests Adhesion tests were onduted following n ISO 2819:1980 Metlli otings on metlli sustrtes. Eletrodeposited nd hemilly deposited otings. Review of methods ville for testing dhesion. The dhesion test involves ross-ut nd tpe tests. It is first required to srie down to the metl, then, n dhesive tpe with peeling fore >180g/m is pplied on the surfe nd pulled off quikly. If there is ny oting peeled wy with the tpe, the dhesion is onsidered s nonstisftory. 2. Therml shok tests The tests were onduted ording to Interntionl Stndrd ISO 2819, whih determines the tehnique of the test. Aording to the stndrd the smples must e heted up t the reommended temperture. The smples re then quikly thrown in room temperture wter. 150 C is the reommended temperture for tin plting over Al, Cu, nd Zn lloys nd steel sustrtes. Smples re then exmined. If oting is listering, peeling or exfoliting, then the dhesion is onsidered not stisftory. Aording to the therml shok test, the dhesion of tin plting on luminum is not signifintly ffeted y short exposure to temperture up to 200 C. For smples exposed to n elevted temperture for longer period of time, the dhesion of the plting egins to deteriorte. Aording to results of the sriing test, the Type 3 plting survives longer exposure to high temperture thn Type 1 nd Type 2 pltings. 2

3 0108DB0602 Therml Aging Study of Tin Plting on Aluminum 02/2007 Dt Bulletin Figure 2: Adhesion Test on Type 2 Aged Smple Plting thikness mesurements Tin nd ronze thikness mesurements hve een done on eh SEM psule (Figure 3), ontining three prts of eh r: one prt from the middle of the r nd two prts from the edges of the r. Considering the differenes etween oting on urved side nd liner side, mesurements were tken on eh side in three different ples. Averge vlues of tin plting nd ronze underplting for Type 1 smples re given in Tle 1. For smples of Type 2 (Alstn 88) nd Type 3 (Bondl ), the SEM study shows tht tin plting nd underplting thikness re homogenous. Averge vlues of the thikness re given in Tle 1. Figure 3: SEM Smple for Thikness Mesurements Sriing ws pplied to every smple efore nd fter therml shok. Aording to results of sriing fter therml shok t 150 C, ll smples plted using ll three tehniques, pssed the test nd the oting n e onsidered properly dhesive. In order to study the qulity of the plting eyond the limit of 150 C, therml shok test ws performed lso t 200 C. After therml shok t 200 C the surfe hd n iridesent purple tint. No hnge in the dhesiveness of the oting ws oserved. IV. Qulity of Non-Aged Tin Plting on Aluminum, Bsed on SEM/EDS Study The qulity of the tin-plted luminum us r ws investigted using SEM/EDS metllogrphi nlysis to determine: A. the thikness of tin plting nd pre-plting lyer (opper or ronze); B. the presene of pores, voids, nd gps long eh interfe (Al-Cu/ronze, Cu/ronze-Sn); C. morphology of tin plting ross the lyer. D. hemil omposition of opper/ronze pre-plting lyer. All mesurements hve een performed using XL Series Snning Eletron Mirosope from Phillips Eletron Opti with n EDAX olumn for EDS nlysis. For SEM study, the smples were enpsulted with n epoxy resin polymerizing t room temperture. It is to e noted tht polymeriztion proess is heting smples t 70 C within few minutes. A slight differene in thikness is oserved etween urved nd liner sides. This well-known phenomenon is the result of differenes in the eletril field. For ll smples, inluding different plting th life yles, different positions in the th, nd different sides of the smples (liner or urved), tin plting thikness vries in the rnge etween 7.1 nd 13.9 µm. Bronze under-plting thikness vries rnges etween 0.7 nd 1.5 µm. Thikness of oth plting nd underplting re in greement with OEM speifitions. Tle 1: Thikness of tin plting nd underplting lyers on luminum us rs Plting Tehnique Numer of Mesurements Tin Plting Thikness (µm) Underplting Thikness (µm) Type 1 (Alstn 80) (ronze) Type 2 (Alstn 88) (ronze) Type 3 (Bondl ) (opper) 3

4 Therml Aging Study of Tin Plting on Aluminum 0108DB0602 Dt Bulletin 02/2007 SEM/EDS nlysis of omposition nd qulity of non-ged tin plting on luminum SEM mirophotogrph of ross setion nd hemil omposition of Type 1 plting is shown in Figure 4. Figure 4: SEM mirophotogrph nd EDS dt of rndomly seleted Type 1 smple #5: ross setion (), omposition of se metl - luminum (), omposition of underplting - tin ronze () nd the upper lyer - tin (d). The upper lyer of the plting onsists of pure tin, nd the underlyer is omposed of Sn nd Cu with the proportion orresponding to 70Sn30Cu type of ronze (70% Sn nd 30% Cu). Results of the SEM nd EDS studies of freshly plted Al using the Type 1 tehnique show tht the qulity of non-ged plting is good: no seprtion, voids, or rks hve een found. X-ry nlysis onfirmed the omposition of plting s pure tin, nd the underplting s tin-ronze for Type 1 smples. SEM nlysis shows tht non-ged Type 2 smples plted hve no pores, voids, or gps deteted long eh interfe (Al-Bronze, Bronze-Sn) (Figure 4, ). SEM nlysis hs shown tht non-ged smples plted using the Alstn 88 proess hve no pores, voids or gps deteted long eh interfe (Al-ronze, ronze-sn) (Figure 5). The qulity of Type 3 smples is good s well: no pores, voids or gps deteted long eh interfe (Al-Cu, Cu-Sn). Figure 5: Cross setion of Type 2 non-ged tin plting on luminum V. SEM/EDS Study of Plting Deteriortion in Aging Test vs. Aging Terms nd Plting Tehnique d SEM Anlysis of Type 1 smples ws performed fter 1, 4 nd 8 weeks of therml ging. For two other types of plting, SEM nlysis ws done fter 1, 2, 3 nd 4 weeks of exposure. All types of tin plting on luminum show serious deteriortion fter exposure to elevted temperture (Figures 6 8, nd Tle 2). The detils nd rte of deteriortion my differ slightly for different plting proedures, ut none of the plting withstnds the ging test. It ws found tht Type 1 nd Type 2 pltings survived the first week of exposure to high temperture, nd Type 3 plting survived 2 weeks, ut then the deteriortion proess proeeded rpidly. 4

5 0108DB /2007 Figure 6: Therml Aging Study of Tin Plting on Aluminum Dt Bulletin SEM of the Type 1 plting fter therml ging: 1 week (), 4 weeks (), nd 8 weeks () Figure 7: We suggest tht t lest three different mehnisms ould use deteriortion of tin plting on luminum during exposure to high temperture for n extended period of time: different ility of three mterils (Sn, Cu or ronze nd Al) to expnd t elevted tempertures, possile pre-existing mehnil stress in the plting, nd the qulity of tin plting on luminum. SEM of the Type 2 plting fter therml ging: 2 weeks (), 3 weeks (), nd 4 weeks () 1. Differene in therml expnsion of three lyers. Bse metl is Al, middle lyer is Cu or ronze nd upper lyer is Sn. If the differene in therml expnsion is lrge enough, then therml shok or temperture elevtion n produe mehnil stress for oting different thn for sustrte, whih my use delmintion of the plting or form rks through the plting. However, therml expnsion oeffiients for Sn (27 x10-6 /oc) nd Al (24 x10-6 /oc) re quite lose, it is not likely tht ronze with Sn s mjor omponent will e signifintly different. 5

6 Therml Aging Study of Tin Plting on Aluminum Dt Bulletin Figure 8: 0108DB /2007 deteriortion. Most evident proof of this hypothesis is SEM oservtion tht more rks, voids nd oting peeling re seen on stressed sides thn of liner sides of the ged smples. SEM of the Type 3 plting fter therml ging: 2 weeks (), 3 weeks (), nd 4 weeks () 3. Qulity of plting proedure. In ft, during the different steps of the plting proess, inluding surfe tivtion nd lening, plting interfes re exposed to severl hemils, some of them with proprietry omposition. If, in the ourse of the plting proess, ny of the tivtion nd rinsing phses re not properly done, residues of hemils my pollute the plting interfes. Test results show tht these impurities, if present, do not produe visile dmge to the plting efore they re exposed to long-term therml stress. But s soon s smples hve een heted for period of just one week, the plting hs een wekened enough to fil dhesion test. Over time (longer thn 1 week) the hemils' residues on interfes ould produe ules of pressurized gses tht ter the plting from inside. Detil SEM/EDS study my revel smll mounts of suh elements s K, N nd C on interfes. There ould lso e other light elements inluded into omposition of non-dislosed hemils, nd in the mterils used in the th ruer lining, suh s S nd F. Even Cl my e found on the surfes rinsed with hlorinted wter. VI. Summry 1. Aging studies of vrious types of tin plting on luminum hve een performed to determine n influene of therml exposure on the qulity of tin plting. 2. Three different types of tin plting over Al, inluding vrious ynide nd non-ynide proesses, hve een studied using multiple testing tehniques, suh s: dhesion test, therml shok test, SEM metllogrphy, EDS X-ry nlysis, nd thikness mesurements. 3. The qulity of plting hs een studied efore nd fter it ws exposed to the temperture of 150 C in ir for up to eight weeks. All types of plting in s-reeived smples demonstrted good dhesion properties ording to the dhesion tests nd therml shok tests. SEM study did not disover ny void, gps, or rks in s-reeived plting of ny type. Strong dhesion qulity ws determined for Type 1 plting fter 200 C (elow Sn melting temp) with therml shok test tht would revel ny dhesion issues. These results re onsistent with strong dhesion of oth the plting nd the underlyer over the r. 2. Mehnil stress. It is known tht mehnil stress in the plting is higher on urved nd ngulr sides of us r thn on liner sides. In proessing, mehnil stress is sored nd ontined in existing defults. Heting helps to relese this stress, leding to defults propgtion, retion nd multiplition. Therefore heting nd mehnil stresses re supporting eh other in the proess of mteril 6 4. Aording to the dhesion test for ged smples, the dhesion of the plting egins to deteriorte for the smples exposed to the elevted temperture for one week. Aording to the results of sriing test, Type 3 plting survives longer exposure to high temperture thn Type 1 or Type 2 plting. 5. All three types of tin plting displyed poor plting dhesion fter ging test. SEM study determined tht tin plting shows ging-relted rks, voids, nd seprtion ppering t the plting interfes; lthough in different onentrtion nd progression rtes depending on plting tehnique.

7 Therml Aging Study of Tin Plting on Aluminum 0108DB0602 Dt Bulletin 02/2007 Tle 2: Results of SEM Study of the Aged Smples Therml Aging, Weeks Type 1 Plting, Alstn 80 (Figure 6) Type 2Plting, Alstn 88 (Figure 7) Type 3 Plting, Bondl (Figure 8) 1 No pores, voids, or gps No pores, voids, or gps No pores, voids, or gps Multiple pores, voids nd gps long eh interfe Al-ronze, ronze-sn Crks long eh interfe, seprtion nd frtures of long prts of oth plting nd underplting Some voids nd gps re deteted long interfes Al-ronze, ronze-sn, oting is peeling in few lotions Multiple pores, voids nd gps long interfes, oting is peeling in more lotions Multiple pores, voids nd gps long interfes, multiple lotions with oting peeling No pores, voids or gps Some voids nd gps long interfes Al- Cu, Cu-Sn. oting is peeling in few lotions Multiple pores, voids nd gps long interfes, multiple lotions with oting peeling 6. Aelerted ging tests t 150 C disriminte plting types. Aged smples exhiit medium to poor dhesion hrteristis, nd these results re likely relted to the plting proess itself. At the origin of this ehvior, we might suggest therml-indued mehnisms inluding intermetllis formtion nd diffusion, presene of impurities t the plting-r interfe, defet propgtion nd stress relxtion t the interfe. VII. Referenes 1. M Brunovi. Effet of Fretting on the Contt Resistne of Aluminum with Different Contt Mterils IEEE Trnstions on Components, Hyrids, nd Mnufturing Tehnology, V. 2, Issue 1, p , Mrh M Brunovi. Fretting Dmge in Tin-Plted Aluminum nd Copper Connetors, IEEE Trnstions on Components, Hyrids, nd Mnufturing Tehnology, V. 12, Issue 2, p , June M Brunovi. Evlution of Different Pltings for Aluminum-to-Copper Connetions, IEEE Trnstions on Components, Hyrids, nd Mnufturing Tehnology, V. 15, Issue 2, p , April R.J. Gekle. Metllurgil Chnges in Tin-Led Pltings Due to Het Aging, IEEE Trnstions on Components, Hyrids, nd Mnufturing Tehnology, V. 14, Issue 4, p , Deemer M. Brunovi. Effet of Intermetlli Phses on the Performne of Tin-Plted Copper Connetions nd Condutors, Proeedings of the Forty-Ninth IEEE Holm Conferene on Eletril Contts, p , Septemer VIII. VITAS Bell H. Chudnovsky, Ph.D. Shneider Eletri/Squre D 9870 Cresent Prk Drive West Chester, OH (513) hudnov@squred.om Dr. Chudnovsky reeived her MS nd Ph.D. degrees in Physis from the Rostov Institute of Physis in Russi. At Shneider Eletri/Squre D, she onduts reserh in vrious pplition fields. Bell hs uthored multiple sientifi nd tehnil ppers in the fields of mteril siene, orrosion protetive plting, lurition, nd mintenne. She is memer of IEEE nd APS. Vinent Pvgeu Shneider Eletri SA Mteril Reserh Lortory Grenole, Frne vinent.pvgeu@mil.shneider.fr Mr. Pvgeu grduted s mterils engineer from the Eole Ntionle de Chimie t Clermont Ferrnd in Frne. In Shneider Eletri mteril reserh enter, he onduts nlysis nd evlutions in vrious metllurgi R&D projets, supplier nd proess greement nd filure nlysis. Shneider Eletri USA 3700 Sixth St SW Cedr Rpids, IA USA SqureD ( ) Eletril equipment should e instlled, operted, servied, nd mintined only y qulified personnel. No responsiility is ssumed y Shneider Eletri for ny onsequenes rising out of the use of this mteril.