Inkqubo yokugquma yokugqibela PCB imveliso iye yatshintsha kakhulu kule minyaka idlulileyo. These changes are the result of the constant need to overcome the limitations of HASL(Hot air cohesion) and the growing number of HASL alternatives.

Ingubo yokugqibela isetyenziselwa ukukhusela umphezulu wefreyimu yobhedu yesekethe. I-Copper (Cu) yindawo elungileyo ye-welding components, kodwa i-oxidized kalula; I-oxide yobhedu ithintela i-wetTIng ye-solder. Nangona igolide (iAu) ngoku isetyenziselwa ukugubungela ubhedu, kuba igolide ayidibanisi; Igolide nobhedu ziya kusasazeka ngokukhawuleza kwaye zingene kwenye. Nawuphi na ubhedu obonakalisiweyo uya kwenza ngokukhawuleza i-oxide yobhedu engenakususwa. Enye indlela kukusebenzisa i-nickel (Ni) “barrier layer” ethintela igolide nobhedu ekubeni igqithise kwaye inike indawo eqinileyo, eqhubayo yendibano yecandelo.

Iimfuno PCB for non-electrolytic nickel ukutyabeka

Ingubo ye-nickel engena-electrolytic kufuneka yenze imisebenzi emininzi:

Umphezulu wedipozithi yegolide

Eyona njongo iphambili yesekethe kukwenza unxibelelwano kunye namandla aphezulu emzimbeni kunye neempawu zombane ezilungileyo phakathi kwePCB kunye nezinto. Ukuba kukho nayiphi na i-oxide okanye ungcoliseko kumphezulu we-PCB, eli lungu lidityanisiweyo alinakubakho ngokuhamba kubuthathaka kwanamhlanje.

Igolide ifakwa ngokwendalo ngaphezulu kwe-nickel kwaye ayenzi oxidize ngexesha lokugcina ixesha elide. Nangona kunjalo, igolide ayihlali kwi-nickel ene-oxidized, ke i-nickel kufuneka ihlale icocekile phakathi kwebhafu ye-nickel kunye nokupheliswa kwegolide. Thus, the first requirement of nickel is to remain oxygen-free long enough to allow gold to precipitate. Components developed chemical leaching baths to allow 6~10% phosphorus content in nickel precipitation. Umxholo we-phosphorus kwi-non-electrolytic nickel coating uthathwa njengebhalansi ngononophelo yolawulo lokuhlamba, i-oxide, kunye nezinto zombane nezomzimba.

lukhuni

Imigangatho egalelwe i-nickel engena-electrolytic isetyenziswe kwizicelo ezininzi ezifuna amandla omzimba, njengeebheringi zokuhambisa iimoto. Iimfuno zePCB zincinci kakhulu kunezo zicelo, kodwa ubunzima obuthile kubalulekile kwi-wire-bonding, i-touchpad abafowunelwa, i-edge-connetor connectors kunye nokuqhubekeka kokusebenza.

Ukudibanisa ukukhokelela kufuna ubunzima be-nickel. Ukuphulukana nokuxubana kunokwenzeka ukuba isikhokelo sikhubazekile, esinceda ukukhokelela “kunyibilike” kwi-substrate. Imifanekiso ye-SEM ayibonisanga kungena kumphezulu we-nickel ethe tyaba / igolide okanye i-nickel / palladium (Pd) / igolide.

Iimpawu zombane

Ubhedu sisinyithi sokhetho kulwakhiwo lweesekethe kuba kulula ukwenza. Ubhedu luqhuba umbane ngokungcono kunaso sonke isinyithi (itheyibhile 1) 1,2. Gold also has good electrical conductivity, making it a perfect choice for the outermost metal because electrons tend to flow on the surface of a conductive route (the “surface” benefit).

Table 1. Resistivity of PCB metal

ICopper 1.7 (kubandakanya i-Ω cm

Gold (including 2.4 Ω cm

Nickel (including 7.4 Ω cm

Ingubo ye-nickel engena-electrolytic 55 ~ 90 µ ω cm

Although the electrical characteristics of most production plates are not affected by the nickel layer, nickel can affect the electrical characteristics of high frequency signals. Ukuphulukana nomqondiso weMicrowave PCB kunokugqitha kwinkcazo yomyili. This phenomenon is proportional to the thickness of the nickel – the circuit needs to pass through the nickel to reach the solder spot. Kwizicelo ezininzi, imiqondiso yombane inokubuyiselwa kulwazi loyilo ngokuchaza idipozithi ye-nickel engaphantsi kwe-2.5µm.

Ukumelana noqhakamshelwano

Ukumelana noqhakamshelwano kwahlukile ku-weldability kuba umphezulu we-nickel / wegolide uhlala ungafakwanga kubomi bonke bemveliso yokugqibela. I-Nickel / igolide kufuneka ihlale inomdla kunxibelelwano lwangaphandle emva kokuvezwa kwendalo ixesha elide. Antler’s 1970 book expressed nickel/gold surface contact requirements in quantitative terms. Various end-use environments have been studied: 3 “65°C, a normal maximum temperature for electronic systems operating at room temperature, such as computers; I-125 ° C, iqondo lobushushu ekufuneka isebenze kulo izihlanganisi, zihlala zichazwe kusetyenziso lomkhosi; Ngama-200 ° C, obobushushu buye buye babaluleka nangakumbi kwizixhobo zokubhabha. ”

Kumaqondo obushushu asezantsi, izithintelo ze-nickel azifuneki. Njengoko iqondo lobushushu lisonyuka, inani le-nickel elifunekayo ukuthintela ukunyuswa kwe-nickel / yegolide (iTheyibhile II).

Uluhlu 2. Uqhakamshelwano lokuchasana ne-nickel / igolide (iiyure ezili-1000)

Isingxobo seNickel sothintelo olwanelisayo ku-65 ° C kunxibelelwano olwanelisayo kwi-125 ° C kunxibelelwano olwanelisayo kwi-200 ° C

0.0 µm 100% 40% 0%

0.5 µm 100% 90% 5%

2.0 µm 100% 100% 10%

4.0 µm 100% 100% 60%

I-nickel esetyenziswe kwisifundo sika-Antler yanyulwa. Ukuphuculwa kulindelwe kwi-nickel engeyiyo yombane, njengoko iqinisekisiwe nguBaudrand 4. Nangona kunjalo, ezi ziphumo ze-0.5 µm yegolide, apho inqwelomoya ihlala ihambisa i-0.2 µm. Inqwelomoya inokuchazwa ukuba yanele izinto zonxibelelwano ezisebenza nge-125 ° C, kodwa izinto ezinobushushu obuphezulu ziya kufuna uvavanyo olukhethekileyo.

U-Antler ucebisa esithi, “I-nickel ejiyayo, kokukhona umqobo ungcono, kuzo zonke iimeko, kodwa inyani yokwenziwa kwe-PCB ikhuthaza iinjineli ukuba zifake i-nickel eninzi njengoko kufuneka.” Iflethi ye-nickel / igolide ngoku isetyenziswa kwiiselfowuni kunye nee-pager ezisebenzisa indawo yokudibanisa iphedi. The specification for this type of element is at least 2 µm nickel.

Isinxibelelanisi

Ukucwiliswa okungafunekiyo kwe-nickel / ukuntywiliselwa kwegolide kusetyenziswa xa kusenziwa iibhodi zesekethe ezinokulingana kwentwasahlobo, ulindelo-cofa, uxinzelelo olwezantsi kunye nezinye izihlanganisi ezingadityaniswanga.

Izihlanganisi ze-plug-in zifuna ukuhlala komzimba ixesha elide. Kwezi meko, iityhefu ze-nickel ezingezizo i-electrolytic zomelele ngokwaneleyo kwizicelo ze-PCB, kodwa ukuntywiliselwa kwegolide akunjalo. Very thin pure gold (60 to 90 Knoop) will rub away from the nickel during repeated friction. Xa igolide isuswe, i-nickel ebonakalayo i-oxidizes ngokukhawuleza, ekhokelela ekunyukeni kokumelana nokuqhagamshelana.

Ukuntywiliselwa okungadityaniswanga nge-nickel / ukuntywiliselwa ngegolide kusenokungabi lolona khetho lufanelekileyo kwizidibanisi ezinyamezela ukufakwa okuninzi kubomi bonke bemveliso. I-Nickel / palladium / imiphezulu yegolide iyacetyiswa kwizidibanisi ezininzi.

The barrier layer

I-nickel engeyi-electrolytic inomsebenzi wezithintelo ezintathu kwi-plate: 1) ukukhusela ukusasazeka kobhedu kwigolide; 2) To prevent the diffusion of gold to nickel; 3) Umthombo we-nickel owenziwe yi-Ni3Sn4 ye-compmetallic compounds.

Ukusasazeka kobhedu kwi-nickel

Ukuhanjiswa kobhedu nge-nickel kuya kubangela ukubola kobhedu kumphezulu wegolide. The copper will oxidize quickly, resulting in poor weldability during assembly, which occurs in the case of nickel leakage. Nickel is needed to prevent migration and diffusion of empty plates during storage and during assembly when other areas of the plate have been welded. Ke ngoko, ubushushu obudinga umaleko wesithintelo ungaphantsi komzuzu omnye ngaphantsi kwe-250 ° C.

Ukujika kunye no-Owen6 bafunde isiphumo sezithintelo ezahlukeneyo kubhedu nakwigolide. Bafumanise ukuba “… Ukuthelekiswa kwexabiso lokufumaneka kobhedu kwi-400 ° C kunye ne-550 ° C kubonisa ukuba i-chromium ene-hexavalent kunye ne-nickel ene-8-10% yomxholo we-phosphorus zezona zithintelo zisebenza kakuhle. (Itheyibhile 3).

Itheyibhile 3. Ukungena ngobhedu ngokusebenzisa i-nickel ukuya kwigolide

Nickel thickness 400°C 24 hours 400°C 53 hours 550°C 12 hours

0.25 µm 1 µm 12 µm 18 µm

0.50 µm 1 µm 6 µm 15 µm

1.00 1m 1 8m XNUMX µ M XNUMX µm

I-2.00 µm Ukungasasazisi ukungasasazisi okungasasazekiyo

According to the Arrhenius equation, diffusion at lower temperatures is exponentially slower. Into enomdla kukuba, kolu vavanyo, i-nickel engeyiyo i-electrolytic yayingamaxesha ama-2 ukuya kwali-10 ngokusebenza ngakumbi kune-nickel ekhethiweyo. Jika u-Owen abonise ukuba “… A (8%) 2µm(80µinch) barrier of this alloy reduces copper diffusion to a negligible level.”

Kuvavanyo olugqithisileyo lobushushu, ubukhulu be-nickel ubuncinci be-2µm yinkcazo ekhuselekileyo.

Ubunzima benikeli kwigolide

Imfuno yesibini ye-nickel engeyiyo ye-electrolytic kukuba i-nickel ayihambeli “kwiinkozo” okanye “kwimingxunya emihle” efakwe igolide. If nickel comes into contact with air, it will oxidize. Nickel oxide is not soldable and difficult to remove with flux.

Kukho amanqaku aliqela kwi-nickel kunye negolide esetyenziswa njengeziphathi zeceramic. These materials withstand the extreme temperatures of assembly for a long time. Uvavanyo oluqhelekileyo kwezi ndawo zingama-500 ° C imizuzu eli-15.

Ukuvavanya amandla e-nickel ethe tyaba engafakwanga i-electrolytic / igolide efakwe kwimigca yokuthintela i-nickel oxidation, kwafundwa ubungakanani bemigangatho yobushushu. Different heat/humidity and time conditions were tested. Olu phononongo lubonakalisile ukuba i-nickel ikhuselwe ngokwaneleyo yigolide e-leaching, ivumela ukuhlangana kakuhle emva kokuguga ixesha elide.

Ukusasazeka kwe-nickel kwigolide kunokuba yinto ethintelayo kwindibano kwezinye iimeko, ezinje ngegolide ebopha umlilo. Kule sicelo, umphezulu we-nickel / wegolide awuphucukanga kakhulu kune-nickel / palladium / umphezulu wegolide. Iacovangelo investigated the diffusion properties of palladium as a barrier layer between nickel and gold and found that 0.5µm palladium prevents migration even at extreme temperatures. This study also demonstrated that there was no diffusion of copper through 2.5µm of nickel/palladium determined by Auger spectroscopy during 15 minutes at 500°C.

I-Nickel tin edibeneyo yangaphakathi

During surface mount or wave soldering operation, atoms from the PCB surface will be mixed with solder atoms, depending on the diffusion properties of the metal and the ability to form “intermetallic compounds” (Table 4).

Uluhlu lwe-4. Ubunzima bezinto ze-PCB kwinyithi

Ubushushu bentsimbi ° C ukungafani (ii-intshi / umzuzwana.)

Igolide 450 486 117.9 167.5

ICopper 450 525 4.1 7.0

IPalladium 450 525 1.4 6.2

Nickel 700 1.7

Kwiinkqubo ze-nickel / igolide kunye ne-tin / lead, igolide inyibilika kwangoko ibe yitena evulekileyo. The solder forms a strong attachment to the underlying nickel by forming Ni3Sn4 intermetallic compounds. Enough nickel should be deposited to ensure that the solder will not reach underneath the copper.Imilinganiselo ye-Bader ibonakalise ukuba akukho ngaphezulu kwe-0.5µm ye-nickel efunekayo ukugcina isithintelo, nangaphezulu kweesithandathu ubushushu imijikelezo. In fact, the maximum intermetallic layer thickness observed is less than 0.5µm(20µinch).

inyulu

I-nickel / igolide engeyiyo i-electrolytic iye kutshanje yaba yindawo yokugqibela ye-PCB yokugcoba, ngoko ke iinkqubo zoshishino zingenakulungele lo mhlaba. Inkqubo ye-nitric acid steam iyafumaneka ukuvavanya i-porosity ye-electrolytic nickel / igolide esetyenziswa njenge-plug-in connector (IPC-TM-650 2.3.24.2) 9. I-nickel / i-impregnation engasebenzisi-electrolytic ayiyi kuluphumelela olu vavanyo. Umgangatho we-porosity waseYurophu uphuhlisiwe kusetyenziswa i-potassium ferricyanide ukumisela ubungqongqo bemimandla ethe tyaba, enikezelwa ngokwee-pores nge-millimeter yesikwere (bugs / mm2). Indawo elungileyo ethe tyaba kufuneka ibe nemingxunya engaphantsi kwe-10 nge-millimeter yesikwere kwi-100 x yokukhulisa.

siphelo

Umzi mveliso we-PCB unomdla wokunciphisa inani le-nickel efakwe ebhodini ngezizathu zeendleko, ixesha lokujikeleza, kunye nokuhambelana kwempahla. Ubuncinci beenkcukacha ze-nickel kufuneka zincede ekuthinteleni ukusasazeka kobhedu kumphezulu wegolide, ukugcina amandla e-weld elungileyo, kunye nokugcina ukumelana koqhagamshelo kuphantsi. Ubuninzi beenkcukacha ze-nickel kufuneka buvumele ubhetyebhetye kwimveliso yeplate, kuba akukho ndlela imbi yokusilela inxulunyaniswa needipozithi ezinqamlezileyo ze-nickel.

Uninzi loyilo lwebhodi yesekethe yanamhlanje, i-non-electrolytic nickel coating ye-2.0µm (80µinches) bubuncinci be-nickel ubukhulu obufunekayo. Ukuziqhelanisa, uluhlu lweeteksi ze-nickel ziya kusetyenziswa kwindawo yemveliso ye-PCB (Umzobo 2). Utshintsho kubunzima be-nickel luza kubakho kutshintsho lweempawu zeekhemikhali zebhafu kunye notshintsho kwixesha lokuhlala lomatshini wokuphakamisa ngokuzenzekelayo. Ukuqinisekisa ubuncinci be-2.0µm, iinkcukacha ezivela kubasebenzisi bokugqibela kufuneka zidinge i-3.5µm, ubuncinci be-2.0µm, kunye ne-8.0µ ubuninzi.

Olu luhlu luchaziweyo lobunzima be-nickel lubonakalise ukuba lulungele imveliso yezigidi zeebhodi zesekethe. Uluhlu luhlangabezana nokudibanisa, ukuhlala kwishelufa kunye neemfuno zonxibelelwano ze-elektroniki zanamhlanje. Kuba iimfuno zebandla zahlukile kwimveliso enye ukuya kwenye, ukutyabeka umphezulu kungafuna ukwenziwa kwesicelo ngasinye.