Geedi socodka daahan kama dambaysta ah ee PCB wax -soo -saarka ayaa isbaddallo la taaban karo sameeyay sannadihii u dambeeyay. 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.

Dahaadhka kama dambaysta ah waxaa loo isticmaalaa in lagu ilaaliyo dusha sare ee bireedka naxaasta wareegga ah. Copper (Cu) waa dusha sare ee qaybaha alxanka, laakiin si fudud ayaa loo qayilaa; Oksaydhka Copper wuxuu hor istaagaa qoyaanka Alxanka. In kasta oo dahabka (Au) hadda loo isticmaalo in lagu daboolo naxaas, sababtoo ah dahabku ma qayilo; Dahabka iyo naxaasta ayaa si dhaqso ah u kala firirsan doona oo isu dhex geli doona. Naxaas kasta oo soo baxdaa waxay si dhakhso ah u samaysmi doontaa oksay naxaas ah oo aan la qallajin karin. Hal dariiqo ayaa ah in la isticmaalo nikkel (Ni) “lakabka xannibaadda” oo ka horjoogsanaya dahabka iyo naxaas inay wareejiyaan oo ay siiyaan dusha waarta, tabinta ah ee isu -geynta qaybaha.

Shuruudaha PCB ee dahaarka nikkel ee aan korontada lahayn

Dahaarka nikkel ee aan elektroolka lahayn waa inuu qabtaa dhowr hawlood:

Dusha dhigaalka dahabka ah

Ujeeddada ugu dambeysa ee wareegga waa in la sameeyo xiriir leh awood jireed oo sarreeya iyo astaamo koronto oo wanaagsan oo u dhexeeya PCB iyo qaybaha. Haddii ay jiraan wax oksaydh ah ama faddarayn dusha PCB -ga, isku -xidhkan alxanka ahi kuma dhici doono qulqulka daciifka ah ee maanta.

Dahabka ayaa si dabiici ah ugu dul shubaya nikkel oo ma oksideeyo inta lagu jiro kaydinta dheer. Si kastaba ha ahaatee, dahabku kuma dul degi karo nikkel oksaydhka ah, sidaa darteed nikkelku waa inuu ahaadaa mid nadiif ah inta u dhexaysa qubeyska nikkel iyo kala -daadinta dahabka. 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. Waxyaabahan fosfooraska ah ee ku jira dahaarka nikkel-ka ee aan elektrolytka ahayn waxaa loo tixgeliyaa inay tahay dheelitirnaan taxaddar leh ee xakamaynta qubeyska, oksaydhka, iyo guryaha korontada iyo jirka.

darantahay ingeega,

Meelaha dahaarka leh ee nikkel-ka aan lahayn ee korontada ku shaqeeya ayaa loo adeegsadaa codsiyo badan oo u baahan xoog jireed, sida gudbinta baabuurta. Shuruudaha PCB aad bay uga yar yihiin kuwa loogu talagalay codsiyadaan, laakiin adkaanshaha qaarkood ayaa muhiim u ah isku xirka siligga, xiriirada taabashada, isku xirayaasha geesaha, iyo sii wadidda howsha.

Ku xidhnaanta rasaasta waxay u baahan tahay nikkel nikkel. Iskudhicid la’aanta ayaa dhici karta haddii macdanta “ lead ” ay wax u dhinto deg -degga, taas oo ka caawineysa in macdanta “dhalaaleysa” ay gasho substrate -ka. Sawirada SEM ma muujin wax galitaan ah oo dusha sare ee nikkel/dahab ah ama nikkel/palladium (Pd)/dahab.

Sifooyinka korantada

Copper waa biraha xulashada sameynta wareegga maxaa yeelay way fududahay in la sameeyo. Copper wuxuu si fiican u hayaa koronto ka badan ku dhawaad ​​bir kasta (miiska 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

Copper 1.7 (oo ay ku jirto Ω cm

Gold (including 2.4 Ω cm

Nickel (including 7.4 Ω cm

Dahaarka nikkel ee aan korontada lahayn 55 ~ 90 ω 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. Luminta signalada PCB -ga ee microwave -ka ayaa dhaafi kara tilmaamaha naqshadeeyaha. This phenomenon is proportional to the thickness of the nickel – the circuit needs to pass through the nickel to reach the solder spot. Codsiyo badan, calaamadaha korantada ayaa lagu soo celin karaa qeexidda naqshadda iyadoo la tilmaamayo kaydka nikkel ee ka yar 2.5µm.

Xidhiidhka xidhiidhka

Iska caabbinta xiriirku way ka duwan tahay alxanka sababta oo ah nikkel/dahabka dushiisa ayaa weli ah mid aan la ilaalin inta uu nool yahay badeecaddu. Nikkel/dahab waa in uu ahaadaa mid ku dhaqma xiriirka dibadda ka dib soo -gaadhista bay’ada ee dheeraatay. 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; 125 ° C, heerkulka ay tahay in isku -xirayaasha caalamiga ah ay shaqeeyaan, oo inta badan loo cayimay codsiyada militariga; 200 ° C, heerkulkaas ayaa aad iyo aad muhiim ugu noqonaya qalabka duulaya. ”

Heerkulka hooseeya, caqabadaha nikkel looma baahna. Marka heerkulku kordho, xaddiga nikkel ee loo baahan yahay si looga hortago wareejinta nikkel/dahab ayaa kordha (Shaxda II).

Shaxda 2. Iska caabbinta nikkel/dahab (1000 saacadood)

Lakabka caqabad ee nikkel oo ah xiriir lagu qanco 65 ° C xiriir lagu qanco 125 ° C xiriir lagu qanco 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%

Nikelkii loo adeegsaday daraasadda Antler ayaa ahaa mid koronto ku shaqeeya. Hagaajin ayaa laga filayaa nikkel aan koronto lahayn, sida uu xaqiijiyay Baudrand 4. Si kastaba ha ahaatee, natiijooyinkan waxaa loogu talagalay 0.5 goldm oo dahab ah, halkaas oo diyaaraddu sida caadiga ah soo daadiso 0.2 µm. Diyaaraddu waa la qiyaasi karaa inay ku filan tahay walxaha xiriirka ee ka shaqeeya 125 ° C, laakiin walxaha heerkulka sare waxay u baahan doonaan baaritaan khaas ah.

Antler ayaa ka sii dhumuc weyn, carqaladda ayaa ka sii wanaagsan, xaaladaha oo dhan, ”ayuu Antler soo jeedinayaa,“ laakiin xaqiiqooyinka wax -soo -saarka PCB -gu waxay ku dhiirri -gelinayaan injineerada in ay dhigaan oo kaliya nikkel inta loo baahan yahay. Nikkel/dahab saafi ah ayaa hadda loo adeegsadaa taleefannada gacanta iyo bogagga isticmaala meelaha taabashada-taabashada. The specification for this type of element is at least 2 µm nickel.

Xiriiriyaha

Dhexgalka nikkel/dahabka aan elektrolytigga ahayn ayaa loo adeegsadaa soo saarista guddiyada wareegga oo leh guga habboon, riix-riix, sibidhka cadaadiska hooseeya iyo xiriiriyeyaasha kale ee aan alxanka lahayn.

Xirayaasha isku xira waxay u baahan yihiin cimri dherer jireed oo dheer. Xaaladahan, dahaarka nikkel ee aan korontada lahayn ayaa xoog ugu filan codsiyada PCB, laakiin dheelitirka dahabka ma aha. Very thin pure gold (60 to 90 Knoop) will rub away from the nickel during repeated friction. Marka dahabka laga saaro, nikkel -ka soo muuqda ayaa si dhakhso ah u oksida, taasoo keenta kororka iska caabinta xiriirka.

Dahaarka nikkel-ka ee aan korontada lahayn/dhejinta dahabka ayaa laga yaabaa inaysan ahayn xulashada ugu fiican ee isku-xirayaasha ku-xirnaanta ee u adkaysta galitaanno badan inta noloshu socoto. Meelaha nikkel/palladium/dahabka ah ayaa lagula talinayaa isku xirayaasha dhinacyo badan leh.

The barrier layer

Non-electrolytic nickel has the function of three barrier layers on the plate: 1) to prevent the diffusion of copper to gold; 2) To prevent the diffusion of gold to nickel; 3) Isha nikkel oo ay sameysay Ni3Sn4 xeryahooda intermetallic.

Baahinta naxaas ilaa nikkel

Ku wareejinta naxaasta iyada oo loo marayo nikkel waxay keenaysaa in naxaasta lagu daadiyo dahabka dushiisa. 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. Sidaa darteed, shuruudaha heerkulka ee lakabka xannibaadda ayaa ka yar hal daqiiqo oo ka hooseeya 250 ° C.

Turn and Owen6 waxay darseen saamaynta lakabyada caqabadaha kala duwan ee naxaasta iyo dahabka. Waxay ogaadeen in “… Isbarbar-dhigga qiimayaasha xaraashka naxa ee 400 ° C iyo 550 ° C waxay muujineysaa in chromium iyo nikkel hexavalent oo leh 8-10% fosfooraska ay yihiin lakabyada caqabadaha ugu wax ku oolka badan ee la barto “. (shaxda 3).

Shaxda 3. Dhexgalinta naxaas iyada oo loo marayo nikkel ilaa dahab

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 µm 1 µm 1 µ M 8 µm

2.00 µm Non-faafinta non-faafinta aan faafin

According to the Arrhenius equation, diffusion at lower temperatures is exponentially slower. Waxa xiiso leh, tijaabadan, nikkel-ka aan elektroolka lahayn wuxuu 2 ilaa 10 jeer ka waxtar badnaa nikkel-korontada. Turn iyo Owen waxay tilmaamayaan in “… A (8%) 2µm(80µinch) barrier of this alloy reduces copper diffusion to a negligible level.”

Laga soo bilaabo imtixaankan heerkulka ba’an, dhumucda nikkel ee ugu yaraan 2µm waa qeexitaan ammaan ah.

Baahinta nikkel ilaa dahab

Shuruudda labaad ee nikkel-ka aan elektroolka lahayn ayaa ah in nikkelku uusan ka tahriibin “badarka” ama “godadka wanaagsan” ee dahabka lagu xardhay. If nickel comes into contact with air, it will oxidize. Nickel oxide is not soldable and difficult to remove with flux.

Waxaa jira maqaallo dhowr ah oo ku saabsan nikkel iyo dahab oo loo adeegsado sida xambaarayaasha dhoobada dhoobada. These materials withstand the extreme temperatures of assembly for a long time. Tijaabada guud ee meelahaan waa 500 ° C muddo 15 daqiiqo ah.

Si loo qiimeeyo awoodda sagxadaha nikkel/dahabka ah ee dahaarka leh ee korontada si looga hortago oksaydhka nikkel, baaxadda meelaha heerkulka da ‘ayaa la bartay. Different heat/humidity and time conditions were tested. Daraasadahaani waxay muujiyeen in nikkel si ku filan loogu ilaaliyo dahabka dahaarka, taasoo u oggolaanaysa alxanka wanaagsan kadib gabowga dheer.

U-qaybsiga nikkel-ka dahabka ayaa laga yaabaa inay xaddid u tahay isu-imaatinka xaaladaha qaarkood, sida ku-xiridda siligga kuleylka kuleylka. Codsigan, dusha nikkel/dahabka wuu ka horumarsan yahay nikkel/palladium/dusha dahabka. 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.

Nickel tin intergeneric compound

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).

Shaxda 4. Diffusivity ee qalabka PCB ee alxanka

Heerkulka birta ° C baahinta (µinches/ SEC.)

Dahab 450 486 117.9 167.5

Copper 450 525 4.1 7.0

Palladium 450 525 1.4 6.2

Nickel 700 1.7

Nidaamyada nikkel/dahabka iyo daasadda/rasaasta, dahabku isla markiiba wuxuu ku milmaa daasad dabacsan. 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.Cabbiraadaha Bader waxay muujiyeen in aan ka badnayn 0.5µm nikkel loo baahan yahay si loo ilaaliyo caqabadda, xitaa iyada oo la marayo in ka badan lix wareeg oo heerkul ah. In fact, the maximum intermetallic layer thickness observed is less than 0.5µm(20µinch).

jilicsan

Nikkel/dahab aan elektrolytik ahayn ayaa dhowaan noqday daboolka guud ee PCB-ga ugu dambeeya, sidaa darteed hababka warshadaha ayaa laga yaabaa inaysan ku habboonayn dusha sare. Habka uumiga ah ee nitric acid ayaa diyaar u ah tijaabinta porosity ee nikkel/dahab elektrolytigga ah oo loo isticmaalo isku xira furaha (IPC-TM-650 2.3.24.2) 9. Nikkel/impregnation-ka aan elektrolytka ahayn ma dhaafi doono imtixaankan. Heerka porosity -ka Yurub ayaa la soo saaray iyadoo la adeegsanayo potassium ferricyanide si loo go’aamiyo porosity -ka dusha sare ee guriga, kaas oo la siiyo marka la eego daloolada halkii milimitir laba jibaaran (cayayaanka /mm2). Dhulka fidsan ee wanaagsan waa inuu lahaadaa wax ka yar 10 godad halkii milimitir oo laba jibbaaran marka la weyneeyo 100 x.

gabagabeyn

Warshadaha wax -soo -saarka PCB waxay danaynayaan inay yareeyaan xaddiga nikkel -ka lagu dul shubay sababaha qiimaha, waqtiga wareegga, iyo waafaqsanaanta maaddada. Tilmaanta nikkel -ka ugu yar waa inay ka caawisaa ka hortagga fidinta naxaasta ee dahabka, ilaaliso xoogga alxanka wanaagsan, oo iska -caabbinta xiriirka hoos u dhig. Qeexidda nikkel -ka ugu sarreeya waa inay oggolaataa dabacsanaanta wax -soo -saarka saxanka, maadaama aysan jirin qaabab halis ah oo fashil ah oo la xiriira kaydinta nikkel -ka qaro weyn.

Inta badan naqshadaha guddiga wareegga ee maanta, dahaarka nikkel ee aan korontada lahayn ee 2.0µm (80µinches) waa dhumucda nikkel ee ugu yar ee loo baahan yahay. Ficil ahaan, baaxad weyn oo nikkel ah ayaa loo adeegsan doonaa wax -soo -saarka PCB -ga (Jaantuska 2). Isbeddelka dhumucda nikkel wuxuu ka dhalan doonaa isbeddelka sifooyinka kiimikooyinka qubeyska iyo isbeddelka waqtiga degganaanshaha mashiinka qaadista otomaatiga ah. Si loo hubiyo ugu yaraan 2.0µm, qeexitaannada adeegsadayaasha dhammaadku waa inay u baahdaan 3.5µm, ugu yaraan 2.0µm, iyo ugu badnaan 8.0µm.

Qaddarkaan cayiman ee dhumucda nikkel ayaa caddeeyay inay ku habboon tahay soo -saarka malaayiin guddiyada wareegga ah. Baaxadda ayaa buuxinaysa weldability, nolosha shelf iyo shuruudaha xiriirka ee elektiroonigga maanta. Sababtoo ah shuruudaha shirku way ka duwan yihiin badeecad kale, dahaadhka dusha ayaa laga yaabaa inuu u baahdo in la hagaajiyo codsi kasta oo gaar ah.