Ko te tukanga paninga whakamutunga mo PCB he nui nga whakarereketanga i puta i enei tau. 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.

Ka whakamahia te paninga whakamutunga hei tiaki i te mata o te papa parahi ara iahiko. Ko te parahi (Cu) he papa pai mo nga waahanga maitai, engari he waikura ngawari; Ko te waikura konukura e aukati i te MATI o te reehau. Ahakoa te koura (Au) e whakamahia ana inaianei hei hipoki i te parahi, na te mea kaore te koura i te waikura; Ka tere tohatoha te koura me te parahi, ka kikii tetahi ki tetahi. Ko nga parahi kapi ka kitea he waikura parahi kore-pai. Ko tetahi huarahi ko te whakamahi i te nickel (Ni) “paparanga aukati” e aukati ana i te koura me te parahi mai i te whakawhiti me te whakarato i tetahi papa roa, arai mo te kohinga huinga.

Nga whakaritenga PCB mo te paninga nickel kore-hiko

The non-electrolytic nickel coating should perform several functions:

Te mata o te putunga koura

Ko te tino kaupapa o te ara iahiko ko te hanga hononga ki te kaha tinana kaha me nga ahuatanga hiko pai i waenga i te PCB me nga waahanga. Mena he waikura, he poke ranei kei runga i te mata o te PCB, kaore tenei hononga paiherea i te ngoikore o te rere o enei ra.

Ko te putunga koura he maama kei runga noa atu o te nickel, kaore hoki e waikura i te wa e penapena ana. Heoi, kaore te koura e tau ki te nickel kua waikurihia, na me noho tonu te nickel i waenga i te pati nickel me te memeha o te koura. 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. This phosphorus content in the non-electrolytic nickel coating is considered as a careful balance of bath control, oxide, and electrical and physical properties.

pakeke

Kei te whakamahia nga papa niki-korehiko whakakakahu papa i roto i te maha o nga waahanga e hiahia ana kia kaha te kaha o te tinana, penei i te kawe aarai motuka. Ko nga whakaritenga a te PCB he iti ake te kiko atu i era mo enei tono, engari ko te pakeke he mea nui mo te honohono waea, hononga hoapā, hononga honohono-taha, me te tukatuka tukatuka.

Ko te hononga o te kaiarahi te tikanga o te pakeke o te nickel. Ka ngaro te waku ka puta ke te mata o te mata o te puapua, ka awhina te “rewa” o te mata ki te tuapapa. Kaore i whakaatuhia e nga whakaahua SEM te kikii ki te mata o te nickel papatahi / koura, nickel / palladium (Pd) / koura ranei.

Nga waahanga hiko

Ko te parahi te maitai o te maitai mo te ara iahiko na te mea ngawari ki te hanga. He pai ake te hiko o te parahi i te nuinga o nga maitai (teepu 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

Parahi 1.7 (tae atu ki te Ω cm

Gold (including 2.4 Ω cm

Nickel (including 7.4 Ω cm

Kakano nika-kore hiko 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. Ko te ngaronga tohu ngaruiti PCB ka nui ake i nga whakaritenga a te kaihoahoa. This phenomenon is proportional to the thickness of the nickel – the circuit needs to pass through the nickel to reach the solder spot. I te nuinga o nga tono, ka taea te whakahoki mai i nga tohu hiko ki te waahanga hoahoa ma te tohu i nga putunga nickel iti iho i te 2.5µm.

Whakaaetanga taatau

He rereke te aukati whakapiri i te pai o te reera na te mea he kore e mau te mata o te nickel / koura i roto i te roanga o te hua mutunga. Ko te nickel / koura me mau tonu ki nga hononga o-waho i muri o te huranga o te taiao. 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, te paemahana e tika ana kia mahi nga honohono o te ao, he mea whakarite mo nga tono hoia; 200 ° C, kua nui haere te kaha o te mahana ki nga taputapu rererangi. ”

Mo te paemahana iti, kaore e hiahiatia nga aukati nickel. Ka piki ake te mahana, te nui o te nickel e hiahiatia ana hei aukati i te piki o te whakawhiti nickel / koura (Ripanga II).

Ripanga 2. Whakapā atu ki te ātete o te nickel / koura (1000 haora)

Ko te paparanga aukati Nickel e pai ana te whakapiri atu ki te 65 ° C whakapapa pai i te 125 ° C whakapapa pai i te 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%

Ko te nickel i whakamahia i roto i te rangahau a Antler i whakaahihia i te hiko. Ko nga whakapainga ake e hiahiatia ana mai i te nickel kore-hiko, i whakapumautia e Baudrand 4. Heoi, ko enei hua mo te 0.5 µm koura, i reira te rererangi e eke ana ki te 0.2 µm. Ka taea te whakapae i te rererangi kia pai mo nga waahanga whakapā e mahi ana i te 125 ° C, engari ko nga waahanga o te paemahana teitei ake ka hiahiatia he whakamatautau motuhake.

“Ko te matotoru o te nickel, ko te pai ake o te aukati, i roto i nga ahuatanga katoa,” e kii ana a Antler, “engari ko nga ahuatanga o te hanga PCB e akiaki ana i nga kaiwhakangungu kia waiho noa atu te nickel e hiahiatia ana. Kei te whakamahia inaianei te nickel / koura papatahi i roto i nga waea pukoro me nga pagers e whakamahi ana i nga papa whakapiri papa-papa. The specification for this type of element is at least 2 µm nickel.

Te hononga

Kei te whakamahia te nika-kore / rumaki koura i te hanga papa papaahiko me te pai o te koanga, te perehi, te reti iti-nekehanga me etahi atu honohono-kore.

Ko nga honohono mono-mai he roa ake te pumau o te tinana. I enei keehi, ko nga koti nickel kore-hiko he kaha ki nga tono PCB, engari ko te rumaki koura kaore. Very thin pure gold (60 to 90 Knoop) will rub away from the nickel during repeated friction. Ka tangohia ana te koura, ka tere te tere o te nickel kitea, ka hua ake te aukati whakapā.

Ko te paninga nickel kore-hiko / rumaki koura kaore pea i te kowhiringa pai rawa atu mo nga hononga mono-mai e mau ana ki nga whakauru maha puta noa i te koiora o te hua. Ko nga papanga Nickel / palladium / koura e taunakitia ana mo nga hononga tuuroro.

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) Te puna o te nickel i hangaia e Ni3Sn4 whakauru pungarehu.

Te tohatoha o te parahi ki te nickel

Ko te whakawhitinga o te parahi ki roto i te nickel ka pakaru te parahi ki te koura o runga. 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. No reira, ko te whakaritenga o te pāmahana o te papa arai he iti ake i te kotahi meneti i raro iho i te 250 ° C.

Kua tirotirohia e Turn me Owen6 te rereketanga o nga papa arai rerekee ki te parahi me te koura. I kitea e ratou “… Ko te whakataurite i nga uara uruhanga o te parahi i te 400 ° C me te 550 ° C e whakaatu ana ko te hexavalent chromium me te nickel me te 8-10% te kiko o te ūkuikui nga paparanga aukati e tino rangahaua ana. (teepu 3).

Ripanga 3. Te whakauru i te parahi na roto i te nickel ki te koura

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 Korenga-marara kore-marara kore-marara

According to the Arrhenius equation, diffusion at lower temperatures is exponentially slower. He mea whakamiharo, i tenei whakamatautau, ko te nickel kore-hiko he 2 ki te 10 wa te pai ake i te nickel hiko. Huri mai ka tohu a Owen e “… A (8%) 2µm(80µinch) barrier of this alloy reduces copper diffusion to a negligible level.”

Mai i tenei whakamatautau tino mahana, ko te matotoru nickel o te iti rawa 2µm he tohu ahuru.

Te tohatoha o te nickel ki te koura

Ko te whakaritenga tuarua mo te nickel kore-hiko ko te nickel kia kaua e neke ma roto i nga “purapura” me nga “rua pai” ka whakakiihia ki te koura. If nickel comes into contact with air, it will oxidize. Nickel oxide is not soldable and difficult to remove with flux.

He maha nga tuhinga mo te nickel me te koura e whakamahia ana hei kaikawe kokiri uku. These materials withstand the extreme temperatures of assembly for a long time. Ko te whakamatautau noa mo enei papa ko te 500 ° C mo te 15 meneti.

Kia taea ai te arotake i te kaha o nga papa-kore-hiko / papa-kore-koura ki te aukati i te waikura totika, i rangahauhia te pai o te papa-pakeke Different heat/humidity and time conditions were tested. I whakaatuhia enei rangahau ko te nickel e tiakina rawatia ana e te taatai ​​koura, kia pai ai te pai o te peera i muri o te koroheketanga.

Ko te tohatoha o te nickel ki te koura he mea nui hei whakaiti i te kohinga i etahi waa, penei i te taura waea-wera thermalsonic. I roto i tenei tono, he iti ake te anga o te nickel / koura i te papa o te nickel / palladium / koura. 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.

Taimana tihorea whakatipuranga whakatipuranga

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).

Ripanga 4. Te rereketanga o nga rauemi PCB ki te maitai

Te pāmahana whakarewa ° C diffusivity (µinches / hekona.)

Koura 450 486 117.9 167.5

Parahi 450 525 4.1 7.0

Palladium 450 525 1.4 6.2

Nickel 700 1.7

I roto i nga punaha nickel / koura me te tine / mata, ka rewa tonu te koura ki te tine parakore. 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.Ko nga inenga a Bader e whakaatu ana kaore i neke atu i te 0.5µm o te nickel i hiahiatia kia mau tonu te aukati, ahakoa neke atu i te ono huringa huringa mahana. In fact, the maximum intermetallic layer thickness observed is less than 0.5µm(20µinch).

porous

Katahi ano ka riro te nickel / koura korekiko / koura hou hei paninga mata noa o te PCB, no reira kaore pea nga tikanga umanga e pai mo tenei mata. Kei te waatea he mahinga korohuu waikawa nitric hei whakamatautau i te porosity o te nika electrolytic / koura e whakamahia ana hei hononga hono (IPC-TM-650 2.3.24.2) 9. Ko te nickel kore-electrolytic / impregnation kaore e paahitia i tenei whakamatautau. I hangaia he paerewa porosity a te Pakeha ma te whakamahi i te pāhare pāporo ferricyanide hei whakatau i te porohita o te papa papatahi, e hoatu ana mo te pore o ia millimeter tapawha (pepeke / mm2). Ko te papa papatahi pai kia iti ake i te 10 nga poka mo ia millimeter tapawha i te 100 x te whakanui.

mutunga

Kei te hiahia te umanga whakangao PCB ki te whakaheke i te nui o te nickel i whakatakotoria ki runga i te papa mo nga utu, te huringa o te waa, me te hangai o nga rawa. Ma te tohu iti o te nickel te aarai o te parahi o te parahi ki te mata koura, kia mau ki te kaha pai, kia pai te aukati i te whakapiri. Ko te whakaritenga nickel mōrahi me tuku te hangore ki te mahi pereti, na te mea kaore he momo momo ngoikoretanga e hono ana ki nga putunga nickel matotoru.

Mo te nuinga o nga hoahoa poari taiawhio o enei ra, ko te paninga nickel kore-hiko o 2.0µm (80µinches) te matotoru iti o te nickel e hiahiatia ana. Hei mahi, ka whakamahia te whanui o te nickel matotoru ki te waahanga hanga o te PCB (Whakaahua 2). Ko te rereketanga o te matotoru nickel ka puta i te rereketanga o nga taonga o nga miihini horoi me te rereketanga o te waa noho o te miihini whakaara aunoa. Ki te whakarite kia iti te 2.0µm, ko nga whakaritenga mai i nga kaiwhakamahi mutunga me whai 3.5µm, kia 2.0µm te iti, me te 8.0mm te rahinga.

Ko tenei kohinga matotoru o te nickel matotoru kua tika mo te hanga miriona papa poari. Ka tutuki i te whānuitanga te paiherea, te ora me nga whakaritenga whakapiri o nga taonga hiko o tenei ra. Na te mea he rereke nga whakaritenga o te huihuinga mai i tetahi hua ki tetahi atu, me whakapai ake nga paninga mata mo ia tono motuhake.