ʻO ke kaʻina hana uhi hope loa no PCB ua loli ka hana ʻana i nā makahiki i hala iho nei. 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.

Hoʻohana ʻia ka uhi hope loa e pale ai i ka ʻili o ka pepa keleawe keleawe. ʻO ke keleawe (Cu) kahi ʻili maikaʻi no nā mea hoʻoheheʻe, akā maʻalahi ka oxidized; Hoʻopilikia ke kōkō keleawe i ka pulu. ʻOiai hoʻohana ʻia ke gula (Au) i kēia manawa e uhi i ke keleawe, no ka mea ʻaʻole gula i oxidize; E lū koke a gula a keleawe kekahi i kekahi. ʻO kēlā me kēia keleawe kīnā ʻole e hana koke i kahi oxide keleawe non-weldable. Hoʻohana hoʻokahi e hoʻohana i ka nickel (Ni) “pale pale” e pale ai i ke gula a me ke keleawe mai ka lawe ʻana a hāʻawi i kahi papahele paʻa, conductive no ka hui o nā mea.

Nā koina PCB no ka uhi uila non-electrolytic

Pono ka uhi nickel electrolytic non-electrolytic e hana i nā hana he nui:

Ka papa o kahi waiho gula

ʻO ke kumu hope loa o ke kaʻapuni e hana i kahi pilina me ka ikaika o ke kino kiʻekiʻe a me nā ʻano uila maikaʻi ma waena o PCB a me nā ʻāpana. Inā loaʻa kekahi oxide a haumia paha ma ka ʻili PCB, ʻaʻole hiki mai kēia ami i hoʻopili ʻia me ka wai nāwaliwali o kēia lā.

Hoʻokomo maoli ke gula ma luna o ka nickel a ʻaʻole oxidize i ka lōʻihi o ka waiho ʻana. Eia naʻe, ʻaʻole kau ke gula ma ka nickel oxidized, no laila pono ka maʻemaʻe o ka nickel ma waena o ka bath nickel a me ka hoʻopau ʻana o ke gula. 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. Kuhi ʻia kēia ʻike phosphorous i ka non-electrolytic nickel coating ma ke ʻano he kaulike akahele o ka kaukau ʻauʻau, oxide, a me nā pono uila a me nā kino.

paakiki

Hoʻohana ʻia nā ʻili uila non-electrolytic i hoʻohana ʻia i nā noi he nui e koi ai i ka ikaika o ke kino, e like me nā bearings transmitter automotive. ʻOi aku ka ʻoi aku o ke koʻikoʻi o nā koi PCB ma mua o nā mea no kēia mau noi, akā he mea nui kekahi paʻakikī no ka hoʻopaʻa paʻa ʻana i ka uea, nā hoʻopili touchpad, nā hoʻopili pili pili, a me ka hoʻomau ʻana i ka hana.

Pono ka hoʻopaʻa ʻana i kēpau i ka paʻakikī nikala. Hiki ke loaʻa ka nalowale o ka hakakā inā hoʻololi ke kēpau i ka pele. ʻAʻole hōʻike ʻia nā kiʻi SEM i kahi komo i loko o ka pā o nickel pālahalaha / gula a i ʻole nickel / palladium (Pd) / gula.

Nā ʻano hiʻona uila

ʻO ke keleawe ka mea hao o ke koho no ke kaʻapuni no ka mea maʻalahi e hana. Mālama ʻo Copper i ka uila ma mua o kēlā me kēia metala (papa 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

Keleawe 1.7 (me Ω knm

Gold (including 2.4 Ω cm

Nickel (including 7.4 Ω cm

Ka uhi uila non-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. Hiki ke ʻoi aku ka nalo o ka micamela PCB hōʻailona ma mua o nā kikoʻī hoʻolālā. This phenomenon is proportional to the thickness of the nickel – the circuit needs to pass through the nickel to reach the solder spot. I nā noi he nui, hiki i nā hōʻailona uila ke hoʻihoʻi ʻia i ka kikoʻī hoʻolālā e ka wehewehe ʻana i nā waihona nickel o lalo o 2.5µm.

Kūpaʻa hoʻopili

ʻOkoʻa ke kūpaʻa hoʻopili ʻana mai ka weldability no ka mea ʻaʻole paʻa ka pae nickel / gula i loko o ke ola o ka huahana hope. Pono ka nickel / gula e noho conductive i ka hoʻopili kūwaho ma hope o ka hoʻolōʻihi ʻia ʻana o ke kaiapuni. 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, ka mahana e pono ai nā mea hoʻopili o ke ao holoʻokoʻa, i kuhikuhi pinepine ʻia no nā noi pūʻali koa; 200 ° C, ke lilo nei ka mahana i mea nui aʻe no nā pono lele. “

No nā mahana haʻahaʻa, ʻaʻole koi ʻia nā pale nika. Ke piʻi ka mahana, hoʻonui ka nui o nā nickel e pale aku ai i ka hoʻonui ʻana o ka nickel / gula (Papa II).

Pākaukau 2. Kāhea aku i ke kūpaʻa o nickel / gula (1000 mau hola)

Pākuʻi maikaʻi ʻo Nickel papaha ma 65 ° C pili maikaʻi ma 125 ° C pili maikaʻi ma 200 ° C

0.0 µ m 100% 40% 0%

0.5 µ m 100% 90% 5%

2.0 µ m 100% 100% 10%

4.0 µ m 100% 100% 60%

Hoʻohana uila ʻia ka nickel i hoʻohana ʻia ma Antler. Manaʻo ʻia nā hoʻomaikaʻi ʻana mai ka nickel electrolytic non-electrolytic, e like me ka mea i hoʻokūpaʻa ʻia e Baudrand 4. Eia nō naʻe, kēia mau hualoaʻa no ke gula 0.5 µm, kahi e piʻi pinepine ai ka mokulele 0.2 µm. Hiki ke kuhi ʻia ka mokulele e lawa no nā mea pili e hana ana ma 125 ° C, akā e koi ana nā mea mahana wela kiʻekiʻe i ka hoʻāʻo loea.

“ʻO ka mānoanoa o ka nikala, ʻoi aku ka maikaʻi o ka pale, i nā hihia āpau,” e ʻōlelo ana ʻo Antler, “akā ʻo nā ʻoiaʻiʻo o ka hana ʻana a PCB e paipai i nā ʻenekini e waiho wale i ka nui o ka nickel e pono ai. Hoʻohana ʻia i kēia manawa nā nickel / gula pālahalaha i nā kelepona paʻalima a me nā pagers e hoʻohana ai i nā kiko pilina-pad. The specification for this type of element is at least 2 µm nickel.

Ka mea hoʻopili

Hoʻohana ʻia ka immersion non-electrolytic nickel / gula i ka hana ʻana i nā papa kaapuni me ka pono o ka puna, kaomi paʻi, kahe haʻahaʻa haʻahaʻa a me nā mea hoʻopili ʻē aʻe i hoʻopili ʻole ʻia.

Pono nā mea hoʻopili plug-in i ka lōʻihi o ke kino. I kēia mau hihia, lawa ka ikaika o ka pale nickel non-electrolytic no nā polokalamu PCB, akā ʻaʻole hiki i ke komo ʻana ke gula. Very thin pure gold (60 to 90 Knoop) will rub away from the nickel during repeated friction. Ke hoʻoneʻe ʻia ke gula, oxidize wikiwiki ka nickel i hōʻike ʻia, e hopena ai i ka hoʻonui ʻana o ka pale pili.

ʻAʻole paha ka electrolytic nickel coating / immersion gula ke koho maikaʻi loa ʻia no nā mea hoʻopili plug-in e hoʻomanawanui i nā hoʻokomo he nui i ke ola o ka huahana. Paipai ʻia nā nika / palladium / gula no nā mea hoʻopili multipurpose.

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) Kumu o ka nikala i hana ʻia e Ni3Sn4 intermetallic compound.

Diffusion keleawe i nickel

ʻO ka hoʻololi o ke keleawe ma o ka nickel e hopena i ka decomposition o ke keleawe i ke gula kiʻekiʻe. 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 laila, ʻo ka koi o ka mahana o ka pale pale ma lalo o hoʻokahi minuke ma lalo o 250 ° C.

Ua hoʻopaʻa ʻo Turn a me Owen6 i ka hopena o nā pale pale like ʻole ma ke keleawe a me ke gula. Ua ʻike lākou i ka “… ʻO ka hoʻohālikelike ʻana o nā waiwai permeability keleawe ma 400 ° C a me 550 ° C e hōʻike ana hexavalent chromium a me nickel me 8-10% mau mea phosphorous nā papaha pale a ʻoi loa i aʻo ʻia. (papa 3).

Pākaukau 3. Penetration o keleawe ma o nickel i ke gula

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

0.25 1m 12 µm 18 µm XNUMX µm

0.50 1m 6 µm 15 µm XNUMX µm

1.00 1m 1 µm 8 µ M XNUMX µm

2.00 µm Hoʻolahalaha non-diffusion non-diffusion

According to the Arrhenius equation, diffusion at lower temperatures is exponentially slower. ʻO ka mea hoihoi, i kēia hoʻokolohua, ʻo ka nickel electrolytic non-electrolytic ʻo 2 a 10 mau manawa ʻoi aku ka maikaʻi ma mua o ka nickel electroplated. Huli a kuhikuhi ʻo Owen e “… A (8%) 2µm(80µinch) barrier of this alloy reduces copper diffusion to a negligible level.”

Mai kēia hoʻāʻo wela wela loa, kahi mānoanoa nickel o ka liʻiliʻi 2µm kahi kikoʻī palekana.

Diffusion o nika i ke gula

ʻO ka koi ʻelua o ka nickel electrolytic non-electrolytic ʻo ia ka neʻe ʻole o ka nickel ma o nā “grains” a i ʻole nā ​​”hole maikaʻi” impregnated me ke gula. If nickel comes into contact with air, it will oxidize. Nickel oxide is not soldable and difficult to remove with flux.

Nui a hewahewa nā ʻatikala e pili ana i ka nickel a me ke gula i hoʻohana ʻia ma ke ʻano he lawe i ka pālolo pālolo. These materials withstand the extreme temperatures of assembly for a long time. ʻO kahi hōʻike maʻamau no kēia mau papa he 500 ° C no 15 mau minuke.

I mea e loiloi ai i ka hiki o ka pālahalaha non-electrolytic nickel / gula-impregnated surfaces e pale aku ai i ka nickel oxidation, ua hoʻopaʻa ʻia ka paʻa ʻana o nā ʻilikai mehana. Different heat/humidity and time conditions were tested. Ua hōʻike ʻia kēia mau noiʻi ʻana ua pale pono ʻia ka nickel e ka leaching gula, e ʻae ana i ka maikaʻi o ka wili ma hope o ka ʻelemakule lōʻihi.

ʻO ka diffusion o ka nickel i ke gula kekahi mea palena no ka hoʻākoakoa i kekahi mau hihia, e like me ka hoʻopaʻa ʻana i ka uea thermalsonic gula. I kēia noi, ʻoi aku ka maikaʻi o ka pae nickel / gula ma mua o ka nickel / palladium / gold ʻili. 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.

Hui pū intergeneric nickel

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).

Pakuhi 4. Diffusivity o nā mea PCB i ka hoʻoheheʻe ʻana

Mahana pāmahana ° C diffusivity (µinches / kek.)

Gula 450 486 117.9 167.5

Keleawe 450 525 4.1 7.0

Palladium 450 525 1.4 6.2

Nickel 700 1.7

I loko o nā ʻōnaehana nickel / gula a me kēpau / kēpau, hoʻoheheʻe koke ke gula i loko o ka pi momona. 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.Ua hōʻike ʻia nā ana a Bader ʻaʻole i ʻoi aku i ka 0.5µm o ka nickel i koi ʻia e mālama i ka ālai, ʻoi aku ma mua o ʻeono mau pōʻai o ka mahana. In fact, the maximum intermetallic layer thickness observed is less than 0.5µm(20µinch).

porous

ʻO ka nickel / gula non-electrolytic i lilo koke i uhi uhi o ka PCB hope loa, no laila ʻaʻole kūpono i nā kaʻina ʻoihana no kēia ʻili. Loaʻa kahi kaʻina mahu nitric acid no ka hoʻāʻo ʻana i ka porosity o electrolytic nickel / gula i hoʻohana ʻia ma ke ʻano he plug-in (IPC-TM-650 2.3.24.2) 9. ʻAʻole e hala i kēia hoʻokolohua ka nickel / impregnation non-electrolytic. Ua hoʻomohala ʻia kahi hae porosity ʻEulopa e hoʻohana ana i ka potassium ferricyanide e hoʻoholo ai i ka porosity pili o nā papa pālahalaha, i hāʻawi ʻia i nā pores no kēlā me kēia millimeter (bugs / mm2). ʻO ka papa pālahalaha maikaʻi he pono ma mua o 10 mau puka ma kēlā me kēia millimeter ma 100 x hoʻonui.

ka hopena

Makemake ka ʻoihana hana PCB i ka hōʻemi ʻana i ka nui o nā nickel i waiho ʻia ma ka papa no nā kumu kumu kūʻai, manawa pōʻaiapuni, a me nā mea pili pono. Pono ka palena papaha nickel kikoʻī e pale aku i ka hoʻolaha ʻana o ke keleawe i ka ʻāpana gula, e mālama i ka ikaika weld maikaʻi, a mālama haʻahaʻa i ke kūpaʻa ʻana. E ʻae ka hōʻike nickel maximum i ka maʻalahi i ka hana ʻana i ka papa, no ka mea ʻaʻohe ʻano koʻikoʻi o ka holomua e pili me nā waihona nickel mānoanoa.

No ka hapanui o nā hoʻolālā papa kaapuni o kēia lā, ʻo ka uhi uila non-electrolytic o 2.0µm (80µinches) ka palena iki o ka mānoanoa nickel e koi ʻia. I ka hana, e hoʻohana ʻia kahi laulā o ka nickel mānoanoa ma kahi nui hana o ka PCB (Kiʻi 2). ʻO ka loli o ka mānoanoa nikela e hopena ʻia mai ka hoʻololi ʻana i nā waiwai o nā kemika ʻauʻau a me ka loli i ka manawa noho o ka mīkini hāpai kūlou. E hōʻoia i ka palena iki o 2.0µm, pono nā kikoʻī mai nā mea hoʻohana hope i 3.5µm, ka liʻiliʻi o 2.0µm, a me ka nui o 8.0µm.

Ua hōʻoia kēia pae o ka mānoanoa nickel no ka hana ʻana o miliona o nā papa kaapuni. Kūpono ka laulā i ka weldability, ola ola a me nā koi e hoʻopili ai i kēia mau uila uila. Ma muli o ka ʻokoʻa o nā koi o ka ʻaha mai kekahi huahana a i kekahi, pono e hoʻomākaukau ʻia nā pale o luna no kēlā me kēia noi.