Njira yomaliza yomata ya PCB kupanga kwasintha kwambiri m’zaka zaposachedwa. 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.

Kupaka komaliza kumagwiritsidwa ntchito kuteteza pamwamba pazithunzi zamkuwa. Mkuwa (Cu) ndi malo abwino owotcherera, koma ndi oxidized mosavuta; Okusayidi wamkuwa amalepheretsa chonyowa cha solder. Ngakhale golide (Au) tsopano amagwiritsidwa ntchito kuphimba mkuwa, chifukwa golidi samakhazikika; Golide ndi mkuwa zimafalikira mwachangu ndikudzaza. Mkuwa uliwonse wowonekera upanga msanga osakanizika wa oxide wamkuwa. Njira imodzi ndikugwiritsa ntchito faifi tambala (Ni) “chotchinga chotchinga” chomwe chimalepheretsa golide ndi mkuwa kusamutsa ndikupereka malo olimba, oyendetsa bwino pamsonkhano.

Zofunikira za PCB pazovala zosapanga ma electrolytic faifi tambala

The non-electrolytic nickel coating should perform several functions:

Pamaso posungitsa golide

Cholinga chachikulu cha dera ndikupanga kulumikizana ndi mphamvu yayikulu yamphamvu komanso mawonekedwe amagetsi pakati pa PCB ndi zinthu zina. Ngati pali okusayidi kapena kuipitsidwa paliponse pa PCB, cholumikizira choterechi sichingachitike ndikubwera kofooka kwamasiku ano.

Golide amasungika mwachilengedwe pamwamba pa faifi tambala ndipo samasungika nthawi yayitali pakasungidwe. Komabe, golideyo samakhazikika pa faifi tambala ya okosijeni, chifukwa chake faifi tambala iyenera kukhalabe yoyera pakati pa kusamba kwa faifi tambala ndi kutha kwa golide. 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.

kuuma

Malo osakanikirana ndi ma nickel omwe amagwiritsidwa ntchito amagwiritsidwa ntchito muntchito zambiri zomwe zimafunikira mphamvu yakuthupi, monga mayendedwe amagalimoto. Zofunikira za PCB ndizocheperako poyerekeza ndi izi, koma kuuma kwina ndikofunikira kuti kulumikizana ndi waya, kulumikizana ndi touchpad, zolumikizira m’mphepete mwa connetor, ndikukonzekera kukhazikika.

Kulumikizana patsogolo kumafuna kuuma kwa nickel. Kutayika kwa mkangano kumatha kuchitika ngati lead ikulowerera, yomwe imathandizira kuti “isungunuke” mu gawo lapansi. Zithunzithunzi za SEM sizikuwonetsa kulowa mkati mwa faifi tambala / golide kapena nickel / palladium (Pd) / golide.

Makhalidwe amagetsi

Mkuwa ndi chitsulo chosankha pakupanga dera chifukwa ndiosavuta kupanga. Mkuwa umayendetsa bwino magetsi kuposa pafupifupi chitsulo chilichonse (tebulo 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

Mkuwa 1.7 (kuphatikiza Ω cm

Gold (including 2.4 Ω cm

Nickel (including 7.4 Ω cm

Non-electrolytic faifi tambala coating kuyanika 55 ~ 90 µ ω masentimita

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. Kutaya kwa mayikirowevu PCB kumatha kupitilira mawonekedwe a wopanga. This phenomenon is proportional to the thickness of the nickel – the circuit needs to pass through the nickel to reach the solder spot. Muzinthu zambiri, ma siginolo amagetsi amatha kubwezeretsedwanso pamapangidwe ake pofotokozera ma faifi tambala osachepera 2.5µm.

Lumikizanani kukana

Kukaniza kulumikizana ndikosiyana ndi kuwotcherera chifukwa sefa wa faifi tambala / golide amakhalabe wopanda moyo wonse wazomaliza. Faifi tambala / golide ayenera kukhala conductive kwa kukhudzana patapita yaitali kukhudzana zachilengedwe. 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, kutentha komwe zolumikizira zonse ziyenera kugwira ntchito, zomwe zimafotokozedwera nthawi zambiri pazankhondo; 200 ° C, kutentha koteroko kukukulirakulirabe pa zida zouluka. ”

Kutentha kochepa, zotchinga za nickel sizofunikira. As the temperature increases, the amount of nickel required to prevent nickel/gold transfer increases (Table II).

Gulu 2. Kukana kukana kwa faifi tambala / golide (maola 1000)

Faifi tambala chotchinga wosanjikiza kukhudzana zogwira pa 65 ° C kukhudzana zogwira pa 125 ° C kukhudzana zogwira pa 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%

Nickel yomwe adagwiritsa ntchito pophunzira ya Antler idasankhidwa. Zosintha zikuyembekezeredwa kuchokera ku nickel yosagwiritsa ntchito magetsi, monga zatsimikiziridwa ndi Baudrand 4. Komabe, zotsatirazi ndi za 0.5 µm golide, pomwe ndege nthawi zambiri imakhazikika 0.2 µm. Ndege itha kunenedwa kuti ndi yokwanira pazinthu zolumikizana zomwe zimagwira 125 ° C, koma kutentha kwakukulu kudzafuna kuyesedwa kwapadera.

“Ndikakulirakulirabe, ndikofunika kutchinga, nthawi zonse,” akutero Antler, “koma zenizeni zakapangidwe ka PCB zimalimbikitsa mainjiniya kuyika faifi tambala yochuluka momwe angafunire. Faifi tambala / golide tsopano imagwiritsidwa ntchito pama foni am’manja ndi ma pager omwe amagwiritsa ntchito malo olumikizirana. The specification for this type of element is at least 2 µm nickel.

Cholumikizira

Kumiza kosagwiritsa ntchito ma elekitirodi / golide kumagwiritsidwa ntchito popanga ma board board okhala ndi kasupe woyenera, osindikizira, otsika kwambiri komanso zolumikizira zina zosakhala ndi welded.

Zowonjezera zolumikizira zimafunikira kulimba kwakanthawi. Zikatero, zokutira zosagwira ma elekitirolo ndizolimba pamagwiritsidwe a PCB, koma kumiza kwa golide kulibe. Very thin pure gold (60 to 90 Knoop) will rub away from the nickel during repeated friction. Golideyo ikachotsedwa, faifi tambala tomwe timayalulidwa timalowetsedwa msanga, zomwe zimapangitsa kuti pakhale kulumikizana.

Non-electrolytic nickel coating/gold immersion may not be the best choice for plug-in connectors that endure multiple inserts throughout the life of the product. Faifi tambala / palladium / golide amalimbikitsidwa pazolumikizira zingapo.

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) Gwero la faifi tambala lopangidwa ndi Ni3Sn4 mankhwala ophatikizika.

Kusakanikirana kwa mkuwa ndi faifi tambala

Kutumiza mkuwa kudzera pa faifi tambala kumabweretsa kuwonongeka kwa mkuwa pamwamba pagolide. 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. Chifukwa chake, kutentha kwa chotchinga ndikosakwana mphindi imodzi pansi pa 250 ° C.

Turn ndi Owen6 aphunzira momwe magawo osiyanasiyana otchinga amatengera mkuwa ndi golide. Adapeza kuti “… Kuyerekeza kuyerekezera kwamkuwa kwa 400 ° C ndi 550 ° C kukuwonetsa kuti chromium ndi nickel yolemera kwambiri yokhala ndi 8-10% ya phosphorous zili zotchinga kwambiri zomwe zaphunziridwa “. (tebulo 3).

Gulu 3. Kulowa mkuwa kudzera pa faifi tambala mpaka golide

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, M XNUMX µm

2.00 µm Osasokoneza osafalitsa osafalitsa

According to the Arrhenius equation, diffusion at lower temperatures is exponentially slower. Chosangalatsa ndichakuti, pakuyesaku, nickel yosagwiritsa ntchito ma electrolytic inali yothandiza kwambiri kawiri kuposa kawiri kuposa nickel yamagetsi. Turn ndi Owen anena kuti “… A (8%) 2µm(80µinch) barrier of this alloy reduces copper diffusion to a negligible level.”

Kuchokera pamayeso otentha kwambiri, kuchuluka kwa faifi tambala osachepera 2µm ndikofotokozera.

Kusakanikirana kwa faifi tambala ndi golidi

Chofunikira chachiwiri cha faifi-non-electrolytic nickel ndikuti nickel siyimangodutsa “njere” kapena “mabowo abwino” oikidwa ndi golide. If nickel comes into contact with air, it will oxidize. Nickel oxide is not soldable and difficult to remove with flux.

Pali zolemba zingapo pa faifi tambala ndi golide zomwe zimagwiritsidwa ntchito ngati zonyamulira za ceramic. These materials withstand the extreme temperatures of assembly for a long time. Chiyeso chodziwika cha malowa ndi 500 ° C kwa mphindi 15.

Pofuna kuwunika kuthekera kwa malo osanjikiza osagwiritsa ntchito magetsi kapena golide kuti apewe kutsekemera kwa faifi tambala, kuwunika kwa malo azaka zotentha kunaphunziridwa. Different heat/humidity and time conditions were tested. Kafukufukuyu akuwonetsa kuti faifi tambala amatetezedwa mokwanira ndi leaching golide, zomwe zimapangitsa kuti munthu akhale ndi chiyembekezo chokwanira atakalamba kwanthawi yayitali.

Kusakanikirana kwa faifi tambala ndi golidi kumatha kukhala chinthu chochepetsa pamisonkhano nthawi zina, monga kulumikizana kwa waya ndi ma thermalsonic. Pogwiritsa ntchito ntchitoyi, pamwamba pa nickel / golide sapita patsogolo kuposa nickel / palladium / golide. 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 pawiri

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).

Gulu 4. Kukhazikika kwa zida za PCB pakuwotcherera

Kutentha kwachitsulo ° C kufalikira (µinches / SEC.)

Golide 450 486 117.9 167.5

Mkuwa 450 525 4.1 7.0

Masewera a Palladium 450 525 1.4 6.2

Nickel 700 1.7

Mu faifi tambala / golide ndi malata / makina otsogolera, golideyo amasungunuka nthawi yomweyo. 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.Kuyeza kwa Bader kunawonetsa kuti sikufunikiranso 0.5µm ya faifi tambala yomwe imafunika kuti izi zisasokonezeke, ngakhale kupitilira kutentha sikisi. In fact, the maximum intermetallic layer thickness observed is less than 0.5µm(20µinch).

porous

Non-electrolytic faifi tambala / golide wakhala posachedwapa kukhala wamba chomaliza PCB pamwamba coating kuyanika, kotero njira mafakitale mwina sangakhale oyenera padziko lino. Njira ya nitric acid steam imapezeka poyesa kuyesa kwa nickel / golide yamagetsi yogwiritsidwa ntchito ngati cholumikizira (IPC-TM-650 2.3.24.2) 9. Nickel / impregnation yosagwiritsidwa ntchito ndi ma electrolytic siyitha mayeso awa. Muyeso waku Europe wakuwonongeka wapangidwa pogwiritsa ntchito potaziyamu ferricyanide kuti uzindikire kuchuluka kwa malo athyathyathya, omwe amaperekedwa potengera pores pa milimita imodzi (nsikidzi / mm2). Malo athyathyathya ayenera kukhala ndi mabowo ochepera 10 pamamilimita imodzi pakulitsa kwa 100 x.

mapeto

Makampani opanga ma PCB ali ndi chidwi chochepetsa kuchuluka kwa faifi tambala yomwe imayikidwa pa bolodi pazifukwa zamtengo, nthawi yazoyenda, komanso mawonekedwe azinthu. Mafotokozedwe osachepera a faifi tambala ayenera kuthandizira kupewa kufalikira kwamkuwa kumtunda kwa golide, kukhalabe ndi mphamvu yamagetsi, komanso kulimbana ndi otsika. Kutalika kwakukulu kwa faifi tambala kuyenera kuloleza kusinthasintha pakupanga mbale, popeza palibe njira zazikulu zolephera zomwe zimakhudzana ndi ma nickel wandiweyani.

Pazinthu zambiri zamapangidwe amakono amakono, zokutira zosapanga ma elektroni zama 2.0µm (80µinches) ndiye makulidwe ochepera a faifi tambala ofunikira. Pochita izi, makulidwe angapo azitsulo adzagwiritsidwa ntchito popanga PCB (Chithunzi 2). Kusintha kwa makulidwe a faifi tambala kumabwera chifukwa cha kusintha kwa kapangidwe ka mankhwala osamba komanso kusintha kwa nthawi yakukhalamo kwa makina okweza. Kuonetsetsa kuti kuchepa kwa 2.0µm, kutanthauzira kwa ogwiritsa ntchito kumapeto kumafunikira 3.5µm, osachepera 2.0µm, komanso kutalika kwa 8.0µm.

Makulidwe atsopanowa adatsimikizika kuti ndioyenera kupanga mamiliyoni amabwalo azizungulira. Mtunduwo umakwaniritsa kuwotcherera, moyo wa alumali ndi zofunikira pakukhudzana ndi zamagetsi amakono. Chifukwa zofunikira pamsonkhano ndizosiyana ndi chinthu china, zokutira pamwamba zimafunika kukonzedwa bwino pakagwiritsidwe kalikonse.