Inqubo yokugcina yokumboza ye PCB ezokukhiqiza zibe nezinguquko ezinkulu eminyakeni yamuva. 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.

Ukumbozwa kokugcina kusetshenziselwa ukuvikela ubuso besifunda sethusi sethusi. I-Copper (Cu) yindawo enhle yezingxenye ze-welding, kodwa i-oxidized kalula; I-oxide yethusi iphazamisa i-wetTIng ye-solder. Yize manje igolide (i-Au) selisetshenziselwa ukumboza ithusi, ngoba igolide alixhumi; Igolide nethusi kuzosakazeka ngokushesha futhi kugcwale komunye nomunye. Noma yiliphi ithusi eliveziwe lizokwakha ngokushesha i-oxide yethusi engashintsheki. Enye indlela ukusebenzisa i-nickel (Ni) “barrier layer” evimbela ukudluliswa kwegolide nethusi futhi inikeze indawo ehlala isikhathi eside, eqhubayo yokuhlangana kwezinto.

Izidingo ze-PCB zezingubo ze-nickel ezingezona i-electrolytic

The non-electrolytic nickel coating should perform several functions:

Ubuso bediphozi yegolide

Inhloso enkulu yesekethe ukwakha ukuxhumana ngamandla aphezulu omzimba nezimpawu ezinhle zikagesi phakathi kwe-PCB nezinto. Uma kukhona noma iyiphi i-oxide noma ukungcoliswa ebusweni be-PCB, lelijoyinti eline-welding belingenzeki ngokugeleza kwanamuhla okubuthakathaka.

Igolide lifaka ngokwemvelo ngaphezulu kwe-nickel futhi alixhumi lapho ligcinwa isikhathi eside. Kodwa-ke, igolide alihlali ku-nickel ene-oxidized, ngakho-ke i-nickel kufanele ihlale imsulwa phakathi kokugeza kwe-nickel nokuqedwa 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. This phosphorus content in the non-electrolytic nickel coating is considered as a careful balance of bath control, oxide, and electrical and physical properties.

ubulukhuni

Izakhiwo ezifakwe i-nickel ezingezona i-electrolytic zisetshenziswa ezinhlelweni eziningi ezidinga amandla omzimba, njengamabhere wokuhambisa izimoto. Izidingo ze-PCB zincane kakhulu kunalezi zalezi zinhlelo zokusebenza, kepha ubulukhuni obuthile bubalulekile ekuxhumaneni ngezintambo, oxhumana nabo bephedi yokuthinta, izixhumi zomphetho-connetor, kanye nokusebenza kokuqina.

Ukuxhuma okuholayo kudinga ubunzima be-nickel. Ukulahlekelwa ukungqubuzana kungenzeka uma ukuhola kukhubazeka, okusiza ukuhola “kuncibilike” ku-substrate. Izithombe ze-SEM azibonisanga ukungena ebusweni be-nickel / igolide noma i-nickel / palladium (Pd) / yegolide.

Izici zikagesi

Ithusi liyinsimbi yokuzikhethela yokwakheka kwesifunda ngoba kulula ukuyenza. Ithusi liqhuba ugesi kangcono ukwedlula cishe zonke izinsimbi (ithebula 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

Ithusi 1.7 (kufaka Ω cm

Gold (including 2.4 Ω cm

Nickel (including 7.4 Ω cm

I-non-electrolytic nickel coating 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. Ukulahleka kwesiginali ye-Microwave PCB kungadlula ukucaciswa komklami. This phenomenon is proportional to the thickness of the nickel – the circuit needs to pass through the nickel to reach the solder spot. Kuzinhlelo eziningi, amasiginali kagesi angabuyiselwa esicacisweni sokuklama ngokukhomba amadiphozi we-nickel angaphansi kuka-2.5µm.

Ukuphikiswa kokuxhumana

Ukumelana nokuxhumana kuhlukile ekuthweni kalula ngoba indawo ye-nickel / yegolide ihlala ingafakwanga kuyo yonke impilo yomkhiqizo wokuphela. I-Nickel / igolide kufanele ihlale iqhubekile nokuxhumana kwangaphandle ngemuva kokuchayeka isikhathi eside kwemvelo. 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, izinga lokushisa lapho izixhumi zomhlaba wonke kufanele zisebenze khona, okuvame ukucaciselwa ukusetshenziswa kwezempi; Ngo-200 ° C, lelo banga lokushisa liya ngokuya libaluleka kakhulu emishinini yokundiza. ”

Kumazinga okushisa aphansi, izithiyo ze-nickel azidingeki. As the temperature increases, the amount of nickel required to prevent nickel/gold transfer increases (Table II).

Ithebula 2. Ukumelana nokuthintana kwe-nickel / igolide (amahora ayi-1000)

Isendlalelo se-Nickel barrier ogculisayo ku-65 ° C ogculisayo oxhumana naye ngo-125 ° C ogculisayo oxhumana naye ngo-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 esetshenziswe esifundweni sika-Antler yaqokelwa phambili. Ukuthuthuka kulindeleke kusuka ku-non-electrolytic nickel, njengoba kuqinisekiswe nguBaudrand 4. Kodwa-ke, le miphumela ngeye-0.5 µm yegolide, lapho indiza ijwayele ukucwila khona ngo-0.2 µm. Indiza ingacatshangelwa ukuthi yanele izinto zokuxhumana ezisebenza ku-125 ° C, kepha izakhi zokushisa eziphakeme zizodinga ukuhlolwa okukhethekile.

“Uma i-nickel iba nkulu, kuba ngcono umgoqo, kuzo zonke izimo,” kusho u-Antler, “kodwa amaqiniso okukhiqizwa kwe-PCB akhuthaza onjiniyela ukuthi bafake i-nickel eningi kakhulu njengoba kudingeka. I-flat nickel / igolide manje isetshenziswa kumaselula nakuma-pager asebenzisa izindawo zokuthinta ezithinta iphedi. The specification for this type of element is at least 2 µm nickel.

Isixhumi

Ukucwiliswa kwe-nickel / igolide okungasetshenziswanga kusetshenziswa ekwakhiweni kwamabhodi wesifunda anokulingana kwentwasahlobo, ukucindezela-ukulingana, ukushelela okucindezelayo okuphansi kanye nezinye izixhumi ezingashiselwe.

Izixhumi ze-plug-in zidinga ukuqina komzimba okude. Kulezi zimo, ukugcotshwa kwe-nickel okungewona i-electrolytic kunamandla anele okusetshenziselwa i-PCB, kepha ukucwiliswa kwegolide akunjalo. Very thin pure gold (60 to 90 Knoop) will rub away from the nickel during repeated friction. Lapho kususwa igolide, i-nickel evezwe igcwala ngokushesha, okuholela ekwandeni kokumelana nokuxhumana.

Ukucwiliswa kwe-nickel engeyona i-electrolytic / ukucwiliswa kwegolide kungahle kungabi yisinqumo esihle kakhulu sezixhumi ze-plug-in ezibekezelela ukufakwa okuningi kuyo yonke impilo yomkhiqizo. Kunconywa indawo yesakhiwo se-nickel / palladium / yegolide ngezixhumi ezahlukahlukene.

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) Umthombo we-nickel owenziwe yi-Ni3Sn4 compmetallic compounds.

Ukwahlukaniswa kwethusi ku-nickel

Ukudluliswa kwethusi nge-nickel kuzoholela ekonakaleni kwethusi kufakwe igolide. 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. Ngakho-ke, imfuneko yokushisa yesendlalelo sesithiyo ingaphansi komzuzu owodwa ngaphansi kuka-250 ° C.

UTurn no-Owen6 bafunde ngomphumela wezendlalelo ezahlukahlukene zethusi negolide. Bathole ukuthi “… Ukuqhathanisa amanani we-permeability we-copper ku-400 ° C no-550 ° C kukhombisa ukuthi i-chromium ne-nickel ene-hexavalent ene-8-10% yokuqukethwe kwe-phosphorus yizona zingqimba zomgoqo ezisebenza kahle kakhulu ezifundwe “. (Ithebula 3).

Ithebula 3. Ukungena kwethusi ngokusebenzisa i-nickel kuya kwegolide

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 µm 8 µ M XNUMX µm

2.00 µm Okungasabalalisi okungasabalalisi okungafani nokusabalalisa

According to the Arrhenius equation, diffusion at lower temperatures is exponentially slower. Kuyathakazelisa ukuthi kulokhu kuhlolwa, i-nickel engeyona i-electrolytic yayisebenza kahle izikhathi eziphindwe kabili kuya kwezingu-2 kune-nickel ekhethwe ngogesi. UTurn no-Owen baveza ukuthi “… A (8%) 2µm(80µinch) barrier of this alloy reduces copper diffusion to a negligible level.”

Kulesi sivivinyo sokushisa okwedlulele, ubukhulu be-nickel okungenani 2µm ukucaciswa okuphephile.

Ukwehlukaniswa kwe-nickel kuya kwegolide

Isidingo sesibili se-nickel engeyona i-electrolytic ukuthi i-nickel ayidlulisi phakathi “okusanhlamvu” noma “izimbobo ezinhle” ezifakwe igolide. If nickel comes into contact with air, it will oxidize. Nickel oxide is not soldable and difficult to remove with flux.

Kukhona izindatshana eziningana nge-nickel negolide ezisetshenziswa njengezithwali ze-ceramic chip. These materials withstand the extreme temperatures of assembly for a long time. Isivivinyo esivamile salezi zindawo ngu-500 ° C imizuzu eyi-15.

Ukuze kuhlolwe ikhono le-nickel eyisicaba / i-gold-imprennated flat ukuvikela i-nickel oxidation, kwafundwa ukutholakala kwezindawo ezinamazinga okushisa. Different heat/humidity and time conditions were tested. Lezi zifundo zikhombisile ukuthi i-nickel ivikelwe ngokwanele nge-leaching yegolide, okuvumela ukuthambeka okuhle ngemuva kokuguga isikhathi eside.

Ukwehlukaniswa kwe-nickel negolide kungaba yinto ekhawulelayo yokuhlangana kwezinye izimo, njengokufakwa kwe-wire thermalsonic ngocingo. Kulolu hlelo lokusebenza, indawo ye-nickel / yegolide iphansi kakhulu kune-nickel / palladium / igolide. 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 kwakwakhe intergeneric

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).

Ithebula 4. Ubunzima bezinto ze-PCB ekushiseni

Ukushisa kwensimbi ° C ukungafani (ama-intshi / amasekhondi.)

Igolide 450 486 117.9 167.5

Ithusi 450 525 4.1 7.0

IPalladium 450 525 1.4 6.2

Nickel 700 1.7

Ezinhlelweni ze-nickel / zegolide nezethini / zokuhola, igolide licibilika ngokushesha libe uthini ovulekile. 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.Izilinganiso zikaBader zikhombise ukuthi bekudingeka okungadluli u-0.5µm we-nickel ukugcina umgoqo, noma kungaphezu kwemijikelezo yokushisa eyisithupha. In fact, the maximum intermetallic layer thickness observed is less than 0.5µm(20µinch).

i-porous

I-nickel / igolide elingeyona ele-electrolytic lisanda kuba yindawo yokuvala indawo yokugcina ejwayelekile ye-PCB, ngakho-ke izinqubo zezimboni zingahle zingalungeli le ndawo. Inqubo ye-nitric acid steam iyatholakala ukuhlola i-porosity ye-electrolytic nickel / igolide esetshenziswa njengesixhumi se-plug-in (IPC-TM-650 2.3.24.2) 9. I-non-electrolytic nickel / impregnation ngeke iluphumelele lolu vivinyo. Izinga le-porosity laseYurophu lakhiwe kusetshenziswa i-potassium ferricyanide ukuthola ukuthi i-porosity ehlobene yini nendawo eflethi, enikezwa ngokwama-pores ngamamilimitha ayisikwele (izimbungulu / mm2). Indawo enhle eyisicaba kufanele ibe nezimbobo ezingaphansi kwezingu-10 nge-millimeter eyisikwele kukhuliso olungu-100 x.

isiphetho

Imboni yokukhiqiza ye-PCB inesifiso sokwehlisa inani le-nickel efakwe ebhodini ngezizathu zezindleko, isikhathi somjikelezo, nokuhambisana kwempahla. Ukucaciswa kwe-nickel ubuncane kufanele kusize ekuvimbeleni ukusakazeka kwethusi ebusweni begolide, kugcinwe amandla amahle e-weld, futhi kugcine ukumelana nokuxhumana kuphansi. Ukucaciswa okuphezulu kwe-nickel kufanele kuvumele ukuguquguquka ekukhiqizeni amapuleti, ngoba azikho izindlela ezibucayi zokuhluleka ezihlotshaniswa nokufakwa kwemali kwe-nickel.

Emiklamweni eminingi yebhodi lesifunda yanamuhla, ukumbozwa kwe-nickel engeyona i-electrolytic ka-2.0µm (80µinches) ubuncane be-nickel obukhulu obudingekayo. Ngokwenzayo, ubukhulu be-nickel obukhulu buzosetshenziswa kuningi lokukhiqizwa kwe-PCB (Umfanekiso 2). Ushintsho lobukhulu be-nickel luzovela ekuguqulweni kwezakhiwo zamakhemikhali okugeza kanye noshintsho esikhathini sokuhlala somshini wokuphakamisa othomathikhi. Ukuqinisekisa ubuncane obungu-2.0µm, imininingwane evela kubasebenzisi bokugcina kufanele idinge u-3.5µm, ubuncane obungu-2.0µm, nobukhulu obungu-8.0µm.

Lolu hlu olubekiwe lobukhulu be-nickel lukhombise ukuthi lukulungele ukukhiqizwa kwezigidi zamabhodi wesifunda. Ububanzi buhlangabezana nokuqina, impilo yeshalofu kanye nezidingo zokuxhumana ze-elektroniki yanamuhla. Ngoba izidingo zomhlangano zihlukile komunye umkhiqizo ziye komunye, ukumbozwa komhlaba kungadinga ukwenziwa kahle kuhlelo lokusebenza ngalunye.