Ik bo ilana fun PCB iṣelọpọ ti ṣe awọn ayipada pataki ni awọn ọdun aipẹ. 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.

Ibora ikẹhin ni a lo lati daabobo dada ti bankanje Ejò Circuit. Ejò (Cu) jẹ dada ti o dara fun awọn paati alurinmorin, ṣugbọn ni irọrun oxidized; Oxide Ejò ṣe idiwọ tutu OGUN ti solder. Botilẹjẹpe goolu (Au) ni bayi lo lati bo bàbà, nitori goolu ko ṣe oxidize; Goolu ati bàbà yoo yára tan kaakiri wọn yoo si maa wọ inu ara wọn. Eyikeyi Ejò ti o han yoo yarayara fẹlẹfẹlẹ oxide ti kii ṣe weldable. Ọna kan ni lati lo nickel (Ni) “idena idena” ti o ṣe idiwọ goolu ati bàbà lati gbigbe ati pese aaye ti o tọ, idari fun apejọ paati.

Awọn ibeere PCB fun wiwa nickel ti kii ṣe elektrolytiki

The non-electrolytic nickel coating should perform several functions:

Awọn dada ti a idogo wura

Idi pataki ti Circuit ni lati ṣe asopọ pẹlu agbara ti ara giga ati awọn abuda itanna to dara laarin PCB ati awọn paati. Ti o ba wa ni eyikeyi ohun elo afẹfẹ tabi kontaminesonu lori dada PCB, apapọ idapọmọra yii kii yoo waye pẹlu ṣiṣan alailagbara oni.

Awọn idogo goolu nipa ti lori oke nickel ati pe ko ṣe oxidize lakoko ibi ipamọ pipẹ. Bibẹẹkọ, goolu ko duro lori nickel oxidized, nitorinaa nickel gbọdọ wa ni mimọ laarin wẹwẹ nickel ati itu goolu naa. 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.

líle

Awọn aaye ti a bo ni nickel ti kii ṣe itanna ni a lo ni ọpọlọpọ awọn ohun elo ti o nilo agbara ti ara, gẹgẹbi awọn gbigbe gbigbe ọkọ ayọkẹlẹ. Awọn ibeere PCB kere pupọ ju awọn ti o wa fun awọn ohun elo wọnyi lọ, ṣugbọn lile kan jẹ pataki fun isopọmọ okun waya, awọn olubasọrọ ifọwọkan, awọn asopọ asopọ-eti, ati imuduro ṣiṣe.

Isopọ asiwaju nilo lile nickel kan. Pipadanu edekoyede le waye ti o ba jẹ pe aṣiwaju ba idibajẹ jẹ, eyiti o ṣe iranlọwọ fun asiwaju “yo” sinu sobusitireti. Awọn aworan SEM ko fihan ilaluja sinu dada ti nickel alapin/goolu tabi nickel/palladium (Pd)/goolu.

Awọn abuda itanna

Ejò jẹ irin ti o fẹ fun dida Circuit nitori o rọrun lati ṣe. Ejò n ṣe itanna daradara ju fere gbogbo irin (tabili 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

Ejò 1.7 (pẹlu Ω cm

Gold (including 2.4 Ω cm

Nickel (including 7.4 Ω cm

Ti kii-electrolytic nickel ti a bo 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. Pipadanu ifihan ifihan PCB makirowefu le kọja awọn alaye apẹrẹ. This phenomenon is proportional to the thickness of the nickel – the circuit needs to pass through the nickel to reach the solder spot. Ni ọpọlọpọ awọn ohun elo, awọn ifihan agbara itanna le pada si sipesifikesonu apẹrẹ nipa sisọ awọn idogo nickel ti o kere ju 2.5µm.

Kan si resistance

Idaabobo olubasọrọ yatọ si weldability nitori pe nickel/dada goolu wa ni ainidi jakejado igbesi aye ọja ipari. Nickel/goolu gbọdọ wa ni idari si olubasọrọ ita lẹhin ifihan ayika ti pẹ. 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, iwọn otutu eyiti awọn asopọ gbogbo agbaye gbọdọ ṣiṣẹ, nigbagbogbo sọtọ fun awọn ohun elo ologun; 200 ° C, iwọn otutu yẹn n di pataki ati siwaju sii pataki fun ohun elo fifo. ”

Fun awọn iwọn kekere, awọn idena nickel ko nilo. Bi iwọn otutu ti n pọ si, iye nickel ti a nilo lati ṣe idiwọ nickel/gbigbe goolu pọ si (Tabili II).

Tabili 2. Idaabobo olubasọrọ ti nickel/goolu (awọn wakati 1000)

Olubasọrọ nickel idena olubasọrọ ti o ni itẹlọrun ni 65 ° C olubasọrọ ti o ni itẹlọrun ni 125 ° C olubasọrọ ti o ni itẹlọrun ni 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 ti a lo ninu iwadi Antler jẹ itanna. Awọn ilọsiwaju ni a nireti lati nickel aisi-itanna, bi a ti jẹrisi nipasẹ Baudrand 4. Sibẹsibẹ, awọn abajade wọnyi jẹ fun goolu 0.5 µm, nibiti ọkọ ofurufu nigbagbogbo ṣe ṣaju 0.2 µm. Ọkọ ofurufu naa le ni iṣiro lati to fun awọn eroja olubasọrọ ti n ṣiṣẹ ni 125 ° C, ṣugbọn awọn eroja iwọn otutu ti o ga julọ yoo nilo idanwo pataki.

Antler ni imọran, “Nipọn ti nickel, idena dara julọ, ni gbogbo awọn ọran, ṣugbọn awọn otitọ ti iṣelọpọ PCB gba awọn onimọ -ẹrọ niyanju lati ṣafipamọ nickel nikan bi o ti nilo. Alapin nickel/goolu ti lo ni bayi ni awọn foonu alagbeka ati awọn oju-iwe ti o lo awọn aaye ifọwọkan-paadi. The specification for this type of element is at least 2 µm nickel.

Asopọ

Nickel ti kii ṣe elekitirotiki/immersion goolu ni a lo ni iṣelọpọ awọn igbimọ Circuit pẹlu ibamu orisun omi, titẹ-titẹ, sisun titẹ kekere ati awọn asopọ miiran ti kii ṣe welded.

Awọn asopọ ti o nilo afikun agbara ti ara to gun. Ni awọn ọran wọnyi, awọn awọ nickel ti kii ṣe elekitiroti lagbara to fun awọn ohun elo PCB, ṣugbọn imisi omi goolu kii ṣe. Very thin pure gold (60 to 90 Knoop) will rub away from the nickel during repeated friction. Nigbati a ba yọ goolu kuro, nickel ti o farahan ṣe oxidizes ni iyara, ti o yorisi ilosoke ninu resistance olubasọrọ.

Ibora nickel ti kii ṣe elekitirotiki/immersion goolu le ma jẹ aṣayan ti o dara julọ fun awọn asopọ ti o ṣafikun ti o farada awọn ifibọ lọpọlọpọ jakejado igbesi aye ọja naa. Nickel/palladium/awọn aaye goolu ni a ṣe iṣeduro fun awọn asopọ oniruru.

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) Orisun ti nickel ti a ṣe nipasẹ Ni3Sn4 awọn akopọ intermetallic.

Itankale idẹ si nickel

Gbigbe Ejò nipasẹ nickel yoo ja si idibajẹ ti idẹ si goolu dada. 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. Nitorinaa, ibeere iwọn otutu ti fẹlẹfẹlẹ idena jẹ kere ju iṣẹju kan ni isalẹ 250 ° C.

Tan ati Owen6 ti kẹkọọ ipa ti awọn fẹlẹfẹlẹ idena oriṣiriṣi lori bàbà ati wura. Wọn rii pe “… Ifiwera ti awọn iye iṣeeṣe idẹ ni 400 ° C ati 550 ° C fihan pe chromium hexavalent ati nickel pẹlu akoonu irawọ owurọ 8-10% jẹ awọn ipele idena ti o munadoko julọ ti a kẹkọọ “. (tabili 3).

Tabili 3. Ilaluja ti idẹ nipasẹ nickel si goolu

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-tan kaakiri ti kii ṣe kaakiri

According to the Arrhenius equation, diffusion at lower temperatures is exponentially slower. O yanilenu, ninu idanwo yii, nickel ti kii ṣe elekitiroti jẹ 2 si awọn akoko 10 diẹ sii daradara ju nickel elektroplated lọ. Tan ati Owen tọka si pe “… A (8%) 2µm(80µinch) barrier of this alloy reduces copper diffusion to a negligible level.”

Lati idanwo iwọn otutu iwọnyi, sisanra nickel ti o kere ju 2µm jẹ sipesifikesonu ailewu.

Itankale ti nickel si goolu

Ibeere keji ti nickel ti kii ṣe elekitirotiki ni pe nickel ko jade nipasẹ “awọn irugbin” tabi “awọn iho daradara” ti a fi wura ṣe. If nickel comes into contact with air, it will oxidize. Nickel oxide is not soldable and difficult to remove with flux.

Awọn nkan lọpọlọpọ wa lori nickel ati goolu ti a lo bi awọn ti o ni chiprún seramiki. These materials withstand the extreme temperatures of assembly for a long time. Idanwo ti o wọpọ fun awọn aaye wọnyi jẹ 500 ° C fun iṣẹju 15.

Lati le ṣe akojopo agbara ti alapin ti kii ṣe elektrolytiki nickel/goolu ti a ko sinu lati dena ifoyina nickel, weldability ti awọn ipele ti ọjọ-ori ti kẹkọọ. Different heat/humidity and time conditions were tested. Awọn ijinlẹ wọnyi ti fihan pe nickel ti ni aabo to ni aabo nipasẹ fifọ goolu, gbigba gbigba agbara ti o dara lẹhin igba pipẹ.

Itankale ti nickel si goolu le jẹ ipin idiwọn fun apejọ ni awọn igba miiran, gẹgẹ bi isopọ okun waya thermalsonic goolu. Ninu ohun elo yii, dada nickel/goolu ko ni ilọsiwaju diẹ sii ju dada nickel/palladium/goolu. 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 yellow

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).

Tabili 4. Diffusivity ti awọn ohun elo PCB ni alurinmorin

Iwọn otutu irin ° C diffusivity (µinches/ SEC.)

Wura 450 486 117.9 167.5

Ejò 450 525 4.1 7.0

Palladium 450 525 1.4 6.2

Nickel 700 1.7

Ni nickel/goolu ati tin/awọn ọna ṣiṣe, goolu lẹsẹkẹsẹ tuka sinu tin alaimuṣinṣin. 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.Awọn wiwọn Bader fihan pe ko si ju 0.5µm ti nickel ti a nilo lati ṣetọju idena, paapaa nipasẹ diẹ sii ju awọn iyipo iwọn otutu mẹfa lọ. In fact, the maximum intermetallic layer thickness observed is less than 0.5µm(20µinch).

la kọja

Non-electrolytic nickel/goolu ti laipẹ di ibora iboju PCB ikẹhin ti o wọpọ, nitorinaa awọn ilana ile-iṣẹ le ma dara fun dada yii. Ilana nya omi nitric acid wa fun idanwo porosity ti nickel electrolytic/goolu ti a lo bi asomọ plug-in (IPC-TM-650 2.3.24.2) 9. Nickel/impregnation ti kii ṣe itanna kii yoo kọja idanwo yii. A ti ṣe agbekalẹ idiwọn porosity ti Ilu Yuroopu nipa lilo potric ferricyanide lati pinnu porosity ibatan ti awọn aaye alapin, eyiti a fun ni ni awọn ofin ti awọn iho fun milimita onigun mẹrin (awọn idun /mm2). Ilẹ pẹlẹbẹ ti o dara yẹ ki o ni awọn iho to kere ju 10 fun milimita onigun ni titobi 100 x.

ipari

Ile -iṣẹ iṣelọpọ PCB nifẹ lati dinku iye nickel ti a fi si ori ọkọ fun awọn idi idiyele, akoko ọmọ, ati ibaramu ohun elo. Pataki nickel ti o kere julọ yẹ ki o ṣe iranlọwọ idiwọ itankale idẹ si oju goolu, ṣetọju agbara alurinmorin ti o dara, ki o jẹ ki resistance olubasọrọ kere. Sipesifikesonu nickel ti o pọju yẹ ki o gba irọrun ni iṣelọpọ awo, nitori ko si awọn ipo ikuna to ṣe pataki ti o ni nkan ṣe pẹlu awọn idogo nickel ti o nipọn.

Fun pupọ julọ awọn apẹrẹ igbimọ Circuit ti ode oni, ideri nickel ti kii ṣe elekitiro ti 2.0µm (80µinches) jẹ sisanra nickel ti o kere julọ ti o nilo. Ni iṣe, ọpọlọpọ awọn sisanra nickel yoo ṣee lo lori ọpọlọpọ iṣelọpọ PCB (eeya 2). Iyipada ni sisanra nickel yoo jẹ abajade lati iyipada ninu awọn ohun -ini ti awọn kemikali iwẹ ati iyipada ni akoko gbigbe ti ẹrọ gbigbe laifọwọyi. Lati rii daju pe o kere ju 2.0µm, awọn pato lati awọn olumulo ipari yẹ ki o nilo 3.5µm, o kere ju 2.0µm, ati iwọn 8.0µm.

Iwọn yii ti a ti sọtọ ti sisanra nickel ti fihan pe o dara fun iṣelọpọ awọn miliọnu awọn igbimọ Circuit. Iwọn naa ni ibamu pẹlu alurinmorin, igbesi aye selifu ati awọn ibeere olubasọrọ ti ẹrọ itanna oni. Nitori awọn ibeere apejọ yatọ si ọja kan si omiiran, awọn ideri oju le nilo lati wa ni iṣapeye fun ohun elo kọọkan pato.