Iyo yekupedzisira yekupfeka maitiro e PCB kugadzira kwave nekuchinja kukuru mumakore apfuura. 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.

Iyo yekupedzisira kupfeka inoshandiswa kuchengetedza pamusoro penzvimbo yedunhu mhangura foil. Mhangura (Cu) inzvimbo yakanaka yekutungidza zvinhu, asi iri nyore oxidized; Mhangura oxide inotadzisa kunyorovesa SODING. Kunyangwe goridhe (Au) rave kushandiswa kuvhara mhangura, nekuti goridhe haina oxidize; Ndarama nemhangura zvinokurumidza kupararira uye kuzadza mumwe. Chero chero mhangura yakafumurwa inokurumidza kugadzira isina-weldable yemhangura oxide. Imwe nzira ndeye kushandisa nickel (Ni) “barrier layer” iyo inodzivirira goridhe nendarira kubva kuendesa uye inopa yakasimba, inoitisa pamusoro penzvimbo yegungano.

Pcb zvinodiwa kune asiri-electrolytic nickel unhani

The non-electrolytic nickel coating should perform several functions:

Iko pamusoro pechipo chegoridhe

Chinangwa chekupedzisira wedunhu ndechekuumba kubatana nehurefu hwesimba uye hunhu hwakanaka hwemagetsi pakati pePCB uye zvikamu. Kana paine chero oxide kana kusvibiswa pane pcb pechiso, ichi chakasunganidzwa chakabatana hachiitike neinhasi isina simba kuyerera.

Ndarama inoisa zvakasununguka pamusoro penikel uye haina oxidize panguva yakareba yekuchengetedza. Nekudaro, iyo goridhe haigare pane iyo yakasanganiswa nickel, saka iyo nickel inofanira kuramba yakachena pakati penzvimbo yekugezesa uye nekunyungudika kwegoridhe. 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.

neukukutu

Isina-electrolytic nickel yakavharwa nzvimbo inoshandiswa mune zvakawanda zvinoshandiswa zvinoda simba remuviri, senge mota dzinoendesa mabheyaringi. Zvidimbu zvePCBB zvakaomarara zvishoma pane izvo zvekushandisa izvi, asi kumwe kuomarara kwakakosha kune tambo-yekubatanidza, yekubata-padhi yekutaurirana.

Kutungamira kwekubatanidza kunoda nickel kuomarara. Kurasikirwa kwekukonana kunogona kuitika kana iyo lead ikashatisa iyo yekukasira, iyo inobatsira iyo lead “kusungunuka” mukati meiyo substrate. SEM mifananidzo yakaratidza kusa pinda mukati memvura yakapetwa nickel / goridhe kana nickel / palladium (Pd) / goridhe.

Hunhu hwemagetsi

Mhangura ndiyo simbi yesarudzo yekuumbwa kwedunhu nekuti iri nyore kugadzira. Mhangura inoitisa magetsi zvirinani kupfuura zvese simbi (tafura 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

Mhangura 1.7 (inosanganisira Ω cm

Gold (including 2.4 Ω cm

Nickel (including 7.4 Ω cm

Isiri-electrolytic nickel kupfeka 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. Microwave pcb kurasikirwa chiratidzo kunogona kupfuura dhizaini dhizaini. This phenomenon is proportional to the thickness of the nickel – the circuit needs to pass through the nickel to reach the solder spot. Mukushandisa kwakawanda, zviratidzo zvemagetsi zvinogona kudzoreredzwa kune dhizaini dhizaini nekutsanangudza nickel deposits asingasviki 2.5µm.

Bata kuramba

Kutaurirana kurwisa kwakasiyana neweldability nekuti iyo nickel / yegoridhe pamusoro inoramba isina kuvharwa muhupenyu hwese hwekupedzisira chigadzirwa. Nickel / goridhe rinofanira kuramba richitungamira kune vekunze kusangana mushure mekuratidzwa kwenguva refu kwezvakatipoteredza. 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. 200 ° C, tembiricha iyoyo iri kuramba ichiwedzera kukosha pazvinhu zvinobhururuka. ”

Kune yakaderera tembiricha, nickel zvipingamupinyi hazvidiwe. Sezvo tembiricha inowedzera, huwandu hwenickel hunodiwa kudzivirira nickel / kuwedzerwa kwegoridhe kunowedzera (Tafura II).

Tafura 2. Kubata kurwisa nickel / goridhe (1000 maawa)

Nickel chipingamupinyi rukoko hunogutsa kuonana pa 65 ° C zvinogutsa kuonana pa 125 ° C hunogutsa kuonana 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%

Iyo nickel yakashandiswa mukudzidza kwaAntler yakasarudzwa. Improvements inotarisirwa kubva kune isiri-electrolytic nickel, sekusimbiswa naBaudrand 4. Nekudaro, mhedzisiro iyi ndeye 0.5 µm goridhe, uko ndege inowanzo mhanyisa 0.2 µm. Ndege inogona kufungidzirwa kuti inokwana zvinhu zvekubata zvinoshanda pa125 ° C, asi zvepamusoro tembiricha zvinhu zvinoda kuyedzwa kwakasarudzika.

“Kana mukobvu wakakwenenzverwa, nani chipingamupinyi, muzviitiko zvese,” anodaro Antler, “asi chokwadi chekugadzirwa kwePBB chinokurudzira mainjiniya kuisa nickel yakawanda seyinodiwa. Flat nickel / goridhe parizvino inoshandiswa munhare mbozha uye mapaja ayo anoshandisa yekubata-padhi nzvimbo dzekubata. The specification for this type of element is at least 2 µm nickel.

Iyo chinongedzo

Isiri-electrolytic nickel / kunyudzwa kwegoridhe inoshandiswa mukugadzira kwemabhodhi edunhu ane chitubu chakaringana, yekutsikirira-kukodzera, yakaderera-kumanikidza inotsvedza uye zvimwe zvisina-welded zvinongedzo.

Plug-in yekubatanidza inoda kugara kwenguva refu kwemuviri. Muzviitiko izvi, isina-electrolytic nickel machira akasimba zvakakwana maPCB mafomu, asi kunyudzwa kwegoridhe hakuna. Very thin pure gold (60 to 90 Knoop) will rub away from the nickel during repeated friction. Kana iyo goridhe ichibviswa, iyo yakaratidzwa nickel inosanganisa nekukasira, zvichikonzera kuwedzera kwekubatana nemishonga.

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. Nickel / palladium / nzvimbo dzegoridhe dzinokurudzirwa kune akawanda macomputer ekubatanidza.

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) Kunobva nickel kwakaumbwa Ni3Sn4 intermetallic yeimwe.

Kupararira kwemhangura kune nickel

Kuendeswa kwemhangura kuburikidza ne nickel kunoguma nekuora kwemhangura kumusoro kwegoridhe. 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. Naizvozvo, iyo tembiricha inodikanwa yeiyo barrier layer iri pasi peminiti imwe pazasi pe250 ° C.

Tendeuka naOwen6 vakadzidza mabudiro ezvipenga zvakasiyana pamhangura negoridhe. Vakaona kuti “… Kuenzanisa kwemhangura inokwenenzverwa kukosha pa400 ° C uye 550 ° C inoratidza kuti hexavalent chromium uye nickel ine 8-10% phosphorus zvemukati ndizvo zvinonyanya kushanda zvipingaidzo zvakadzidzwa “. (tafura 3).

Tafura 3. Kupinda mukati memhangura kuburikidza nickel kuenda goridhe

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 Yisiri-yekupararira isiri-yekuparadzira isiri-kufambisa

According to the Arrhenius equation, diffusion at lower temperatures is exponentially slower. Sezvineiwo, mukuyedza uku, isiri-electrolytic nickel yaive kakapetwa ka2 kusvika kagumi pane yakasarudzika nickel. Turn naOwen vanonongedza kuti “… A (8%) 2µm(80µinch) barrier of this alloy reduces copper diffusion to a negligible level.”

Kubva pane iyi yakanyanya tembiricha bvunzo, iyo nickel ukobvu inokwana kuita 2µm ndeye yakachengeteka yakatarwa.

Kuparadzaniswa kwe nickel kune goridhe

Chechipiri chinodiwa cheasina-electrolytic nickel ndeyekuti nickel haifambe kuburikidza ne “zviyo” kana “maburi akanaka” akaisirwa goridhe. If nickel comes into contact with air, it will oxidize. Nickel oxide is not soldable and difficult to remove with flux.

Iko kune akati wandei zvinyorwa pane nickel negoridhe zvinoshandiswa seceramic chip inotakura. These materials withstand the extreme temperatures of assembly for a long time. Chiyero chakajairika cheizi nzvimbo ndeye 500 ° C kwemaminetsi gumi nemashanu.

Kuti uongorore kugona kwenzvimbo dzisiri-electrolytic nickel / goridhe-yakaisirwa nzvimbo yekudzivirira nickel oxidation, weldability yetembiricha-makore ane huso akafunda. Different heat/humidity and time conditions were tested. Izvi zvidzidzo zvakaratidza kuti nickel inochengetedzwa zvakakwana neaching yegoridhe, ichibvumira kugona kwakanaka mushure mekukwegura kwenguva refu.

Kuparadzaniswa kwe nickel negoridhe kunogona kuve chinhu chinotadzisa kuungana mune zvimwe zviitiko, senge goridhe thermalsonic waya-kusunga. Mukushandisa uku, iyo nickel / yegoridhe pamusoro haina kumbofambira mberi kupfuura iyo nickel / palladium / yegoridhe pamusoro. 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 tini intergeneric remubatanidzwa

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).

Tafura 4

Simbi tembiricha ° C diffusivity (µinches / SEC.)

Ndarama 450 486 117.9 167.5

Mhangura 450 525 4.1 7.0

Palladium 450 525 1.4 6.2

Nickel 700 1.7

Mune nickel / goridhe uye tin / lead masisitimu, iyo goridhe pakarepo inopararira kuita yakasununguka tini. 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.Zviyero zveBader zvakaratidza kuti hapana inopfuura 0.5µm yenikel yaidikanwa kuchengetedza chipingamupinyi, kunyangwe kuburikidza nematanhatu anopfuura matanhatu tembiricha. In fact, the maximum intermetallic layer thickness observed is less than 0.5µm(20µinch).

porous

Isiri-electrolytic nickel / goridhe ingori ichangobva kuve yakajairika yekupedzisira pcb yekumhara, saka maindasitiri maitiro anogona kunge asiri akakodzera kune ino nzvimbo. Iyo nitric acid steam steam maitiro anowanikwa kuyedza porosity ye electrolytic nickel / goridhe rinoshandiswa se plug-in yekubatanidza (IPC-TM-650 2.3.24.2) 9. Isiri-electrolytic nickel / impregnation haizopasa uyu muedzo. Chiyero cheEuropean porosity chakagadziridzwa pachishandiswa potasium ferricyanide kuona iyo porosity inowoneka nzvimbo dzakatsetseka, iyo inopihwa maererano ne pores pa square millimeter (bugs / mm2). Nzvimbo yakanaka yakati sandara inofanirwa kunge iine maburi mashoma pane gumi pamamirimita pa10 x kukura.

kugumisa

Pcb yekugadzira indasitiri inofarira kudzikisa huwandu hwenickel hwakaiswa pabhodhi nekuda kwezvikonzero zvemutengo, nguva yekutenderera, uye kugarisana kwezvinhu. Iyo shoma nickel yakatarwa inofanira kubatsira kudzivirira mhangura kupatsanurwa kune yegoridhe pamusoro, chengetedza yakanaka weld simba, uye chengetedza kuonana kuramba kushomeka. Iyo yakanyanya nickel kududzirwa inofanirwa kubvumidza kuchinjika mukugadzira kweplate, sezvo pasina modhi dzakakomba dzekukundikana dzinosanganisirwa neakakura nickel deposits.

Kune mazhinji emazuvano edunhu bhodhi dhizaini, isiri-electrolytic nickel yekupfeka ye2.0µm (80µinches) ndiyo shoma nickel ukobvu hunodiwa. Mukuita, huwandu hwesimbi yenickel hunoshandiswa pane yakawanda yekugadzira iyo PCB (Mufananidzo 2). Iko kuchinjika kweiyo nickel ukobvu kunoguma neshanduko yezvivakwa zvemakemikari ekugezesa uye shanduko mune yekugara nguva yemuchina wekusimudza muchina. Kuchengetedza hushoma hwe2.0µm, maratidziro kubva kuvashandisi vekupedzisira anofanirwa kuda 3.5µm, hushoma hwe2.0µm, uye huwandu hwe8.0µm.

Iyi yakatarwa huwandu hwenickel ukobvu yakaratidza kuti yakakodzera kugadzirwa kwemamirioni emadunhu emabhodhi. Iyo renji inosangana neiyo weldability, pasherufu hupenyu uye zvehukama zvinodikanwa zvemazuva ano zvemagetsi. Nekuti izvo zvinodiwa pagungano zvakasiyana kubva pane chimwe chigadzirwa kuenda kune chimwe, machira epamusoro angangoda kukwidziridzwa pane yega yega application.