Usoro mkpuchi ikpeazụ maka PCB n’ichepụta ihe enweela nnukwu mgbanwe n’afọ ndị na -adịbeghị anya. 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.

A na -eji mkpuchi ikpeazụ echedo elu nke foil ọla kọpa. Ọla kọpa (Cu) bụ ala dị mma maka ihe ịgbado ọkụ, mana ọ na -adị mfe oxidized; Ọla kọpa na -egbochi mmiri nke solder. Ọ bụ ezie na ejiri ọla edo (Au) kpuchie ọla kọpa, n’ihi na ọla edo anaghị eme oxidize; Ọlaedo na ọla kọpa ga -agbasa ngwa ngwa ma jupụta ibe ha. Ọla ọ bụla kpughere ga-eme ngwa ngwa ọla kọpa na-enweghị ike ịgbasa. Otu ụzọ bụ iji nickel (Ni) “akwa mgbochi” nke na -egbochi ọla edo na ọla kọpa ịfefe ma na -enye elu na -adịgide adịgide, na -eduzi maka mgbakọ ihe.

Ihe PCB chọrọ maka mkpuchi nickel na-abụghị electrolytic

The non-electrolytic nickel coating should perform several functions:

Elu nke nkwụnye ọla edo

Ebumnuche kacha nke sekit bụ iji mepụta njikọ nwere ike anụ ahụ dị elu yana ezigbo ọkụ eletrik n’etiti PCB na ngwa ya. Ọ bụrụ na enwere oxide ma ọ bụ mmetọ ọ bụla na elu PCB, nkwonkwo a agbadoro ụkwụ agaghị eme na mmụba adịghị ike taa.

Ọla edo na -edobe n’elu nickel ma ghara ịchaze n’oge nchekwa ogologo. Agbanyeghị, ọla edo anaghị edozi na nickel oxidized, yabụ na nickel ahụ ga -adịrịrị ọcha n’etiti ịsa ahụ nickel na mgbasa ọla edo. 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. A na-ewere ọdịnaya phosphorus a na mkpuchi nickel na-abụghị electrolytic dị ka nguzozi nke njikwa ịsa ahụ, oxide, na akụrụngwa eletriki na nke anụ ahụ.

ekweghị ekwe

A na-eji ihe mkpuchi nickel na-abụghị electrolytic kpuchie n’ọtụtụ ngwa nke chọrọ ike anụ ahụ, dị ka nnyefe ụgbọ ala. Ihe PCB chọrọ siri ike karịa nke ndị a maka ngwa ndị a, mana ụfọdụ isi ike dị mkpa maka njikọta waya, kọntaktị mmetụ aka, njikọ njikọ ọnụ, yana nkwado nkwado.

Njikọ njikọ na -achọ ike nickel. Mwepụ esemokwu nwere ike ime ma ọ bụrụ na onye ndu ebibi ngwa ngwa, nke na -enyere ndu ‘agbaze’ n’ime mkpụrụ. Ihe onyonyo SEM egosighi nbanye n’ime elu nickel/ọla edo ma ọ bụ nickel/palladium (Pd)/ọla edo.

Njirimara eletriki

Ọla kọpa bụ igwe nhọrọ maka nhazi sekit n’ihi na ọ dị mfe ịme. Ọla kọpa na -eduzi ọkụ eletrik karịa ihe fọrọ nke nta ka ọ bụrụ metal ọ bụla (tebụl 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

Ọla kọpa 1.7 (gụnyere Ω cm

Gold (including 2.4 Ω cm

Nickel (including 7.4 Ω cm

Ihe mkpuchi nickel na-abụghị electrolytic 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. Ọnwụ mgbaàmà PCB microwave nwere ike karịa nkọwapụta onye nrụpụta. This phenomenon is proportional to the thickness of the nickel – the circuit needs to pass through the nickel to reach the solder spot. N’ọtụtụ ngwa, enwere ike weghachite akara eletriki na nkọwapụta nke imewe site na ịkọwapụta ntinye nickel nke na -erughị 2.5µm.

Kpọtụrụ nguzogide

Nguzogide kọntaktị dị iche na ịgbado ọkụ n’ihi na elu nickel/ọla edo ka na -anọghị na nchekwa n’oge ndụ ngwaahịa a. Nickel/ọla edo ga -anọgide na -eduzi na kọntaktị mpụga mgbe ekpughere gburugburu ebe obibi ogologo oge. 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, ọnọdụ okpomọkụ nke njikọta ụwa niile ga -arụ ọrụ, nke a na -akọwakarị maka ngwa ndị agha; 200 ° C, ọnọdụ okpomọkụ ahụ na -adịwanye mkpa maka akụrụngwa na -efe efe. ”

Maka obere okpomọkụ, anaghị achọ mgbochi nickel. Ka ọnọdụ okpomọkụ na -abawanye, ọnụọgụ nickel achọrọ iji gbochie nickel/mbufe ọla edo na -abawanye (Isiokwu II).

Isiokwu 2. Nguzogide kọntaktị nke nickel/ọla edo (awa 1000)

Nickel mgbochi oyi akwa kọntaktị na -enye afọ ojuju na 65 Celsius C kọntaktị na -eju afọ na 125 ° C kọntaktị na -eju afọ na 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 e ji mee nchọpụta Antler bụ electroplated. A na-atụ anya nkwalite site na nickel na-abụghị electrolytic, dịka Baudrand 4 gosipụtara. Agbanyeghị, nsonaazụ ndị a bụ maka 0.5 µm ọla edo, ebe ụgbọ elu na -ebutekarị 0.2 µm. Enwere ike ịkọwa ụgbọ elu ahụ ka o zuo maka ihe kọntaktị na -arụ ọrụ na 125 Celsius, mana ihe dị elu nke okpomọkụ ga -achọ nnwale pụrụ iche.

Antler na -atụ aro, sị, “Ọkpụrụkpụ nickel ahụ, ọ ga -aka mma mgbochi, mana ihe dị iche iche nke nrụpụta PCB na -agba ndị injinia ume itinye naanị nickel dị ka achọrọ. A na-ejizi nickel/ọla edo dị larịị na ekwentị mkpanaaka na peji nke na-eji akara kọntaktị. The specification for this type of element is at least 2 µm nickel.

Njikọ ahụ

A na-eji imikpu nickel/ọla edo na-enweghị eletriki na-arụpụta bọọdụ sekit nwere mmiri dabara adaba, pịa-dabara, mmịfe dị ala na ihe njikọ ndị ọzọ na-ejikọtaghị.

Ihe nkwụnye nkwụnye chọrọ ogologo anụ ahụ. N’ọnọdụ ndị a, mkpuchi nickel na-abụghị electrolytic siri ike maka ngwa PCB, mana imikpu ọla edo abụghị. Very thin pure gold (60 to 90 Knoop) will rub away from the nickel during repeated friction. Mgbe ewepụrụ ọla edo ahụ, nickel a na -ekpughere na -egbu ngwa ngwa, na -ebute mmụba na nguzogide kọntaktị.

Ihe mkpuchi nickel na-enweghị elektrik/imikpu ọla edo nwere ike ọ gaghị abụ nhọrọ kacha mma maka njikọ nkwụnye na-atụnye ọtụtụ ntinye n’ime ndụ ngwaahịa a. Nickel/palladium/elu ọla edo ka akwadoro maka njikọta ọtụtụ.

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) Isi mmalite nke nickel nke Ni3Sn4 jikọrọ ọnụ jikọrọ ọnụ.

Mgbasa ọla kọpa na nickel

Ịbufe ọla kọpa site na nickel ga -ebute irekasị ọla kọpa na ọla edo elu. 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. Ya mere, ọnọdụ okpomọkụ achọrọ maka ihe mgbochi bụ ihe na -erughị otu nkeji n’okpuru 250 Celsius.

Turn na Owen6 amụọla mmetụta ihe mgbochi dị iche iche na ọla kọpa na ọla edo. Ha chọpụtara na “… Ntụnyere ụkpụrụ ịdị mma ọla kọpa na 400 ° C na 550 ° C na-egosi na chromium na nickel hexavalent nwere ọdịnaya phosphorus 8-10% bụ ihe mgbochi mgbochi kachasị dị irè amụrụ “. (tebụl 3).

Isiokwu 3. Ịbanye n’ọla kọpa site na nickel ruo ọlaedo

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 Mgbasa mgbasa ozi na-abụghị mgbasa ozi na-abụghị mgbasa ozi

According to the Arrhenius equation, diffusion at lower temperatures is exponentially slower. N’ụzọ na-akpali mmasị, na nnwale a, nickel na-abụghị electrolytic dị ugboro 2 ruo 10 karịa nickel electroplated. Turn na Owen rụtụrụ aka na “… A (8%) 2µm(80µinch) barrier of this alloy reduces copper diffusion to a negligible level.”

Site na nnwale oke okpomọkụ a, ọkpụrụkpụ nickel nke opekata mpe 2µm bụ nkọwapụta echekwara.

Mgbasa nke nickel na ọla edo

Ihe nke abụọ chọrọ nke nickel na-abụghị elektrọnik bụ na nickel anaghị ebugharị site na ” ọka ” ma ọ bụ ” oghere dị mma ” nke ejiri ọla edo mee. If nickel comes into contact with air, it will oxidize. Nickel oxide is not soldable and difficult to remove with flux.

Enwere ọtụtụ akụkọ gbasara nickel na ọla edo eji dị ka ndị na -ebu mgbape seramiiki. These materials withstand the extreme temperatures of assembly for a long time. Nnwale a na -ahụkarị maka ihu ndị a bụ 500 Celsius C maka nkeji iri na ise.

Iji tụọ ike ala dị larịị na-abụghị elektrọnik nickel/ọla edo etinyere iji gbochie ọzere nickel, a mụtara ịgbado ọkụ nke ihe ndị merela agadi. Different heat/humidity and time conditions were tested. Ihe ọmụmụ ndị a egosila na nickel na -echekwaba nke ọma site na ịchacha ọla edo, na -enye ohere ịgbado ọkụ dị mma mgbe ịka nká.

Mgbasa nke nickel na ọla edo nwere ike bụrụ ihe na-egbochi nzukọ n’oge ụfọdụ, dị ka njikọta eriri waya thermalsonic. N’ime ngwa a, elu nickel/ọla edo adịchaghị elu karịa elu nickel/palladium/ọla edo. 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 ogige

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).

Isiokwu 4. Diffusivity nke ihe PCB na ịgbado ọkụ

Ọla igwe ° C mgbasa ozi (µinches/ SEC.)

Ọla edo 450 486 117.9 167.5

Ọla kọpa 450 525 4.1 7.0

Palladium 450 525 1.4 6.2

Nickel 700 1.7

Na sistemụ nickel/gold na tin/lead, ọla edo na -agbaze ozugbo n’ime gbamgbam rụrụ arụ. 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.Ihe atụ Bader gosiri na ọ dịghị ihe karịrị 0.5µm nke nickel ka achọrọ iji dobe ihe mgbochi, ọbụlagodi ihe karịrị usoro okpomọkụ isii. In fact, the maximum intermetallic layer thickness observed is less than 0.5µm(20µinch).

porous

Nickel/ọla edo na-abụghị electrolytic abụrụla ihe mkpuchi PCB ikpeazụ ikpeazụ, yabụ na usoro ụlọ ọrụ nwere ike ọ gaghị adị mma maka elu a. Usoro uzuoku nitric acid dị maka inwale porosity nke nickel/ọla edo electrolytic ejiri dị ka njikọ nkwụnye (IPC-TM-650 2.3.24.2) 9. Nickel/impregnation na-abụghị electrolytic agaghị agafe ule a. Emebela ụkpụrụ porosity nke Europe site na iji potassium ferricyanide iji chọpụta porosity nke ala dị larịị, nke a na -enye n’usoro pores kwa milimita square (ahụhụ /mm2). Ezi ala dị larịị kwesịrị inwe ihe na -erughị oghere 10 n’otu milimita ọ bụla na mbuli 100 x.

ọgwụgwụ

Ụlọ ọrụ na -emepụta PCB nwere mmasị ibelata ego nickel edobere na bọọdụ maka ọnụ ahịa, oge okirikiri na ndakọrịta ihe. Nkọwapụta nickel kacha nta kwesịrị inye aka gbochie mgbasa ọla kọpa n’elu ọla edo, jigide ike weld dị mma, ma mee ka nguzogide kọntaktị dị ala. Nkọwapụta kacha nke nickel kwesịrị ikwe ka mgbanwe dị n’ichepụta efere, n’ihi na enweghị ụdị ọdịda ọ bụla jikọtara ya na nkwụnye nickel buru ibu.

Maka imirikiti atụmatụ bọọdụ sekit taa, mkpuchi nickel na-abụghị electrolytic nke 2.0µm (80µinches) bụ obere ọkpụrụkpụ nickel achọrọ. Na omume, a ga -eji oke nịkịkị mee ihe na PCB mepere emepe (Onyonyo 2). Mgbanwe nke ọkpụrụkpụ nickel ga -esite na mgbanwe nke kemịkalụ ịsa ahụ na mgbanwe n’oge obibi nke igwe na -ebuli akpaka. Iji hụ na opekempe nke 2.0µm, nkọwapụta sitere na ndị ọrụ njedebe kwesịrị ịchọ 3.5µm, opekempe 2.0µm, yana kacha nke 8.0µm.

Ogologo oke nickel a akọwapụtara nke ọma maka imepụta nde nde bọọdụ sekit. Mpaghara a na -eme ka ịgbado ọkụ, ndụ nchekwa na ihe kọntaktị chọrọ nke elektrọnik nke taa. Maka mkpa ọgbakọ dị iche site n’otu ngwaahịa gaa n’ọzọ, enwere ike ịkwalite mkpuchi elu maka ngwa ọ bụla.