SMT資料profile對(duì)reflow制程的影響

1、profile curve http:/ oc175ocheatingpreheatingsoakingreflowcoolingheating : solvent evaporationpreheating :flux reduces and metal oxidessoaking : solder balls melt, wetting and wicking begin.reflow : solder melting completes, surface tension takes over.cooling : cool down phase.http:/ zone :*solder p

2、astes viscosity : 1.solvent evaporation cause viscosity higher. 2.heating solvent will cause viscosity down.high heating rateviscositylow heating ratetemperaturehttp:/ softness point : flux softness point will decrease solder paste viscosity. high heating ratelow heating ratevery low heating ratevis

3、cositytemperaturehttp:/ zone :1.solvent evaporate completely2.flux activation and oxidation3.preheating time and temperature 3.1 for n2 oven the preheating time can be longer. 3.2 for air oven the preheating time should shorter than n2 oven4. pcb board bending controlbefore preheatingafter preheatin

4、gpcbpcbhttp:/ bgaafter preheating.plastic bgapcb bendinghttp:/ zone :*homologous heating (pcb, components and solder paste)*solder paste viscosity control*solder wetting and wicking begin.*surface solder balls melting.soaking zone.plastic bga substrate (tg :1750c)pcb bendinghttp:/ 123 2 lead 1 body

5、3 padnormal solderingwickingbridge by wickingmore heat from the bottomless heat from the top 2 lead 1 body 3 pad 3 pad 2 lead 1 body parameter setting :http:/ :t1t3dt2condition which causes tombstoning shall be : t1 + t2 t3 * in order to overcome the problem, the momentum relation must become as bel

6、ow ; t1 + t2 t3 t1 + t2 t3 t1t3dt2partial meltinghttp:/ temperature and reflow time should be controlled*the flowing ability(surface tension) of solder (high good) *void formation*component and / or board damage*n2 concentration reflow zone :http:/ zone :*cooling down speedn2 concentrationhttp:/ 0.7

7、 0.8mmn0808 1.1 1.2mmn12.6 1.952.1mmn鋼板形狀http:/ pointnslump resistivitynpad間文字面的白漆，或trace線http:/ se4-m953i及se4-m1000等系統(tǒng)上大量使用。http:/ (process window放寬很多)n我們的結(jié)論是，應(yīng)用廠商可採用和緩加溫或鞍狀加溫的溫度曲線，只要能確保流焊爐的熱量足夠讓所有溶劑揮發(fā)，但是，我們的建議是所應(yīng)用的溫度曲線的決定必需全盤考量pcb底材和零件的熱平衡以確保每個(gè)零件焊接點(diǎn)的品質(zhì)，而不必太考慮錫膏在流焊製程中的表現(xiàn)。http:/ beads(邊球)，錫橋(bridgin

8、g)和其他缺點(diǎn)，如下張圖:graph-1http:/ beads的機(jī)會(huì)，但是，可能因此使得錫膏在鋼版的應(yīng)用時(shí)間和粘滯力維持的時(shí)間縮短。http:/ components)流焊組裝製程時(shí)smt零件在pcb上的分佈密度並不高，而且零件間的熱含量差異相當(dāng)小，這種簡(jiǎn)單的p.c板結(jié)構(gòu)容許應(yīng)用“和緩溫昇，無恆溫區(qū)”的溫度曲線，而不會(huì)有任何問題。http:/ ir)流焊爐時(shí)，因?yàn)闊崃糠謥巡痪?，再加上使用“和緩溫昇型”的溫昇曲線(甚至於“馬鞍狀，恆溫型溫度曲線”)，很難在零件間達(dá)到熱平衡。http:/ phase reflow process)，但是因?yàn)榧蓖Φ臒崃刻嵘斐傻牧慵验_及墓碑效應(yīng)、溶劑的毒性、cfc溶劑的禁用等問題，汽相流焊很快就不受歡迎了。n後來研發(fā)的強(qiáng)迫空氣對(duì)流流焊製程(forced air conv