Cony,



For 0201 / 01005 pad, the quantity of the paste applied is quite small and

result that the flux amount available is considered less.  Besides, it is

the area where the hottest point exist so that the degree of flux

exhaustion would be more significant than other components.  If the flux is

exhausted significantly during the soak, the powder cannot completely melt

together as shown in the photo provided.



Here is my suggestion



1. Try the short profile expecially in the temperature region between 150 -

217 deg. C



2. If the high soak is needed for your assemblies, you may need to find the

paste which can withstand the hot soak.



Jackson Chan

Cookson Electronics - Alpha Metals (Hong Kong)



Low cost, high reliable alloy - SACX0807





                                                                           

             Cony Su                                                       

             <Cony.Su@TTELECTR                                             

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             2008/07/29 上午           [TGA] 葡萄珠现象                    

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                  Cony Su                                                  

             <Cony.Su@TTELECTR                                             

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各位IPC专家大家好：

    现在有一个问题想向大家请教一下：由于现在的一些小的表面贴装元件（比如

0201，01005等）已经进入了量产阶段，随之也产生了一个新的问题：葡萄珠现象。就

是在无铅工艺中，从回流焊出来的小的元件焊点上的表面看起来有很多颗粒状锡

珠，像锡膏未融，又像冷焊，但是做切片后，它又是完全焊好的。供应商分析那些焊

点表面颗粒是氧化了的锡粉由于在回流中助焊剂被过早的挥发掉了。IPC-A-610标准里

对此现象还没有定义应是可接受还是拒收条件。不知道在做的同行是否碰到类似的问

题。现在我们已经尝试更换多种锡膏，调试profile，扩大钢网孔径等方法，效果已有

很大改善，但是葡萄珠问题仍然存在。





Best Regards

Cony Su

 [attachment "graphing.jpg" deleted by Jackson Chan/AlphaMetalsHK/Cookson]

[attachment "Cross section of joint with graping.jpg" deleted by Jackson

Chan/AlphaMetalsHK/Cookson]