Hello,


I agree with the analysis below as one of two root causes.





We did a process mapping before on the solder-on-golden-finger, and found that:





- 90% of the solder was caused by solder contamination by the bottom side of stencil.


- Only 10% of the solder was caused by solder splash (flux explodes inside the liquid solder) during reflow.





How ever, different case may have different pareto distribution. Suggest that you can do the mapping station by station.





Best regards,


Brian


Flextronics Computing PE











-----Original Message-----


From: TGAsia [mailto:[log in to unmask]] On Behalf Of Jackson Chan


Sent: Thursday, May 31, 2007 12:22 PM


To: [log in to unmask]


Subject: Re: [TGA] 请教





LH,





Based on these two photos, it is likely that the spot is flux drop + solder


drop resulted from the splattering during the solder paste reflow process.





Below is the possible solutions :





1. Shield the gold finger by using the high temperature tape or other


masking plate





2. Different solder paste may produce different result. << different


composition in the sense of chemistry >>





3. Tune the profile -





  a. Longer preheat or higher soak << different paste may have different


response, several experimental runs are needed >>


  b. Reduce the ramp rate of temperature slope before reflow  (e.g. 0.25 to


0.5 deg. C/s)








Regards,





Jackson


Technical Services Manager


Cookson Electronics - Alpha Metals








                                                                           


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             31/05/2007 11:27          [TGA] 请教                          


                                                                           


                                                                           


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Dear all,





  请教各位附件图片1和图片3金手指上的点是怎样产生的及如何来改善?谢谢!








Best regards,


LHKang











[attachment "1.bmp" deleted by Jackson Chan/AlphaMetalsHK/Cookson]


[attachment "3.bmp" deleted by Jackson Chan/AlphaMetalsHK/Cookson] a








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