Hi Colin,



You are not giving all the details. Are you talking about ENIG and if you are, then what is cracking, solder/pad interface?



Regards,



Vladimir

SENTEC

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

From: colin mcvean

Sender: TechNet

To: [log in to unmask]

ReplyTo: TechNet E-Mail Forum

ReplyTo: colin mcvean

Sent: Aug 13, 2009 23:04

Subject: [TN] Reflow profile



Folks,

 

From my previous question regarding pattern crack we are seeing on a wire-bonded flex-rigid PCB, I have now found more evidence that the presented FPCB is ok, but after reflow for SMT assembly, this is where the cracking is first found (rather than after wire-bond process). The reflow profile being used peaks at 245oC, but rapidly cools from peak to 135oC in about 30s. This seems to me to be too rapid a cool rate, and with the pad metallics being 0.2uM gold over 10uM Nickel over 30uM copper pad. Are CTE rates on cooling the same as CTE rates for heating? I think I may have CTE mismatch on the coatings, which when cooled too rapidly, are causing the crack. Any metallurgists out there willing to comment?

 

Thanks

 

Colin





      



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