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de-wetting: A Yield Menace

For sometime now, our SMD line experienced this problem. We are doing a Pb free process, and one of our component supplier provided so. The component's termination are pure tin and the solder paste we're using is 96.5Sn/ 3.5 Ag. This is being reflowed to 240-270 °C with a dwell time of 20-40 sec above 221 °C. The performance of de-wetting is unstable, it does not affect 100% of the components but it pose as our top defect. We did an analysis on the affected units and it doesn't show any impurities or whiskers as common source of this problem. Other methods were introduced like increase in paste height, prolong dwell and others did not have an impact.

Need your expert advise on how to approach this defect. Your prompt reply os very much appreciated.

Charles Ian Ferraris
- Manila, Philippines
2003

If you e-mail a photo of the defect, this information will help. Are you sure you have de-wetting or nonwetting? What is the base material?

Karl Weyermann
- Lebanon, Kentucky, USA
2003