Backward Compatibility with QFPs

2012.12.14

This project looked at the scenario where lead free boards and Koki Lead Free Solder Paste S3X58-M406 were used along with tin lead finished QFPs.

The pictures show 2 leads from a Sn15Pb 0.65 pitch QFP alongside two pads with only lead free solder paste.

It can clearly be seen that lead from the QFP finish is leaching into the lead free solder paste and eventually induces the paste to start melting at around 210°C which is below the melting point of the paste itself. The final alloy of the finished solder joint would then be a tin lead silver copper alloy or mixture of alloys of unknown thermal and mechanical characteristics.



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