Effects of Solder-Dipping as a Termination Re-Finishing Technique
Pecht, Michael G.
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Solder-dipping may be used to replace tin-rich finishes with eutectic tin-lead for tin-whiskering risk mitigation purposes. However, re-finishing also subjects electronic parts to new risks, including damage from the thermal re-finishing profile, finish non-uniformity, incomplete replacement of the pre-existing finish and poor solderability from re-finishing. This study overviews solder-dipping as a re-finishing technique and identifies key process and part parameters that could result in risks. A physical analysis procedure was developed and implemented to assess these risks on electronic parts. A quantitative metric was established to assess propensity for thermo-mechanical damage for solder-dipping parts. Surface mount dipped parts were prone to exposure of base-metal or interfacial intermetallics at termination corners, knees and heels. Solder-dipped insertion-mount parts showed regions of low finish thickness and possible deviations from eutectic tin-lead composition at portions close to the part-body.