Surface Mount International Conference Proceedings

Embrittlement of Surface Mount Solder Joints by Hot-Dipped, Gold-Plated Leads

Author: Paul T. Vianco
Company: Sandia National Laboratories
Date Published: 8/23/1993   Conference: Surface Mount International

Abstract: The detachment of beam-leaded transistors from several surface mount circuit boards following modest thermal cycling was examined. Microstructural analysis of the package leads and bonding pads from the failed units indicated that gold embrittlement was responsible for a loss of solder joint mechanical integrity that caused detachment of transistors from the circuit boards. An analysis of the hot dipping process used to remove gold from the leads prior to assembly demonstrated that the gold, although dissolved from the lead, remained in the nearby solder and was subsequently retained in the coating formed on the lead upon withdrawal from the bath. This scenario allowed gold to enter the circuit board solder joints. It was hypothesized, and later confirmed by experimental trials, that increasing the number of dips prevented gold from entering the solder coatings.

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