Reliability of printed circuit boards containing lead-free solder in aggressive environments

Lead-free solders were never an industry choice until government legislation, their wide spread use is still in its infancy due to long term reliability issues. A specific SAC (Tin-Silver-Copper) family of solder alloys has emerged as the favourite to offer technical advantages as well as meeting those legislative requirements. This paper investigates accelerated life behaviour of lead-free solder joints and printed circuit boards using thermal and electrical stress cycling. The aim is to understand the degradation of these materials in a practical operating environment. Whilst corrosion and debris deposits have been found, no significant evidence has been obtained for tin whiskering. EDX analysis has shown the presence of high concentrations of elements considered to arise from the packaging material. Thermal cycling tests have presented an aggressive environment to the samples and the effect on them has been supported by microscopic and macroscopic observations of debris and corrosion. The electrical behaviour, i.e., the joint resistance, has not however, significantly degraded.

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