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.