Bhanu Sood1 and Michael Pecht1
1CALCE, Center for Advanced Life Cycle Engineering, Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20740, USA
Moisture can accelerate various failure mechanisms in printed circuit board assemblies. Moisture can be initially present in
the epoxy glass prepreg, absorbed during the wet processes in printed circuit board manufacturing, or diffuse into the printed
circuit board during storage. Moisture can reside in the resin, resin/glass interfaces, and micro-cracks or voids due to defects.
Higher reflow temperatures associated with lead-free processing increase the vapor pressure, which can lead to higher
amounts of moisture uptake compared to eutectic tin-lead reflow processes. In addition to cohesive or adhesive failures
within the printed circuit board that lead to cracking and delamination, moisture can also lead to the creation of low
impedance paths due to metal migration, interfacial degradation resulting in conductive filament formation, and changes in
dimensional stability. Studies have shown that moisture can also reduce the glass-transition temperature and increase the
dielectric constant, leading to a reduction in circuit switching speeds and an increase in propagation delay times. This paper
provides an overview of printed circuit board fabrication, followed by a brief discussion of moisture diffusion processes,
governing models, and dependent variables. We then present guidelines for printed circuit board handling and storage
during various stages of production and fabrication so as to mitigate moisture-induced failures.