Micromechanics of multilayer printed circuit boards

Analytical and experimental techniques are reported for the evaluation of micromechanical components in multilayer printed circuit boards. The concern in this investigation comes from the Z-axis thermal mismatch between epoxy-glass and copper that generates stresses when the board is subject to a temperature change. Finite-element modeling for both plated through-holes (PTH) and buried via (PV) structures is used to calculate the stresses in the copper barrel and at the via junctions. A simple experiment is designed to measure the thermomechanical strain in the PTH barrel. Also discussed are the PTH peel and PV pull techniques which have been used to characterize the barrel-laminate adhesion and the via junction strength.