Estimation of plated-hole barrel stress from thermally induced out-of-plane displacement gradients measured by electro-optic holographic interferometry.

Electro-optic holographic interferometry was used to measure the thermally induced out-of-plane displacement field around both sides of a plated hole on a single layer, FR-4 laminate. The unique features of the electro-optic holographic interferometry technique are described as well as a method for estimating the stress in the barrel from the deflections of the pad. The pad deflections were observed to be roughly axisymmetric and were nearly the same on the front and back of the laminate. The stress was observed to increase at a more rapid rate for temperatures above the glass temperature than below and is of sufficient magnitude to cause plastic deformation in the barrel although none was observed. [ABSTRACT FROM AUTHOR]