Analysis of Transient Thermal Strains in a Plated Through Hole Using Current Induced Heating and Transient Moire Interferometry

The increased use of high aspect ratio, non soldered filled plated through holes (PTH) to support high I/O BGA and other SMT packaging technologies has lead to growing interest in the question of thermo-mechanical deformation in the PTH and the associated fatigue life of the copper barrel. In addition, this interest more frequently includes the case of transient thermal loads on the PTH and the surrounding board material. This might arise from multi-step assembly process, product operation with rapid on/off cycles and in the lab where quick reliability tests are sought. In these situations, it is important to know how the temperature gradients in the surrounding board material affect PTH strains compared to the case of uniform heating. As a first step in determining the reliability of PTH under a transient thermal loading, this paper shows the use of Transient Moire Interferometry technique to dynamically record the displacement field in a PTH coupon. The heat source is the Current Induced Thermal Cycle (CITC) developed at IBM. The experimental results are compared with a transient nonlinear finite element model of the PTH barrel.