FATIGUE LIFE ESTIMATION OF ELECTROPLATED THROUGH HOLE IN PWB BY FEM WITH THIN CU MATERIAL PROPERTIES

摘要

This study applies a mechanical fatigue test methodology to the Plated Through Hole (PTH) reliability of Printed Wiring Boards (PWBs). We observed stress vs. strain curves from a dumbbell-shaped electroplated copper (Cu) specimen and did a Low-Cycle Fatigue Test (LCFT) using an hourglass-shaped FR4 epoxy resin specimen with electroplated thin Cu. The LCFT gave us the relationship between equivalent inelastic strain and the number of fatigue cycles to failure. Then, we built FEM mesh models of PWB parts with a PTH and fabricated test boards. By determining inelastic strain per cycle from FEM simulations, we estimated the number of accelerated temperature cycles to failure. Finally we did a Temperature Cycling Test (TCT) using the test boards with the designated electroplated Cu thicknesses. Fatigue life estimated by FEM simulation in the LCFT agreed with the TCT results. Moreover, the failure mode of the Cu plating was almost identical between the specimens of the LCFT and test boards of the TCT. The results demonstrate that FEM simulation can replace the conventional TCT.