Fatigue life prediction of plated through holes(PTH) under thermal cycling

PTH(plated through hole) integrity becomes primary PCB(printed circuit board) reliability concern during component mounting process or subsequent field condition. Main cause of PTH failures is traced to significant differences in the amount of thermal expansions between copper barrel and surrounding glass epoxy. When the different expansion due to thermal stresses makes strain that exceeds the fracture toughness of copper barrel or interconnection, ruptures develop in the latter. It results in open circuits or intermittent contacts in FR-4 PCB which leads to system failures. This paper presents a prediction results of PTH thermal fatigue life on field condition based on Coffin-Manson life model. Experiments are conducted with 0.3 mm dia. PTH under 2 thermal cycle conditions (-55~125, -3~125 with 10 min. dwell time). The thickness of PCB is 1.6 mm with 4 multilayers. The resistance of PTH is monitored one minute interval. Material constant are obtained after thermal cycling test. Crack propagation at failed PTHs is examined with optical microscope. For each test, thermal cycling failure data has been analysed using two parameter Weibull models to predict B₁₀ life of PTH. Acceleration factor of PTH under thermal cycling test is obtained. Life Prediction of PTH thermal fatigue on field condition is conducted.