Evaluation of fatigue crack initiation and extension life in microelectronics solder joints of surface mount type

Fatigue tests on solder joints of surface mount type electronic package models were carried out at different temperatures, cycling frequencies and controlled displacement amplitudes in order to examine the crack initiation life Nc, crack extension rate da/dN, crack extension path and crack extension life. The crack initiation life (Nc)(cat) of solder joints was estimated using maximum equivalent inelastic strain calculated by three-dimensional elasto-inelastic finite element method (3D-FEM). The ratios Nc/(Nc)(cal) were found 2.4 - 9.8. Further, 2D-FEM crack extension analyses were performed to examine crack extension behavior. The FEM analyses showed that crack extension path and rate were controlled by maximum opening stress range at crack tip, Delta sigma(theta max), in plastic zone under rather complicated stress tensor field, Experimentally obtained crack extension rate was found to be related to Delta sigma(theta max) in FEM analysis as da/dN = beta[Delta sigma(theta max)](alpha), with alpha = 2.0 and beta = 2.65 x 10(-10) mm(5)/N-2 being determined independently of the test conditions. The calculated values of crack extension life by the FEM analyses using the above equation were in good agreement with the experimental ones.