Investigation on enhancement of copper ball bonds during thermal cycle testing

Copper ball bond failures of resin molded ICs during thermal cycle test are found to be caused by crack propagation along coarse grain boundaries in the roots of balls. An investigation of the critical grain size leading to the wire break in the roots of ball bonds during thermal cycle and of the ball-forming conditions to obtain a grain size of less than the critical value is discussed. Grain size less than 10 mu m in the roots of balls is essential to enhance the reliability of ball bonds. The appropriate grain size is obtained if the optimum bonding condition is employed.>