Development of micromechanical testing machine and its application

In this study, a small-sized DC motor type axial mechanical testing machine was developed to be utilized for fatigue testing of electronic parts such as ICs, etc. Thermal fatigue cracking in a beam lead in μBGA, a type of chip scale package (CSP), was identified as a major failure mode in the quality assurance test or in the field. The beam lead was made with copper foil. Thus, the reliability of the μBGA was strongly dependent on the fatigue characteristics of the copper used. In this study, the four kinds of beam leads made by different processes, were tested to obtain the tensile strength and fatigue characteristics and compared them with each other. The tensile and fatigue strength of the beam lead fabricated by a chemical polishing process with dipping time of 50 min is the best among the beam leads tested. The result of this study enables us to estimate the reliability of the μBGA without the temperature cycling test of a fully assembled μBGA