Improvement of fatigue life of solder joints by thickness control of solder with wire bump technique [power modules]

The solder joint between the ceramic substrate and the copper base plate is of critical importance to the reliability of the power module. An improvement of the fatigue life of the solder joint is essential to achieve a reliable module. The development of a new assembly technology for the power module improves the fatigue life of solder joints between the ceramic substrate and the copper base plate. The effect of the solder thickness on the fatigue life has been investigated with the elasto-plastic finite element analyses and experiments. The principal factor was the minimum thickness of solder, not the average thickness. The tilt of the substrate caused the solder thickness to become small partially. So the key technology to improve the fatigue life of the solder joint is to prevent the tilt of the substrate, and to control the solder thickness in high-precision level. The technique of setting spacers on the soldering area of the substrate has been examined, and the wire bump technique has been newly developed. In this technique, some small spacers called the wire bump are stitch-bonded near the comers using the aluminum bonding wire.