Implementation of flip chip technology for BGA packages

An increasing number of flip chip interconnection technologies have emerged during the last few years. While flip chip assembly in combination with MCMs offers many advantages, several aspects prevent this technology from entering the high volume market. Among these are the limited availability of bumped chips and the costs for substrates with coefficient of thermal expansion matching to the chip. Actually, many of these problems have been solved to a satisfactory degree. This paper presents some novel approaches to flip chip technology, implementing ball bumping with existing wire bond equipment. Based on this technology, the application of soldering techniques as well as adhesive joining is shown. The specific requirements of flip chip assembly for BGA packages are shown. The reliability evaluation was performed with specific regard to the metallurgical degradation in solder joints and to the interface reactions between polymers and metal surfaces in adhesive contacts. The electrical and mechanical performance of the solder and adhesive bonds was studied by evaluating initial contact resistance and mechanical adhesion as a function of temperature and humidity. The successful implementation of ball bumping in combination with soldering and adhesive joining is the result of the studies presented in this paper.