Semiconductor backend flip chip processing, inspection requirements and challenges

With the growing acceptance of flip chip packaging comes product and processing complexity requiring unproved process control and quality assurance capabilities. This paper describes the inspection requirements and challenges associated with flip chip processing. 100% 3-D inspection has become an important and integral part of the flip chip back-end process at various stages. The two major areas that constitute 3-D inspection are process control and quality assurance. The typical flip chip process includes bumping of the wafer, dicing of bumped wafers, flip chip die attach, final packaging, and electrical test. Final packages are usually in the form BGA, Micro BGA, CSP, and PGA. The two important measurement features common throughout the process at different stages are coplanarity and height. We describe the different techniques that have been introduced to provide 3-D measurements of these features at various stages. Of all methods, 3-D laser has proved to be the most versatile method.