Enhancements to Picosecond Acoustic Metrology for application in FO-WLP Process

Abstract Fan out wafer level packaging (FO-WLP) is one of the fastest growing advanced packaging segments due to its versatility for a wide variety of applications. It's compatibility with large scale, low cost, ultra-thin and high-density packages has made it very attractive. Cu redistribution layer and multiple metal under bump metallization stack play critical role in the FO-WLP process especially with shrinking line/space size and increasing density. We previously discussed the adaptation of PULSE™ technology, with the integration of a visible reflectometer and high resolution camera as a comprehensive in-line metrology tool for the advanced packaging applications. In this paper, we present results from some recent work on enhancements to the configuration for measurements of very thick, rough RDL films. The modifications provided significant improvement (9×) to throughput while maintaining gage capable repeatability. Cross-section SEM measurements on 1μm RDL structures were used to validate the exten...