Reliability characterization in Ultra CSPTM package development

Ultra CSP^TM is a wafer-level chip scale package developed by Flip Chip Technologies. This package provides a low cost packaging solution for various applications such as integrated passive, flash memory, DRAM, and Direct RDRAM^TM devices. This paper presents a brief update of the Ultra CSP development effort. Two design concepts were evolved in the development process and product implementation to address the requirements of different applications. Solder joint reliability of Ultra CSP was evaluated at board level under thermal cycle test. A solder joint fatigue database was generated using Weibull analysis. The effect of die size (DNP), bump standoff, substrate pad size, and solder ball size are discussed. Continued improvement in the package reliability is achieved through Design of Experiments. Issues encountered in the qualification stage are addressed in terms of accelerated test strategy, process quality control, package design, and substrate design