Board Level Reliability Investigation of FO-WLP Package

As current technology development trend of microelectronic industry driven by portable and wearable electronic products, adopting advanced IC fabrication process technology and a powerful integrated fan-out (InFO) wafer level system integration (WLSI) technology has been developed to integrate application processor chip with memory package for smart mobile devices[1][3]. This fan-out wafer level package (FO-WLP) to extend the functionality performance within thin form-factor for fulfilling product application requirements is essential and important to a successful new product development, especially for Application Processor, Field Programmable Gate Array (FPGA) and power management IC (PMIC) products[1]. FO-WLP is good electrical performance package by its very short distance package level interconnection, and it has been rapidly adopted for 12 inch copper fabrication process technologies. Knowing its very thin package without package substrate as stress buffer between IC chip and system board, board level reliability performance of FO-WLP becomes challenge as products moving to large die size for enabling more functionality on the same or less space due to higher package stress induced by larger die size[2]. The board level underfill(UF) has been implemented in Surface Mount Technology(SMT) assembly process to prevent mechanical stress induced solder ball and redistribution layer (RDL) damage[4]. In general, the UF will help to reduce the mechanical stress to impact solder joint reliability. However, due to less sophistication of SMT UF process compared with flip-chip assembly UF process, such as no pre-plasma treatment, high dispensing speed and no CSAM inspection to detect the dispensing quality, SMT UF dispensing quality brings a great of quality and reliability concern to the FO-WLP package joint on board, especially electrical leakage issue due to small ball pitch of the package. Therefore, it becomes the objective of this study on SMT production quality and reliability risk of FO-WLP package on board with focusing on board level UF filling into BGA balls of FO-WLP package impact to product reliability.