Reliability of eWLB (Embedded Wafer Level BGA) for Automotive Radar Applications

With shrinking of chip sizes, Wafer Level Chip Scale Packaging (WLCSP) becomes an attractive and holistic packaging solutions with various advantages in comparison to conventional packages, such as Ball Grid Array (BGA) with flipchip or wirebonding. With the advancement of various fan-out (FO) WLPs, it has been proven to be a more optimal, low cost, integrated and reliable solution compared to fan-in WLP because of the greater design flexibility in having more input/output (I/O), improved mechanical and thermal performance. In addition, FO-WLP shows superior high-frequency electrical performance due to its shorter, finer and simpler interconnection scheme compared to flipchip packaging. eWLB (embedded wafer level BGA) is a type of FO-WLP that enables applications requiring smaller form factor, excellent thermal performance and thin package profiles and it has the potential to evolve into various configurations with proven yields and manufacturing experience based on more than 8 years of high volume manufacturing of over 1.5B unit shipment. This paper discusses the recent advancements in robust board level reliability performance of eWLB for automotive application, where a review of a Design of Experiment (DOE) study will demonstrate improved Temperature Cycle on Board (TCoB) reliability. Several DOE studies were planned and test vehicles were prepared with various variables, such as materials, redistribution layer (RDL) design, copper (Cu) and under bump metallurgy (UBM) thickness, and a printed circuit board (PCB) pad design. The final test vehicle passed over 1000 times temperature cycles (TC) with optimized design factors of these parametric studies and reliability tests. To investigate potential structural defects after the reliability test, both destructive analyses were performed under industry standard test conditions, Daisy chain test vehicles were used for TCoB reliability performance.