A comparison of polymers and solder alloys by reliability tests on multi-layer redistribution lines in Fan Out Wafer Level Package

Abstract

Portable electronic products have been extended for high performance and high-density silicon node applications in recent years. In order to meet customer increased expectations regarding functionality, size, power dissipation, thermal performance and cost. This requires more robust and more reliable WLP solution, where Fan-Out Wafer Level Package will play an emphasized role in terms of system integration, low profile and high density for logic devices. One of the major concerns of electronic packages is the reliability performance because fracture or layer delamination of the fine joint parts could be encountered. The organic passivation as polyimide (PI) and polybenzoxazole (PBO) will dominate PKG reliability. [1] In terms of material selection for high reliable package solution, it is interesting to clarify which passivation material is best to release the stress during TCT, drop, and other reliability tests. In this study, a low profile fan out wafer level package was successfully demonstrated with 14.0 × 14.0mm package dimension. Polyimide (PI), Polybenzoxazole (PBO) and redistribution metal layer thickness was designed for both simulation and reliability tests. As per simulation result, Polyimide (PI) is expected to show good reliability and provide a better solution for fan out wafer level package. [2] Board level reliability studies have been performed on another test vehicle with 7 × 7 mm package with different RDL thickness, polymer thickness, with or without UBM structure and SAC solder alloy which base on material selection results of larger package size test vehicle. [3-6] The parts of SAC solder alloy were assembled at 3 different suppliers. All of the RDL structure studied leg passed the minimum drop shock requirements of 30 drops. For board level temperature cycle, a minimum of 500 cycles was targeted as a passing result. This study shows that thicker UBM structure has better reliability performance than others and thicker passivation thickness also can improve package performance on without UBM structure.