Ultra-thin Double Side SiP Technology with Embedded Trace Substrate

SiP (System In Package) technology has been growing in popularity recently for a lot of different applications like mobile devices, wearable devices and IoT (Internet of Things), as it can provide size reduction and high level of functional integration compared to individual IC and components. Consumers always require electronic products to be more portable and multi-functional. To satisfy these demands, not only normal single side SiP, but double side SiP package has also been growing significantly in recent years. Double side SiP enables even smaller form factor [1], [2] and increased performance by enabling the shortest connection between top and bottom side components within a package.In this paper, we present an ultra-thin double side SiP (total stack-up thickness 850um) using an ultra-thin ETS (Embedded Trace Substrate, 3 Layers total height 85um). This double side SiP has silicon die at the package bottom side and multiple types of passive components at the package top side with both top and bottom sides encapsulated using a molding compound material for protection. ETS substrate in the middle helps provide connections between the top and bottom sides. After completing top and bottom side assembly followed by over molding, laser ablation process was used to make TMV (Through Molded Via) openings which was then followed by ball placement to finish the connections as the output I/O of the final structure.This study covers the assembly process characterization details and process flow using ultra-thin ETS substrate, and compares two different flows –"Bottom Die First" flow and "Top SMT (Surface Mount Technology) First" flow. We also optimized the stand-off height of the passive components area for optimum mold flow to ensure no MUF voiding underneath the passive components. ENIG (Electroless Nickel Immersion Gold) was chosen as the surface finish for the ETS substrate. LA (Laser Ablation) DOE (Design of Experiment) was performed comparing the UV and CO2 processes to assess process capabilities for the two and understand which one can achieve better surface condition with higher yield for ball placement. Based on the extensive DOEs and process characterizations, most optimum process flow was finalized, and target performance was achieved with successful validation in production.