Low Warpage Liquid Compression Molding (LCM) Material for High Density Fan-out and Wafer Level Packaging Applications

Abstract

Wafer level encapsulation is an important packaging process for several components in mobile and high-performance computing applications. In mobile applications, electronic components like application processors, radio-frequency System in Package (RF-SiP) and antenna modules are being manufactured using wafer level fan-out processes. In HPC, wafer level encapsulation is used for chip-on-wafer (CoW) processing and 2.5D / 3D packaging that enables wafer level packaging of processors and high band width memory devices. Although encapsulant materials are currently used in mass production, many pain points remain unresolved. These are predominantly related to lowering the wafer level warpage to enable better handling of wafers during processing, addressing the environmental and EU REACH regulatory compliance, providing better total cost of ownership to the end user by improving throughput and various other factors. In our development, we aim to address these pains and we will present our progress in this research paper. As the structural material in the package, molding compound can cause severe warpage issue during process, becoming the limiting factor to pursue thinner packaging design and causing serious wafer handling issues in the equipment during wafer processing. However, we considered a new material design route to develop ultra-low warpage LCM materials that can dramatically reduce the warpage thereby benefitting various WLP packaging design, such as Fan-in or Fan-out type. We have successfully demonstrated more than 70% improvement in warpage compared to traditional LCM compound. This new type of LCM material is REACH compliant and shows good warpage stability after high temperature annealing process. The polymer relaxation study shows the unique relaxation behavior leading to the warpage stability that is critical in many Fan-out processes. Dynamic Mechanical Analysis is the useful tool to study the relaxation behavior that can differentiate the impact of various chemistry on epoxy molding materials. Another key advantage of our LCM is the excellent gapfilling capability that can lead to the protection of high density structures in semiconductor packages with finer die-to-die or die-to-substrate spacing, meanwhile enabling low-warpage and simpler processing steps. Moreover, the new LCM design can help further shorten the molding time, allowing for increased throughput resulting in lower cost of ownership for the end users.