Innovations in Soldering Materials and Optimization of Solder Paste Printing and Inspection Parameters for System-in-Package Assembly

Abstract

System-in-Package (SiP) assembly has become a popular solution for the challenges of continued miniaturization in the semiconductor industry. The continued and expected growth of the semiconductor industry in the coming years is driving more advanced assembly methods within System-in-Package and advanced packaging in general, and more advanced semiconductor assembly materials are required to meet those challenges such as solder paste specifically designed for SiP assembly, with fine solder powder and specifically formulated flux vehicles. Fine feature solder paste printing as an assembly method continues to be a challenge for SiP assembly. Small stencil aperture designs have necessitated fine-powder solder pastes, with type 5, type 6, and type 7 being common, as well as there being a need for type 8 for future, more advanced designs. Additionally, as more components are being packed into a SiP, solder paste rheology becomes an important characteristic to consider. Printing transfer efficiency, stencil life, and resistance to slump, are other important paste attributes to consider when evaluating solder paste for SiP assembly. While material properties are important to consider, proper equipment setup for a certain paste formulation is also necessary to maximize throughput and minimize assembly defects. The effects of solder paste printer parameters on fine-feature printing performance will be discussed, such as print speed, separation speed, separation distance, and stencil material. This paper will first focus on common failure modes in SiP assembly, and the technology advancements in both solder paste formulation and substrate design which help eliminate those failure modes. Then, this paper will discuss how proper stencil printer setup can reduce assembly defects, and will highlight designs-of-experiment outlining which stencil printer parameters are statistically significant in improving process yields of SiP assemblies with fine powder solder pastes, both with respect to pre-reflow inspection and post-reflow component placement. This paper will also discuss the importance of solder paste inspection with respect to assembly defects, and will highlight important parameters to optimize to accurately inspect solder paste deposits below 90 microns.