An Advanced Finite Element Model of the Cu Pillar Solder Reflow Assembly

The recently emerged Cu pillar technology has drawn a lot of attention in the wafer-level packaging field due to its fine pitch and superior electrical performances. Flip-chipping Cu pillar dies to low-cost PCBs is considered a promising and cost-effective packaging approach. This paper focuses on developing a thermal-mechanical finite element model to identify how different Cu pillar and board configurations impact Cu pillar shear stresses. Furthermore, this model extracts shear stresses from Cu pillar solders in various positions, providing valuable information about Cu pillar shear strengths when compared to the visual inspection results of the package’s cross-section. This model is a significant step towards the further development and standardization of the Cu pillar flip-chip technology.