Publication: Computational fluid dynamics Analysis of capillary underfill flow In heterogeneous packaging.
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Date
2025-08
Authors
Azman, Muhammad Aqil
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Abstract
This study uses computational fluid dynamics (CFD) to optimize capillary underfill flow (CUF) in heterogeneous chip packages by examining geometric and dispense setup attributes. The investigation into geometric attributes, specifically the spacing between Chip 1 and Chip 2 (𝑆12) and chip thickness (𝑡𝑐), identified an optimum spacing of 𝑆12 at 5.71, allowing the underfill to reach Chip 3 and fill Chip 1 and Chip 2 almost simultaneously. Additionally, greater chip thickness ratios (𝑡𝑐𝑟) of 22.29 improve flow efficiency by providing a larger cross-sectional area, reducing hydraulic resistance. The study also examined the effect of dispense setup attributes, such as underfill dispense weight (𝐷𝑠𝑊) and length (𝐷𝑠𝐿), on CUF dynamics. Optimal dispense weight ratios (𝐷𝑠𝑊𝑟) of 1.00 and length ratios (𝐷𝑠𝐿𝑟\) of 0.70 significantly improve flow uniformity and reduce void formation, ensuring a reliable
encapsulation process. Furthermore, analysis of varied dispense patterns (𝐷𝑠𝑃) and lengths (𝐷𝑠𝐿) in a four chips arrangement showed that the double-I pattern optimizes
CUF behavior by minimizing voids and ensuring efficient underfill distribution. A 50% dispense length was identified as optimal, achieving full coverage more rapidly than 100% and 30% lengths, with negligible void percentages. This approach provides valuable insights for optimizing chip package designs, enhancing performance and reliability.