Mitigation of warpage for large 2.5D Through Silicon Interposer (TSI) package assembly

Abstract

In recent years, tremendous research and attention have been focused on 2.5D/3D IC (integrated circuit) integration within a TSI (Through Silicon Interposer) package. Integration of multiple ICs with the use of TSI technology could bring about higher integration density, shorter interconnection path and smaller device structure for the next-generation semiconductor devices. In this paper, we investigated the warpage behavior of our Chip-on-Chip-on-Substrate (CoC)-oS TSI package using the Chip-on-Chip (CoC) first assembly approach. The C4 (controlled collapse chip connection) bumps on the CoC TSI package was attached using both flux-based ball drop process and laser solder ball jetting process. Warpage analysis and profile for each assembly part/package in the CoC-first assembly was measured using the shadow moire method. Two guest dies were assembled onto a large (38.70mm × 26.70mm) and thin (0.10mm) TSI package using flip-chip thermo-compression bonding. The assembled CoC TSI package was then mounted onto an organic substrate. Warpage measurement was conducted from a temperature range of 25°C to 250°C. From the shadow moire measurement results, the warpage difference between the organic substrate and the assembled CoC TSI package with C4 bumps via laser solder ball jetting process is much smaller than using the ball drop process, at room temperature during the initial package placement prior to the reflow process. High warpage difference between the organic substrate and the assembled CoC TSI package with C4 bumps would result in opened and stretched solder joint interconnections issues, especially around the edges and peripheral of the package. Opened solder joint would result in no electrical connection and stretched solder joint would increase the risk of solder joint breakage and affect the long-term reliability of the package. Hence, the initial warpage difference between the assembled package and organic substrate during the assembly process can induce significant effects. In summary, we have demonstrated that the assembly process with the use of laser solder ball jetting process would reduce the warpage of CoC TSI package with C4 bumps, thus reduce the warpage difference with the organic substrate. Hence, the reduction in warpage of the assembled CoC TSI package can improve the process control of the CoC-first assembly flow.