Stacking order impact on overall 3D die-to-wafer Stacked-IC cost

Three-dimensional Stacked IC (3D-SIC) is a promising technology gaining a lot of attention by industry. Such technology promises lower latency, lower power consumption and a smaller footprint as compared to planar ICs. Reducing the overall 3D-SIC manufacturing cost is a major challenge driving the industry. The process of stacking the dies together is an integral part of 3D-SIC manufacturing process; hence, it impacts the overall cost. This paper introduces out-of-order stacking and compares it with the conventional in-order stacking from cost point of view. In-order stacking restricts the stacking of the dies in a bottom-up sequential order, while out-of-order stacking poses no restrictions and the order is free as long as it is realistic. The simulation results show that out-of-order stacking ends up in lower cost than in-order stacking, and that the difference increases for larger stack sizes and lower stacking yield. For example, our case study shows that for a 3D-SIC with a stack size of 6 layers, out-of-order stacking outperforms the in-order one with up to 6% using the optimal test flow.