Stacked resin structure for reducing warpage of transfer-molded modules

The transfer-molded package with ceramic substrate is widely developed for power modules in the industrial and automobile applications. However, the difference in coefficient of thermal expansion (Δ CTE) between the ceramics and the molding resin is a significant problem, which is the fundamental cause of “warpage”. This research provides a new concept where the stacked resin structure is composed of two kinds of molding resins and as a result, the advantage of reduced warpage can be confirmed. Generally, the warpage is designed to be reduced by adjusting the properties of the molding resins to minimize the ACTE from the substrate. Meanwhile, our FEA simulation revealed that using two molding resins with the large and small ACTE from the substrate reduce more effectively the warpage than the one with the small ACTE. This mechanism is due to warping stress contribution from the stacked resins in the opposite of the original warpage direction. We fabricated the transfer-molded package with the stacked-resin structure and confirmed that the warpage can be reduced compared to the conventional structure. Also, the experimental results of the warpage showed good agreement with the simulation results.