Suppression of Cohesive Cracking Mode Based on Anisotropic Porosity in Sintered Silver Die Attach Encapsulated by Epoxy Molding Compounds

This paper investigates the suppression of the cohesive cracking mode (CCM) in the sintered silver (s-Ag) die layer by intentionally introducing anisotropic porosity through two press sintering methods. Full press (FP) and local press (LP) bonding represent the s-Ag formed by pressing the die-attached assemblies (DAAs) on either the entire top surface or only on the silicon carbide (SiC) top surface, respectively. The fabricated DAAs were encapsulated with epoxy molding compounds. Degradation was evaluated using a nine-point bending test (NBT) under cyclic force between 0 and 270 N with a triangle waveform for 3 min per cycle at 150 °C. Scanning tomography images after 500 NBT cycles showed that the LP reduced the inner degradation ratio by up to 21.1% compared to the FP. Cross-sectional scanning electron microscopy revealed that the FP progressed cracking in the s-Ag die layer, whereas the LP showed no evidence of cracking. A finite element analysis revealed that in the FP, the accumulated plastic strain (APS) was concentrated in the s-Ag layer within the inner SiC chip. In contrast, the APS of the LP was preferentially concentrated outside the SiC chip. This preferential localization of damage outside the chip presents a promising approach for enhancing the reliability of packaging products.