Direct Cu bonding is considered an ideal way to achieve inter-chip vertical connections for TSV (through silicon via), due to size miniaturization and low electrical resistance. In this study, drop testing of packages comprising sputtered copper on Si chips joined with electroplated copper on Al2O3 substrates assembled by thermal compression bonding was performed. Experimental results show that pre-treatment using Xenon flash can be accomplished in a very short time, but a remarable improvement of drop resistance for direct-copper bonds can be achieved. With a proper light irradiaiton, the drop test performance of directly-bonded daisy chains was superior than thosed jointed by impact resistant solders. However, excessive flash exposure led to a degraded drop life. The variation in drop performance was related to residual stress conditions on faying copper surface. This finding is very crucial for 3D packaging for portable usages