Laser-Based Target Preparation in 3D Integrated Electronic Packages

The trend toward 3D integration in electronic packaging requires that failure analysis procedures and target preparation methods are adapted from conventional discrete packages to these emerging packaging technologies. This paper addresses the feasibility of laser-based target preparation in 3D integrated devices, especially stacked-die packages. Various laser technologies such as ultrashort-pulse lasers, excimer lasers, and diode-pumped solid-state (DPSS) lasers with different wavelengths and pulse durations were evaluated. In particular, it was found that ultrashort-pulse lasers with pulse durations in the femtosecond range were not suitable for ablation of the molding compound (MC). Picosecond lasers were applicable with certain constraints. It was found that for MCs with high filler content, DPSS lasers with pulse durations in the nanosecond range were the best choice. For the removal of stacked silicon dies, the laser wavelength was the most important factor in artifact-free thinning. Laser cross sections through several silicon dies with remarkably small heat-affected zones were also demonstrated. The distinct removal of the MC, silicon dies, and metal interconnected with a single laser source offers new opportunities for laser-based target preparation in 3D integrated electronic packaging devices.