Ultrafast intense pulsed light bonding process for multi-die stacked packages

In this study, we report the first demonstration of the intense pulsed light (IPL) flip-chip bonding process for multi-die stacked package assemblies (2-, 3-, and 4-die configurations). While conventional methods struggle with thermal management in 3D stacks, this work demonstrates that the IPL process inherently produces a top-down temperature and time above liquidus (TAL) gradient, optimized at 50, 70, and 110 pulses for each respective configuration via FEM simulation. The resulting intermetallic compound (IMC) thickness (0.7–2.0 μm) exhibited a precise layer-by-layer gradient consistent with the predicted thermal distribution. The IPL process completed bonding within 0.5–1.1 s, achieving 29–78 % thinner IMC layers and fewer interfacial defects compared to conventional mass reflow. Thermal cycling tests revealed that IPL-bonded packages sustained 1.9–4.7 times more cycles to failure than their reflow counterparts. Notably, the transition from interface failure to solder crack failure in the 2-die package underscores that reduced thermal exposure preserves interfacial integrity. These results demonstrate that the IPL bonding process is a viable high-speed alternative for 3D multi-die packaging, offering improved microstructural control and enhanced thermomechanical reliability compared to mass reflow.