Thermodynamic Analysis of Multi-Stage Thermal Compression Bonding for Fabricating Vertically Stacked Micro-Led Array

Vertical full-color Micro-LEDs based on flip-chip bonding technology are of great significance in high-resolution display applications, as they have many advantages such as high pixel density, high brightness, and wide color gamut. However, the construction of vertical full-color Micro-LEDs requires multiple thermal compression bonding (TCB). Therefore, thermal stress analysis during multiple TCB is necessary. In this work, the surface thermal stress of a 5×5 vertical Micro-LED array during multi-stage TCB is studied by finite element method (FEM) simulations. The stresses at LED-LED bonding interface and stacked LED-backplane bonding interface as well as the interactions between the two bondings are investigated. The results of different bonding temperatures, material combinations, and interconnected metal diameters and depths on the mean stresses at the bonding interface are analyzed, and then the adequacy of bonding and risk of debonding are assessed. The results show that among the hybrid bonding material combinations set in the simulation, the Cu/ Al<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> has the largest interfacial stress. In addition, decreasing the interconnected metal diameter and lowering the bonding temperature can relieve the interfacial stress, while the interconnected metal depth has no significant effect on the bonding stress. The key advantage of this work is that it can help establish design and process guidelines to shorten the development cycle of vertical full-color Micro-LEDs based on flip-chip bonding technology.