Accelerated Induction Heating and Fast Bonding of Microchips Based on a Design of Hollow Magnetic Flux Concentrator

As micro-electro-mechanical system (MEMS) technology advances and system-in-package (SIP) finds widespread use, the on-chip integration of heterogeneous devices has emerged as a key research focus. Induction heating, which implements the electromagnetic influence effect to convert electricity into heat, is expected to tackle this challenge. However, the unavoidable magnetic dispersion effect renders it difficult for raising magnetic field density in a small area, thus limiting the application of induction heating. In this work, we proposed a conical hollow magnetic flux concentrator (HMFC) by integrating soft magnetic particles with a polymer matrix, which demonstrates the superior capability of magnetic field focusing. The results show that the maximum heating temperature in 15 s was enhanced by 161.2% compared with the induction heating method without the concentrator, successfully reflowing Sn96.5Ag3.5Cu0.5 (SAC305) solder paste on $300\times 300\times 20~\mu $ m immersion gold copper pads. Compared with the reflow soldering method, the HMFC-focused induction heating enhanced the bonding strength of 0402-type chips by 18.1% with improved consistency. Besides, we demonstrate the potential of this chip-bonding solution for curved electronics manufacturing. With these fast and reliable bonding characteristics, the as-proposed HMFC-assisted focused induction heating method is a promising strategy for the effective bonding of microchips.