Ultrasonic-assisted soldering for graphite films as heat sinks with durably superior heat dissipating efficiency

Graphite film (GF) is considered as an unrivaled candidate of heat sink in thermal management applications. The inappropriate thermal interface material (TIM), however, could severely restrain the application of GF as heat sink. In this study, GF heat sink was assembled with SAC305 (Sn-3.0Ag-0.5Cu, wt. %) solder through ultrasonic-assisted soldering approach. Due to ultrasonic effects, the soldered interface for heat transfer exhibited compact structure. The forming of Ag3Sn and Cu6Sn5 nanoparticles at interface could improve the interfacial coefficient gradient of thermal expansion. Comparing to traditional thermally conducted packaging method, soldering-assembled GF heat sinks exhibited excellent cooling efficiency, which could be maintained after more than 50 thermal cycles from 0 to 100 degrees C, and after thermal aging treatments for over 48 h under 150 degrees C in air. In the mechanical performance tests, the ultrasonic-assisted soldered GF joints showed high structural stability. These findings reinforce the significant potential of ultrasonic-assisted soldered GFs in thermal management.