Study of electroless Sn-coated Cu microparticles and their application as a high temperature thermal interface material

Abstract

A series of CuSn reactions were studied for the electroless plating of Sn onto Cu microparticles. The Cu microparticles were more temperature-sensitive than the planar Cu substrate when electrolessly plated with Sn. The coordination ligand (L) thiourea complexing agent played a key role in the interface reaction between the inner Cu core and the outer Sn shell and also significantly impacted the surface morphology of the outer coating layer. Cu@Sn core-shell structured particles with a thick coating layer were successfully fabricated, and a powder preform was developed by pressing these particles together. The outer Sn layer melted at 250°C; then, it depleted and completely transformed into CuSn intermetallic compounds (IMCs) as the reflow process proceeded. The Cu particles uniformly embedded in the CuSn IMC networks, forming interconnections with a considerably higher remelting temperature. The preform reflowed at a low temperature (250°C) for only 8min but formed a thick bondline with a high remelting point up to 425°C. The newly fabricated thermal interface material exhibited high shear strength at high temperatures (up to 500°C) and good thermo-mechanical performance. The preform also showed good electrical and thermal conductivity due to the uniformly dispersed Cu particles in the CuSn IMCs in the bondlines.