Coelectrodeposited Solder Composite Films for Advanced Thermal Interface Materials

A novel coelectrodeposition process was explored to form composite solder thin films as advanced bonding layers with potentially superior thermal and mechanical properties. The solder electrolyte was modified with SiC and graphite particles to electroplate the solder composite films. The stability of the particles was enhanced with cetyltrimethylammonium bromide (CTAB) as the surfactant. CTAB also enhanced the positive charge of the surface, measured as zeta potential, to further improve the electrophoretic deposition of the particles. Dynamic light scattering was used, for the first time, to characterize the particle size distribution and zeta potential for the graphite-tin electrolyte suspensions. Incorporation of CTAB enhanced the zeta potential from 17 to 33 mV and improved the particle dispersion resulting in much homogeneous plating with higher particle content in the films. X-ray diffraction, energy dispersive spectroscopy, and scanning electron microscopy were utilized to characterize the plated composites. Bonding was demonstrated with solder composites having high particle loading. Pressure-assisted bonding enhanced solder wetting on particles and improved the bonding characteristics.