Low-Pressure-Assisted Large-Area (>800 mm2) Sintered-Silver Bonding for High-Power Electronic Packaging
Nanosilver paste, as a kind of new thermal interface material (TIM) with superior thermal performance, has the potential to be a replacement for the conventional TIMs, such as greases, gels, and phase-change materials. In this paper, by combining double-print method and rapid-dry process, we achieved robust large-area bonded profile (>800 mm2) based on low-pressure-assisted sintering of silver paste. The low-temperature sintering process and sintering mechanism were discussed. The silver paste consists of nanosilver particles, microsilver flakes, and organics including dispersants, binders, and thinners. According to the thermogravimetric analysis and corresponding scanning electron microscopy observation, most organics were removed at temperature range from 70 °C to 160 °C. The nanosilver particles were instantly sintered and formed sintering necks at temperature range from 200 °C to 220 °C. The sintering of microsilver flakes needs higher temperature and longer time than the sintering of nanosilver particles. At 275 °C, microsilver flakes grew into spherical microsilver big particles at the expense of smaller nanosilver sintering necks and small microsilver flakes. Finally, robust sintered-silver-bonded plates were achieved by an optimized low-pressure-assisted sintering profile. The large-area bonded plate showed low porosity and high shear strength. Effects of a couple of sintering factors, including dry temperature, pressure on sinter quality, and fracture mode, were studied. The large-area bonded plates showed cohesive failure in sintered-silver bond line.