Voiding Control of Indium Thermal Interface Materials

Thermal interface materials (TIMs) are widely used in a variety of applications. Solder thermal interface materials (sTIM) are particularly suitable for high-power electronic components. In addition, pure indium metal is the best choice for thermal interfaces, attributed to its exceptional combination of high thermal conductivity and compliance. However, voids contain low thermal conductivity materials, such as gases or flux residues, and can significantly reduce thermal conductivity. It is critical to develop a flux vehicle for indium-TIM preforms, along with an appropriate process, to avoid significant voiding. Numerous factors, including the size and thickness of the indium preforms, the surface finish of the substrates, as well as the amount and type of the liquid flux, are thought be responsible for voiding. In addition, prebaking conditions and reflow profile also have a strong influence on void formation. All of these factors were examined in this study, and the results showed that many factors could have certain effects on voids. Moreover, these effects were found to be interrelated: voiding increased as the liquid flux amount increased. Prebaking with a higher temperature for a longer time within the necessary limits contributed to the reduction of voids. It was found that a reflow profile with a higher peak temperature had more voids than a profile with a lower peak temperature. To investigate the outgassing behavior of flux, thermal gravimetric analysis (TGA) was performed for each flux. The rate of weight loss before reaching the melting point (156°C) of indium was found to have a major influence on voiding performance.