Study of Thermal Conductivity and Reliability of InAg Soldering Thermal Interface Material by Formic Acid Reflow for TIM1 IC Module Package

Indium and indium-containing alloys such as indium silver (InAg) alloys have generally been paid considerable attention as thermal interface materials for usage in thermal management of microprocessors such as CPU, GPU and AI accelerator. This is, especially true for high-performance computing electronics with high power density. Reflow process parameters of InAg preforms with differing compositions of Ag ranging from 3 to 10 wt% as well as various thicknesses were extensively studied bonding Cu to Cu to achieve optimum properties and performance of the InAg soldered joint using formic acid vacuum reflow. Basic characterization was also completed including basic physical properties such as density, modulus and phase transition. Moreover, X-ray scanning and confocal scanning acoustic microscopy (C-SAM) were used to identify voids and delamination of the InAg soldered joints, respectively. Laser Flash Analysis (LFA) was employed to measure thermal conductivity of the soldered joint bonding Cu to Cu after the reflow process in the determined optimum conditions. Thermal cycling testing (TCT) was conducted with a profile of -40°C to 125°C, 30 min of dwell time and highly accelerated stress testing (HAST) with a profile of 110°C/85%RH/0.22 MPa/264 hr, to evaluate reliability of the soldered joints, the initial characterization testing was repeated at several intervals. To further understand the change of microstructure after the given number of thermal cycling, cross-sectional samples were prepared and scanning electron microscopy (SEM) was used to characterize morphologies of the soldered joints. In this presentation, the influence of the different compositions of InAg alloys and bond line thickness (BLT) on the voiding performance, delamination and thermal conductivity of the soldered joints, as well as the results of reliability are discussed.