materials Article A Comparative Study of Thermal Aging Effect on the Properties of Silicone-Based and Silicone-Free Thermal Gap Filler Materials A S M Raufur Chowdhury 1, * , Monjur Morshed Rabby 1,2 , Mehzabeen Kabir 1 , Partha Pratim Das 1,2 , Rabin Bhandari 1 , Rassel Raihan 1,2 and Dereje Agonafer 1   Citation: Chowdhury, ASMR.; Rabby, M.M.; Kabir, M.; Das, P.P.; Bhandari, R.; Raihan, R.; Agonafer, D. A Comparative Study of Thermal Aging Effect on the Properties of Silicone-Based and Silicone-Free Thermal Gap Filler Materials. Materials 2021, 14, 3565. https:// doi.org/10.3390/ma14133565 Academic Editors: Jie Sun and Alexander A. Lebedev Received: 17 April 2021 Accepted: 23 June 2021 Published: 25 June 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Mechanical and Aerospace Engineering, University of Texas at Arlington, Arlington, TX 76019, USA; monjurmorshed.rabby@mavs.uta.edu (M.M.R.); mehzabeenbinte.kabir@mavs.uta.edu (M.K.); parthapratim.das@mavs.uta.edu (P.P.D.); rabin.bhandari@mavs.uta.edu (R.B.); mdrassel.raihan@uta.edu (R.R.); agonafer@uta.edu (D.A.) 2 Institute of Predictive Performance and Methodologies, University of Texas at Arlington Research Institute, Fort Worth, TX 76118, USA * Correspondence: raufur.chowdhury@uta.edu Abstract: Thermal conductive gap filler materials are used as thermal interface materials (TIMs) in electronic devices due their numerous advantages, such as higher thermal conductivity, ease of use, and conformity. Silicone is a class of synthetic materials based on a polymeric siloxane backbone which is widely used in thermal gap filler materials. In electronic packages, silicone- based thermal gap filler materials are widely used in industries, whereas silicone-free thermal gap filler materials are emerging as new alternatives for numerous electronics applications. Certainly, characterization of these TIMs is of immense importance since it plays a critical role in heat dissipation and long-term reliability of the electronic packages. Insubstantial studies on the effects of various chemical compounds on the properties of silicone-based and silicone-free TIMs has led to this study, which focuses on the effect of thermal aging on the mechanical, thermal, and dielectric properties of silicone-based and silicone-free TIMs and the chemical compounds that cause the changes in properties of these materials. Characterization techniques such as dynamic mechanical analysis (DMA), thermomechanical analysis (TMA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and broadband dielectric spectroscopy (BbDS) are used to study the mechanical, thermal, and dielectric characteristics of these TIMs, which will guide towards a better understanding of the applicability and reliability of these TIMs. The experiments demonstrate that upon thermal aging at 125 ◦ C, the silicone-free TIM becomes hard, while silicone-based TIM remains viscoelastic, which indicates its wide applicability to higher temperature applications for a long time. Though silicone-based TIM displays better mechanical and thermal properties at elevated temperatures, dielectric properties indicate low conductivity for silicone-free TIM, which makes it a better candidate for silicone-sensitive applications where higher electric insulation is desired. Keywords: thermal gap filler material; dynamic mechanical analysis; thermomechanical analysis; differ- ential scanning calorimetry; Fourier transform infrared spectroscopy; broadband dielectric spectroscopy 1. Introduction Thermal interface material plays a significant role in the electronic packages to enhance the heat transfer between contact surfaces. Due to miniaturization, heat dissipation from the electronic devices has become one of the limiting factors in device performance and reliability. For the optimum performance and better reliability of a device, it is important to dissipate heat efficiently from the device during its normal operation. When two mating parts are attached in an electronic device, voids can be formed in between these two mating surfaces. Generally, these voids are filled with air, which increases thermal Materials 2021, 14, 3565. https://doi.org/10.3390/ma14133565 https://www.mdpi.com/journal/materials