Gas-Generation Mechanism of Silicone Gel in High-Temperature Thermal Decomposition for High-Voltage and High-Power Device Encapsulation

As high-voltage and high-power electronic devices, such as insulated gate bipolar transistors (IGBTs) develop toward higher levels, the generated heat and operating temperature rise rapidly, causing the problem of insulation packaging failure to become more serious. In this article, to study the gas production mechanism of the high-temperature thermal cracking reaction of silicone gel material, the thermogravimetric–infrared spectroscopy (TG–IR), thermogravimetric–mass spectrometry (TG–MS), pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS), and molecular dynamics simulation are used to test and simulate the changes of functional groups, thermal cleavage products, and minor molecule gases during the high-temperature thermal cleavage of silicone gel with temperature in an argon atmosphere. Research indicates that under the action of high temperature, the thermal cracking reaction of silicone gel begins at about 330 °C, and the degree of reaction reaches its maximum at about 561 °C. The main products of high-temperature thermal cracking of silicone gel contain two parts. First, H2, CH4, C2H6, C2H4, CO2, $\text{H}_{{2}}\text{O}$ , H4Si, CH $_{{2}}\text{O}$ , and other small molecular gases. From the microscopic level analysis, CH $_{{2}}\text{O}$ is the first to be produced in the thermal cracking process of silicone gel than other oxygen-containing gases, and the source of oxygen comes from independent chain breakage. Therefore, the generation of CH $_{{2}}\text{O}$ means that the structural quality of the silicone gel has changed, which will lead to the failure of the insulation package. If $\text{H}_{{2}}\text{O}$ , CO2, and other oxygen-containing gases are generated, it means that the failure of the insulation package will be aggravated. Second, the macromolecular products are mainly cyclosiloxanes, esters, aldehydes, alcohols, acids, and other functional organics. The generation of minor molecular gases during thermal decomposition primarily originates from reactions within the side chain groups. Therefore, changes in the side chain structure can enhance the thermal resistance of silicone gel. The conclusions drawn in this article can offer a specific theoretical basis for monitoring insulation fault gases in silicone gel to encapsulate high-voltage and high-power semiconductor devices.