Printed Circuit Board material must flame-resistant, it can’t be burned at a certain temperature and only be softened. The temperature point is called the glass transition temperature (Tg);Ordinary PCB materials at high temperatures, not only will be softened, deformation, melting and other phenomena, but also the mechanical and electrical properties decline sharply. General FR4 Tg is 130-140 centigrade, moderate Tg is greater than 150-160 centigrade, High-Tg is greater than 170 degrees;The higher of Tg, the better the performance of PCB heat resistance, moisture resistance, chemical resistance, stability and other characteristics.When the working temperature reaches the melting point, that means the temperature exceeds the Tg value, the status of PCB material will be changed from glassy to liquid, which will affect the function of PCB. And this value is related to the stability of the PCB dimension;As usual, made with Tg ≥ 170℃ PCB material, which is called a high Tg printed circuit board. With the rapid development of the electronics industry, high Tg material is widely used in computers, communication equipment, precise apparatus, and instruments, etc.