What is Glass Transition Temperature, also known as TG?
Sometimes you can see TG150/TG170, etc. on the PCB material. What does this TG mean?
TG(Glass Transition Temperature) is one of the most important characteristics of all plastic and epoxy resin materials. In fact, TG(Glass Transition Temperature) value is also one of the quality indicators of glass fiber for PCB.
When the temperature is lower than the glass transition temperature (TG), the plastic enters glassy state which is rigid but with brittle characteristics. Just like the characteristics of glass, it is hard but easily brittle.
When the temperature is higher than the glass transition temperature (TG), the plastic parts will show a soft and flexible rubbery state. Therefore, the glass transition temperature (TG) is generally the temperature at which the plastics undergo a phase transition from the glassy state to the rubber state.
As PCB’s TG(Glass Transition Temperature) increasing, the heat resistance, moisture resistance, chemical resistance, and resistance stability characteristics of PCB prodution will be strengthened and improved. The higher the TG(Glass Transition Temperature) value, the higher temperature PCB can endure, especially in the lead-free manufacturing process, where there are more applications of high TG(Glass Transition Temperature).
High TG(Glass Transition Temperature) refers to high heat resistance. The development of high functionalization and high multi-layering requires higher heat resistance of PCB substrate materials as an important guarantee. The emergence and development of high-density mounting technologies represented by SMT and CMT have made PCBs increasingly require specifications with high heat resistance of substrates in terms of small apertures, fine lines, and thinning.
Thus, regards PCB production, the difference between FR-4 and high TG FR-4 is that in a high temperature state, especially when heated after moisture absorption, the material’s mechanical strength, dimensional stability, adhesiveness, water absorption, thermal decomposition, and thermal expansion.