What is high Tg PCB?

What is high Tg PCB?
There are many customers request to manufacture PCB with high Tg, so what is high Tg PCB?
Normally high Tg refers to high heat resistance in PCB raw material, the standard Tg for copper clad laminate is between 130 – 140℃, High Tg is generally greater than 170℃, and middle Tg is generally greater than 150℃. if PCB with Tg≥170℃, we call it high Tg PCB. 
Now more and more industry products, especially for the computer as the representative of electronic products, developing toward the more and more better performance, high multilayer requires PCB substrate material with higher heat resistance to ensure high reliability. Also, SMT soldering develope to a higher level, CMT with high density pcb assembly technology, the PCB manufacturing with small hole size, fine lines and thin thickness are more and more inseparable from the support of high heat resistance.
TG means Glass Transition Temperatures that are associated with long term operations must be considered in the manufactured of printed circuit boards that will be exposed to high thermal loads. The function of a circuit board will be affected if its temperature exceeds the designated Tg value.