Tg means Glass Transition Temperature. As flammability of printed circuit board (PCB) is V-0 (UL 94-V0), so if the temperature exceeds designated Tg value, the board will changed from glassy state to rubbery state and then the function of PCB will be affected.
If working temperature of your product is higher than normal (130-140C), then have to use high Tg material which is > 170C. and popular PCB high value are 170C, 175C, and 180C. Normally the PCB Tg value should be at least 10-20C higher than working temperature of product. If you 130TG board, working temperature will be lower than 110C; if use 170 high TG board, then maximum working temperature should be lower than 150C.
Here are some popular High Tg board raw material in market:
HR-01 & HR-02: Mica-AVA; MCL-E-679: Hitachi;
Also there're a lot of different hi-tg material not listed here, different country, different company prefer using different material. Please view datasheet for each of them to choose most suitable material for you. If without special notice, normally we will use S1170 from SYL.
170Tg raw material is also popular in LED industry, because heat dissipation of LED is higher than normal electronic components, and same structure of FR4 board is much cheaper than that of MCPCB or Ceramic board. The normal Tg value of MCPCB is the same as normal FR4 PCB as 130-140C, and customer can also ask for high TG (170-180C) for MCPCB, but the thermal conductivity can only be (0.3-0.4W/m.k).
If printed circuit board working temperature is higher than 170/180C, such as 200C, 280C, or even higher, then you'd better use Ceramic board which can go through -55~880C.
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