Tg stands for Glass Transition Temperature, which is one of the most important properties of PCB base materials, meaning the temperature at which the glass fibers inside the FR4 or Polyimides are softening and the base material becomes mechanically unstable.

High Tg PCBs are those printed circuit boards manufactured with High Tg base materials with Tg value starting at around 170°C. Besides, most high Tg manufacturing materials up to Tg170°C. If the PCB should be exposed to high thermal loads, the necessary long-term operating temperature must be determined early on, in order to select an appropriate base material. If lack of consideration, the PCB is probably going to be melting and broken.

Many people only know Hi-Tg PCBs are FR4 rigid PCBs, but don’t know they also can be flex-rigid PCBs and flex PCBs due to FCCL always contain glass fiber. As a high Tg Printed Circuit Board (PCB) manufacturer, we always keep enough PCB materials of high Tg FR4 CCL and FCCL in stock.

What is High Tg Material?

Refer to the following as classifications:

• Low Tg: around 130°C
• Middle Tg: >=150°C
• High Tg: >=170°C

High Tg PCB boards are always multilayer PCBs. Generally, we suggest using high middle to high Tg materials to manufacture multilayer boards with layer count equal or more than 4 layers. In all HDI boards manufacturing, almost are middle and high Tg materials.

High Tg PCB Features:

Why Need a High Tg Printed Circuit Board?

As a leading PCB board manufacturer and provider, we are always asked when and why need a high Tg PCB. Of course, if your PCB will be worked in a thermal load no greater than 25°C (i.e. 77°F) below the Tg value, you need a high Tg circuit board for your applications. There are 3 popular main reasons you need high Tg PCBs. The 1^st is the working temperature is high. The 2^nd is for RoHS reaching and electronic components maybe broken under the high SMT reflow temperature around 260°C. The 3^rd is multilayer PCB pursuit of PCB durability and products stability.

Why Sometimes No Tg Mentioned in Material Datasheets?

Some common high-frequency materials don’t mention Tgs in their datasheets. Because the original meaning of Temperature of Glass Transition. Some ceramics and PTFE materials don’t contain any glass fiberglass and so have no technical Tg. Generally, this fact also applies to Polyimides (flexible PCB materials). But FPC materials, no matter adhesive or adhesive-less FPC materials, always are not pure PI but contains some degrees of epoxy. Temperature resistance of FPCs are limited through the epoxy, not the polyimide.