What is high Tg PCB (printed circuit board)

What is high Tg PCB (printed circuit board)

TG’s meaning in PCB specification is glass-transition temperature, which is an important character of the PCB base material.

In recent years, there are more and more customers requesting to manufacture PCB with high Tg. In the following we would like to describe what is high Tg PCB and how to choose PCB base material.

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℃. Basically the printed circuit board with Tg≥170℃, we call high Tg PCB.

The background of using high Tg base material

As the rapid development of electric industry, especially for the computer as the representative of electronic products, developing toward the high performance, high multilayer requires PCB substrate material with higher heat resistance to ensure high reliability. On the other hand, as a result of development of SMT, 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.
If the Tg of PCB substrate is increased, the heat resistance, moisture resistance, chemical resistance and stability of printed circuit boards will be improved as well. The high Tg applicates more in the lead free pcb manufacturing process.

When start a PCB design,How to choose PCB base material

Therefore, the difference between general Tg FR4 and high Tg FR4 is, in the hot state, especially in the heat absorption with moisture, the high Tg PCB substrate will perform better than general FR4 in the aspects of mechanical strength, dimensional stability, adhesiveness, water absorption and thermal decomposition.

Usually, manufacture are would like to choose high Tg material to produce high layers PCB(especially ≥10L ) or multi-layer heavy copper PCB(≥3oz) to improve high reliability/high quality. The common use high Tg material are like ITEQ IT180,Shengyi S1000-2,EMC EM827. Isola(370HR) are not common use and need specially purchase and price will more expensive than common use high Tg material.

There are also material which Tg value can reach to more than 190℃ or 210℃, but it is rare to use it, the price is higher than 370HR, like Isola FR408HR, this also belong to high frequency material.

What is the standard reference on PCB base material.

IPC-4101 is an intentional standard to specify the PCB base material.

When you order PCBs,You can specify your PCB material in your specification according to IPC-4101, the high tg PCB base material must neet IPC-4101/126,and and then the PCB manufacturere will choose correct material accordingly.

Tg (min) C150110110150170110150170170
Td (min) C325310310325340310325340340
CTE Z 50-260 C3,5%4%4%3,50%3%4%3,50%3,50%3%
T260 (min) minutes303030303030303030
T288 (min) minutes555515551515
Fillers > 5%YesYesNANAYesYesYesNAYes
Dk/Permittivity (max)5,45,45,45,45,45,45,45,45,4

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