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High-Tg circuit boards (HTg)

For printed circuit boards exposed to high thermal loads, the necessary long-term operating temperature must be determined early on, in order to select an appropriate material.

The Tg value of the base material can be used for this purpose as a reference. Below we have summarized the details for you.

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Typical application areas

  • Multilayer boards with many layers
  • Industrial electronics
  • Automobile electronics
  • Fineline trace structures
  • High temperature electronics


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Tg Value

The glass transition temperature (Tg) is an important normative dimension for the base material that determines the temperature at which the resin matrix converts from a glassy, brittle condition into a soft, elastic one.

The Tg value of the base material sets here an upper boundary, at which the resin matrix decomposes and a subsequent delamination occurs. The Tg is thus not the value of the maximum operational temperature, but rather that which the material can endure for only a very short time.

A guideline for a continuous thermal load is an operating temperature approximately 25°C below the Tg.

When the glass transition temperature (Tg) is over 170°C, it is referred to as a high Tg material.

High Tg materials have the following properties:

  • High glass flow temperature value (Tg)
  • High temperature durability
  • Long delamination durability
  • Low Z axis expansion (CTE)
* at 1MHz
Material for High-Tg boardsTgCTE-zεr, Dk- PermittivityElectric strengthSurface resistivityCTIThermal conductivityTd valuePeel strength
FR4 HTg, CAF-Enhanced
180°554,0448,0 x 10^630,5350°1,2
FR4 HTg, CAF-Enhanced
170°454,0543,0 x 10^630,4350°1,3
175°454,4453,0 x 10^10--345°1,4
Shengyi S1000-2
180°454,8*637,9 x 10^73-345°1,4
Polyimid HTg
250°554,20*571,6 x 10^9-0,2387°1,2

CAF - Conductive Anodic Filament: an undesirable conducting filament in the substrate of a circuit board


The CTE value shows the thermal expansion of the base material. CTE-z represents the z-axis and is e.g. due to the stability of the vias, of high importance. A higher Tg value favors a low CTE-z value which represents the absolute expansion in the z-axis. Errors like pad lifting, corner cracks and cracks within the via can be prevented through a low CTE-z value.

T260 - T288 value, Td

The decomposition temperature Td of a resin system depends on the binding energies within the polymers, and not on the glass transition temperature Tg. A good indicator for this characteristic is the T260 or T288 value, which specifies the time until delamination at 260°C or 288°C, respectively.

A very important indicator of the heat resistance is the time-to-delamination at a certain temperature. This test is preferably performed at 260 °C or 288 °C. The T260- or T288-value is the time to delamination of the tested material at 260 °C or 288 °C, repectively.

Td: Temperature-of-decomposition indicates the temperature at which the base material has lost 5% by weight and is an important parameter for the thermal stability of a base material. Through exceeding this temperature an irreversible degradation and damage to the material by the decomposition occurs.