High glass-transition temperature can be useful in an HDI material system, but Tg alone does not predict survival through lamination, reflow and field use.
What to consider
Compare Z-axis expansion, decomposition behavior, time-to-delamination data, moisture handling and process compatibility. Test methods matter when comparing Tg values. A high-Tg laminate still requires a qualified microvia structure and an assembly profile consistent with the fabrication and material guidance.
A practical review example
When two candidate materials list different Tg values, first check whether the measurements use DSC, TMA or DMA. Then compare the rest of the thermal data and the factory’s experience with your construction.
Checks before release
- Compare like-for-like test methods.
- Include repeated reflow or rework in the requirement.
- Avoid treating Tg as the board’s maximum operating temperature.
Connect this decision to fabrication
Use the material selector to organize the initial discussion. Keep proposed values separate from the approved drawing and document the effect of any change on the rest of the construction.
- Identify the exact grade, glass style, resin content and copper foil.
- Compare Dk and Df only with their frequency and test method.
- Confirm the material system is qualified for the proposed via structure.
Technical references
FR408HR material and processing resourcesMEGTRON6 material family and test conditionsRO4000 laminate data and processing resourcesReferences checked 2 October 2026. Manufacturer data describes its stated construction and is not an HDIPCB.org manufacturing commitment.