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To the data check →High-Tg PCBs use FR-4 materials with an elevated glass transition temperature. They are an option for applications with increased thermal demands and demanding manufacturing processes. Material selection depends not only on Tg, but also on thermal expansion, delamination resistance and the specific PCB construction.
Typical properties of the selected High-Tg material. Material designation and complete datasheet available on request.
Temperature changes cause the base material and plated through-holes to expand differently, creating mechanical stress. A suitable material with low Z-axis expansion can help reduce this stress. Reliability also depends on board thickness, hole geometry, copper quality and thermal exposure. Tg alone is therefore not a sufficient selection criterion and does not represent the permissible continuous operating temperature.
Suitability for lead-free soldering and repeated thermal exposure is assessed against the material, PCB construction and intended process profile.
Low expansion through the board thickness can reduce mechanical stress on plated through-holes. The properties of the selected material are decisive.
High-Tg is appropriate when manufacturing or operating requirements justify it. Material selection and cost are assessed for each project.
An example comparison of a Tg-150-class FR-4 material and a Tg-175-class High-Tg FR-4 material.
| Property | FR-4 Tg-150 class | High-Tg FR-4 Tg-175 class | Significance |
|---|---|---|---|
| Glass transition temperature Tg by DSC | 157 °C | 175 °C | Characterises the glass transition |
| Decomposition temperature Td at 5% weight loss | 352 °C | 345 °C | Characterises thermal decomposition |
| Z-axis CTE below Tg | 37 ppm/K | 45 ppm/K | Expansion coefficient below Tg |
| Z-axis CTE above Tg | 230 ppm/K | 210 ppm/K | Expansion coefficient above Tg |
| Total Z-axis expansion 50 – 260 °C | 2.8% | 2.7% | Relative thickness change over the test range |
| T260 | > 60 min | > 60 min | Time to delamination at 260 °C |
| T288 | > 30 min | > 30 min | Time to delamination at 288 °C |
| Dk at 1 GHz and 50% resin content | 4.6 | 4.4 | Dielectric constant |
| Df at 1 GHz and 50% resin content | 0.016 | 0.015 | Dissipation factor |
Typical properties of selected FR-4 materials available through LEXINGTON. Values are provided for comparison and depend on the material and construction. They are not general specification limits for the respective material class. Material designations and complete datasheets are available on request. We can help you select the appropriate material for your project.
High-Tg may be suitable for these applications. Selection depends on the specific operating conditions, manufacturing processes and PCB requirements.
The points below are what most often comes back as a query after data review. Settling them before layout freeze saves a loop.
Consider board thickness, hole geometry, soldering processes and operating conditions. Layer count alone does not determine material selection.
The selected materials must be compatible with each other and with the manufacturing process. The same Tg value alone does not demonstrate compatibility.
State Tg, its test method and other relevant requirements in the fabrication documentation. Permitted alternative materials should be explicitly agreed.
Agree the material and stack-up before production. Drilling, lamination and other processing steps depend on the complete material system and PCB geometry.
No. The appropriate material depends on thermal, electrical and mechanical requirements, as well as the manufacturing process. A higher Tg alone does not guarantee greater reliability.
Selection depends on the required specification. In addition to Tg and its test method, properties such as Z-axis expansion and delamination resistance must be considered. Similar Tg values alone do not make materials interchangeable.
High-Tg alone does not prevent warpage. Important factors include stack-up symmetry, copper distribution, material properties and process control.
Yes. Halogen-free High-Tg materials are available. Suitability must be checked against the project specification. Halogen-free status alone does not demonstrate compliance with a particular industry requirement.
Send us your requirements or fabrication data. We can help with material selection and a feasibility review. Material designations and complete datasheets are available on request.