The capability extract shows in thirty seconds what runs as standard and what carries a surcharge.
See capabilities →Send the files and an engineer reviews them against your build — free, before you enquire.
To the data check →The obvious reading is that High-Tg is for hot applications. The more useful one is that it is for thick ones: the reduced z-axis expansion is what keeps via barrels intact through multiple press and reflow cycles, and that matters at eight layers whether or not the product ever runs warm.
High-Tg uses a more densely cross-linked resin system than standard FR-4. The headline number is the glass transition temperature — 170 to 180 °C instead of 150 — but the property that earns its keep is z-axis expansion, which drops from around 4.5 % to below 3.5 % over the same temperature range.
That difference decides whether a plated barrel survives. Every reflow cycle, the laminate expands vertically and pulls on the copper inside the hole. In a two-layer board the total movement is negligible; in a 3 mm, 20-layer build with a 0.2 mm hole it is the dominant failure mechanism. High-Tg does not remove the stress, it reduces it by roughly a quarter — which in practice is the difference between passing and failing thermal shock.
Td above 340 °C leaves real margin over a 260 °C reflow peak, including rework passes and any selective soldering afterwards.
Lower z-axis expansion means less stress on plated holes through every thermal cycle. In thick builds this is the difference between passing and failing thermal shock.
At 10 – 20 % over standard FR-4, it is one of the cheapest reliability improvements available in the whole build.
| Property | High-Tg | Standard FR-4 | Why it matters |
|---|---|---|---|
| Glass transition Tg | 170 – 180 °C | 150 °C | Resin stays rigid further up the temperature range |
| Decomposition Td | > 340 °C | > 300 °C | Margin over a 260 °C lead-free reflow peak |
| CTE z-axis | < 3.5 % | 4.0 – 5.0 % | The figure that decides via barrel survival |
| Dk (1 GHz) | 4.2 – 4.6 | 4.3 – 4.7 | Marginally lower, rarely the reason to choose it |
| Df | 0.010 – 0.020 | 0.015 – 0.025 | Slightly better, still not an RF material |
| Layer count | 4 – 40+ | 2 – 16 | Practical ceiling, not an absolute limit |
| Reflow cycles | ≥ 5 | 2 – 3 | Including rework and selective soldering |
| Surcharge | + 10 – 20 % | baseline | Against FR-4 at the same layer count |
Guide values for pre-selection. Binding values are confirmed per project against your data.
The points below are what most often comes back as a query after data review. Settling them before layout freeze saves a loop.
A cool-running 20-layer board still needs High-Tg. The z-axis stress comes from the build, not from the operating environment.
Cores and prepregs of different resin systems expand differently and shear against each other in the press. Keep the whole build in one grade.
High-Tg has to be specified — we will not substitute it silently on a job quoted as FR-4. Put the Tg requirement in the drawing, not just in the enquiry email.
The harder resin is more abrasive on drill bits, so drilling parameters and bit life change. This is our problem, not yours — but it is why the surcharge is not zero.
It is always at least as good, but on a four-layer board running at room temperature you are paying for margin you will never use. Below eight layers and two solder cycles, standard FR-4 is the rational choice.
In practice they behave similarly and both are quoted as one grade. Where a customer specification names a figure we match it exactly; otherwise we take whichever the plant has qualified, which is usually Tg 170.
Indirectly. It does not fix an asymmetric build — nothing does — but the stiffer resin holds its shape better through the press cycle, so a symmetrical High-Tg build tends to come out flatter than the same build in standard FR-4.
Yes. Halogen-free High-Tg grades exist and are common in railway work, where EN 45545-2 and high layer counts often arrive together. Expect the two surcharges to stack.
Send us your data or a rough sketch. We check feasibility, name the cost drivers and answer within one working day.