Copying a High Tg board is not harder to trace than any other rigid board of the same layer count — the copper work is the copper work. What makes High Tg PCB copy different is that the laminate is a functional part of the design, not a substrate you can substitute freely. Get the glass transition temperature, resin system, and stackup thicknesses wrong and the duplicate passes electrical test, then fails after a few hundred hours at temperature. That material call is the real deliverable.
This page is written for the engineer or purchasing lead holding a board out of a power converter, an automotive module, a downhole tool, or an LED driver that runs hot — someone who needs to know what we can determine from the physical sample and what we can’t.
Why the laminate matters more than the trace routing
Tg is the temperature at which the resin stops behaving like a rigid glass and starts behaving like rubber. Standard FR-4 sits somewhere around 130–140 °C. High Tg material is usually quoted at 150 °C, 170 °C, or 180 °C and above, and the difference shows up in three places you care about:
- Z-axis expansion. Above Tg the CTE in the thickness direction climbs sharply. That’s what cracks plated barrels and pulls pads. A board with 0.3 mm vias through 2.4 mm of stackup is living on the material’s Z-axis behavior.
- Assembly survival. Lead-free reflow peaks push the laminate close to its limits. Multiple reflows, plus rework on a big BGA, plus a hot operating environment is a cumulative load.
- Long-term dielectric stability. Resin systems with higher Tg generally also have better decomposition temperature (Td) and lower moisture uptake. For anything that sees 105 °C ambient continuously, that’s not a nicety.
So when someone asks for a copy of a High Tg board and says “just use normal FR-4, it’s cheaper,” the honest answer is that you may not see the difference on the bench. You’ll see it in the field return rate.
How we figure out what the original laminate actually was
Nobody prints “Tg 170” on a board. Identification is inference from several independent clues, and we tell you which clues we found rather than asserting a grade with false confidence.
Markings and legend
Many boards carry a UL recognition mark, a manufacturer logo, and a flammability rating in the silkscreen or as an etched copper legend on an outer layer. Sometimes there’s a material code. Sometimes there’s a date code that at least brackets the era, which narrows the plausible resin systems. This is the cheapest evidence available and it’s often partially legible under solder mask, so we photograph it under raking light before anything else.
Physical and thermal behavior
Color and translucency of the laminate at a cut edge tell you something — many high-Tg systems are visibly different in tone from commodity FR-4. Resin hardness, how the material behaves under the router, and how the drill dust smells and clumps are all recognizable to someone who has sectioned a few hundred boards. None of these is conclusive alone. Together they usually put us in the right family.
Cross-section
This is the part that actually settles the stackup. We sacrifice one board, pot and polish a section through a via field, and measure under a microscope: copper weight per layer, dielectric thickness between each layer pair, prepreg versus core construction, glass style where it’s resolvable, plating thickness in the barrel, and whether there are any blind or buried structures. The measured stackup is what the new fabricator builds to.
If the board is dense enough that layer count is uncertain from the edge alone, we X-ray first to map the via structure before deciding where to cut. That saves sacrificing a second sample.
What we can and can’t tell you
We can usually tell you: layer count, copper weights, dielectric thicknesses, drill sizes and plating, surface finish, solder mask and legend, and whether the material behaves like a high-Tg system or a commodity one. We generally cannot tell you the exact brand and grade — “this is Panasonic R-1755 versus Isola 370HR” — from the board alone without material analysis that costs more than most projects justify. What we do instead is specify a laminate class with the properties that matter (Tg, Td, CTI where relevant, halogen-free or not) and let you approve the substitution.
What changes in the copy process compared to standard FR-4
The tracing, netlist, and schematic work is the same discipline as any rigid board — strip, image, correlate, verify. What shifts is everything downstream of the copper.
| Step | Standard FR-4 board | High Tg board |
|---|---|---|
| Layer separation | Routine chemical and mechanical delayering | Harder resin resists etch-back; slower, more controlled removal |
| Drilling in the rebuild | Standard feeds and speeds | Fabricator needs adjusted parameters; more heat, faster bit wear |
| Stackup documentation | Nominal thicknesses often good enough | Measured thicknesses required — Z-axis behavior depends on them |
| Material call-out in the package | “FR-4, 1.6 mm” | Tg/Td range, resin family, glass style, halogen status, CTI |
| First-article verification | Continuity plus visual | Continuity, cross-section of the new build, and thermal cycling if the application warrants it |
The delayering point deserves emphasis. High-Tg resin systems are deliberately more chemically and thermally stable, which is exactly the property that makes controlled removal slower. On a six- or eight-layer high-Tg board, expect the imaging phase to take meaningfully longer than the same geometry in ordinary FR-4. This is also where a board that shares characteristics with a high-density PCB copy job gets expensive — tight geometry plus stubborn laminate compounds.
What to send us, and what comes back
Feasibility and pricing depend on things we can only see. Send this and you’ll get a real answer instead of a range:
- Clear photos of both sides, whole board in frame, on a dark non-reflective background, plus close-ups of any UL mark, laminate code, or manufacturer legend.
- Board dimensions and overall thickness, measured with calipers. Thickness plus layer count is the first constraint on any stackup reconstruction.
- Markings on the main ICs — full part number lines, including date and lot codes, photographed legibly.
- The operating environment. Ambient temperature, duty cycle, whether it’s potted, whether it sees vibration. This drives the material recommendation more than anything else you can tell us.
- Which deliverables you need, in one line: Gerbers and drill only, or Gerbers plus BOM, or full schematic recovery, or a working assembled prototype.
- Quantity of samples available. Cross-sectioning consumes a board. If you have exactly one, say so up front — it changes the plan.
What comes back from us: a feasibility statement naming what we can and can’t determine, a lead time, and a price. If cross-section is required and you only have one sample, we’ll say that explicitly and offer non-destructive alternatives with their limits stated.
The handover package for a High Tg PCB clone normally includes Gerber and drill files, a measured stackup drawing with material specification, an impedance note where controlled impedance is in play, a BOM, and — if you ordered it — a schematic. Details on the standard file set and how the copy workflow runs apply here too; the addition on high-Tg jobs is the material and stackup documentation.
Where this gets hard, and where we say no
Honest limits, because they save you money on a quote that would have gone sideways:
- One sample, high layer count, no schematic. If we can’t sacrifice a board and can’t verify a reconstructed stackup, we’ll produce Gerbers with a documented assumption set, not a verified copy. That’s a different product and we price and label it as such.
- Potted or conformally coated assemblies. High-Tg boards live in harsh environments, so potting is common. Removing epoxy potting without destroying fine traces is possible but slow, and some compounds win. We evaluate a corner before quoting the whole board.
- Discontinued laminate grades. If the original material is no longer made, we substitute to equivalent or better properties. “Equivalent” is a judgment call and you should review it, especially if the design is qualified to a customer specification.
- Boards where high Tg was over-specified. Sometimes the original designer picked 170 °C material for a board that never exceeds 60 °C. We’ll tell you when a lower grade is defensible, and when it isn’t.
- Buried passives, embedded components, or exotic hybrid constructions. These occasionally show up in high-reliability high-Tg builds and can push a job from difficult to not worth attempting.
One more constraint worth naming: on a board that is both high-Tg and running fast edges, the material properties feed into signal integrity as well as thermal survival. Dk and Df of the substitute laminate matter, and the geometry has to be re-solved rather than blindly copied. That work overlaps heavily with a high speed PCB copy and we’ll flag it if we see it.
On the legal side: we work on boards you own or are authorized to work on. You’re responsible for holding the rights to the design and for complying with applicable IP law in your market. Every project runs under NDA, and we don’t retain your files after handover unless you ask us to.
Legitimate reasons people come to us with these boards
Almost every High Tg PCB copy job we take falls into one of four buckets. A line went down and the OEM board is a twelve-week lead time or discontinued outright. A design owner still ships the product but the original CAD is gone with the engineer who drew it. A qualified laminate went end-of-life and the build has to be respun to a current material without redes
Working on a board like this?
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