FR-4 rigid boards, one to 32 layers
FR-4 is what most boards are made of, which is exactly why it is the easiest laminate to buy badly. These are the limits we hold on FR-4 and high-TG FR-4, and the five decisions on the drawing that change what a quote comes back as.
- Layers1 – 32
- Thickness0.2 – 8.0 mm
- Copper0.5 – 12 oz
- Min line/space0.06 / 0.06 mm
What FR-4 is, and when to ask for high TG
The name describes the resin system, not the board. Everything that decides the price is chosen per order.
FR-4 is woven glass cloth in an epoxy resin, pressed into a sheet and clad with copper. Nothing in the name tells you the thickness, the copper weight or the glass transition temperature — which is why the same word covers a 0.2 mm two-layer board and a 3.2 mm sixteen-layer one.
The one variant worth deciding before you order is high TG. Standard FR-4 softens somewhere around 130 to 140 °C; high-TG laminate is typically 150 to 180 °C (supplier datasheets — the figure that governs is the one on the laminate you buy, not a general rule). It matters because lead-free reflow takes the board to roughly 260 °C at the peak. A thin board that is reflowed once usually survives that on standard FR-4. A board that is reflowed twice for double-sided assembly, that is thick enough for the inner layers to lag the surface on heat-up, or that is likely to be reworked on the line is where high TG earns the premium.
High TG is on our base-material list, next to CEM1, CEM3, FR1, FR2, 94V0, Rogers, F4B, Taconic and aluminium. What we do not do is quote a laminate grade you did not ask for and will not be told about — if the board needs high TG, it is written on the quote. The rest of the material list is in the fabrication table.
FR-4 fabrication limits
The numbers we hold on FR-4 and high-TG FR-4. Everything else on the process list — mask colours, silkscreen, finishes, special processes — applies to every laminate and is on the fabrication table.
| Layer count | 1 – 32 layers |
| Board thickness | 0.2 – 8.0 mm (± 10%) |
| Copper weight | 0.5 oz – 12 oz |
| Minimum line width / spacing | 0.06 mm / 0.06 mm |
| Maximum board dimensions | 650 mm × 1,100 mm (25.6 in × 43.3 in) |
| Minimum drill hole diameter | 0.1 mm |
| Minimum laser-drilled hole | 0.075 mm |
| Minimum slot width | 3.0 mm (0.12 in / 120 mil) |
| PTH wall thickness | > 0.025 mm |
| PTH hole diameter tolerance | ± 0.076 mm |
| NPTH hole diameter tolerance | ± 0.05 mm |
| Hole position deviation | ± 0.076 mm |
| V-score depth | 20–25% of board thickness |
| Solder mask | Double-sided green LPI as standard; red, white, yellow, blue, black and purple available |
| Silkscreen | Single- or double-sided, in white, yellow, black, or negative |
| Surface finish | HASL, ENIG, immersion tin, immersion silver, OSP, ENEPIG, electrolytic hard gold, gold fingers, ENIG + OSP |
| Quality standard | IPC-A-600F / MIL-STD-105D |
| Design files accepted | Gerber RS-274X and 274D, KiCad, Eagle, Altium/Pro-E, AutoCAD DXF and DWG |
| Order quantity | 1 – 500,000 |
| Lead time | Prototype 3–4 days; mass production 8–16 days |
Impedance control, blind and buried vias, half holes and countersunk holes are all available on an FR-4 stackup; they are listed under special processes. What they need from you is a stackup drawing, not just the Gerber.
Five things that change an FR-4 price
None of them is the laminate itself. Read this before you ask for a cheaper board.
| Decision | What it does to the price | What to do about it |
|---|---|---|
| Layer count | Every pair of layers is another press cycle, another drill program and another imaging pass. The step from 2 to 4 layers is cheaper than the step from 12 to 16. | Ask what the design needs, then ask whether a layer could be dropped by rerouting. On boards copied from an old design the answer is often yes. |
| Copper weight | Heavier copper is etched from thicker laminate: more material, slower etch, wider minimum lines. | Keep the heavy copper on the layers that carry current. A 4 oz plane and 1 oz signal layers is a normal, cheaper combination. |
| Panel utilisation | You pay for the panel, not only for the board. A board that tiles badly leaves the rest of the panel as waste. | Rotating the outline or trimming a few millimetres can move a board into a better panel count. It costs nothing to ask us to try. |
| Surface finish | HASL is the cheapest; ENIG, immersion silver and hard gold add cost and add process steps. | Match the finish to the smallest pitch on the board, not to the last board you bought. The comparison is here. |
| Quantity | Setup, tooling and test are fixed: the unit price falls steeply from 1 to 100 and slowly after that. | Order the quantity the project actually needs. There is no minimum order here, which makes a 20-piece run viable. |
Surface finish is the decision most often made by habit rather than by requirement: the six finishes side by side is written for exactly that comparison.
Where an FR-4 board fits, and where it does not
FR-4 is the right board if…
You want a different family if…
Not sure whether your design is still an FR-4 design? Compare the five board types — the answer is usually decided by one sentence in the specification.
Same plant, other families: HDI build-up · flexible and rigid-flex · aluminium and heavy copper · high-frequency laminates.
Common questions
How many layers can you fabricate in FR-4?
One to 32. The same range applies to high-TG FR-4 and to the rest of our laminate list: CEM1, CEM3, FR1, FR2, 94V0, Rogers, F4B and Taconic, plus aluminium.
What finished thickness can an FR-4 board be?
0.2 to 8.0 millimetres, held to plus or minus 10 percent.
Do you build high-TG FR-4, and when is it necessary?
Yes — high TG is on our base-material list. It matters when the board goes through lead-free reflow more than once, when it is thick enough that the inner layers lag the surface on heat-up, or when it will be reworked. Standard FR-4 softens around 130 to 140 degrees Celsius; high-TG laminate around 150 to 180.
What is the finest line and the smallest hole you hold on FR-4?
0.06 millimetres line and spacing, 0.1 millimetre drilled holes, and 0.075 millimetres for laser-drilled microvias.
How long does an FR-4 prototype take?
Three to four days for fabrication, and eight to sixteen days for mass production. Assembly is scheduled separately — a board that is being populated is not finished when the bare board is.
Send the stackup, not just the Gerber
A Gerber gives us the outline and the copper; the stackup decides whether the board is buildable at the price you were quoted. Send both and the layer count, copper weight and finish come back confirmed within 24 hours.