The capability extract shows in thirty seconds what runs as standard and what carries a surcharge.
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To the data check →Glass-reinforced epoxy laminate, and the reference point every other material is priced against. Around eight out of ten boards we build start here, and for good reason: it is predictable, universally available and the cheapest thing that works.
FR-4 is woven glass cloth impregnated with epoxy resin and cured. The designation is a flammability and material class rather than a single product — behind it sit dozens of laminates from different makers with slightly different resin systems, all interchangeable enough that availability is essentially never a problem.
Its limits show up in two places. Above roughly 150 °C the resin softens, and above about eight layers or two lead-free reflow cycles the accumulated thermal load starts to matter. Neither is a hard wall — but both are the point at which a 10 – 20 % surcharge for High-Tg buys a disproportionate amount of process margin.
Multiple qualified suppliers per plant. No allocation risk, no single-source qualification, no lead-time surprise on the laminate itself.
The reference price for the whole industry. Everything else in this list is quoted as a surcharge on it.
Every drilling, plating and lamination parameter is long settled. That shows up as yield, which shows up in price.
| Property | Value | Test / note |
|---|---|---|
| Glass transition Tg | 150 °C | DSC, IPC-TM-650 2.4.25 |
| Decomposition Td | > 300 °C | TGA, 5 % mass loss |
| Dielectric constant Dk | 4.3 – 4.7 | At 1 GHz; rises at lower frequency |
| Loss factor Df | 0.015 – 0.025 | Too high for RF above a few GHz |
| CTE z-axis | 4.0 – 5.0 % | 50 – 260 °C, the figure that matters for vias |
| Thermal conductivity | 0.3 W/mK | Poor — heat spreads sideways in copper, not resin |
| Water absorption | ≤ 0.15 % | Bake before reflow after long storage |
| Flammability | UL 94 V-0 | Achieved with brominated flame retardant |
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.
Beyond about eight layers the press cycle puts enough cumulative thermal load on standard FR-4 that z-axis expansion starts stressing via barrels. That is the practical trigger for High-Tg, more than the operating temperature.
Lead-free reflow peaks around 245 – 260 °C. One pass is fine; three passes plus rework is where standard FR-4 begins to delaminate. Count the cycles, including any rework you expect.
The loss factor is an order of magnitude worse than an RF laminate and Dk drifts with frequency and temperature. For anything with a real link budget, use a hybrid build.
FR-4 absorbs moisture slowly but steadily. Boards stored for months should be baked before assembly — trapped moisture flashes to steam at reflow and causes blistering.
No — the designation covers a family. Resin systems differ in Td, CTE and how they drill. For most designs the difference is invisible; for high layer counts or tight aspect ratios it is not, and we will name the specific laminate on the build.
Three triggers: more than about eight layers, more than two lead-free solder cycles, or an operating temperature above roughly 110 °C sustained. Any one of them makes the 10 – 20 % surcharge good value.
Standard FR-4 is not — it reaches UL 94 V-0 with brominated flame retardants. If you need halogen-free, that is a separate material group with its own handling rules.
Not as supplied. Depth-routed to a thin residual thickness it can take a single controlled bend — that is what semi-flex is. For repeated bending you need polyimide.
Send us your data or a rough sketch. We check feasibility, name the cost drivers and answer within one working day.