The capability extract shows in thirty seconds what runs as standard and what carries a surcharge.
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To the data check →Take a normal FR-4 board and mill a channel in the bend area until only two or three tenths of a millimetre remain. It will now fold once, cleanly, and hold its position — for maybe a third of what the equivalent rigid-flex would cost.
Semi-flex is a machining operation, not a material. Standard FR-4 is routed from one side to a controlled residual thickness — typically 0.20 to 0.30 mm — leaving enough glass and resin to carry the copper but little enough that the section will bend. The copper in the bend zone is normally left as a solid unbroken area or as widely spaced tracks.
The value is entirely economic. A board that needs to fold once during assembly to fit a housing does not need polyimide, coverlay, rolled annealed copper or the panel-utilisation penalty that comes with them. It needs a milled channel. The moment the fold repeats in service, though, semi-flex is the wrong answer and no amount of care in the routing changes that.
Standard laminate, standard process, one extra machining step. Typically 20 – 40 % over a rigid board rather than the 80 – 150 % polyimide commands.
The material is the FR-4 you already use. Nothing in your material declaration, IMDS entry or supplier approval changes.
Once folded the section stays put, which in many housings removes the need for a retaining clip or a second fastener.
| Parameter | Standard | Advanced | Note |
|---|---|---|---|
| Residual thickness | 0.30 mm | 0.20 mm | Thinner bends easier, breaks easier |
| Bend radius | ≥ 10 mm | ≥ 6 mm | Larger than any polyimide flex needs |
| Bend angle | ≤ 90° | ≤ 120° | Beyond this the outer fibres crack |
| Bend cycles | 1 | ≤ 5 | Static only — not for service movement |
| Copper in bend | 35 µm max | 18 µm | Thinner copper survives the fold better |
| Channel width | ≥ 3 mm | ≥ 2 mm | Routed zone along the fold line |
| Layers | 2 – 4 | 6 | Bend zone stays a single dielectric |
| Tolerance, residual | ± 50 µm | ± 40 µm | Depth-routing accuracy |
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.
The fold is a one-way operation. Bending back to check something, or unfolding during rework, cracks the resin — usually invisibly, and the board fails later.
Same rule as rigid-flex: no plated hole in or near the bend, minimum 1 mm from the channel edge. The barrel has no compliance at all.
Fine parallel tracks across a semi-flex bend concentrate strain at their edges. A continuous copper area, or a few wide tracks, survives the fold far better.
If the process allows, bend the bare board. Folding a populated assembly puts the strain in with components already soldered near the hinge.
One reliably. Up to about five with a generous radius and thin copper, but every additional fold is a gamble. If the specification says the product will be opened for service, treat that as a dynamic application and use polyimide.
No. Reverse bending is the fastest way to crack a semi-flex hinge. Get the fold direction right in the assembly instruction.
No — that is the whole point. It is your existing FR-4 with a milling operation. Some suppliers offer bend-optimised laminates, but standard material works within the limits above.
Roughly a third to a half of the rigid-flex price for a comparable board. On a static single fold that saving is essentially free.
Send us your data or a rough sketch. We check feasibility, name the cost drivers and answer within one working day.