Rigid + flex

Rigid-Flex

Rigid zones where components sit, flexible zones where the board has to fold. One part instead of three, no connectors, no assembly step for the cable — and the failure mode that connectors bring with them disappears with them.

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At a glance

Layer count 2 – 20

Flex layers up to 10, 18 advanced

Bend radius ≥ 6 × thickness

Base material Polyimide

Bend cycles dynamic possible

Rigid-flex replaces a rigid board, a flat cable and two connectors with a single part. That removes the two most common field failures in a folded assembly at once — the connector contact and the solder joint that holds it — and it removes the assembly step that mates them.

The engineering shifts to the transition zone, where the rigid section ends and the flex begins. That boundary is where nearly every rigid-flex problem originates: a plated hole placed in the bend, a track crossing the transition at a right angle, or a bend radius specified tighter than the material tolerates.

What it delivers

[ Overview ]

Connectors removed

One part instead of board, cable and two connectors. Fewer contact points means fewer field failures and one less assembly operation.

Fits three-dimensional housings

The board follows the enclosure instead of dictating it. In tightly packed devices this is often what makes the mechanical concept work at all.

Dynamic bending possible

With rolled annealed copper and a correctly sized radius, the flex zone survives repeated bending — not just the single fold during assembly.

Build and options

[ Datasheet ]

Feature	Specification
Material	FR-4, polyimide, Rogers — bonded rigid and flexible layers
Layers	2 – 12 standard, 13 – 20 advanced
Final thickness	0.3 – 3.0 mm standard, up to 4.0 mm advanced (differs between rigid and flexible zones)
Copper	12 – 105 µm (standard 18 or 35 µm), RA copper in the flex
Cover	Polyimide coverlay over the flex, solder mask over the rigid areas
Surface finish	ENIG, OSP, immersion silver/tin, lead-free HASL
Typical use	Aerospace, medical, wearables, automotive and industrial electronics

The usual build for this line. Anything outside it is normally still possible — ask and we will confirm.

Rigid-flex limits

[ Specification ]

The flex zone, not the rigid section, sets the limits. Values below apply to the flexible part of the build. Advanced is controlled, but requires a special check before it is confirmed.

Parameter	Standard	Advanced	Note
Total layers	2 – 12	13 – 20	Flex layers counted within the total
Flex layers	up to 10	up to 18	More flex layers stiffen the zone considerably
Final thickness	0.3 – 3.0 mm	0.3 – 4.0 mm	Differs between rigid and flexible zones
Aspect ratio (mech.)	10 : 1	12 : 1	Board thickness against smallest hole diameter
Line / gap (flex)	100 / 100 µm	75 / 75 µm	Flex zones tolerate less than rigid sections
Bend radius, static	≥ 6 × t	≥ 3 × t	Single-sided flex zone; double-sided 7 – 10 × t, multilayer 10 – 15 × t
Bend radius, dynamic	≥ 40 × t	≥ 20 × t	Requires rolled annealed copper
Coverlay	Polyimide 25 µm	Polyimide 12 µm	Adhesive or adhesiveless build
Copper (flex)	RA 18 – 35 µm	RA 12 µm	Rolled annealed, not electrodeposited
Stiffener	FR-4 / polyimide	Steel / aluminium	For connector and mounting areas

Guide values for pre-selection. Binding values are confirmed per project against your data.

Typical applications

[ Use cases ]

Camera modules and display assemblies

Hearing aids and implantable-adjacent devices

Automotive dashboard and cluster wiring

Foldable industrial handhelds

Aerospace and defence avionics packages

Robotics joints with repeated articulation

Design rules

[ Layout ]

The points below are what most often comes back as a query after data review. Settling them before layout freeze saves a loop.

No plated holes in the bend zone

A via in the flex area is a crack waiting to happen. Keep all drilled features at least 1 mm clear of where the bend begins.

Cross the transition at 90°

Tracks should meet the rigid-to-flex boundary perpendicularly and never run diagonally through it. Angled entries concentrate stress on the outer copper edge.

Stagger tracks on opposite flex layers

Copper stacked directly above copper stiffens the zone and raises the neutral-axis stress. Offset the tracks between layers so the bend stays compliant.

Specify static or dynamic explicitly

A one-time fold during assembly and ten million articulation cycles are different products. The copper type, radius and coverlay all change — tell us which one you need.

Frequently asked

[ FAQ ]

When is semi-flex the better choice?

When the board is bent once during assembly and then stays put. Depth-routed FR-4 costs well below a polyimide rigid-flex build and does the job. As soon as the bend repeats in service, you need real flex.

How many bend cycles will it survive?

With rolled annealed copper, a radius of at least twenty times the flex thickness and staggered tracks, dynamic applications in the millions of cycles are routine. Cut the radius in half and the figure drops by roughly an order of magnitude.

Why is rigid-flex so much more expensive?

Polyimide costs several times what FR-4 does, the panel utilisation is worse because flex outlines nest badly, and the process has more steps. Against that, count the connectors, the cable, the assembly labour and the field returns you no longer have.

Can components sit on the flex section?

On a stiffened area of it, yes — a local FR-4 or polyimide stiffener under the pads makes it possible. On the free-bending part, no.

Not sure what fits?

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Applications in the vehicle