Rigid-Flex Assembly: Process Sequence and Handling
A rigid flex board is assembled while flat and folded into shape afterwards. The process sequence is longer than for a rigid board, the materials are less tolerant, and the opportunities for damage are concentrated in a few steps.
What a Rigid Flex Contains
The rigid sections carry the components and the flexible sections carry the connections between them. The two are laminated together, and the flexible material passes through the rigid section to reach the outside world.
The transitions between the rigid and flexible regions are the critical areas. The materials change, the thickness changes, and the copper must be handled so that it does not crack at the boundary.
The flexible layers are usually bonded to the rigid layers with a no flow prepreg that does not flow into the flexible region during lamination. Our multilayer flexible notes describe the process.
Assembly Sequence
The board is assembled flat, which is the reason for using the construction at all. Printing, placement, reflow and inspection are performed on the flat board exactly as on a rigid one.
Where the design has rigid sections on different planes, the assembly is performed before the fold. Folding after assembly means that the components are already attached and must survive the forming operation.
Where a section must be folded, the support during the fold matters. A tool that controls the radius protects the flex and the joints. Our breakaway notes describe the related panel handling requirements.
Baking and Moisture
The flexible materials absorb moisture and their adhesives have a lower temperature limit than a rigid laminate. The bake before assembly must therefore be at a lower temperature and for a longer time.
The rigid sections may require a bake at the standard temperature, which conflicts with the flexible material. The lower of the two limits governs, and the schedule must be established for the combination.
A part that has absorbed moisture will blister at the rigid and flexible transition during reflow, which is the most common defect of the construction. Our coating notes describe the related cure limits.
<img src="https://www.gopcba.com/wp-content/uploads/2026/08/3.png" alt="Rigid-flex panel held flat in a carrier” />
Support During Assembly
The board must be supported so that it does not sag during printing and placement. A rigid flex panel is inherently flatter than a bare flex, and the flexible regions still need support.
A carrier or a pallet that supports the flexible region without pressing on it is the usual solution. The support must not bridge across a component on the underside of a rigid section.
The panel is often designed with the flexible regions held in place by tabs until the assembly is complete, which keeps the panel rigid until the last step. Our design release checklist notes where the panel configuration is recorded.
Handling After Assembly
A populated rigid flex is delicate in the flexible regions, and the components add mass that increases the strain during handling. The handling instructions should state the minimum bend radius and prohibit bending near a component.
Where the flex must be folded in the enclosure, the fold should be formed before the connectors are mated so that the board is not under load while being handled.
The assembly should be supported during installation, since the flex carries the weight of the rigid sections if it is unsupported. A support bracket or a foam pad is often the answer.
Inspection and Testing
The inspection after assembly must cover both the rigid sections and the flexible regions, and the flexible regions require a different inspection method because the traces are under a coverlay.
A flying probe test is often used on a rigid flex because it accesses both sides without a fixture and does not require the board to be flat. Our inspection notes describe the automated methods available.
A continuity check of the flexible traces before and after any folding operation is a useful confirmation that the fold did not break a trace, and it is cheap.
Design Measures That Reduce the Risk
Keep the flexible regions free of components and of vias, and keep the copper pattern wide and uniform there. The design rules for a dynamic flex apply to any flexible region that will be folded more than once.
Place the rigid and flexible transitions away from high stress areas and give them a generous radius. A transition that coincides with the fold line is the classic failure location. Our board design notes describe how the copper is arranged to spread heat, which is also relevant where a rigid section carries power.
Process Control and Verification
On a design of this kind, carrier is the item that decides how the rest of the board is arranged. Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage. Keeping a sample from the panel turns a dispute into a measurement, because the same coupon can be re-examined by both parties without rebuilding the batch.
Reviewing the design before the data is released is cheaper than correcting it after the panel is in the tank, because every step downstream inherits the decision made at the front end. Documenting the assumption is part of the design work, and a short note on the drawing prevents a question that would otherwise arrive a day later and cost a day of schedule.
The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed.
Process Control and Verification
On a design of this kind, carrier is the item that decides how the rest of the board is arranged. Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage. Keeping a sample from the panel turns a dispute into a measurement, because the same coupon can be re-examined by both parties without rebuilding the batch.
Reviewing the design before the data is released is cheaper than correcting it after the panel is in the tank, because every step downstream inherits the decision made at the front end.
Process Control and Verification
On a design of this kind, carrier is the item that decides how the rest of the board is arranged. Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage. Keeping a sample from the panel turns a dispute into a measurement, because the same coupon can be re-examined by both parties without rebuilding the batch.
FAQ
Can a rigid flex be reworked? The rigid sections can be reworked as usual. The flexible regions cannot be reworked without risk, because the coverlay must be opened and resealed.
How many times can the flex be folded? A static fold is intended to be made once. Repeated folding requires a dynamic flex design with a rolled copper and a defined radius.
What does gopcb provide for rigid flex? We provide stack-ups with no flow prepreg, bake schedules that respect the flexible adhesive limits, panel and carrier designs that support the flex during assembly, folding tools and radius control, and continuity testing before and after forming.
