A rigid-flex board can pass continuity and still be wrong. The transition zone can be under-filled, the plated barrels in the flex-to-rigid junction can be cracked, the bend region can carry residual adhesive that will seed a fracture in service — and none of it shows on a netlist test. IPC-6013 is the performance and qualification specification that defines what "acceptable" actually means for flex and rigid-flex boards, and the acceptance criteria that matter most for rigid-flex live in the places a basic inspection never looks. This guide explains what IPC-6013 governs, how Class 1/2/3 differ, the rigid-flex-specific acceptance criteria for the transition, bend, and plating, and gives you a checklist for both RFQ and incoming inspection.
TL;DR
- IPC-6013 is the performance spec for flex AND rigid-flex boards — the flex-side counterpart to IPC-6012, which covers rigid boards. On a rigid-flex board, both can apply: 6012 to the rigid portion, 6013 to the flex and transition.
- Class drives everything. Class 1 (general), Class 2 (dedicated service), Class 3 (high reliability) set the acceptance limits, microsection requirements, and documentation depth.
- The transition zone is the highest-risk feature. Inspect for resin/adhesive flow into the bend, coverlay registration, and a clean rigid-to-flex boundary.
- The bend region must be clean and balanced. No adhesive squeeze-out, correct copper type, defined keepouts — these are acceptance items, not just design preferences.
- Plated interconnect is verified by microsection. Plating thickness, copper wrap, and barrel integrity at the flex-to-rigid junction are the criteria that separate Class 2 from Class 3.
- Specify it on the drawing. Revision, class, construction type, and required test evidence belong on the fab drawing and PO — not assumed.
For the rigid-side counterpart, see the IPC-6012 PCB qualification standard guide. For a buyer-focused RFQ walkthrough of IPC-6013 across all flex constructions, see the IPC-6013 flex PCB RFQ and inspection checklist. To build rigid-flex that passes the first time, start with the rigid-flex design guidelines and the rigid-flex service overview.
What IPC-6013 Governs (and What It Does Not)
IPC-6013 is the Qualification and Performance Specification for Flexible and Rigid-Flex Printed Boards. It defines the acceptance framework for the finished bare board: conductor integrity, plating quality, coverlay and bond quality, dimensional and registration limits, and the test evidence that proves them. It is the document your quality team judges a delivered rigid-flex lot against.
What it is not:
- It is not a design standard. The design rules live in IPC-2223 (flex sectional design) — IPC-6013 tells you whether the built board meets performance, not how to lay it out.
- It is not a visual workmanship guide. That role belongs to IPC-A-600 (acceptability of printed boards), used during inspection.
- It does not replace the rigid-board spec. On a rigid-flex board the rigid islands are still judged against IPC-6012.
| Document | Governs | Used when |
|---|---|---|
| IPC-2223 | Flex / rigid-flex design rules | Before layout release |
| IPC-6013 | Flex / rigid-flex performance & qualification | RFQ, FAI, lot release |
| IPC-6012 | Rigid board performance & qualification | The rigid portion of a rigid-flex board |
| IPC-A-600 | Visual acceptability of printed boards | Inspection, dispute resolution |
| IPC-TM-650 | Test methods for coupons | Generating qualification evidence |
The practical takeaway for rigid-flex: a complete acceptance package references both IPC-6012 (rigid) and IPC-6013 (flex/transition). The IPC-6012 guide covers the rigid-only contrast in detail; this guide focuses on the flex and rigid-flex side.
IPC-6013 Classes: What Changes
The performance class is the single most important callout. It sets the acceptance limits, how much microsection evidence is required, and how strict the release gate is.
| Class | Typical use | Acceptance intensity | What changes |
|---|---|---|---|
| Class 1 | General / non-critical electronics | Lowest | Minimal inspection and documentation |
| Class 2 | Dedicated-service electronics | Standard | Standard industrial/commercial acceptance and evidence |
| Class 3 | High-reliability electronics | Tightest | More microsection, tighter plating/wrap limits, fuller documentation, stricter release |
The right question is not "Can you build Class 3?" but which features of the rigid-flex construction actually require it. Over-calling Class 3 on the whole board adds cost without improving field life; under-calling it and then demanding Class 3 evidence at incoming inspection creates disputes. For rigid-flex specifically, the transition and plated junctions are usually where Class 3 earns its cost.
Rigid-Flex-Specific Acceptance Criteria
This is where rigid-flex inspection diverges from rigid-board inspection. Three feature areas carry most of the rigid-flex risk.
Transition Zone
The rigid-to-flex boundary is the highest-risk feature on the board. Acceptance items:
- No resin or adhesive flow into the bend. No-flow prepreg at the transition must stay put; resin squeeze-out into the flex stiffens it and seeds cracks. IPC-6013 limits allowable flow into the flex region.
- Coverlay registration and adhesion at the transition — the coverlay must terminate cleanly and bond fully, with no lifting or voids that exceed the class limit.
- A clean, void-free rigid-to-flex bondline confirmed by microsection on qualification or first-article lots, especially for Class 3.
- Transition geometry matching the drawing — the flex must emerge free of the rigid stack where the design intends. The design side of this is the transition zone design rules guide.
Bend Region
The flex section that actually bends has its own acceptance criteria:
- No adhesive squeeze-out into the dynamic bend — this is both a design keepout and an inspection item.
- Correct copper type for the bend duty — rolled annealed (RA) copper for dynamic bends; the construction record should confirm it.
- Coverlay keepout held back from the bend per the drawing, with no encroachment that stiffens the bend.
- No cracking, crazing, or measling in the bend region beyond the class limit.
For dynamic-bend products, the cycle-life mechanics behind these criteria are in the hinge flex bend cycle guide, and you should validate radius against thickness with the bend radius calculator.
Plated Interconnect
The plated through-holes and vias that carry signals between layers — especially near the flex-to-rigid junction — are verified by microsection:
- Plating thickness in the barrel meets the class minimum (Class 3 is tighter than Class 2).
- Copper wrap at the target land meets the requirement where called.
- No barrel cracks at the flex-to-rigid junction, where thermal and mechanical stress concentrate.
- No nodules, voids, or delamination in the plated structure beyond class limits.
These are the criteria most likely to separate a Class 2 board from a Class 3 board, and they are only visible in microsection — which is why the coupon and microsection strategy must be agreed before the panel is built.
RFQ Checklist: Specify It Before Quoting
If the drawing only says "build to IPC-6013," you are inviting interpretation. Put these on the fabrication drawing and PO:
- Exact IPC-6013 revision (or approved internal baseline)
- Required performance class (1 / 2 / 3) — and which features drive it
- Construction type: rigid-flex layer count, flex-section layer count, flex-in-core vs flex-on-outer
- Bend intent: static fold or dynamic bend, radius, and cycle count if dynamic
- Reference to IPC-6012 for the rigid portion where applicable
- Required test evidence: coupon report, microsection photos (transition + plated junction), peel strength, impedance data, bend validation
- Coupon strategy confirmed as production-representative
The construction and class side of this maps directly to the layer count guide and stackup construction guide; model the build with the stackup builder.
Incoming Inspection Checklist
When the lot arrives, confirm it matches the quoted construction and class — not just that it "looks okay":
- Part number, revision, and IPC-6013 class match the PO
- Lot traceability and Certificate of Conformance present
- Microsection evidence for the transition zone and plated flex-to-rigid junction (Class 3)
- No adhesive/resin flow into bend or transition regions
- Coverlay registration clean on fine-pitch and exposed-pad zones
- Bend region free of cracks, crazing, measling beyond class limit
- Plating thickness and copper wrap evidence meets the class minimum
- Construction thickness correct at connector and stiffener zones
- Packaging, dryness indicators, and storage condition acceptable
For the broader reliability-test context — IST, thermal cycling, bend validation — read the flex PCB reliability testing guide. Application examples where these criteria bite hardest include rigid-flex PCB for smart glasses, flex PCB for wearables, and the dense, high-speed AR/VR headset rigid-flex design — where multiple plated display and sensor junctions all have to pass the same transition and plating criteria. The system-level case for rigid-flex over a cabled rigid design is in the rigid-flex vs rigid PCB guide.
FAQ
What does IPC-6013 cover that IPC-6012 does not?
IPC-6013 is the performance and qualification spec for flexible and rigid-flex boards; IPC-6012 covers rigid boards. On a rigid-flex board the rigid islands are judged against IPC-6012, while the flex sections, the rigid-to-flex transition, coverlay quality, bend reliability, and flex-specific plating are judged against IPC-6013. A complete rigid-flex acceptance package references both.
What are the most important IPC-6013 acceptance criteria for rigid-flex?
The transition zone (no resin/adhesive flow into the bend, clean coverlay registration, void-free bondline), the bend region (no adhesive squeeze-out, correct copper type, defined keepouts, no cracking), and the plated interconnect (barrel plating thickness, copper wrap, no barrel cracks at the flex-to-rigid junction). The plating and transition criteria are verified by microsection and are where Class 2 and Class 3 most often differ.
Do I need Class 3 for a rigid-flex board?
Only where the construction features require it — typically the transition and plated junctions in high-reliability products. Over-calling Class 3 across the whole board raises cost without improving field life; under-calling it and then demanding Class 3 evidence at incoming inspection causes disputes. Identify which features drive the class and state that on the drawing.
How is the IPC-6013 transition zone inspected?
Primarily by microsection on qualification or first-article lots: a cross-section through the rigid-to-flex boundary shows whether resin or adhesive has flowed into the flex, whether the coverlay terminates and bonds cleanly, and whether the bondline is void-free. Visual inspection per IPC-A-600 catches gross defects, but the bondline and plating evidence requires microsection.
Get a Rigid-Flex Inspection Plan
Send us your stackup, class target, and bend intent, and we will define the coupon and microsection strategy, the transition and plating acceptance criteria, and the test evidence package for your rigid-flex build — so procurement, engineering, and quality are all buying the same board. Request a quote or talk to our engineering team.
References:
- IPC — Association Connecting Electronics Industries. IPC-6013 Qualification and Performance Specification for Flexible and Rigid-Flex Printed Boards
- IPC-6012 Qualification and Performance Specification for Rigid Printed Boards
- IPC-2223 Sectional Design Standard for Flexible Printed Boards
