Two flex PCBs can be built from the same Gerber files and still be held to completely different quality bars. The difference is the IPC-6013 performance class you specify. Ask for Class 2 when your program needs Class 3, and you may accept boards that will not survive the field; ask for Class 3 when Class 2 is enough, and you pay for margin you do not need.
This guide explains what IPC-6013 is, how Class 2 and Class 3 actually differ, and how to choose the right class for your flex or rigid-flex build. When you are ready to spec a board, the IPC-6013 spec & RFQ checklist builder turns these decisions into a checklist you can send to a manufacturer.
What IPC-6013 Is
IPC-6013 is the qualification and performance specification for flexible and rigid-flex printed boards. It is the flex-specific companion to IPC-6012 (rigid boards) and sits under the IPC-6011 umbrella. Where a design standard like IPC-2223 tells you how to design a flex circuit, IPC-6013 defines what the finished board must meet — conductor geometry, plating thickness, annular ring, dielectric integrity, markings, and the inspection and test criteria used to accept or reject it.
IPC-6013 defines performance classes rather than a single pass/fail line. The class you name on your drawing or purchase order sets the acceptance criteria the manufacturer builds and inspects to.
The Three IPC Performance Classes
IPC uses a common three-class model across its performance specs:
- Class 1 — General Electronic Products. Limited life, function is the only requirement. Rare for flex; mostly disposable or low-cost consumer items.
- Class 2 — Dedicated Service Electronic Products. Continued performance and extended life are required, and uninterrupted service is desirable but not critical. The workhorse class for most industrial, consumer and commercial flex.
- Class 3 — High-Reliability Electronic Products. Continued high performance or performance-on-demand is critical. Equipment downtime cannot be tolerated, and the end use may be life-support or mission-critical. Typical for medical, automotive safety, and demanding industrial systems.
Almost every real flex PCB decision comes down to Class 2 vs Class 3, so that is where the rest of this guide focuses.
IPC-6013 Class 2 vs Class 3: What Actually Changes
Moving from Class 2 to Class 3 tightens acceptance criteria across several dimensions. The exact numeric limits live in the current revision of IPC-6013 and depend on board construction, but the direction of every requirement is the same: Class 3 leaves less margin for defects.
| Requirement | Class 2 | Class 3 |
|---|---|---|
| Overall intent | Continued service, life important | Continued performance on demand, downtime unacceptable |
| Annular ring (plated holes) | Minimum ring allowed, some breakout permitted | Larger minimum ring, effectively no breakout |
| Plating & defect allowances | Wider tolerance on voids, nicks, dishdown | Tighter limits on voids and copper defects |
| Conductor width/spacing reduction | More reduction tolerated | Minimal reduction from design values |
| Coverlay & registration | Standard registration tolerance | Tighter registration, less misalignment |
| Inspection & documentation | Sampling typical | More inspection, coupons and records expected |
This table shows the direction of the requirements, not exact acceptance values. The precise limits (annular-ring dimensions, void percentages, conductor-width reduction, etc.) are defined by the current revision of IPC-6013 and vary with board construction — always work to the specific revision your program cites.
The practical takeaway: Class 3 is not a different board, it is a tighter version of the same board — smaller allowable defects, larger safety margins on annular ring and plating, and more inspection evidence. That is why Class 3 usually carries higher cost and can affect yield and lead time.
Static vs Dynamic Flex Changes the Answer
Performance class is only half the specification. The other half is whether the circuit is static (flex-to-install) or dynamic (repeatedly flexed in service).
- Static flex is bent once during assembly and then stays put. A wider material set and standard copper are usually fine.
- Dynamic flex bends thousands to millions of times. It typically needs adhesiveless polyimide, rolled-annealed (RA) copper, a larger bend radius, and often strain relief and coverlay placement designed for the neutral bend axis.
A dynamic Class 3 application (for example, a medical device hinge that flexes for years) stacks the strictest material and acceptance requirements together. State both the class and the flex type on your RFQ so the stack-up is engineered correctly the first time. Our flex PCB reliability testing guide covers the bend, thermal-cycling and coupon tests that back these classes up.
How to Choose the Right Class
Use this as a starting point, then confirm with your manufacturer:
- Choose Class 2 for most industrial, consumer and commercial electronics where a field failure is inconvenient but not dangerous or business-critical.
- Choose Class 3 for medical devices, automotive safety-relevant systems, aerospace-grade industrial equipment, and anything where a single failure carries safety or major cost consequences.
- Do not over-specify. Class 3 on a product that only needs Class 2 raises cost and can hurt yield without adding useful reliability.
- Do not under-specify. If your end use is life-support, safety, or high-cost downtime, Class 2 acceptance limits may pass boards that will not last.
When medical reliability is in scope, the quality system behind the board matters as much as the class. Our flex boards are produced at ISO 9001 and ISO 13485 certified manufacturing facilities, and we build to IPC-6013 Class 2 and Class 3 requirements depending on your program — see our flex PCB manufacturing service for capabilities.
From Class to Quote
Once you know your class, flex type, layer count, base material and test requirements, you have everything a manufacturer needs to quote accurately. The fastest way to capture it is the IPC-6013 spec & RFQ checklist builder — pick your options and it generates a clean specification summary and a checklist you can copy into your enquiry or send straight to an engineer for a free DFM review.
Frequently Asked Questions
Is IPC-6013 Class 3 the same as "military grade"?
No. Class 3 is IPC's high-reliability commercial class. Some defense, avionics and space programs layer additional space- or military-specific requirements on top of Class 3 — through separate IPC space/military addenda or customer program specifications — but Class 3 by itself is a commercial high-reliability standard used widely in medical and automotive work. Confirm the exact standard, addendum and revision your program requires with your manufacturer.
Does Class 3 cost more than Class 2?
Usually yes. Tighter annular ring, smaller allowable defects and more inspection reduce yield and add documentation, which raises unit cost and can extend lead time. The premium is worth it when downtime or failure is unacceptable, and wasteful when it is not.
Can I mix classes on one board?
You specify a single default class for the board, but you can call out specific features or nets to a higher class through your drawing notes. Discuss any mixed-class requirements with your manufacturer early so the stack-up and inspection plan account for them.
What is the difference between IPC-6013 and IPC-6012?
IPC-6013 covers flexible and rigid-flex printed boards; IPC-6012 covers rigid boards. They share the same class model (1/2/3) but have construction-specific requirements. A rigid-flex board is judged against IPC-6013.
