Direct Answer
IPC-600 classes define the acceptance criteria for bare PCB appearance and quality, dividing boards into Class 1, 2, and 3 based on intended end-use reliability. Class 1 is for general consumer products, Class 2 for dedicated service electronics, and Class 3 for high-reliability applications where failure is not acceptable. Your class selection directly controls inspection strictness, fabrication tolerances, and cost.
What IPC-600 Actually Covers
IPC-600 is the visual and dimensional acceptance standard for bare printed circuit boards. It establishes what constitutes an acceptable board at the point of fabrication, before any components are placed. The standard covers copper plating thickness, solder mask registration, hole wall quality, conductor width, surface finish, and cosmetic defects such as scratches, pits, and stains.
It is important to distinguish IPC-600 from related standards. IPC-A-600 is the companion document that applies to finished boards, while IPC-6012 specifies the performance requirements for rigid PCBs. For a deeper comparison of the finished-board acceptance criteria, see our article on IPC-A-600 Class 2 vs. Class 3: What Are the Main Differences?. The IPC-6012 document, meanwhile, focuses on electrical and mechanical performance rather than purely visual criteria. If you are deciding between those two classes for a rigid board, review our breakdown of IPC 6012 Class 2 vs Class 3: What Are the Main Differences.
The practical implication is that your class choice is not just a label. It changes what the fabricator inspects, how tightly they control their processes, and what defects they are allowed to ship. A Class 3 board with a minor solder mask misregistration might be rejected, while the same defect on a Class 1 board could be perfectly acceptable.
Class 1: General Consumer Electronics
Class 1 applies to products where the primary requirement is function at the lowest possible cost. These are typically disposable or short-life products where a field failure is inconvenient but not dangerous and does not cause significant economic loss.
Typical Class 1 applications include:
- Children's toys
- Low-cost consumer electronics
- Disposable medical sensors
- Simple LED lighting products
- Basic remote controls
For Class 1 boards, the fabricator has the most latitude in cosmetic criteria. Minor solder mask voids, slight conductor edge roughness, and small scratches are generally acceptable as long as the board functions electrically. Copper plating thickness requirements are at the lower end of the acceptable range, and hole wall quality tolerances are more relaxed.
The cost benefit of Class 1 comes from higher yield. A fabricator can accept boards that would be rejected under Class 2 or Class 3 criteria, which reduces scrap and lowers the per-board price. However, the reliability risk is real. If your product is likely to be repaired, reused, or exposed to thermal cycling, Class 1 may not be sufficient even if the product is consumer-grade.
Class 2: Dedicated Service Electronics
Class 2 is the default for most commercial and industrial electronics. It applies to products that need continuous, reliable performance over a reasonable lifetime, but where failure does not create a safety hazard or catastrophic economic loss.
Common Class 2 applications include:
- Industrial control systems
- Telecommunications equipment
- Computers and peripherals
- Automotive infotainment systems
- Medical devices that are not life-supporting
- Test and measurement instruments
Class 2 allows minor cosmetic imperfections as long as they do not affect the electrical function or long-term reliability. Solder mask registration can have slight misalignment, conductor width reductions are permitted within defined limits, and small voids in plated through-holes are acceptable if they do not compromise the hole wall integrity.
The inspection criteria for Class 2 are meaningfully tighter than Class 1. The fabricator must check copper plating thickness more carefully, verify hole wall quality with microsection analysis on a defined sampling basis, and control solder mask coverage more precisely. This increases the cost of fabrication slightly, but the reliability improvement is substantial for products that will operate for years.
Most PCB manufacturers default to Class 2 when no class is specified. If you are ordering a standard FR4 board with 1 oz copper and a standard green solder mask, you are almost certainly receiving a Class 2 board. This is why it is critical to state your class explicitly in your procurement documents.
Class 3: High-Reliability and Mission-Critical Electronics
Class 3 is reserved for products where failure is not an option. These are systems where downtime is unacceptable, where failure could cause injury or death, or where the cost of failure is catastrophic. Class 3 boards must perform continuously under harsh conditions and have extended service lives.
Class 3 applications include:
- Aerospace and avionics systems
- Military and defense electronics
- Life-support medical devices
- Implantable devices
- Automotive safety systems such as airbag controllers
- Missile guidance and launch systems
- Satellite communications equipment
For Class 3, the acceptance criteria are dramatically stricter. Copper plating thickness must be at the higher end of the specification range. Solder mask registration must be nearly perfect. Hole wall quality must be free of voids, cracks, and significant roughness. Conductor width reductions are tightly controlled, and any defect that could compromise long-term reliability under thermal or mechanical stress is cause for rejection.
The fabrication process for Class 3 boards requires more rigorous process control. The fabricator must perform more frequent microsection analysis, use tighter etch tolerances, and implement more comprehensive final inspection. This increases cost and lead time, but the resulting board is engineered for decades of reliable service.
> Practical note: If you are designing a Class 3 board, do not assume that your standard fabricator can produce it without process changes. Verify their capability statement and ask for microsection data from a pre-production coupon before committing to a full production run.
How Class Selection Affects Fabrication Processes
Your IPC-600 class choice does not just change inspection criteria; it changes how the board is actually fabricated. The tolerances required for higher classes force the manufacturer to use different process parameters and more careful control at each step.
Copper Plating and Hole Wall Quality
For Class 1, the fabricator can run plating lines at higher throughput with less monitoring. For Class 2, plating thickness is checked more frequently, and for Class 3, the plating process may need to be slowed down to achieve more uniform deposition in high-aspect-ratio holes.
Hole wall quality is one of the most significant differentiators. In Class 3, the plated copper in the through-hole must be free of voids, cracks, and nodules. This requires careful control of the electroless copper deposition step and the subsequent electroplating. The fabricator must also ensure that the drill quality is excellent, because rough hole walls from worn drill bits will result in poor plating adhesion.
Solder Mask Registration
Solder mask registration is the alignment between the solder mask pattern and the copper features beneath it. In Class 1, slight misregistration is acceptable as long as the mask still covers the traces. In Class 2, the mask must cover the traces but small gaps at the edges of pads are permitted. In Class 3, the mask must be registered tightly enough that there is no exposed copper on traces and no solder mask encroachment onto the pads that could affect solder joint formation.
This affects the fabrication process because tighter registration requires more precise imaging equipment and more careful handling of the board during the solder mask cure. Some fabricators use direct imaging (laser) for solder mask instead of traditional photo tools to achieve Class 3 registration.
Conductor Width and Etching
The minimum conductor width and spacing requirements are tighter for Class 3. This means the etch process must be more controlled to prevent undercutting, which reduces conductor width below the design value. The fabricator may need to use finer etch chemistries, more precise spray patterns, and tighter conveyor speed control in the etch line.
For heavy copper boards, the class selection becomes even more critical because the etching process is inherently less precise at higher copper weights. If you are working with heavy copper, review the Different Production Process Between Heavy Copper PCB and FR4 PCB to understand how the fabrication steps diverge.
Practical Example: Specifying Class for a Medical Device
Consider a medical device that monitors a patient's vital signs in a hospital setting. The device is not life-supporting, but a failure would require a replacement and could delay treatment. This is a Class 2 application under IPC-600.
Your stackup is a 6-layer FR4 board, 1.6 mm total thickness, with 1 oz copper on all layers. The critical parameters are:
- Minimum hole size: 0.3 mm
- Minimum copper plating thickness in holes: 20 µm (Class 2 requirement)
- Solder mask registration: ±75 µm
- Surface finish: ENIG with 3-6 µm gold over 3-6 µm nickel
In your RFQ, you should state:
- IPC-600 Class 2
- Minimum copper plating thickness: 20 µm in the barrel
- Solder mask registration: ±75 µm
- No solder mask voids on exposed pads
- Microsection report required for the first article
If you had specified Class 3 instead, the copper plating thickness requirement would be higher, the solder mask registration tolerance tighter, and the microsection sampling frequency greater. This would increase the board cost by an estimated 15-30% without providing any reliability benefit for a hospital monitoring device that will be replaced every few years.
Common Mistakes When Choosing an IPC-600 Class
Engineers make several recurring mistakes when specifying IPC-600 classes.
Assuming Class 3 is always better. Class 3 boards cost more and take longer to produce. If your product does not need the reliability margin, you are wasting money. A consumer drone does not need Class 3; it needs Class 2 at most.
Assuming your supplier defaults to Class 3. Most fabricators default to Class 2. If you do not specify a class, you will receive a Class 2 board. If your design requires Class 3, you must state it explicitly and verify that the supplier's inspection plan matches.
Confusing IPC-600 with IPC-A-610. IPC-600 applies to bare boards. IPC-A-610 applies to assembled boards. Your bare board can be Class 3, but if your assembly house uses poor soldering processes, the final product will still fail. The class of the bare board does not guarantee the reliability of the assembled product.
Ignoring the impact on assembly. A Class 3 board with tight solder mask registration will produce better solder joints because the solder paste will not be displaced by mask encroachment. This is particularly important for fine-pitch components. If you are using a reflow process, the solder mask quality directly affects the reflow outcome. Understanding the Differences Between Reflow Soldering and Wave Soldering will help you see why solder mask registration matters for assembly yields.
Not specifying the class in the RFQ. The class must be in your procurement documents. If it is not, you have no contractual basis to reject a board that does not meet your reliability expectations.
How to Verify the Class Before Production
Before you commit to a production run, verify that your fabricator can meet the class you have specified. Here is a practical verification process:
1. Request the capability statement. Ask the fabricator for their documented capability statement, which should list the maximum class they can produce and the inspection methods they use.
2. Review the inspection plan. Ask for their inspection plan for your class. This should include the sampling frequency for microsection analysis, the AOI coverage, and the final visual inspection criteria.
3. Request microsection data. For Class 2 and Class 3, ask for microsection data from a coupon that is representative of your board. The microsection will show the copper plating thickness in the hole barrel, the hole wall quality, and the integrity of the inner-layer connections.
4. Order a pre-production sample. If the board is complex or the reliability requirements are critical, order a small pre-production batch. Inspect it against the IPC-600 criteria for your class before approving the full production run.
5. Confirm the certificate of conformance. For Class 3, request a certificate of conformance that documents the inspection results and confirms that the boards meet the specified class.
> Caution: A fabricator's capability statement is a marketing document. The actual inspection data from your specific board is the only evidence that matters. Always request the data, not just the statement.
What to Include in Your RFQ
Your RFQ should be explicit about the class and the critical parameters. A well-written RFQ includes:
- The IPC-600 class (e.g., Class 2)
- The minimum copper plating thickness in holes
- The minimum conductor width and spacing
- Solder mask registration tolerance
- Surface finish requirements
- Whether microsection reports are required
- Whether a certificate of conformance is required
- The sampling plan for inspection (e.g., IPC-600 Class 2 sampling level)
If you are working with flexible circuits, the class requirements apply differently because the substrate is not rigid. Flexible boards have additional considerations for bend radius, flexural endurance, and coverlay registration. See our article on Flexible LED PCBs: Advantages, Applications, and Design Considerations for guidance on how flex materials change the fabrication and inspection picture.
The Cost and Reliability Tradeoff
The class you choose is a direct tradeoff between cost and reliability. Class 1 is the cheapest but has the highest field failure risk. Class 3 is the most expensive but offers the highest reliability margin. Class 2 sits in the middle and is appropriate for the majority of commercial and industrial products.
The cost difference between classes comes from several factors:
- Inspection time: Higher classes require more inspection time per board, which increases labor cost.
- Scrap rate: Higher classes reject more boards, which increases the effective cost of each shipped board.
- Process control: Higher classes require tighter process control, which may mean slower production lines and more frequent equipment calibration.
- Materials: Higher classes may require better laminate materials with tighter thickness tolerances.
For a typical 4-layer FR4 board, the cost difference between Class 2 and Class 3 is roughly 15-30%. The difference between Class 1 and Class 2 is smaller, typically 5-15%.
When to Involve Your Manufacturer
Involve your PCB manufacturer early in the design process if you are targeting Class 3 or if your design has features that push the limits of the class. This includes:
- Very small holes (below 0.2 mm)
- High layer counts (above 12 layers)
- Heavy copper (above 3 oz)
- Fine-pitch BGA packages with tight solder mask registration requirements
- Controlled impedance with tight tolerances
For these designs, the fabricator can tell you whether your stackup and feature sizes are achievable at your target class. They can also recommend design changes that will improve yield without compromising reliability.
At Omini, we work with customers to match the IPC-600 class to the actual reliability requirements of the product. We provide inspection data and microsection reports so you can verify that the boards meet the specified class before assembly begins. If you are unsure which class is appropriate, start with the application requirements and work backward to the class rather than starting with the class and hoping it fits the application.