What Is X-Out PCB? Causes, AQL Standards & Should You Accept It

If you’ve ordered PCBs in panel format, you’ve probably encountered the term “X-out” during the quoting process. Your manufacturer may have asked whether you’d accept X-out boards, or you noticed a price difference between the two options. Understanding X-out PCBs helps you make smarter procurement decisions and potentially save significant costs.

In this guide, I’ll explain what X-out boards are, why they happen, the industry standards around them, and help you decide whether accepting them makes sense for your project.

What Is an X-Out PCB?

An X-out PCB (also called “cross-out board,” “X-board,” or “crossed board”) is a defective printed circuit board within a panelized array that has been marked with an “X” to indicate it shouldn’t be used. The marking is typically done with a permanent marker, creating a large, visible X across the board surface.

When PCBs are manufactured in panels containing multiple identical boards, some individual units inevitably fail quality inspection. Rather than scrapping the entire panel because of one defective board, manufacturers mark the bad ones with an X and ship the panel with the good boards intact.

Here’s the important part: you don’t pay for X-out boards. They’re shipped within your panels but aren’t counted toward your order quantity. If you order 100 boards and some panels contain X-outs, the manufacturer produces additional panels to ensure you receive your full 100 good boards.

Why Do X-Out PCBs Occur?

X-out boards aren’t necessarily a sign of poor manufacturing quality. PCB fabrication involves over 100 distinct processes, and every board has some chance of developing a defect. Even top-tier manufacturers experience X-outs—the difference is in the rate and how they’re managed.

Common Causes of X-Out Boards

Panel Size Affects X-Out Probability

The more boards per panel, the higher the chance of having at least one X-out. If each board has a 2% defect probability:

This is why high-count panels with many small boards almost inevitably contain some X-outs—it’s simply statistics, not poor quality.

Industry Standards for X-Out PCB Acceptance

While there’s no single universal standard, the PCB industry has widely accepted guidelines:

Typical AQL (Acceptable Quality Level) Limits

Additionally, total X-out boards across the entire shipment should not exceed 10% of total quantity.

IPC Class Considerations

IPC-6012 defines three product classes that influence X-out expectations:

• Class 1 (General Electronics): Higher X-out tolerance acceptable
• Class 2 (Dedicated Service): Moderate standards
• Class 3 (High Reliability): Minimal or no X-outs expected

How X-Out PCBs Affect SMT Assembly

One of the biggest considerations is how X-out boards impact your assembly process. Many procurement teams focus only on PCB price, but assembly efficiency can significantly affect total cost.

SMT Line Handling Methods

Modern assembly lines handle X-outs through several methods:

Bad Mark Recognition: The SMT machine’s vision system detects a specific mark and skips that board position. This requires consistent marking and programming time.

Fiducial-Based Skip: A fiducial on the defective board is blocked, causing the machine to skip it automatically.

Manual Programming: Operators inspect incoming panels and program skip positions for each batch containing X-outs.

Batch Segregation: Panels with X-outs are separated and processed with special programming, while perfect panels run at full speed.

Efficiency Impact

For a 4-up panel with 1 X-out board (25% affected):

• Component placement efficiency drops to ~75%
• Overall line throughput decreases 10-15%
• Risk of component waste if skip fails

For high-volume automated assembly, this efficiency loss can be significant and may outweigh PCB cost savings.

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What Is X-Out PCB? Causes, AQL Standards & Should You Accept It

Should You Accept X-Out PCBs? Decision Framework

When to Accept X-Out Boards

Accepting X-outs makes sense when:

• Prototyping or development work — Lower cost, faster delivery
• Cost-sensitive products — Consumer electronics, hobbyist items
• Manual assembly operations — Operators easily skip marked boards
• Many boards per panel — Perfect panels are expensive or impossible
• Flexible SMT capability — Your assembler handles X-outs efficiently

When to Reject X-Out Boards

Require perfect panels when:

• High-reliability applications — Medical, aerospace, automotive safety
• Contract requirements — Customer mandates no X-outs
• High-volume automated assembly — Efficiency matters more than PCB savings
• Simple board designs — Low X-out rates make premium small
• IPC Class 3 requirements — Quality system demands it

Cost Comparison Example

The price premium for no X-out typically ranges from 5% for simple boards to 50%+ for complex HDI designs with many boards per panel.

X-Out PCB Marking Methods

Most manufacturers use permanent markers as the standard method. If you need automated skip detection, specify drilled hole marking or discuss options with your supplier.

Best Practices for Managing X-Out PCBs

Document Your Policy

Include X-out terms in your purchase specifications:

X-Out Policy:☐ Accept X-out (standard AQL limits)☐ No X-out accepted (premium pricing applies)Maximum per panel: ___Maximum per shipment: ___%

Communicate with Your Assembler

Before ordering PCBs, discuss with your contract manufacturer:

• Their preferred handling method
• Any additional charges for X-out panels
• Efficiency impact estimates

Monitor Performance

Track X-out rates by supplier and technology. Investigate if rates exceed:

• 3% for simple 2-4 layer boards
• 5% for standard multilayer
• 10% for complex/HDI designs

Frequently Asked Questions

What exactly causes a board to be marked as X-out?

Boards fail electrical testing (opens, shorts) or visual inspection during pcb manufacturing. The X marking prevents defective boards from reaching assembly or field use.

Do I pay for X-out boards?

No. The manufacturer ensures you receive your ordered quantity of good boards, producing extra panels if needed.

Can X-out boards ever be used?

Never in production. However, they’re useful for training, fixture development, and destructive testing.

How do SMT machines skip X-out boards?

They don’t automatically recognize X markings. Machines must be programmed to skip specific positions, or boards need machine-readable markers like drilled holes.

What X-out rate should I expect?

Simple 2-layer boards should have less than 1-3% X-out rate. Standard 4-6 layer boards typically see 2-4%. Complex multilayer boards (8+ layers) commonly have 3-5%. HDI and advanced technology boards may see 5-15% or higher. Additionally, more boards per panel increases the probability of X-outs appearing in any given panel, even if the per-board rate remains low.

Conclusion

X-out boards are a normal part of PCB manufacturing—not a quality failure. The decision to accept or reject them depends on your specific situation: product requirements, assembly process, volume, and cost sensitivity.

For most prototype and low-volume projects, accepting X-outs saves money without meaningful quality impact. For high-reliability or high-volume production, the no X-out premium may be worthwhile.

Whatever you decide, document your policy clearly, communicate with suppliers and assemblers, and make it a deliberate choice rather than a default. That’s the mark of smart PCB procurement.

Quick Reference: X-Out Decision Matrix

Useful Resources

Industry Standards:

• IPC-6012: Qualification and Performance Specification for Rigid Printed Boards
• IPC-A-600: Acceptability of Printed Boards
• IPC-9252: Guidelines for Electrical Testing

Organizations:

• IPC (www.ipc.org) — Industry standards, training, and certification programs
• SMTA (www.smta.org) — Assembly technology resources and networking