PCB Via Explained: Tenting vs. Opening

When placing a PCB order, many engineers and buyers often encounter a common question: What should I choose—via tenting (cover oil) or via opening? This confusion is especially common when design files are not created according to standard conventions. Mixing up pad (plated through-hole for components) and via (conductive hole for interlayer connection) can lead to serious manufacturing errors, miscommunication, and even customer complaints.

This article explains the difference between via tenting and via opening, highlights the pad vs via attribute issue, and shows how to design files correctly in software like Protel and PADS.

Via Tenting (Via Cover Oil) vs. Via Opening

Via Tenting

• The via is covered with solder mask (oil ink).

• Copper around and inside the via is not exposed.

• Purpose: insulation, preventing solder from flowing into the via, reducing oxidation, and avoiding shorts under fine-pitch components such as BGAs.

Via Opening

• The solder mask is opened around the via pad, leaving copper exposed.

• Vias can be plated with surface finishes like ENIG or HASL.

• Purpose: test point accessibility, heat dissipation, and occasionally additional soldering.

Summary:

• Via tenting = covered, non-exposed, protected.

• Via opening = exposed, solderable, testable.

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The Pad vs. Via Confusion

One of the most frequent issues in customer design files is mixing up pads and vias:

• Some designers use pad attributes for vias, or via attributes for component holes.

• This inconsistency causes manufacturing errors, such as component holes being mistakenly covered with solder mask or conductive vias being left open.

For flex PCB manufacturers, CAM engineers sometimes “fix” these problems based on experience. While this helps production, it also means the designer never realizes their file is non-standard. This creates long-term risks and recurring complaints.

Rule of thumb:

• Pad = component hole (plated through-hole for connectors, components, or plug-in parts).

• Via = interlayer connection hole.Always use the correct attribute in your CAD software.

Common Problems When Files Are Incorrect

1. Gerber Conversion Issues

If the Gerber file is exported incorrectly, the factory cannot distinguish between vias and pads.

• Any hole with a solder mask opening will be treated as via opening.

• If the order specifies via tenting, but the file has all vias open, the circuit board may suffer shorts or solder wicking problems.

2. Pad and Via Mixed Usage

• If a pad is mistakenly defined as a via, it may get covered with solder mask, making it impossible to solder components.

• If a via is mistakenly defined as a pad, it may be opened, causing unnecessary exposure or oxidation.

How to Design Via Tenting Correctly in Protel and PADS

Protel / Altium Designer:

• In the via properties, there is a “Tenting” option.

• Checking this box means the via will be covered with solder mask (via tenting).

PADS:

• When exporting solder mask layers, there is an option for via opening.

• If you select via under “solder mask top,” all vias will be opened.

• If you leave it unchecked, vias will be tented (covered).

Best Practices for Designers and Buyers

1. Always differentiate pad and via attributes clearly.

2. When sending original design files, specify whether vias should be tented or opened.

3. When sending Gerber files, carefully review the solder mask layers to confirm that they match your intention.

4. Never rely on the factory to “guess” your intent—factories process files as provided.

   
   

Conclusion

Choosing between via tenting and via opening is not just a checkbox—it directly impacts PCB reliability, solderability, and testing. The key is to maintain strict pad vs via discipline in your design files and double-check Gerber exports before submitting them to the flex PCB manufacturer.

At Flex Plus, we specialize in flexible PCB and rigid-flex PCB, and we understand how critical correct file preparation is to avoid production delays and costly mistakes. If you have questions about via tenting, via opening, or PCB manufacturing standards, our engineering team is ready to help.

Contact us today to review your flex PCB design files and ensure smooth, error-free production.

Email: info@flexplusfpc.com

FAQ

Q1: What is via tenting in PCB design?

Via tenting means covering vias with solder mask (cover oil), so the copper pad is not exposed. This prevents solder wicking, oxidation, and shorts in high-density areas such as BGA packages.

Q2: What is via opening in PCB design?

Via opening means leaving the via pad exposed (solder mask opening). This allows for soldering, electrical testing, or improved heat dissipation.

Q3: When should I choose via tenting instead of via opening?

Choose via tenting if your PCB has BGAs, fine-pitch components, or if you want to prevent solder leakage.

Choose via opening if you need test points, additional solder joints, or better thermal conductivity.

Q4: What is the difference between pad and via?

Pad is a plated hole designed for soldering components (like resistors, connectors, ICs).

Via is a conductive hole only used to connect copper layers inside the PCB.

Q5: How do I set via tenting in CAD tools like Protel or PADS?

In Protel: use the “Tenting” checkbox in via properties.

In PADS: during Gerber export, uncheck vias in the solder mask output if you want via tenting.