PCB Via Tenting: When to Use It, and How to Specify It Correctly

Vias are the plated holes that carry signals between layers of a PCB. Left uncovered, they can trap solder paste, moisture, and flux residue — problems that show up as weak joints, shorts, or long-term corrosion. Via tenting is the simplest and lowest-cost way to prevent this: covering the via with solder mask so the copper is no longer exposed.

This guide focuses on the practical decision every designer eventually faces — should this via be tented, and how do I tell my fabricator exactly what I want — rather than the full theory of via protection methods. For a complete comparison of tenting versus plugging versus filling (including the IPC-4761 classification), see our engineering guide to via tenting, plugging, and filling.

On This Page

• What Is Via Tenting?
• Why Tent a Via?
• When Should You Tent a Via? (The Size Rule)
• When Should a Via Be Left Exposed Instead?
• How to Specify Via Tenting in Your Gerber Files
• Limitations of Tenting
• FAQ

What Is Via Tenting?

Via tenting covers a via with a layer of solder mask so the hole is sealed rather than left as bare, exposed copper. The mask "bridges" the opening the way a tent covers the ground beneath it — hence the name. Tenting can be applied to one side of the board (single-sided) or both sides (double-sided).

Why Tent a Via?

Tenting is used to protect vias from conditions that can degrade a board over its lifetime:

• Prevents solder wicking — on wave-soldered through-hole boards, an untented via near a pad can pull solder down into the hole instead of forming a proper joint.
• Blocks contamination — moisture, flux residue, and dust cannot settle in a sealed via, which reduces the risk of corrosion over time.
• Reduces short-circuit risk — sealed vias can't bridge to adjacent conductive material during assembly or in service.
• Keeps cost low — tenting adds no extra manufacturing step beyond standard solder mask application, unlike plugging or resin filling.

When Should You Tent a Via? (The Size Rule)

Whether a via can be reliably tented depends mainly on its diameter. As a general rule used across the industry:

• Vias 12 mil in diameter or smaller tent reliably with standard LPI (liquid photoimageable) solder mask.
• Vias in the 12–15 mil range can often still be tented, but reliability starts to drop as diameter increases.
• Vias larger than 15 mil are generally too large for the solder mask to fully bridge, and the "tent" is more likely to leave a small pinhole opening.

You should specifically tent vias in these situations:

• Vias located close to SMT pads, to stop solder paste from wicking into the hole during reflow.
• Vias used in dogbone-style BGA breakout routing, where the via sits directly next to the pad escape.
• Through-hole boards that will be wave soldered, to keep solder from flowing through the via to the opposite side.

When Should a Via Be Left Exposed Instead?

Tenting isn't always the right call:

• Larger vias (>15 mil) are better left exposed and protected by the board's surface finish (such as ENIG) rather than relying on a solder mask bridge that may not fully close.
• Thermal vias under an exposed pad (e.g., under a QFN or power device) should generally not be tented — a sealed tent can trap outgassing during reflow and cause voiding in the thermal joint. Leaving them open, or fully resin-filled and capped, gives a cleaner thermal path.
• Test or rework points during prototyping are sometimes left exposed intentionally so vias can be probed or reflowed for debugging.

How to Specify Via Tenting in Your Gerber Files

Miscommunication about via tenting is a common source of DFM delays. To avoid a back-and-forth with your fabricator:

1. Set it in your CAD tool before export. Most PCB design tools let you control solder mask expansion/clearance per via; setting the mask clearance to zero (or below the via's annular ring) is what creates the tent.
2. Call it out in your fabrication notes — state explicitly which vias (or via classes) should be tented, single- or double-sided, especially if your design mixes tented and exposed vias.
3. Check the rendered Gerber output before submitting. Solder mask layer errors are easy to miss visually in your CAD tool but obvious once rendered. You can drag and drop your files into our free online Gerber viewer to confirm which vias are actually tented versus exposed before you order.
4. Run a DFM check. Our HQDFM design analysis tool flags via tenting and solder mask clearance issues automatically, so undersized tenting or inconsistent settings get caught before fabrication instead of after.

Limitations of Tenting

Tenting is cost-effective, but it isn't a perfect seal. Because LPI solder mask is applied as a liquid and cured afterward, it has to bridge across the via opening rather than being pressed into it. On larger vias, or with inconsistent process control, this bridge can leave a small pinhole rather than a fully closed tent — which defeats the purpose of tenting in the first place. This is one reason via plugging or resin filling is specified instead for high-reliability applications like aerospace, medical, and high-density BGA designs. Our via protection comparison guide covers when it's worth paying the extra cost for plugging or filling instead of tenting.

Frequently Asked Questions

What is the maximum via size for reliable tenting?

As a general guideline, vias up to about 12 mil in diameter tent reliably with standard LPI solder mask. Above roughly 15 mil, the solder mask is less likely to fully bridge the opening, and plugging or filling becomes the more reliable choice.

Does via tenting affect electrical performance?

Tenting itself doesn't change the electrical properties of the via — the copper barrel still carries the signal. Its role is purely protective (moisture, contamination, and solder wicking), not electrical.

Is via tenting required for BGA designs?

It's not a formal requirement, but it's standard practice for vias used in dogbone-style BGA escape routing, since untented vias next to a BGA pad can wick solder paste away during reflow and produce a weak joint.

What's the difference between via tenting and via plugging?

Tenting bridges the via opening with a layer of solder mask only. Plugging partially or fully fills the via barrel itself with a non-conductive material (such as epoxy resin) before the surface is covered. Plugging costs more but seals more reliably, especially on larger vias. See our tenting vs. plugging vs. filling comparison for a full cost and reliability breakdown.

Which standard defines via tenting classifications?

IPC-4761, "Design Guide for Protection of Printed Board Via Structures," is the industry standard that defines the different via protection types, including tenting, plugging, filling, and capping.

Ready to Order?

Whether you're finalizing via tenting settings on a new design or need a second look before submission, we can help.

Get an Instant PCB Quote · Run a Free DFM Check · Talk to an Engineer