PCB Vias 101: Tented vs. Untented

July 23, 2025Hooman Javdan

PCB Vias 101: Tented vs. Untented (and When to Go Beyond Tenting)

Ever notice some vias on a PCB are covered by solder mask while others are left exposed? That design choice isn’t random—it directly impacts manufacturability, reliability, testability, and cost. Here’s a practical guide you can reference the next time you’re laying out a board.

What Exactly Is a Via?

A via is a plated hole that carries an electrical connection between copper layers in a multilayer PCB. Because vias expose copper, designers decide whether to cover them with solder mask (“tent” them) or leave them open.

via

Tented Vias (Covered With Solder Mask)

Definition: The via’s hole and annular ring are covered—“tented”—by the solder mask layer.

Why tent?

Oxidation protection: Mask keeps air/moisture off copper.
Stops solder steal: Open vias can wick solder away from nearby pads during reflow.
Reduces shorts in dense areas: The mask adds insulation between closely spaced copper features.

Watch-outs: Simple masking can crack, blow off during reflow, or fail under aggressive cleaning. If the design is mission-critical, tenting alone may not be robust enough.

Untented (Exposed) Vias

Definition: The via opening is left unmasked.

When it’s useful:

Test access: Low-cost probe points during production or debug.
Thermal or solder pathways: Sometimes you intentionally want solder or heat to flow through the via.

Risks:

Solder wicking/bridging: If an exposed via sits too close to a component pad, it can siphon solder or create a bridge—hurting yield.

Beyond Tenting: Plugging, Filling & Capping (IPC-4761)

For high-reliability or high-density designs (think BGAs), consider the options defined by IPC-4761:

Type I/II – Tented: Mask on one or both sides; may not fully seal the hole.
Type III/IV – Plugged: Via hole is plugged (often epoxy) from one or both sides; mask may or may not cover it.
Type V – Filled: Hole completely filled (resin/conductive) and planarized.
Type VI – Filled & Capped: Filled then covered with copper or mask to create a flat surface—ideal for via-in-pad.
Type VII – VIPPO (Via-in-Pad Plated Over): Filled, capped, and plated to form a solderable pad surface.

These add cost but dramatically improve reliability, planarity, and cleanliness.

DFM Tips & Common Mistakes

Mind the spacing: Keep exposed vias away from component pads to avoid solder wicking.
Via size matters: Large vias are harder to tent reliably—consider plugging or filling.
Avoid “flux buckets”: Half-tented vias can trap flux/chemicals.
Communicate early: Masking processes vary by fabricator—clear fab notes prevent surprises.

Quick Checklist for Choosing Via Treatments

Need test access? → Leave it open or use dedicated test pads.
Via near a pad? → Tent or fill it to prevent solder steal.
Multiple reflow/cleaning cycles? → Prefer filled/capped options.
Under a BGA/fine-pitch part? → VIPPO or filled/capped per IPC-4761.
Cost-sensitive and moderate reliability? → Standard tenting may suffice.

FAQ

Do tented vias always stay sealed?
Not always—mask can crack or blow out. For harsh environments, choose plug/fill options.

Can I leave all vias exposed for probing?
You could, but it increases solder-bridging and cleanliness risks. Dedicated test pads are cleaner.

What standard defines via protection methods?
IPC-4761 lists tented, plugged, filled, capped, and VIPPO options.

Need Help? Talk to Circuits Central

Circuits Central delivers complete turnkey electronics manufacturing—component sourcing, PCB assembly, testing, programming, quality control, and post-production support. We’ll help you lock in the right via strategy before you hit the production line.

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