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What are tented vias?

Tented vias have a mask covering over a via opening. The covering forms a membrane; it does not by itself mean the hole is filled through its depth. The intended side, mask process, hole dimensions and neighboring openings determine what must be reviewed. Treat tenting as a specified surface feature rather than a universal default for every via on a board.

The immediate design question is usually whether the location should remain exposed or covered. Answer it using assembly needs, electrical-test access and the fabricator's confirmed process. If the requirement is a filled cavity with a metal surface, use the PCB via-filling guide instead. That distinction avoids pricing and manufacturing a different structure from the one the designer intended.

Separate mask artwork from a manufactured tent

In CAD, removing a solder-mask opening can express the intention to cover a via. It does not demonstrate that a particular mask system will form and retain a membrane across the actual hole. The fabricator needs to evaluate the opening size, film or ink process, material behavior and required final condition. A layer image is a manufacturing instruction, not inspection evidence.

Tenting one side is also different from tenting both sides. Identify the component side, solder side or named outer copper layer rather than relying on an ambiguous 鈥渢op.鈥� The reference must remain meaningful when the board is rotated in a panel or assembled on both sides. Explain any selective exclusions, including probe points or openings that serve another process purpose.

Check the space between a tent reservation and a pad opening

The worksheet models a circular via beside a circular exposed pad opening. It reserves a stated amount of mask beyond the via opening, subtracts the adjacent opening radius and a combined relative registration allowance, then compares the remaining corridor with your entered requirement. Use controlled dimensions for the intended mask side.

In the illustrative example, the center spacing is 0.50 mm. The neighboring opening radius is 0.20 mm, the via radius plus reserved overlap is 0.15 mm, and the combined relative allowance is 0.05 mm. The remaining corridor is 0.10 mm. Compared with the example requirement of 0.08 mm, the calculated margin is 0.02 mm. None of these numbers is a universal mask capability.

A negative corridor means the requested reservation overlaps the adjacent exposed opening under the entered assumptions. A positive corridor can still be smaller than the project requirement. Both conditions should remain visible in the review. Increasing an arbitrary mask expansion to clear one pad may consume the same narrow corridor that the tent needs, so evaluate the two features together.

A clear corridor does not prove the hole can be tented

The calculator is a plan-view geometry check. It does not predict film bridging, pinholes, cured thickness, adhesion or behavior during subsequent processing. These depend on the actual mask process and construction. Record the source of the hole-size and film requirements rather than turning the worksheet's example into a fabrication rule.

A mask tent should not be described as a hermetic seal. Its purpose and expected condition must be agreed for the application. If the requirement includes environmental protection, contamination control or a defined sealing performance, communicate that separately and ask what process and evidence are needed. A covered opening in artwork is not sufficient evidence for those claims.

The solder-mask engineering page explains the broader mask task. The IPC-4761 classification guide distinguishes covering and filling terminology. The official is useful for understanding the document's scope, but the licensed applicable standard, revision and drawing determine the actual requirements.

Decide from the solder interface outward

First identify whether the via is near a solder land, within a solder land, or outside the component-attachment area. A nearby opening can affect the available mask geometry. A via inside the land raises a separate question about the surface presented to solder paste. Do not assume that simply tenting an in-pad via provides the same assembly interface as a deliberately filled and metal-capped construction.

For a dense package, show the mask openings and the proposed via treatment in the assembly review. Include the stencil and land-pattern requirements relevant to that package. The package manufacturer may provide an application-specific recommendation, but it should be checked against the actual board and process rather than expanded into a general rule for all components.

When the task concerns a BGA land, continue with the BGA via-in-pad review. When the task is a nearby tented via, use this page's corridor result to identify the local conflict. This separation keeps the question concrete: whether the assembly needs an exposed solderable surface, a protected adjacent opening, or a different arrangement altogether.

Preserve intentional access for inspection and probing

An exposed via can sometimes be part of a test-access strategy, but that role should be deliberate. Covering it may remove a contact location expected by a fixture or test program. Conversely, leaving every via exposed does not create a well-designed test plan. Identify which nets need access, where the probe can reach and which finished surfaces are acceptable for the intended method.

Review both assembled and bare-board needs. A location reachable on the unassembled board may be obstructed after components are installed. A surface suitable for one probing method may not serve another. The PCB electrical-testing page addresses electrical verification separately from mask appearance; use it to define the test task, then preserve the required access in the mask data.

The same discipline helps during rework. If a repair process expects an exposed connection or inspection location, covering it should be an explicit design decision. Record the change so that assembly, test and service teams do not discover different assumptions after boards have been manufactured.

Resolve an adjacent-pad conflict without guessing

Consider an illustrative board where a via sits close to an exposed component pad. The initial mask artwork shows a broad opening around the pad and a tent over the via. A geometry review shows that the two requested areas leave less than the agreed mask corridor. The issue is not solved merely by labeling the via 鈥渢ented鈥� in a fabrication note.

Possible design discussions include moving the via, changing the routing approach or revisiting an approved opening arrangement with the assembly team. Each option affects a different requirement. Reducing the pad opening without checking component attachment could exchange one problem for another. Moving the via may affect trace clearance or the layer-access plan. Compare the complete local geometry after the revision.

Keep the original and revised dimensions in the review record. State the mask process and registration basis used for the comparison, then ask the fabricator to confirm the proposed feature. The worksheet brief can document the arithmetic; it cannot substitute for that process confirmation.

Export instructions that survive the handoff

Use a consistent board revision across copper, drill, mask and assembly data. If selective tenting is required, provide an unambiguous map or rule tied to the released via populations. Distinguish mechanical and component holes from vias. Check that the fabrication notes do not contradict the actual mask layers, particularly after copying a rule from another design.

Before asking for a quotation, send the intended treatment, relevant hole dimensions, side definitions and any constrained neighboring pads. Identify whether process alternatives are acceptable. A focused question such as 鈥渃an this specified hole group be covered on L1 with this mask arrangement?鈥� is more useful than a generic request for the smallest tentable via.

For a broader build discussion, the HDI PCB manufacturing page provides the construction route. You can also send the drawing directly through Contact. Completing the calculator is optional, and its inputs are not automatically transferred to the enquiry form.

Tenting questions before fabrication