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To the data check →An open via next to a pad drinks solder paste. Closing it is routine — but there are five different ways to do it, they cost very different amounts, and picking the wrong one causes voids rather than preventing them.
IPC-4761 names seven via protection types; four of them matter in practice. Tented means solder resist bridges over the hole from one or both sides without entering it — cheap, and only reliable up to about 0.3 mm diameter. Plugged means resist is pushed into the hole. Filled means the hole is completely filled, usually with a non-conductive epoxy, then planarised. Filled and capped adds a plated copper lid, which is what makes via-in-pad possible.
The failure everyone eventually meets is one-sided closure. Tent a via from the top only and the hole becomes a sealed pocket containing air and residual process chemistry. At reflow that expands, blows through the resist and leaves a void — often taking the neighbouring solder joint with it. Close both sides or neither.
A via in or beside a pad drains paste down the barrel during reflow. Closing it keeps the solder volume where the joint needs it.
Filled and capped vias let the via sit inside the component pad — essential below 0.4 mm BGA pitch where there is nowhere else to escape.
Closed vias keep flux residue, cleaning fluid and conformal coating out of the barrel, which matters in high-voltage and high-humidity designs.
| Type | Method | Suitable for | Cost |
|---|---|---|---|
| Tented, one side | Resist over the hole | Not recommended — outgassing risk | lowest |
| Tented, both sides | Resist over both openings | Ø ≤ 0.3 mm, not in pads | low |
| Plugged | Resist pressed into hole | Ø ≤ 0.5 mm, general protection | low |
| Filled | Epoxy fill, planarised | Thermal vias, flat surface needed | medium |
| Filled + capped | Epoxy fill, copper plated over | Via-in-pad, BGA escape | high |
| Conductive fill | Silver-filled epoxy | Thermal and current-carrying vias | high |
| Max. diameter | 0.5 mm plugged | Larger holes need filling | — |
| Flatness after cap | ± 15 µm | Required for reliable BGA placement | — |
Guide values for pre-selection. Binding values are confirmed per project against your data.
The points below are what most often comes back as a query after data review. Settling them before layout freeze saves a loop.
A sealed pocket of air and process chemistry expands at reflow and blows out through the resist. Specify both sides, or leave the via open.
Plugging with resist is not enough inside a solder pad — the surface will not be flat and the placement suffers. Filled with epoxy and plated over is the only reliable form.
Thermal vias under a package often want conductive fill while signal vias want plain tenting. A blanket instruction gets you the expensive option everywhere.
Tenting fails above roughly 0.3 mm and plugging above roughly 0.5 mm — the resist simply cannot span the gap. Larger holes have to be filled.
Tenting is effectively free — it is a solder mask decision. Plugging is a small surcharge. Filled and capped is a real process step with its own planarisation and plating, and adds meaningfully to both price and lead time.
Non-conductive epoxy is the default and is right for almost everything, including thermal vias — the copper barrel does the conducting, not the fill. Conductive silver fill is for cases where the fill itself must carry heat or current.
Up to 0.3 mm and away from pads, yes, and it costs nothing. Larger vias and anything inside a solder pad need a real fill.
The usual cause is an open or resist-plugged via in the pad. Paste drains into the barrel during reflow and the remaining volume cannot form a proper joint. Filled and capped fixes it.
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