Via Repair by Wire or Fill

Section Overview

Section 7.2 rebuilt a via with a rivet; this section takes up the vias a rivet does not suit — too small, too damaged, or awkwardly placed — and restores them by two other means: a wire through the hole, or a fill (§7.2). The first is the through-wire: a fine wire threaded through the via hole and soldered to the ring on each face, so that the wire carries the connection from side to side where the barrel no longer can — in effect a tiny two-sided wire link (§5.4). It suits a hole that will take a wire but not a rivet, and it makes a strong, low-resistance connection because the conductor is solid metal (wire gauge). The second is the conductive fill: filling the hole itself with a conductive material — solder wicked through, or a conductive paste or epoxy — so the fill bridges the faces in place of the barrel. A solder fill is best where it works, being true metal, but where a hole is too large or a wire will not thread, a conductive paste or epoxy fills it, at the cost of higher resistance and lower current-carrying capacity than metal, much as conductive ink is to a trace (§5.2; current-carrying capacity). Both methods share the rivet's boundary: they restore a reachable via, not a barrel or connection buried deep in a multi-layer board, which is a bypass or a referral (§5.5; §4.5). And both are verified the same way, face-to-face through the via (§5.6). Learn when a wire or a fill suits a via, how to make each, their limits against a rivet, and how to verify them — and the vias a rivet cannot take are still repairable.

Why This Matters

A rivet is not always the right way to rebuild a via, so knowing the wire and fill methods — and their limits — is what lets you repair the vias a rivet cannot take. This matters because not every via suits a rivet: a hole too small for a rivet, an odd shape, or a spot too tight for a setting tool leaves a via a rivet cannot repair, and a wire or fill is what saves it (§7.2). This matters because the wire method is often the strongest: a solid wire soldered through the hole makes a low-resistance metal connection as good as the rivet's, so it is frequently the first choice, not a fallback (§5.4). It matters because a fill has real limits: a conductive paste or epoxy fill has higher resistance and a lower current-carrying capacity than solder or wire, so using it on a via that carries real current invites the same failure as conductive ink on a power trace (§5.2; §2.4). It matters because the method must match the via's job: a signal via tolerates a fill that a power via would not, so the choice of wire, solder fill, or conductive fill turns on the current the via must carry. And it matters because the boundary is the same as the rivet's: wire and fill restore only a reachable via, so a buried or deep-inner-layer fault is still a bypass or a referral, and knowing that keeps you from a fill that cannot hold (§5.5; §4.5). Match the method to the via and its current, and even a via a rivet cannot take is repaired soundly.

Required Prerequisites

• Via Repair by Rivet or Eyelet — Section 7.2 taught the rivet method and the reaming and verification a via repair shares; wire and fill are for the vias a rivet does not suit.
• Magnet Wire Repair — Section 5.4 taught the wire link, sized and soldered, that a through-wire via repair is built from. This is an advanced hands-on hot-work repair section — read the Safety Notes before starting.

Recommended Consumables

• Fine magnet or insulated wire in the gauges a via needs — the conductor for a through-wire repair (§5.4)
• Conductive paste or epoxy, and fine solder — the materials for a solder or conductive fill
• Flux, fine solder, and isopropyl alcohol — to solder the wire and clean the hole and rings (§5.3)
• A solder mask pen — to reseal the repaired rings and bare copper
• Scrap boards with failed vias of various hole sizes — to practise on; do NOT practise on any device you intend to use, sell, or return

Recommended Practice Hardware

• A temperature-controlled soldering iron with a fine tip — to solder a through-wire or reflow a solder fill (§5.3)
• Fine tweezers and a reamer — to thread the wire and clean the hole (§7.2)
• A magnifier or loupe and a bright light — to place a fine wire in a small via and inspect the joints
• A multimeter with continuity and a low-ohms range — to verify the connection face-to-face and compare it to a known-good via (§5.6)
• A way to cure a conductive fill — air-dry time or gentle heat per the product — to bring a paste or epoxy fill to full conductivity (§5.2)
• Good ventilation — to keep solder, flux, and fill fumes out of your breathing air

Real-World Applications

Wire and fill repairs restore the vias a rivet cannot take, a common need on boards with small or oddly-placed vias. A technician facing a via too small for any rivet threads a fine wire through the hole and solders it to the ring on each face (§5.4). Someone repairing a via in a spot too tight for a setting tool runs a through-wire rather than force a rivet (§7.2). A repairer restoring a small signal via wicks solder through the cleaned hole to fill it, remaking the metal connection. A technician on a via a wire will not thread and solder will not fill uses a conductive paste, accepting its higher resistance because the via carries only a light signal (current-carrying capacity). And a repairer tempted to fill a power via with conductive paste chooses a wire instead, because the fill could not carry the current (§2.4). The failures this skill prevents: forcing a rivet where a wire fits better, filling a current-carrying via with a high-resistance paste, and treating a buried via as a fillable one (§4.5).

Common Challenges

• Filling a current-carrying via with paste. A conductive paste fill has a low current-carrying capacity — use a wire or solder fill for a via that carries real current (§2.4).
• A wire that will not thread. A tiny or blocked hole may not take a wire — ream it, or use a solder or conductive fill instead (§7.2).
• Soldering only one face. A through-wire or fill sound on one side can be open on the other — solder and verify both faces (§5.6).

Safety Notes

Risk Level: Medium. Wire and fill repairs are soldering work with the added handling of conductive pastes and epoxies, so hot-work and chemical cautions apply together.

Professional Tips Before Starting

• Reach for the wire first. A soldered through-wire is a strong, low-resistance repair — prefer it where the hole will take a wire (§5.4).
• Match the fill to the current. Use solder or wire for a current-carrying via and a conductive paste only for a light signal — a paste fill cannot carry power (§2.4).
• Solder and verify both faces. A via connects through the board — plan to solder and check the wire or fill on each face (§5.6).

Rebuilding a Via's Connection by Wire or Fill

Recap and Frame

Section 7.2 rebuilt a reachable via with a rivet, and this section covers the same reachable vias by two other routes for when a rivet will not do (§7.2). The frame to hold is that all three methods do the same thing — put a conductor back through the hole where the barrel failed — and differ only in what that conductor is: a rivet is a metal tube, a through-wire is a threaded wire, and a conductive fill is the hole filled with conductive material (barrel). The choice among them turns on the hole and the current. A rivet needs a hole it fits and room for its tool; where the hole is too small, oddly shaped, or awkwardly placed, a wire or a fill serves instead. And the conductor's quality matters: a wire and a solder fill are solid metal, low in resistance and able to carry current, while a conductive paste or epoxy fill is a compromise — it conducts, but with higher resistance and a lower current-carrying capacity, fit for a signal via but not a power one (current-carrying capacity; §2.4). The two methods this section teaches are therefore the wire, usually the stronger, and the fill, for where a wire will not go. Both share the rivet's boundary — a reachable via only, never a buried or deep-inner-layer fault, which is a bypass or a referral (§5.5; §4.5). So the section walks when wire or fill suits a via, the wire method, the fill method, choosing among the methods, and verifying the result. Hold the frame — a conductor back through the hole, matched to the hole and the current — and the vias a rivet cannot take are still repairable.

When a Wire or Fill Suits a Via

Wire and fill are for the reachable vias a rivet does not suit, and telling which method fits turns on the hole, the access, and the current the via carries (§7.2). A wire suits many vias, and often best. Where a via's hole will take a fine wire — and most will — a through-wire makes a solid-metal connection as low in resistance and as current-capable as a rivet, so it is the method to reach for when a rivet does not fit, and often even when one would (§5.4). It especially suits a hole too small for any rivet, a via too tightly placed for a setting tool, or a via where a wire can be dressed neatly to the rings. A fill suits the vias a wire cannot serve. Where a hole is too fine or blocked to thread a wire, or where filling is simply cleaner, the hole is filled with a conductor instead: a solder fill where the hole and rings will let solder wick through and hold, and a conductive fill of paste or epoxy where solder will not. The current decides between solder and paste. A solder fill or a wire is true metal and carries current well, so either suits a via of any normal current, while a conductive paste or epoxy fill has a much lower current-carrying capacity and suits only a light signal via — never a power one (§2.4; §5.2). And all of this applies only to a reachable via: a buried via, or one whose broken connection is on an inner layer, cannot be threaded or filled from the surface and is a bypass or a referral (§5.5; §4.5). Weigh the hole, the access, and the current, and the right method — wire, solder fill, or conductive fill — becomes clear. Match the method to the via, and the repair is sound from the start.

The Wire-Through-Hole Method

The through-wire is the wire method: a fine wire passed through the via hole and soldered to the ring on each face, rebuilding the connection as solid metal (§5.4). Prepare the hole and the wire: ream the hole clean and clear enough to pass the wire, clean the rings on each face to bright copper, and choose a wire whose gauge suits the via's current and whose diameter threads the hole (§7.2; wire gauge). If the wire is magnet or insulated wire, strip and tin its ends as for any wire link (§5.4). Thread the wire through: pass it through the hole so a short length stands proud of the ring on each face, using tweezers and magnification for a small via. Solder each face: solder the wire to the ring on each face, flowing a little solder to wet the wire and the ring into one joint, so the wire is joined to the copper on both sides the via connects (§5.3). Trim the ends: cut the wire close to each joint so no stub stands proud to snag or short, leaving a neat soldered connection flush with each ring. Keep the heat brief: the rings are small and the wire fine, so a quick, hot joint avoids lifting a ring, and working under magnification keeps the solder off neighbours (§4.3). A wire threaded through the hole and soldered flush to a sound joint on each face carries the via's connection again, as solid metal. Thread, solder each face, and trim, and the through-wire rebuilds the via with the strongest conductor of the three.

The Fill Method

Where a wire will not thread, the hole is rebuilt by filling it — with solder where solder will hold, or with a conductive fill of paste or epoxy where it will not — so the fill bridges the faces in place of the barrel. Consider solder first. A solder fill is true metal and the better fill where it works: clean and ream the hole, flux it, and flow solder into it from each face so it fills the hole by capillary action and wets the rings, remaking a metal connection through the board — note this is solder drawn into the hole, not desoldering braid, which only removes solder (§7.2; §5.3). Solder fills a small hole with sound rings well, but it will not hold in a large hole or bridge to poor copper, and it is easy to leave a hole only part-filled and open through the middle, so verify it carefully. Where solder will not fill, use a conductive paste or epoxy. A conductive fill of conductive paste or epoxy is worked into the cleaned hole so it contacts the rings on each face and, once cured, conducts through the board (§5.2). Cure it fully: let the paste or epoxy reach its rated conductivity and strength by air-drying or gentle heat per the product, because an under-cured fill is weak and high in resistance, just as with conductive ink (§5.2). Respect its limit: a conductive-paste fill has a much higher resistance and a much lower current-carrying capacity than solder or wire, so it suits a light signal via and never a power one, and if the via carries real current a wire is the honest choice instead (§2.4). Check the fill through: a fill can look complete on the surface yet be open through the middle of the hole, so it must be verified face-to-face, not just inspected (§5.6). Fill with solder where it holds and conductive paste only for a light signal, cure it fully, and verify it through — and a hole no wire could thread carries its connection again. Fill the hole with the right conductor for its current, and even an unthreadable via is restored.

Choosing the Method, and the Limit

With three methods in hand — rivet, wire, and fill — the advanced skill is choosing well, and knowing the boundary all three share. Weigh the hole and the tools: a rivet for a hole it fits with room to set it, a wire where the hole threads, and a fill where neither serves (§7.2). Weigh the current above all: a via carrying real current needs solid metal — a rivet, a wire, or a solder fill — while only a light signal via can accept a conductive-paste fill, whose low current-carrying capacity would fail a power via (§2.4). Weigh reliability: a wire and a rivet are the most robust, a solder fill is sound in a small hole, and a conductive-paste fill is the least reliable and the last resort — a genuine repair, but the weakest conductor. Prefer the strongest method the via allows: reach for a wire or rivet before a fill, and a solder fill before a paste, using the paste only where nothing else will serve and the current is light. And hold the boundary all three share. Every one of these methods restores a reachable via — one whose hole and rings you can work from a surface (§7.1). None can reach a buried via, or a connection broken deep on an inner layer where the surface cannot reach: those are a surface bypass between accessible points, or, where even that is impossible, a referral (§5.5; §4.5). Choose the strongest method the via and its current allow, and refer what no surface method can reach — and every repairable via gets the soundest repair it can. Match the method to the via and know where all of them stop.

Soldering, Curing, and Verifying Both Faces

However the via is rebuilt — wire, solder fill, or conductive fill — the repair is finished only when the joint is sound and the connection is verified through the board (§5.6). Finish the joint first: a soldered wire or solder fill should be shiny and well-wetted to the ring on each face, and a conductive-paste fill should be fully cured to its rated conductivity, with no cold joint and no under-cured, high-resistance fill (§5.2). Verify the through-connection: measure continuity and resistance face-to-face through the via, confirming the wire or fill carries the connection from the ring on one face to the ring on the other, near the value of a known-good via (§7.1). Watch the fill especially: a fill can read continuous on the surface of each face yet be open through the middle of the hole, so the face-to-face measurement, not a surface check, is what proves it. Verify each ring to its trace: confirm the repaired via reaches the trace on each face it should serve (annular ring). Check for shorts: confirm the wire, its trimmed ends, or the fill touch only the rings they should. Test in service where the via's current matters: a fill or wire should carry the via's current without heating, and a paste fill that warms is carrying too much current and must be replaced with metal (§2.4). Protect it: reseal the rings and bare copper with a solder mask pen. A via rebuilt by wire or fill that carries continuity face-to-face near a known-good via, holds, shorts to nothing, and carries its current without heating is a finished repair; one open through the hole or warming under load is not. Verify face-to-face and under the via's real current, and the wire or fill repair is proven as sound as the method allows.

Common Mistakes

• Using a paste fill on a power via. A conductive-paste fill cannot carry real current — use a wire or solder fill for a current-carrying via (§2.4).
• Leaving a fill open through the middle. A hole can look filled on the surface yet be open inside — verify the fill face-to-face, not by inspection (§5.6).
• Under-curing a conductive fill. An uncured paste or epoxy is weak and high-resistance — cure it fully before trusting it (§5.2).
• Forcing a wire that will not thread. A blocked or tiny hole may not take a wire — ream it or use a fill instead (§7.2).
• Filling a buried via. A buried via cannot be filled from the surface — bypass or refer it (§5.5; §4.5).

Troubleshooting Guidance

Wire and fill problems come down to a connection that is not made, not sound, or beyond the method. If a wire will not thread the hole: ream the hole clear, or switch to a solder or conductive fill (§7.2). If the via reads open after a fill: the fill is open through the middle — clear and refill, verifying face-to-face (§5.6). If a paste fill reads high or warms under load: it cannot carry the current — replace it with a wire or solder fill (§2.4). If a solder fill will not hold in the hole: the hole is too large or the copper poor — thread a wire instead (§5.4). If a ring lifts while soldering: you are overheating — solder faster and cooler and heat-sink (§4.3). If a conductive fill stays weak: it is under-cured — give it the full cure (§5.2). If a wire stub shorts to a neighbour: trim it flush and re-inspect. If the via is buried or its fault is on an inner layer: no surface wire or fill reaches it — bypass or refer (§5.5; §4.5). The throughline: thread a wire or fill the hole with the right conductor for the current, solder or cure it, and verify face-to-face.

Verification & Testing Methods

Confirm the wire or fill via repair on both faces and through the board before trusting it:

• [ ] I restored the via with a through-wire soldered to the ring on each face and trimmed flush, or with a fill (§5.4).
• [ ] I matched the method to the current — a wire or solder fill for a current-carrying via, a conductive fill only for a light signal (§2.4).
• [ ] I verified continuity and resistance face-to-face through the via near a known-good via, confirming the connection is not open through the middle (§5.6).
• [ ] I verified each ring to its trace, confirmed no short, and cured any conductive fill fully (§5.2).
• [ ] I confirmed the repair carries the via's current without heating and referred or bypassed any via no surface method could reach (§4.5).

Then try the practice exercises below — hands-on repair practice on scrap boards; scenarios differ from the quiz.

Practice Exercises

1. Thread a through-wire (7 minutes, hands-on). On a scrap board, ream a failed via, thread a fine wire through it, solder it to the ring on each face, and trim the ends flush (§5.4).
2. Fill a via (7 minutes, hands-on). On a small via a wire will not thread, fill the hole with solder wicked through, or with a conductive paste cured per the product, so it bridges the faces (§5.2).
3. Choose the method (5 minutes, reasoning). For several vias of different hole sizes and currents, decide for each whether a wire, a solder fill, a conductive fill, or a bypass is the right method (§2.4).
4. Verify face-to-face (6 minutes, hands-on). Measure continuity and resistance through a repaired via from face to face against a known-good via, confirming it is not open through the middle (§5.6).

These core ideas — when wire or fill suits a via, the wire method, the fill method and its limits, choosing among the methods, and verifying face-to-face — are tested in the Chapter Quiz at the end of this chapter, where a score of 80% is required to continue.

Key Takeaways

• For a reachable via a rivet does not suit, a through-wire — a fine wire threaded through the hole and soldered to each face — makes a strong, low-resistance connection, and is often the first choice (§5.4).
• Where a wire will not thread, the hole is rebuilt by a fill: a solder fill of true metal where it holds, or a conductive fill of paste or epoxy where solder will not.
• A conductive-paste fill has a much lower current-carrying capacity than metal, so it suits a light signal via and never a power one — for which a wire or solder fill is used (§2.4; §5.2).
• Prefer the strongest method the via allows — wire or rivet, then solder fill, then conductive paste only as a last resort — and match it to the via's current (§7.2).
• All three methods restore only a reachable via, and are verified face-to-face through the board near a known-good via; a buried or deep-inner-layer fault is a bypass or a referral (§5.5; §4.5).

Skills Learned

• You can now judge when a wire or fill repair suits a via a rivet does not.
• You can now restore a via with a wire threaded through the hole.
• You can now restore a via with a solder or conductive fill.
• You can now weigh the limits of a fill against a wire or a rivet.
• You can now choose between wire, fill, rivet, bypass, and referral.
• You can now verify a wire or fill via repair on both faces.

Glossary Additions

• through-wire — a fine wire passed through a via's hole and soldered to the ring on each face to restore the connection the failed barrel carried, in effect a tiny two-sided wire link fitted in the via. A through-wire makes a solid-metal, low-resistance connection as strong and current-capable as a rivet's, so it is often the first choice for a reachable via a rivet does not suit — a hole too small for a rivet, a spot too tight for a setting tool, or a via a wire bridges neatly. The wire is threaded through the reamed hole, soldered to the copper on each face, and trimmed flush so no stub stands proud to snag or short.
• conductive fill — the repair of a failed via by filling its hole with a conductive material — solder wicked through where it will hold, or a conductive paste or epoxy where solder will not — so the fill bridges the faces in place of the lost barrel. A solder fill is true metal and the better fill where the hole and rings allow it, while a conductive paste or epoxy fill conducts but with much higher resistance and a much lower current-carrying capacity, fit for a light signal via but never a power one. A fill must be cured (for a paste or epoxy) and verified face-to-face, because it can look complete on the surface yet be open through the middle of the hole.

Suggested Next Sections

Must read next:

• Via Repair Verification — Section 7.4 closes the chapter by drawing together how to prove any via repair sound — that it carries its connection from layer to layer and holds under service, whichever method rebuilt it.

Recommended:

• Via Repair by Rivet or Eyelet — the rivet method and the reaming and verification a via repair shares.
• Magnet Wire Repair — the wire link a through-wire via repair is built from.