Trace, via & reflow repair¶

After a battery leak or a SMD capacitor leak, the board is often eaten: cut traces, missing vias, dissolved pads. Here is how to rebuild cleanly.

Assessing corrosion damage¶

Under SMD caps / around the battery: scrape the solder mask, inspect under the microscope. A trace can be conductive on the surface but eaten underneath (rising resistance, intermittent contact).
Point-to-point continuity against the schematic (or a reference board): find the open or resistive links.
Through-hole vias: corrosion attacks the inner copper → a layer-to-layer link can be cut while looking intact on the surface.

Cleaning first (mandatory)¶

Neutralise the electrolyte (conductive/corrosive): IPA + brush; alkaline battery leak → a little vinegar then IPA rinse, dry.
Remove the attacked solder mask around the area, take the copper bare (gentle scrape, glass fibre).
Do not refit a part until the area is clean and dry.

Repairing a cut trace¶

Short gap: solder bridge or a small wire (30 AWG wrap) soldered between two sound, tinned copper points. Secure with lacquer/glue.
Long break: wrap wire point to point (pin to pin of the part), pressed down and glued; re-do the solder mask (UV lacquer) to protect.
Rebuild a lifted pad: adhesive pad/eyelet kit, or solder the part's leg directly to the re-tinned trace + reinforcement.

Repairing a via¶

Cut through-hole via: run a thin wire through the hole, solder both sides (recreates the layer link). On multilayer, if an inner plane is cut, the wire must reach the correct node per the schematic.
Crimp eyelets (via repair kit) for a cleaner result.

Rebuilding an edge-connector pad ✅¶

Atari's procedure, as printed in The Book (1980)

The edge-connector pad is the wear part of an arcade board: it is what gets plugged, unplugged, rubbed and sometimes burned. The Book (Atari TM-129, chapter 1, section 5) gives the full rebuild — "Regardless of cause, the technique of repairing them is the same."

1. Remove what is left of the old pad. ⚠️ This is not cosmetic: "so that later you won't have any dirt or debris causing short circuits between adjoining edge-connector pads". Cut through the pad with an X-Acto knife, lift it with a scribe, then scrape off all carbon, dirt and debris from the fibreglass, down to a smooth clean surface.

2. The material — and how to ask for it. Atari prescribes copper tooling, a copper foil, ⓘ "can be purchased in almost any hobby shop in the country. You should ask for copper foil, because most hobby shops will not know what 'tooling' is". Sold in a 12-inch-wide sheet.

⚠️ And what not to buy: "Do not buy thin adhesive-backed copper [foil] available at electronic hobby shops. This is generally too thin for edge-connector repairs." The thin adhesive copper from electronics shops will not hold here.

3. Prepare the strip. Cut it to exactly the width of the original pad, then clean it thoroughly with a pencil eraser to remove oxide. The through-plated hole has already been tinned — a small amount of solder was applied to the board.

4a. If pins 1 and A are common (through-plated holes along the connector): solder one side of the strip to the solder side, turn the board over, wrap the copper around the end, and make sure it closely conforms to both surfaces. Cut the strip to the length that just covers the through-plated hole — ⚠️ not longer. Clamp it with a locking surgeon's clamp, which keeps the copper flush with the board. Then bring the iron in just enough to heat the already-tinned area — ⚠️ do not apply more solder. Let it cool, remove the clamp, clean with flux remover, and scrape away any hairline solder bridges between neighbouring pads.

4b. If pins 1 and A are not common (no through-plated holes): ⚠️ you cannot wrap the copper around the board — "you would cause a short". Bond it to one side only: solder at one end, and at the other, slightly lift the copper and apply Krazy Glue or another instant adhesive underneath, holding the strip down on the fibreglass.

ⓘ The detail that stops it catching: when trimming the copper that overhangs the board edge, aim for a convex surface — "That will keep it from catching on the edge connector when you plug the connector back on."

5. Finish. Clean the whole connector with a soft pencil eraser — ⚠️ not an ink eraser, which is abrasive.

Cutting and rejoining a trace — the gestures that fail ✅¶

What The Book photographs as the wrong way

Cutting. With an X-Acto knife, in one single cut — which takes real pressure. ✅ Angle the blade to undercut the trace, leaving an overlapping tongue of foil: that tongue is what makes the repair possible. A clean cut lifts only one side of the foil; to rejoin, you push that side back down and solder over it.

⚠️ The pocket knife is explicitly excluded: "a pocket knife is a tool you should not use — an X-Acto knife is the proper tool". It does not slice, it tears: the document shows a trace cut in several places with a wide gap in the middle, which then has to be jumpered, "solder will not flow across such a large gap".

Bridging a wide gap. Lay a jumper wire across it: the solder then flows along the wire instead of balling up. ⚠️ And the step the photo does not show, says the text: trim both ends of the jumper right next to the solder.

ⓘ The cold joint, described so you can recognise it: "dull grey, has excessive solder, and is not smooth at all". The lump eventually gives way to vibration and the connection opens up.

Modification wire and solder wick — two short rules

Mod wire lies flat. ⚠️ "The wire is lying flat on the PCB, and not underneath components" — otherwise it vibrates in play and in transit, the fatigue reaches the joints next to it, and they break. Keep it as short as is physically possible, and stop the stripped insulation right next to the pin that terminates it, so it shorts nothing.

⚠️ A big loop in the air is a double trap: it vibrates until it breaks, and it catches on something when you pull the board out of the cabinet.

The wick never sits still. "Keep the wick moving on the PCB. If you apply heat constantly to one area, you'll cause the traces to come loose and damage the board." It is the stationary heat, not the braid, that lifts the copper.

EPROM legs / oxidised sockets¶

Blackened legs: clean, re-tin; if a leg is eaten, solder a leg stub or replace with a fresh programmed EPROM (EPROM).
Fit a turned-pin socket for future removals/refits.

Reflow & reball (QFP/BGA customs)¶

Cracked joints on a QFP (fine pitch): reflow with hot air + flux, or rework pin by pin with a fine iron + wick for bridges.
BGA (recent customs): reball with a preheater + hot air, stencil and balls — a delicate job, last resort.
Always preheat the board (multilayer) to avoid ripping traces and vias.

Sources & attribution¶

Synthesis of established PCB repair techniques (retro/arcade).

Review & corrections

How this space is used

Spotted a wrong value, an outdated procedure, a chip reference that does not match your board? Say so here, with what you observed (model, board revision, serial number, measurement). Every report is cross-checked against a source before anything changes — an unverifiable correction is published as “reported by …, not cross-checked” rather than silently applied.

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