Via and Through-Hole Repair

A plated through hole intact (a), with its barrel torn or corroded (b), repaired with a wire through the hole (c), and repaired with an eyelet (d). After Ray Carlsen and Circuit Technology Center procedure 5.1.

Via and through-hole repair restores the connection through the board at a via or a plated component hole whose copper lining has failed. A via is a small hole drilled through the board and plated with metal, often copper, to join tracks on different layers; a plated through hole does the same and also holds a component lead. When the plating corrodes away or is torn out, the tracks on the two sides are no longer joined.

The repairs are a single strand of wire passed through the hole and soldered on both sides; a wire from the track on each side to another point on the same net, leaving the via out of the circuit; and an eyelet set in a drilled-out hole. A hole that connects to inner layers of a multilayer board needs more than an eyelet, and Circuit Technology Center rates that repair for expert technicians only.

When to use it

• A via has been eaten by electrolyte from a leaking capacitor or battery. On one Amiga 1200 the via under C334 that joined Paula's audio ground to ground had "totally rotted through", leaving the ground pin floating at about 2.8 V.
• The plating of a component hole has torn out during desoldering. Ray Carlsen calls this the worst kind of board damage: a copper-coloured blob on the pin of a removed chip is torn-out plating, and because the joint is made on the other side, the top of the hole is no longer connected.
• A track has cracked where it meets a via, as on corroded Acorn A7000 boards.
• A via has failed open without visible damage, as under C70 on one Acorn Risc PC 700 board.

Recognise it with a meter: measure from the track on one side of the board, through the via or hole, to the track on the other side; it should read as a direct connection. Corroded vias may also look green or black; one Psion Series 5mx Pro board had green, corroded vias, and the vias under the clock cell on a Sharp X1turbo III sub-board were black. Continuity Testing and Signal Tracing covers the measurement.

A pad that has lifted with its hole is covered in PCB Pad Repair; a track broken elsewhere along its length in PCB Trace Repair.

Safety

• Unplug the machine and remove any batteries before working on the board.
• Rosin (colophony) flux fume can cause occupational asthma. Use fume extraction while soldering.
• Drilling, milling and scraping the board can generate static charge. Take anti-static precautions, and clean away the debris afterwards.

Tools and materials

• A meter with a continuity range, and a magnifier or microscope.
• A temperature-controlled iron with a fine tip, flux, leaded solder and desoldering braid; see Through-Hole Desoldering and Recommended Tools.
• Stranded hook-up wire, to provide single strands for wiring through holes.
• Fine insulated wire, such as 30 AWG Kynar wire-wrap wire, for bypassing a via.
• A knife or scraper to take solder mask and coating off the copper round the hole.
• For eyelets: eyelets of the right size, a pin gauge and caliper to measure the hole, a ball mill or drill in a hand tool grip or small drill, and setting tools (a flare tool and a flat tool) in an eyelet press or tool grip and base.

Eyelet selection (Circuit Technology Center, procedure 5.1)

Dimension	Rule
Inside diameter	0.075 to 0.500 mm (0.003 to 0.020 in) larger than the component lead
Drilled hole	The eyelet goes in without force; the hole is no more than 0.125 mm (0.005 in) larger than the eyelet's outside diameter. The drilling step gives 0.025 to 0.125 mm (0.001 to 0.005 in) larger than the outside diameter.
Length under the flange	0.63 to 0.89 mm (0.025 to 0.035 in) longer than the board is thick, so that enough protrudes to set
Flange diameter	Small enough not to touch neighbouring lands or tracks

Procedure

Find the failed via or hole

The RP201 position on a backlit Macintosh Portable board with the resistor network removed: corrosion residue and a via eaten away under the part (photo: Scouter3D).

1. Switch off and unplug the machine, and take the board out so that both sides can be reached.
2. Measure from the track on one side, through the via, to the track on the other side.
3. Remove a part that covers a suspect via if the via cannot be reached. On a Macintosh Portable, the eaten via was under the resistor network RP201.
4. Clean off any electrolyte and corrosion and neutralise the residue, as in Battery Explosion, Capacitor or Corrosion Damage.
5. Inspect the hole and the copper round it on both sides under magnification.

Wire through the hole

This is Ray Carlsen's repair for torn through-hole plating on double-sided Commodore boards, and it works the same way for a via.

1. Clear the solder from the hole.
2. Scrape the paint and coating off the copper round the hole on both sides, down to bare copper.
3. Take a single strand from a piece of stranded hook-up wire.
4. Push the strand through the hole.
5. Solder it to the copper on both sides of the board.
6. Trim the ends and clean off the flux.
7. If it is a component hole, fit the socket or part, and do not heat the repaired hole more than necessary, or the repair will lift.

Bypass the via

Where the via cannot be soldered, run a wire from the track on one side to another point on the same net on the other side, and leave the via out of the circuit. On a Commodore 64 whose bridge rectifier had lost its ground through a via damaged by an earlier repair, a short wire from the rectifier's ground pin to a ground point under the power switch restored it. Route and secure the wire as described in Jumper Wire Repair.

Fit an eyelet

This is Circuit Technology Center's procedure 5.1 for a hole with no inner-layer connection, rated High conformance and intermediate skill.

1. Clean the area.
2. Measure the existing hole with a pin gauge and caliper, and choose an eyelet using the table above.
3. Drill out the hole with a ball mill or drill, removing all the plating, to 0.025 to 0.125 mm larger than the eyelet's outside diameter.
4. Clean the area.
5. Apply a little flux to the lands or tracks round the hole on both sides, tin them, and clean the area again.
6. Insert the eyelet. A new track can be run into the drilled hole first, so that the eyelet flange clamps it in place.
7. Turn the board over and rest the eyelet's flange on the lower setting tool.
8. Press firmly and evenly with the flare tool to flare the barrel.
9. Change to the flat-ended tool and press again to flatten the flare.
10. Inspect the eyelet for damage.
11. Flux and solder the eyelet's flanges to the lands on both sides, and clean the area.

Hollow rivets sold for plated-through-hole repair, a sieve that stands them upright, and rivets threaded on a wire for inserting them (photo: Ossip Groth, CC BY-SA 3.0).

Ossip Groth, who sells small hollow rivets for this job, sets them without a press: he inserts the rivet from the top, solders its head to the top pad, and on the underside solders the component lead, the rivet and the pad together.

Where a multilayer board's hole has a damaged land but an intact barrel, Circuit Technology Center fits the eyelet inside the existing barrel instead of drilling it out (procedure 5.2, Medium conformance). This reduces the hole's inside diameter, so check that the lead still fits. Restoring an inner-layer connection in a damaged barrel means milling down to the inner layer and soldering an eyelet's barrel to it, then filling the counterbore with epoxy (procedure 5.3); Circuit Technology Center says to use it only when other methods are unacceptable. Drilling out the plating on a multilayer board removes any inner-layer connection the hole had.

Checking the repair

• Measure continuity from the track on one side to the track on the other, through the repaired hole, and on to the next part on the net.
• Check for shorts between the repair and neighbouring lands and tracks, especially round an eyelet flange.
• For an eyelet, inspect it for cracks or damage and check that the solder has flowed and wetted round both flanges and lands. Circuit Technology Center refers to IPC-A-610 for eyelet acceptance.
• Check that the finished hole still takes the component lead.
• Power the machine and test every function that passes through the repaired area.

Common mistakes

• Heating a repaired hole again for too long lifts the repair. Carlsen fits the socket with no more heat than necessary on that hole.
• Drilling out a hole on a multilayer board cuts any inner-layer connection it carried.
• An eyelet with too large a flange touches the next land or track; one that is too short does not protrude far enough to set.
• Circuit Technology Center limits the drilled hole to 0.125 mm over the eyelet's outside diameter.
• Drilling without checking the board's drawings can cut a surface or inner track nearby.
• Assuming a via is sound without measuring it. The failed vias on the A1200 and Risc PC 700 boards above both sat under capacitors.
• Repairing a via without cleaning off the electrolyte that ate it.

Worked examples on this wiki

• Amiga 1200 Troubleshooting Guide: a via under C334 rotted through, leaving Paula's audio ground floating; a wire through the via cured it.
• Philips P2000C Troubleshooting Guide: a failed through-board via on the terminal board, repaired by soldering a wire through it.
• Commodore 64 Voltage Regulator Replacement: a via damaged by an earlier repair bypassed with a short wire to a ground point.
• Commodore 64 PLA Replacement: two vias damaged by a non-factory socket, bypassed with jumper wires.
• Commodore 64C RAM Replacement: torn through-hole plating bridged with a single strand of wire soldered on both sides.
• Macintosh Quadra 605 Troubleshooting: three vias under C136 and C137 corroded by electrolyte; after they were repaired the board reached a Sad Mac screen.
• Macintosh Portable Troubleshooting: a via eaten under a resistor array behind a "No reserve battery power" warning.
• Acorn Risc PC 700 Troubleshooting Guide: the via under C70 found open in a CMOS backup fault.

Related pages

• PCB Trace Repair
• Jumper Wire Repair
• PCB Pad Repair
• Burnt PCB Repair
• Through-Hole Desoldering
• IC Removal and Socketing
• Continuity Testing and Signal Tracing
• Battery Explosion, Capacitor or Corrosion Damage
• Recommended Tools