Pinball Rehab

pinball repair and restoration

Pad and Trace Repair Pad and Trace Repair Hot video

When it comes to pad and trace repair the two common solutions are copper foil or jumpers.  Both methods are functionally equivalent and which one you select depends on the specific situation and how original you want the board to look. 

One other method I should mention, since I get asked about it a lot, is liquid trace or silver conductive epoxy.  Other than a few specific situations, like repairing the glass on a DMD, I stay away from them.  Both solutions add some resistance to the circuit, which can sometimes cause problems, and both will melt if hit with a soldering iron, which could create a serviceability issue.

Before I go into the details, I should explain my three considerations when doing board rework (in descending order of priority).

  1. Performance and Reliability.  The repair should have the same performance as the original trace/pad and be able to stand up to the rigors of a pinball machine.
  2. Serviceability.  If someone works on the game in the future they shouldn't have to wrestle with or redo any traces/pads I've repaired.  For example, if I'm attaching a jumper to the leg of an IC, I will first install a chip socket.  This way the IC can be replaced in the future without messing with the jumper.
  3. Cosmetic.  I try to make my repairs look as original as is reasonable (considering cost and time) and be as invisible as possible.

Equipment and Supplies

Copper foil comes in several variations.  Circuit frames are pre-cut traces/pads made from copper foil (see Image 1, pads and traces on the upper left and traces on the upper right).  They will either have a heat activated adhesive on the back, called dry film, or come with a two-part epoxy.  Which one you use is really a matter of preference.

Circuit Medic manufactures dry film circuit frames, Pace makes dry film and epoxy circuit frames and Best offers circuit board repair kits that include either type of circuit frame.  You can purchase both the Circuit Medic and Pace products direct or at Stanley Supply & Services.  Another good source for circuit frames and tracks is Soldertools.net.

Image Gallery

Pad and Trace Repair
Pad and Trace Repair
Pad and Trace Repair
Pad and Trace Repair
Pad and Trace Repair
Pad and Trace Repair
Pad and Trace Repair
Pad and Trace Repair
Pad and Trace Repair
Pad and Trace Repair
Pad and Trace Repair
Pad and Trace Repair
Pad and Trace Repair
Pad and Trace Repair
Pad and Trace Repair
Pad and Trace Repair

Circuit frame pads with a diameter of  .050/.060" are appropriate for IC's, small connectors, resistors and capacitors.  For larger components use the .070/.080" size pad.  For traces most circuit frames include a variety of sizes.

Datak manufactures a Circuit Fix Kit  (see Image 2) that includes a spring clamp cutting guide for cutting traces from the included adhesive backed (3M) copper foil.  The kit also includes a variety of copper pads.  Both the traces and pads are installed using a burnishing tool

The advantage of the Datak product is you can cut custom traces in any shape needed.  Be aware though, it's pretty difficult to make very small traces (1/64") with this product.

Kapton Tape

Kapton, or Polyimide, tape (high temperature tape that leaves no residue on the board) rates its own section since it makes installing jumpers about 1,000 times easier.  it is available cut into dots from Circuit Medic or in a roll from numerous sources (see Image 1).  Although more expensive, I prefer the dots since they are translucent, which helps when placing jumpers.

To use the dots, first stick your jumper on the dot and then place the tip of an X-Acto blade under the dot (see Image 3).  Use the X-Acto knife to position the dot and trace and then press down on the dot while removing the blade (see Image 4).

Firmly press the dot in place, bend or reposition the exposed portion of the jumper (as needed) and then solder it in place (see Image 5).  After removing the dot you can hold the soldered joint in place with another dot or a solder pick while you solder the other end of the jumper.

Connector Repair, Dry Film

The first example is a 9 pin IDC connector (see Image 6) with pads.  Pin 9 on the right IDC connector has a broken trace on both sides of the pad and pin 5 has a broken trace on the right side (pin 9 is at the top and pin 1 at the bottom).

I have selected a pad and trace combination (see Image 7).  Technically you could just add two traces on each side of the pad (since it's in good shape), but I thought I'd also cover the technique to use when the pad is damaged.

Be forewarned that while this technique will produce results that are pretty much invisible it takes excellent eyesight and hand-eye coordination.  Following are the steps for completing this process with the Circuit Medic product, and at the end of the article is a video which covers the Best product.

  1. Using either an X-Acto knife or emery paper remove the solder mask from the traces you will be soldering onto (see Image 6).
  2. Tin the board traces where you will be overlapping the new trace with the existing trace.  Use solder wick to remove any excess solder.
  3. Remove any oxidation on the pad with emery paper.
  4. Clean the area with Isopropyl Alcohol and a lint-free cloth.
  5. On the back of the circuit frame scratch off about 3/8" of the adhesive where it will overlap onto the existing trace and be soldered in place.
    Note: You can leave the adhesive on the pad portion of the circuit trace unless you are placing the pad over a plated through-hole.  In the latter case the adhesive must be removed to provide conductivity with the through-hole and proper solder flow.
  6. Cut out the pad/trace from the front and remove it.
  7. Place the pad/trace on the Kapton tape, copper side on the adhesive) and after positioning, press down on the tape (see Image 8).
  8. Set your soldering iron to 475 degrees and heat the pad/trace through the Kapton tape, while pressing down, for 30 seconds.
    Note: Some manufacturers recommend different procedures, so follow the directions with the product you are using.
  9. Remove the Kapton tape.
  10. Let the epoxy cure for 24 hours.
  11. Solder the overlapping portions of the new and existing traces (see Image 9).  Use a solder or dental pick to press down on the new trace to ensure good contact with the existing trace.
  12. Apply solder mask, paint or green conformal coating over any exposed copper (see Solder Mask section).

Circuit Medic sells a bonding press with heated bonding tips of various shapes for sealing the circuit frame on the board.  I have never had a problem using a soldering iron instead, and most other manufacturers recommend the soldering iron method.

The same general technique is used for a trace circuit frame.

Additional information is available on the Circuit Medic website.

Using Jumpers

For low current circuits (the size of the existing trace is a good indicator) I use 30 gauge wrap wire (available at Radio Shack).  For ground, supply voltages and higher current circuits I use 22 gauge wire with a PTFE (Teflon) coating.  The PTFE coating allows you to trim the leads much shorter since it won't shrink or melt as quickly as standard shielding when soldering.

The equivalent solid wire size for various trace widths are as follows: .025" trace and less - 30 gauge, .082" - 26 gauge and .125" - 23 gauge.

According to IPC standards the maximum run for a bare wire is half an inch.  If you're running a longer jumper, or crossing over any other traces (even if they have solder mask on them) trim each end of your jumper and leave the coating in the middle.

Best practices are to route the jumper along the same path as the original trace.  If you are running a long jumper it should be attached to the board in one or more spots (depending on its length).  I use clear RTV silicone since it can easily be removed later.  Wire dots are also a good option.

Although optional on short jumpers, adhesive will help maintain the integrity of a jumper if there is reflow during other soldering operations.  For short jumpers I use high temperature epoxy.

Connector Repair, Jumper

Next I'll use a jumper method to repair pin 9, which if you remember has broken traces on both sides of the pad.  In this case I'll use some 30 gauge wrap wire with a loop in the middle that will fit around the pin on the connector (see Image 10).  If the trace was only broken on one side of the pad I could instead run the jumper through the hole for the pin (I'll cover that approach later).

Strip the insulation from a 1 inch piece of wire  and form it around one of the connector pins.  Remove the solder mask from each side of the connector where you will be soldering to the trace and lightly tin.  Place the wire(s) on the pin connectors and install the connector (see Image 11).

Solder the connector in place making sure that solder flows through the hole and onto the loop of wire.  Trim the ends of the wire to fit and then solder the wire on each side to the trace.  Press down while soldering with a solder or dental pick to ensure good contact.  You can see the finished product in Image 12 (I was thinking about the article instead of what I was doing and installed jumpers on both pins 9 and 5).

Always check your trace connections by pushing on the wire with a solder pick.  Finish by covering the bare wire and trace with a coating (as previously described).

Damaged Plated Through-Hole and Trace

The first step when dealing with plated through-holes is to make sure they are intact.  Inspect them visually for damage (with a magnifier) and then check continuity from one side of the board to the other.  In this case the through-holes were damaged.

Normally I use eyelets when repairing a plated through-hole, but if you also have to repair a trace, you could instead use the jumper method and fix both at the same time.   On the other hand, if the traces are cracked right at the through-hole the eyelet may overlap the trace (once pressed) and you won't need a jumper.  See reference on Repairing Plated Through-Holes.

In Image 13 you can see where 2 traces have been damaged next to their plated through-holes, which where also damaged.

Follow the same steps as previously to prepare the wire and trace.  This time though feed the wire through the board.  Use Kapton tape to hold the wire while you solder it to the trace and then fill the through-hole with solder.  In Image 14 you can see the finished product with the resistors installed.

You could also use dry film traces and an eyelet for this type of repair.  Install the trace first and then install the eyelet so it overlaps the trace (remove the adhesive backing where they overlap).

Jumper with Eyelet

In Image 15 you can see where I've installed eyelets on every through-hole on the left side of the IC.  In addition the traces were damaged on several of the pins.  In most cases the eyelet overlapped the damaged traces, but on pins 10, 11 and 13 (pin 1 is at the bottom-right and then count counter-clockwise) I will need to add jumpers. 

On pin 11 the trace was broken in two places so I ran a longer jumper wire and attached it to the left side of the resistor.  Many people feel more comfortable with this method rather than tacking onto a board trace.  If you're in that category, that's fine, it's a perfectly acceptable solution.

This is also a good example of a situation where you could use dry film traces to replace the damaged trace.  Where the trace makes a turn use two pieces of circuit frame and slightly overlap them (remove the adhesive backing where they overlap). 

In Image 16 you can see the area with the socket and IC installed.  Once it's cleaned up and a protective coating is applied the repair will be almost invisible.

Pad Repair

Coming soon.

Solder Mask

Although commonly called conformal coating, the green coating on pinball circuit boards is actually a solder mask. 

Solder masks are applied during the production process to prevent solder bridges and to provide long-term protection against oxidation.  They are not applied to any areas of the board where solder will be applied (pads, through-holes, etc.).

Conformal coatings, which are commonly used in marine applications, are typically clear and applied to the entire board to prevent oxidation.  They can be applied over pads and through-holes since the conformal coating will melt during any solder rework.

The most common approach to touch-up the solder mask is to use a green conformal pen (see Image 10).  While the pen's are great for doing small traces, they are rather tedious on larger areas.  I am also not thrilled with the color match or flow of the paint.

Of course you could use green solder mask, but it is difficult to work with and almost impossible to match the original finish.  From a repair perspective we don't really care about the chemical properties of the solder mask, only that it will protect the traces from oxidation and have an original look. 

A lot of people use Testors 1601 Transparent Candy Emerald Green.  It is available in a 3 oz. spray can and will match a lot of boards.  For small areas just spray a little into a small cup and then brush on.

Another option is Pebeo Vitrio 160 a transparent paint used on glass.  It can be airbrushed or applied with a brush, although it does require heat curing.  The Mint 37 is a touch darker than the Testors, but still looks good, and if you need darker yet try the Tea Green 15.

When using paint do not cover leads or pads since it makes them impossible to solder without removal of the paint.