Introduction: Method of Applying a Copper Ground Plane to Strip-board (e.g. Veroboard)
This inscrutable describes a reliable method of applying a ground plane to “Veroboard” (strip-board or pad-board) using adhesive copper foil and clear adhesive-backed plastic. Adhesive copper foil can be used to shield an electric guitar cavity from electrical noise. It is also sold as a way of repelling slugs and snails from eating garden plants.
The method described here requires all the holes in the ground plane to be made before the electronic components are placed, so the circuit layout needs to be planned in advance. The picture shows an example of a circuit I built using this technique.
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Step 1: Make All Breaks in Copper Strips.
If you are using strip-board (as opposed to pad-board) and need to make breaks in the copper strips, then you should do this BEFORE applying the adhesive copper foil to the top side (component side) of the board. This is because the process of cutting strips can cause pieces of copper debris to fall through the holes of the board. If the adhesive foil was already in place, then these pieces of debris would stick to the adhesive back of the foil and be extremely difficult to remove from the holes. The debris could then give an unwanted connection between the strips and the foil. So it is best to make all the breaks in the strips first and inspect the board against a light source to make sure that all holes are free of debris.
TIP: Finger sweat will corrode the copper strips, so you may want to wear latex gloves when handling the board.
Step 2: Apply Adhesive Copper Foil to the Component Side of the Board
Stick a layer of adhesive copper foil to the side of the board that will take the components. If the foil is not wide enough to cover the entire board, then you will need to use several strips of foil and overlap them a little. Make sure that the edges of the strips of foil lie between the rows of holes in the board rather than over the holes (see the overlap in the picture) or it will be hard to cut tidy holes in the foil. Note that the adhesive used on the foil is often not (fully) conductive and so the seams between the separate strips will need to be soldered together in one of the later steps.
Step 3: Find a Correctly Sized Jewellers' Screwdriver.
The foil needs to have holes cut in it so components can be placed in the board. Most component legs will need to pass through the foil without touching it. The following steps outline what I have found to be the most reliable way of making holes in the foil. It is tempting to try and pierce a hole in the foil with a sharp object like a needle, or cut a hole in it with a drill bit, but I found both of these methods to be bad for different reasons. I found that a drill bit is too aggressive and it will cut and tear the foil in an uncontrolled way. The only way I could make a tidy hole using a drill bit was to make a large chamfered hole, and this is not a good option if you need to make holes that are close together (e.g. for an IC socket). On the other hand, trying to make a hole in the foil by piercing it with a needle is no good either, since it does not actually cut a hole, i.e. it does not remove any material, but instead tears the foil and pushes it to one side of the hole in the board. A component that uses the hole might then make an unwanted contact with the foil. The method described here avoids both these problems.
The trick is to use a jewellers’ screwdriver that is slightly too big to fit in a hole in the board. The outer edges of the screwdriver should be supported by the edges of a hole in the board, but you should not be able to push the screwdriver into the hole. It is the outer edges of the screwdriver that will do the cutting. The top screwdriver in the picture is the correct size. The lower screwdriver is too small because it can be pushed through a hole. If you zoom in to the picture of the top screwdriver you will see that the sides of the blade are worn down slightly (probably due to all the cutting that I have done with it) and this actually makes it easier for the screwdriver to be supported by the holes in the board.
Step 4: Hole Cutting Technique: Stage 1 - Create Depressions
Rotating the screwdriver back and forth between the fingers, apply gentle downward pressure so that the foil is depressed into the hole in the board as shown in the picture. DO NOT PIERCE THE FOIL!!! The aim is to first produce a circular depression in the foil with a clean sharp ”step” along the entire circumference of the hole. That is where we want the foil to weaken and break. The picture shows a set of 8 depressions (to the right of the screwdriver) and the screwdriver is making a 9th depression. Note that there are no cuts in the foil at this point.
Step 5: Hole Cutting Technique: Stage 2 - Increase Pressure
Now while continuing to rotate the screwdriver back and forth between the fingers, gradually increase the downward force until the foil is cut cleanly around the entire circumference of the hole. You can tell this has happened when you see dust from the board in the hole. With practice, the process of cutting a hole won’t take more than a couple of seconds.
Step 6: Hole Cutting Technique: Stage 3 - Remove Cut-out Pieces of Foil.
To remove the cut-out pieces of foil, use a needle or a smaller jewellers' screwdriver (seen in the top corner of the picture) to push each cut-out piece of foil down into its hole and out of the other side. After all the necessary holes have been made, hold the board up to the light and ensure that all holes are free of debris. The cut-out pieces of foil have a tendency to stick to the strip-side of the board, so check the strip-side of the board and brush away any offending pieces.
Step 7: Create Ground Vias and Solder the Foil Seams
Some component legs will need to be connected to ground. I do not recommend soldering these directly to the foil. It is tidier to solder the leg to a strip on the bottom of the board, and for the strip to connect to the foil through another hole using a via. In other words, the only connections to the foil should be through dedicated vias to the strips.
To create a via between a strip and the foil, take a short fat piece of solid bare wire (1st picture) and push it through the foil and into the hole (from the foil side of the board). I use wire with a diameter that is the same as the hole. Push the wire as far as it will go into the board so that it is level with the foil. Then solder it to the foil on the top and to the strip on the bottom.
If you have used several strips of copper foil, then after all vias have been soldered in place, solder the entire length of the seam between overlapping strips of foil.
In all the soldering, try to make sure that the resulting foil surface is as flat and level as possible. The 2nd picture shows a ground via below the set of 9 holes, and the soldered seam.
Step 8: Apply Clear Adhesive-backed Plastic to the Ground Plane.
This stage is important!!! We need to apply an insulating layer to the ground plane to guarantee that component legs cannot touch it. It will also allow bare wires to be used on the top surface of the board.
Stick a layer of clear adhesive-backed plastic over the copper foil (this is called “sticky-backed plastic” in the UK). It is sold in long rolls like aluminum cooking foil, and is available from stationary stores. The plastic is too thick to tear and it needs to be cut to size with scissors or a sharp blade.
I do not recommend using sticking tape as a substitute because it will be too thin, likely to tear, and in my experience the adhesive does not age well.
To make a hole in the plastic layer (so that a component can be placed), use a sharp needle to pierce the plastic from the component side of the board, and then gradually push the needle down fully into the board and wiggle it to widen the hole. DON’T USE A SCREWDRIVER OR BLADE TO DO THIS!!! The reason for using a needle (and not using sticking tape) is to avoid making a linear cut or tear. We need the plastic to line the entire rim of the hole, and a tear would prevent that from happening and could expose a portion of foil. The aim is to make sure that the plastic gradually curves into the hole and seals all the foil edges.
Step 9: A Simpler, But Less Reliable Method of Making Holes. (Useful As a "fallback" Option).
It is possible to place components without going through the procedure of cutting holes in the foil with a jewellers’ screwdriver.
The simplified process is this...
1) Make all necessary breaks in the strips. Check all holes are free of debris.
2) Apply adhesive copper foil to the component side of board.
3) Solder all vias between the foil and the strips. Then solder all foil seams along their entire length.
4) Apply clear adhesive-backed plastic to the foil.
5) To make a hole for a component leg, use a sharp needle to pierce both the plastic layer and foil layer in a single operation. Push the needle down into each hole and wiggle it to fully widen the hole.
I don't think it is as reliable a method since no foil is actually removed, and it is definitely not reliable if no plastic layer is used. However it is still useful to know that you can make holes this way as a “fallback” option.
For example, after you have soldered lots of components into the board you may discover that you accidentally forgot to make a hole in the foil at some location. It won’t be possible to remove the plastic layer and cut a hole in the foil (because components have already been placed through the plastic). So the only option is to pierce a hole through both layers in a single operation using a needle. That has worked for me on all the occasions that I needed to do it, but I have only done that around 50 times so I can't say how reliable it is. I have done close to 1000 holes using the "screwdriver method" and have never had a problem with accidental connections to the ground plane.
Step 10: Place Components and Solder Them
TIP: It’s a good idea to have some of the foil extend beyond the board during the construction phase, so you always have an easy connection point for a multimeter, no matter which way up the board is laying.
Both BEFORE and AFTER each component is soldered in place, use a multimeter to check for any unwanted connection between the component’s legs and the ground plane. If there is an unwanted connection, make sure the hole is fully widened with a needle, and bend the component leg away from the edges of the hole. If that doesn’t work, you can try to add an extra layer of plastic to the problem hole (since the original plastic may have torn so that there is an exposed piece of foil). I have never actually needed to do that though.