Place the PCB, green side up, in a small sealable plastic back (1 quart sandwich bags are used in the US). You will need rubber gloves, a secondary container and eye protection to etch.
Never etch without gloves and eye protection!
Seal the plastic bag and place in the secondary container. In this example, a simple disposable food container from the supermarket is used. It ensures any leakage from the back does not spill.
The instructor will poor the acid into the bag.
The acid is either Ferric Chloride, sold on Amazon in the US and Europe, or can be made by the hobbyist with hydrogen peroxide (2%) found at the pharmacy/supermarket and hydrochloric acid (HCL) 30%, which is sold at many pool stores to balance the pH of pools and also home improvement stores for etching concrete. It is sold under the name Muriatic Acid. To make your own etchant:
- Put three parts water into a plastic container.
- Put two parts hydrogen peroxide into the water.
- Put one part HCl into the peroxide/water mixture.
This is a diluted form of etchant. Note: the perodixe/HCl etchant is exothermic and the liquid will heat up during etch. Ensure you have a stable container that can handle the heat (usually simply warm to hands if small amount is used).
INSTURCTOR ONLY: Carefully pour the etchant into the bag, just covering the PCB.
Use a foam roller to roll back-and-forth across the board. You should see the green foil as you roll. This is to mix the etchant and ensure a fresh coat continually covers the board surface. Etching time is reduced through rolling and is more uniform.
As you roll, the board will turn colors and the etchant will turn black (Ferric Chloride) or blue (peroxide/HCl). The edges will etch first, so that you will start to see bare PCB at the board edges first, and then more of the board will appear bare – moving from the outside edges to the center.
The image below shows a small area of copper left on the lower right. You can see that it etches gradually, so the copper has a feathered edge. A few more rolls, and this board will be done.
INSTRUCTOR ONLY: Wearing cloves and eye projection, carefully remove the PCB and place on an absorbent paper towel. Close bag and place in a storage container for proper disposal.
Wipe the board with an absorbant paper towel. Then use acetone (finger nail polish remover) to clean the board. The acetone will remove the green foil and toner.
After wiping the front and back to remove any acid (use a moist cloth). Your finished board should look like this.
The back maybe cleaned with alcohol to remove the shellac, however you will be able to solder directly to it (the heat will remove the shellac).
The board should now be cut into the respective circuits. Make sure to cut such that you align edges of circuits where connectors will be placed. We use a simple “tin snip” which is used to cut thin metal for roofing and is available on Amazon and in home improvement stores. A heavy-duty paper cutter also works well and provides straighter edges.
Please wear eye protection and be aware of anyone around you without eye projection – move to a location without other people or have others put on eye protection also.