Either because you want to have your prototype done in a few hours or because you have an urgent simple board replacement to accomplish, or maybe because this would be your first steps in the electronics world, knowing how to etch PCBs is something easy to understand and that you should know how to do it. Having a step-step by step guide with tips and receiving feedback from the experience of others will also be very useful.
Basically, the process will always include transferring the PCB to the copper clad board. This could be done by transferring toner or by using photo-resistive boards.
We recommend you to know both, but this article is about using the photo-resistive boards method. We recommend this method because although it could be a bit more expensive you only need to make a good mask template once and with only one template several PCBs can be made. Also it allows to create thinner tracks, once you've mastered the whole process you'll notice this method is more reliable than the other one.
Let’s get down to work!
1. PCB design
Today’s market offers a lot of options when it comes to PCB design. You’ll need to use be careful while you make the light sensitive design. A bad design we’ll make the transfer imposible or we’ll add errors.
2. Steps for image transfer to the board
- Print PCB design on a Transparency
- Place it with sensitive board, side with ink should be against the board. This means the side with ink goes facing up.
- Light exposure should be UV but since maybe you don’t have access to it you should know that it is also possible to use sunlight for this.
In most cases 10 minutes should be enough, be aware that the sunlight hit the board perpendicularly. Also you can use a regular lamp, keep a 10 cm distance between lamp and board, and leave it from 9 to 12 minutes.
Here consider that time is not an exact point is more like a window. There’s a minimum time you’ll have to exceed and a maximum time you must not exceed. The lower quality of your transparency printing, the smaller this window. So get the transparency well printed with maximum quality. Is very important that the ink is opaque.
Three possible scenarios:
- Short time: The area that received light is the area that should be detached but if the exposure time was less than necessary this will not happen
- Correct time: only the exposed area emerges and the other areas stays the same
- Maximum time exceeded: The photosensitive layer is removed in both areas, those exposed to light and those not. It may be a partial or total defect.
- When working, there should not be much light or work with red light
- When retracting the film that covers the plate, be careful that it is not exposed more than a few seconds to light, the plate may be damaged
- Leave the borar 5 minutes in the insoler or leave it 9 minutes under lamp
- If you have to prepare the solution, store the plate in a dark box while you do it
3. PCB development
You can use a developer in spy or also a mixture of caustic soda and water.
Spray: If you use the spray, let it act for about 30 seconds and gently clean it so as not to leave the film in places that should remain.
Caustic soda: If you want to use caustic soda, find below How to prepare the development solution:
|● Use 3 g of caustic soda / sodium hydroxide in strong water. Important note: wear glasses and gloves, this is toxic and corrosive.
● Dissolve in ¼ liter of water, we recommend the one that comes in pearls
● Quickly close the caustic soda pot easily moistens.
● Use a plastic tupper for the process.
● When revealing the PCB, it is recommended to work with red light or practically without light
- Expose the plate to the light source, always use wood or plastic tools to handle the plate.
- The side of photosensitive varnish should always go up.
- Shake the plate inside tupper, When you see that copper appears it is time to stop and rinse it.
- Then rinse in water, if necessary use sponge to remove traces of protective material
4. PCB Etching
In this part of the process we remove excess copper leaving tracks we need. This will be done by the acids or an etchant. For acid you have different options for example Ferric chloride Sodium persulfate or a mix of hydrochloric acid and hydrogen peroxide. We’ll explain here how to do it with the etchant.
The etchant comes in a pack of white powder. You can mix it with 650cc of water. You can heat the water to 100 °C before adding the etchant and put the mix on a plastic plate.
Shaking it will accelerate the process. Remember to perform this operation with the red light on.
You’ll be able to use this etchant many times again so we suggest you to save it properly. Once the etchant turns a little bit blue you’ll realize that is time for doing recycle process.
|Once you notice that copper begins to leave the PCB, pay attention not to leave it too long. Please never throw the etchant into the sewers, it is very polluting.
You then rinse with water and sodium bicarbonate. The PCB It can be cleaned with a brush. We can go to work with normal light.
The final step would be to remove the varnish, this can be done with acetone or with alcohol.
We know it could sound a little bit long the process but, once you do it once the second one is done much faster and better. We’ll hope this guide was useful and we wait for your comments about it.