How to etch PCB is critical in the manufacturing of circuit boards. At first, a PCB comprises a copper plate, but the copper is only on the circuit design pattern on the final board.
This guide will elaborate on removing the excess copper from the circuit board. This process is simple, but you must get things right for a successful etching. Let us get started.
What is PCB Etching?
It is a process in PCB manufacturing whereby you remove the excess copper from the plate to reveal the circuitry on the board.
Before commencing on etching, there are some critical processes that you must undertake to create a pattern on the board.
Primarily, you must impose the circuit patterns you want via the photolithography process onto the board.
The above process is critical in creating an outline on the PCB board that reveals the copper layers you need to remove to remain with a typical circuit board.
Notably, the plate features a tin layer outside, the etch resist layer. On the other hand, the plate has a photoresist layer on the inside which is similarly an etch resist.
To etch each of these layers, you will require the two main techniques discussed below.
Dry Etching
Illustrating Etching.
It is a process whereby you use a plasma that activates a chemical digestion process of the laminate’s atoms to remove the excess copper.
Also, you may use lasers for dry etching, as we’ll highlight below.
Plasma Etching
It is an etching process critical in minimizing liquid waste disposal during PCB manufacturing.
The etching technique involves directing a stream of high-speed gas mixture (a glowing plasma) onto the PCB, which expels excess copper from the surfaces.
Its advantages include the following:
- The process is highly selective, thus making it a better alternative to wet etching techniques.
- It is also non-abrasive and clean, given that you don’t require any chemicals.
- Thirdly, it is the ideal technique for precise etching, especially when dealing with PCBs with a high circuitry network concentration.
However, the technique is quite pricey compared to others and can significantly balloon the cost of PCB assembly, primarily if you’re operating on a large scale.
Laser Etching
Rather than using a stream of gases like in plasma etching, this technique uses a highly precise laser printer that carves out the unwanted copper on the substrate.
The process is quick and doesn’t require extensive procedures like the plasma etching method.
It’s also not abrasive because it doesn’t involve applying chemicals. But it also comes with some downsides.
- Laser etching on an extensively wide circuit board is challenging.
- Also, removing the etching residues is quite an issue, and the process is also pricey.
Wet Etching
Chemical Etching for PCBs.
As its name suggests, this process involves using a solvent (chemical solution) to dissolve the unwanted copper traces from the circuit board.
Since wet etching involves toxic chemicals, you must always wear protective equipment during the etching process.
There are two main wet etching methods.
Alkaline etching
It is very effective in removing copper from the outer surface of a PCB board. The method involves directing a high-speed spray of etchant fluid to expel the copper from the surface.
Once all the copper has been removed, we call this stage the breakpoint, and it signals the end of the etching.
It is highly effective, although it requires caution, as leaving the board too long on the alkaline can damage its integrity.
Acidic etching
Unlike alkaline etching, the acidic method helps remove copper from the board’s inner layer using ferric chloride etchant or sometimes cupric chloride.
We use the latter chemical etchant for a more complete and efficient job as it has an excellent etch rate.
So why do we use acid etching methods to etch inner layers?
- First, the method is not abrasive and doesn’t react with the photoresist.
- Also, it significantly minimizes lateral erosion of the materials you’re removing.
Nonetheless, this procedure is more time-consuming than the other techniques we covered.
Difference Between Wet Etching and Dry Etching
The table below highlights the key differences between the two etching methods.
| Dry Etching | Wet Etching |
| It uses plasma to dislodge copper from the PCB surface and only applies chemicals in its gaseous phase. | The chemical etching process uses acidic or alkaline liquids with chemicals in the liquid phase. |
| Its etch rate is relatively low. The processes take more etching time than wet etching. | It has a comparatively high etch rate, making it ideal for bulk processing PCBs during assembly. |
| It doesn’t require high maintenance practices, although the installation costs of its equipment are high. | The maintenance costs are high as you need to replenish the etching chemicals (acids or bases). But since it’s a typical wet digestion process, the initial equipment costs are low. |
| The technique is highly precise thanks to applying the anisotropic etching process. | Its precision is quite low, and it uses the isotropic process. Therefore, it is not suited for commercial etching. |
| Dry etching is clean and leaves the working environment less messy. | The chemical process of wet etching is messy and leaves the working environment soiled with acids and bases. |
| It is also safe as it doesn’t apply chemicals to remove unwanted copper. | The technique applies hazardous chemicals; hence you must undertake safety measures as its accidents can be fatal. |
What stage of the manufacturing process is Etching?
Industrial PCB assembly for electronic components.
Etching occurs right near the last step of the PCB assembly process. Before etching, you must coat the PCB with tin to protect the copper lines you want to create.
Here’s a detailed process of the etching process after the application of tin.
Apply the etchant solution on the PCB board to remove the layer of copper outside the margins defined by the tin layer.
Next, if you used a wet etching method, dry the PCB before subjecting it to a tin-stripping machine.
This removes the tin to reveal the copper underneath via digesting the upper layer with nitric acid.
Removal of tin signals the end of the etching procedure, meaning you can continue with the subsequent manufacturing stages.
Factors to consider before choosing the etching process
A PCB with components.
Before settling on an etching technique, you must consider critical determinants of the procedure’s success.
Selectivity of Etching
When etching PCBs, you must know the ratio of the etch rates between the materials you have at hand.
This helps determine the tin layer’s mask thickness.
Direction of Etching
We have two primary etching directions.
Isotropic Process
We apply this process in wet etching, and its main feature is that the etching rate occurs in all directions.
While it is effective, it is not easy to control the etching speed as the isotropic process doesn’t happen in a strategically organized manner.
Anisotropic Process
It’s the opposite of the above technique, and it happens during dry etching, whereby the copper layer is removed in an organized manner.
Its primary upside over the isotropic process is the ability to control the direction of etching.
The Benefits of Etch a PCB by Yourself
Tracks of Printed Circuit Board close-up.
- First, it ensures that you’re in control and thus can make as many pieces as you want. Otherwise, manufacturers require you to make a minimum order quantity (MOQ).
- It is a great way to practice the skills learned on a DIY process that improves your understanding of the PCB assembly processes.
- Thirdly, it helps you cut manufacturing costs.
- Lastly, the process is faster than it would take suppose you ordered the PCBs from an overseas manufacturer. It makes sense to use it, especially when dealing with a small number of PCBs.
Common Issues While Etching
- Using wet etching techniques, you risk getting injured by the dangerous chemicals involved.
- Also, industrial PCB assembly is more precise than DIY etching. This means there will be a discrepancy in the PCB quality between the PCB you etch by yourself and another one you buy.
- Disposing of the toxic chemicals used in the etching process is also challenging.
How to Etch PCB Boards at Home?
The chemical etching equipment.
Finally, how do you etch PCBs at your home? Here are the five main steps you need to follow.
Design your PCB
Employ Fritzing, Adobe Illustrator, or Eagle to design your PCB, and flip it once you’re done to have two copies lying side to side.
You also need to apply Ohm’s law in this process to determine if the components you want to include in the circuit can function effectively.
Once you have designed it, print it on a transfer sheet of paper. You should impose it on the shiny side.
Sand your Copper Plate
Wear safety equipment like gloves, then sand the copper surface with sandpaper.
This step ensures it is rough enough for your design to effectively paste on the copper plate.
Pay attention to the edges to ensure you evenly sand the plate.
Wash the plate
Next, apply water and alcohol to the copper board, then allow it to dry. Once well dried, place the transfer paper upside down on the now polished and clean copper plate.
Laminate
Now run the tracing paper with the design facing upside down on the copper plate through a laminator.
The aim is to get the copper plate hot, which will be imperative in imposing the design.
Remove the Transfer Paper
Now soak the plate in a cold water bath to remove the trace paper. This should leave the design printed on the copper plate.
Etch the Copper Plate
Now, it’s time to remove the excess copper from the plate. Immerse the copper plate with the design into an etching solution (for wet etching).
This will dissolve all the copper leaving the design conspicuous in the middle.
Clean with Alcohol
Once the etching is complete, you need to remove any trace of the ink that may have spilled over to the parts of the plate. Use alcohol and a wipe to erase this ink.
Drill Holes
Finally, make holes in the board via a drill bit. There are the points whereby you’ll attach the components.
Summary
Etching is a straightforward process; with our guide, everything will be a breeze if you want to undertake the process at your lab.
For commercial manufacturing of PCB, the above procedure may not be viable as it is relatively slow.
Hence companies often resort to the dry etching techniques we covered earlier.
Thanks for your time, and we wish you the best as you take up your circuit board etching experiment.