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Whether faced with PCB design for the first time or trying to minimize costs in the daily work with electronics, designers are looking for more affordable alternatives at every stage of manufacturing. In this article, we will tell you the most popular methods to remove pcb from keyboard and analyze the advantages and disadvantages of each of them.
In most cases, it is necessary to remove the surface layer of grease or dirt and to reveal the structure of the materials. In the artistic processing of metals for applying a relief pattern, in the production of printed circuit boards and integrated circuits (by photolithography), tracks and pads are formed in this way. Membranes are also made by etching holes. Sometimes the surface is polished in this way after unsuccessful machining.
To understand why etching is necessary, let's briefly consider the main stages of the development of printed circuit boards:
Preparing the keyboard for applying a protective layer: The whole process comes down to cleaning and degreasing the surface. Depending on the degree of contamination, several cleaning options are used, respectively, the cleaner, the easier. If the keyboard is not very dirty, then it is enough to wash it with an abrasive brush or washcloth, if necessary, adding a finely dispersed abrasive powder.
But if a thick oxide film is found, it will need to be removed with a solution of ferric chloride and treated for 5 seconds. After, be sure to rinse under cold running water.
To degrease the surface, wipe it with a lint-free cloth (microfiber is great) dipped in acetone, alcohol, or gasoline. Monitor the quality of the mixture so that there are no additional impurities in them. After processing, rinse the keyboard under running water. If there are no drops left on the surface, then the degreasing was successful.
You can apply a drawing manually on fiberglass using a marker (not washed off with water) or a drawing pen. The minimum value of the track thickness reaches 0.5 mm. The process is time-consuming and is popular only in those cases where it is required to produce one small board.
A lighter option is to transfer a pattern printed on a laser printer into a mirror image on an aluminum foil substrate. The next step is to transfer the toner to the cleaned textolite , using heat from a heated iron (the most commonly used method). The width of the tracks is thinner than the previous method - 0.3 mm. With the help of a laser engraver, it is much easier to put a trace on the keyboard.
No special effort is required. In a special program, the necessary drawing is developed in size. Then it is loaded into the engraver program. Textolite is covered with black matte paint and placed under the engraver. After a short amount of time, the drawing will be completely transferred. Using a photoresist, you can achieve the most accurate and high-quality results. A photoresist is applied to the surface of the board, then a photomask is applied and illuminated. After that, the excess areas are cleaned from the photoresist with the NaOH solvent.
Etching. It is necessary to remove the surface layer from the keyboard without affecting the track pattern.
Board mounting: It is necessary to drill holes in the places marked in advance. The diameter of the holes is selected depending on the details. After, sand the places of drilling from burrs with sandpaper. How the tinning will be carried out (by immersing the radio component in solder or using a soldering iron) is decided by the developer himself.
The most commonly used chemical method is the simplest and most affordable. Let's take a closer look at the etching process:
Do not neglect safety precautions, as hydrogen can be released when pickling metals.
To avoid damage to the keyboard, it is required to protect the surface and edges with special masks. With prolonged interaction with the etchant, the material can be etched off at the edges of the mask.
In some areas, the chemical reaction may differ in speed from the main area. Because of this, etching is selective.
There are many ways to remove copper with an unprotected area mask. Let's consider the main ones.
100 grams of ferric chloride FeCl3 are diluted in warm water H2O (300 ml). You should get a rich golden yellow liquid. The richer the emulsion, the faster the process will be, but usually takes 15 to 60 minutes.
Also, the speed is affected by mixing (you can use a compressor that constantly mixes the liquid) and temperature (you can periodically heat it up). After the end of the procedure, it is necessary to thoroughly rinse the board underwater, it is better to use soap to remove residues. The rest can be stored in an airtight container and used several times.
Among the shortcomings, one can note the low speed of the process and the formation of waste on the surface of the board. You should be careful when working with this method since hard-to-remove yellow spots appear when it hits any objects.
· Nitric acid (HNO3) - rarely used due to high volatility, pungent odor, and strong hygroscopicity. For use, you will need to dilute the acid with water in a ratio of 1/3.
The main thing is not to forget about the mixing sequence. Acid is poured into water, not vice versa. Before lowering the keyboard into the etchant, check for the moment of complete drying of the varnish that protects the tracks. Otherwise, the solution will corrode it. The whole process takes no more than 5 minutes, which is why it is used. Take precautions when handling nitric acid.
· Copper sulfate (CuSO4) and table salt (NaCl) and in water
They are used quite rarely, due to the release of poison and the slow process (up to 8 hours).
In half a liter of water heated to 50 degrees, dissolve 100 grams of salt, then add 50 grams of copper sulfate. In order for the etching to proceed faster, it is necessary to maintain the temperature up to 80 degrees.
Bleeding occurs within an hour. Reuse is possible if stored in a dark place and an unsealed container. Has the ability to regenerate by adding peroxide.
4 tablets of hydroperoxide are added to 300 ml of sulfuric acid in water. The temperature should be maintained at room temperature, and the solution should be stirred periodically. Carefully monitor the ratio of components. If you do not want to get a slow reaction, then make sure that bubbles do not appear, which means an excess of hydrogen peroxide.
For preparation, you will need to dissolve 35 g of a crystalline substance in 65 g of water. The whole process takes about 10 minutes. For optimal action, it is required to maintain a temperature of about 40 degrees, and stir occasionally.
· Citric acid in hydrogen peroxide
All thanks to its low cost, fast operation, and respect for the photoresist.
For a quality process, you need to pour 100 ml of hydrogen peroxide into a small bath, lower the board into it and add 30 g of citric acid. The reaction will happen instantly. Etching occurs very quickly, but if heated, the process will accelerate. Also, to speed up, add 3 grams of salt, which enhances the reaction.
Bleeding occurs evenly. The liquid quickly changes its color from clear to blue. To understand the end time, you need to periodically rinse the board or slightly stir the bath.
Among the disadvantages can be noted the constant release of gases, which can irritate the respiratory tract and eyes. If you decide to heat the solution, it is recommended to perform this procedure in the fresh air. Keep an eye on the temperature, as with strong heating, excessive aggression and an explosion are possible.
The emulsion is not stored. Regeneration is possible, but not necessary, since it is much easier to make a new batch, given its low cost. And it's easier to calculate the proportions too. It leaves no indelible marks. Regardless of the method you choose, remember to follow safety rules, especially when working with poisons and acids. The best option is to work outdoors.