Etching of printed circuit boards in ammonium persulfate solution
On the Internet, there are quite a lot of ways described how to etch a printed circuit board in a solution of ferric chloride or hydrogen peroxide with citric acid. In this case, another method of etching is undeservedly forgotten - in a solution of ammonium persulfate. It combines a high etching rate, low cost ingredients, ease of process. Ammonium persulphate can be bought in stores of radio components, it costs about the same as ferric chloride.It is a white powder with a slight chemical smell.Step 2. Knead the etching solution. The instructions on the jar with the chemical indicated the proportions “250 g of persulfate per 500 ml of water”, however, at such proportions, the etching rate is very low, and the consumption is huge. Experimentally, I found that the etching rate is maximized by stirring 1 part of persulfate into 8-10 parts of water (1: 8-10). The consumption of powder is very small. It also does not hurt to add a little salt to the solution, it will positively affect the etching rate. Ammonium persulfate must be taken with a plastic or wooden spoon, no metal. The container must also be plastic.A feature of etching boards in ammonium persulphate is that the solution must have a temperature of more than 40 degrees, otherwise the reaction will not proceed at all. Therefore, the water must be taken sufficiently warm, so that it does not have time to cool down while the board is being etched.Overdoing in the water temperature is also not worth it, the tracks can move. You can also heat the board during the etching process, for example, in a water bath or using a home-made hot plate, as I do.Step 3. We lower the board into the warm prepared solution. The etching process starts right away. It does not hurt to periodically shake the board in the solution, mixing it. The advantage of ammonium persulfate is that its solution, unlike ferric chloride, remains clear, you can monitor the process without removing the board. In addition, when etching in persulphate, there are almost no gas bubbles, as in hydrogen peroxide solution, the tracks do not come off, and the board does not float to the surface.After 20 minutes, the board was completely etched,now it remains only to remove the toner, drill holes, tin. Thus, this method of etching is a good alternative to the popular chlorine iron and hydrogen peroxide.Advantages:
So, how do I etch the board in ammonium persulfate solution?Step 1. Prepare a board from which to bleed copper. You can draw tracks with indelible marker, nail polish, or transfer a drawing from a computer using LUT, photoresist.I use laser-iron technology.
- High etching rate.
- Transparency of the solution.
- Absence of bubbles.
- The need to heat the solution.
- Ammonium persulphate is quite a rare item in stores.
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