Guide on Different PCB Etching Solution

Etched circuit boards

If you have a well exposed and cleanly developed circuit board, the subsequent PCB etching process is no longer really critical, here the possibility of making mistakes is not nearly as great as with exposure and development.

We etch PCB with sodium persulfate, which is dissolved in a concentration of 220 grams per liter in about 45 degrees of warm water. We always prepare the etching solution fresh, the etchant is inexpensive enough for it. You can also use the PCB etching solution several times until the PCB etching performance decreases. Do not dump the used etching solution into the drain, but collect it and take it to the hazardous waste point!

Use a tight-fitting plastic can with a snap lid during PCB etching

plastic etching

There are different ways to get the circuit board into the etchant, you can use a tight-fitting plastic can with a snap lid, which is constantly shaken slightly during the PCB board etching solution.

A little caution is required here: After the lid is put on, the remaining air in the can heat up and expands, which usually pushes a few drops of caustic outwards. I always do this in an old sink in the basement, latex protective gloves, safety glasses and old clothes are required! After a short time, the copper takes on a matt structure at the areas to be etched.

The PCB board must now be rinsed well with water and dried, then it can be drilled.

After drilling (of course no longer applies to pure SMD boards), the remaining photoresist must be removed. This can either be done with alcohol or by exposure again with UV light without template and subsequent development.

We usually spray the finished board with SK10 solder varnish, this protects the board from corrosion and it is very easy to solder the circuit boards. However, you should let the solder varnish dry for a few hours, otherwise, it is slightly sticky and sensitive to fingerprints.

Of course, this is just one of the simple methods of etching circuit boards, there are of course other options that lead to the same goal. For larger quantities of boards, you’d better consult with us directly.

Ensure health and clothing during the PCB etching process

In order to create circuit boards (e.g. prototypes), some measures to ensure health and clothing must be observed. When etching the circuit boards, an apron and acid-proof gloves should be worn to protect hands and clothing from the acid. After the PCB etching work has been completed, make sure that the chemicals are disposed of properly (special waste) and not simply washed down in the sink.

When printing out the layout with an inkjet printer e.g. CANON IP4600, the highest resolution must be selected so that the printed conductor tracks become opaque.

Preparation of PCB etching service

Create PCB layout

With a layout program, e.g. For example, the “Target SMART”, the layout is created and printed on the film. If necessary, two printouts must be printed out and placed one above the other so that the blackness of the printout is deep enough. It is important to ensure that when creating a one-sided layout, the printout usually represents the underside of the board and not the component side. For templates that have been printed or are available on paper, you can make the layout transparent with the article CONTACT 243 (Pausklar 21) and thus simplify the exposure.

PCB Exposure

The protective film is removed from the photo-coated circuit board and placed on the layout film (print side) and exposed. The exposure will work well without an exposure unit if you place the board on a not too soft foam pad and then lay the layout on the circuit board. So that the layout does not slip, place the glass plate over it. The closer the PCB layout is to the circuit board, the more accurate the exposure will be. The spectral sensitivity of the photo coating is around 400 nm. The exposure time depends on the light source and its distance.

Overexposure is not a problem with a qualitative base material. On the other hand, underexposure complicates or prevents a good quality result in the development.

PCB Development

Prepare the developer bath: Add 10 gr. Of developer to approx. 1.1 liters of warm water (approx. 40-50 °) and stir well. The container should offer enough space for the fingers with the printed circuit board to fit in without problems. Before the exposed circuit board is immersed in the developer bath, please put on the gloves. If the PCB layout has a sharp contour, you should immediately remove the board from the developer bath and rinse it thoroughly with clear water. If the developer bath is no longer fresh, it is helpful to slowly move the board up and down in the developer bath during development. Make sure that you don’t rinse with a rag when rinsing, as this could blur the contours of the layout.

If the layout has “gone” because the developer bath was too strong or the board has been in the developer bath for too long, you can coat the board again with photoresist KONTAKT 235 (positive 20) after it has been freed from the developer and dried too thick) and repeat the procedure of exposure and development.

Circuit board etching process

A container e.g. fills the etching bowl from the article “development set” with hot water (approx. 50-60 °). About 0.4 liters of water are required for 100 gr. Of etchant. Both must be stirred until the etchant has completely dissolved. The faster this process is completed, the hotter the etching bath remains, which speeds up the actual etching process. It should be noted that rising water vapors are not inhaled.

Depending on the temperature of the etching bath, approx. 15-30 minutes should be planned for the etching process. It is important that acid-resistant gloves are worn to move the board in the PCB etching bath. By swiveling the circuit board, some oxygen comes into the etching bath, which accelerates the PCB etching process.

A successful process can be achieved very well with the article “Etching Device 1” without having to intervene yourself, but being able to observe the etching process.

The progress of the printed circuit board etching process for epoxy boards can be recognized from the fact that the contours of the layout stand out and the board appears transparent. If the desired layout is achieved and there are no longer any connections between the conductor tracks, the etching process must be ended. The circuit board is then rinsed under clear water (still with acid-resistant gloves) and dried with paper towels or compressed air.

The conductor tracks, which are now covered with photoresist, can be exposed again and then placed in the developer bath to reveal the pure copper. After the photoresist has been removed from the copper, the board must be cleaned and dried. Alternatively, photoresist residues can also be used with e.g. Alcohol, acetone or alcohol can be removed.

In order to protect the conductor tracks from corrosion, we recommend covering the circuit board with a protective lacquer, e.g. KONTAKT 227 (solder lacquer SK 10).

Now the board can be drilled, assembled and then tested or used.

The advantages of PCB etching solution

Quite simply: You have built a good circuit on a breadboard, but somehow the whole thing doesn’t look very professional. What could be more obvious than professionally etching the circuit onto a circuit board? Looks better and is not so prone to errors, because anyone who has ever built a complete Europlatine with botch wire will notice how exhausting it is to re-solder a wire that has started.

But now to the etching:

The principle is very simple: a film on which the conductor tracks are applied is used to expose a photosensitive circuit board.

As a result, the applied photoresist becomes fragile where light has come. This will remove the paint on the fragile areas. The copper is then removed in the PCB etching process at the points where the paint has been destroyed.

Creating the slide:

We won’t go into that here. There are many programs with which the PCB layouts can be designed. We can name Eagle as an example. There is a free version of this on the manufacturer’s website. With these programs, the circuit diagram is drawn and the layout is created.

This is put on film with a printer (Attention: with inkjet printers you need special film).

It is best to print out the film twice and stick these two printouts together. This is necessary because the ink usually does not cover enough, and the conductor tracks would then fray when etching.

Exposing the printed circuit board:

The circuit board is a plastic plate with a copper coating and photoresist. This paint becomes brittle when exposed to light.

The first thing to do is saw the circuit board. Then it is exposed. This is best done with a halogen spotlight (I use a 500W spotlight with a distance of 1.50m). The protective film is removed from the printed circuit board and the printed film is placed on it (note: make sure that the copper side is the underside afterward, so put it upside down). Now the halogen spotlight is switched on. You have to find out the exposure time yourself (preferably with small test pieces) since it depends on the manufacturer of the circuit board. It is important to mention that you should remove the glass plate from the halogen spotlight.

What makes the photoresist brittle is UV light, and glass filters UV light.

To build the exposure frame

Developing the PCB:

After exposure, the circuit board must be developed. This removes the brittle photoresist and only the varnish where there was no light is retained.

One remark in advance: The acids used in the following descriptions are not very skin-friendly, so: gloves on!

This is placed in the amount as stated on the packaging (approx. 1 spoon per liter of water) in a plastic bowl and dissolved with water. Incidentally, this is best done while the circuit board is exposed.

After exposure, the circuit board is immediately placed in the solution, otherwise, it will be overexposed and therefore unusable. After some time in the solution, you can see how the brittle paint is removed and detached from the circuit board (the places where the smile is still there are darkened by a built-in dye). A little stirring helps. If you can clearly see the structures of the conductor tracks (as dark lines), the circuit board has been fully developed. If she is left in for too long, she will be overdeveloped.

After the circuit board has been removed from the solution, it is rinsed off with water.

The acid can only be used for a few hours and is then used up.

However, it belongs to hazardous waste and not in the drain.

Etching the PCB:

Now the circuit board only needs to be etched (i.e. the copper at the exposed locations is removed).

It is supplied in powder form and must be dissolved in water. This circuit board etching solution can be used for many months to years. However, they should not be kept in an airtight container. I just put a bike valve in the lid.

As a container for etching, I simply use a square plexiglass case. But a normal bowl does it too.

The liquid should be warmed up first (it is best to simply place the storage container in a hot bath). So the solution works better. Then the solution is poured into the etching container. Now all you have to do is insert the circuit board (tie it up, then it will be easier to get it out).

The circuit board is ready after approx. 30-45min. The copper has been removed from all exposed areas. Now the circuit board is rinsed with water and dried.

You can speed up the etching process by placing a hose in the etching container and connecting it to an air pump (e.g. for aquariums). The resulting oxygen supply accelerates the etching process. The left picture shows the finished PCB boards.

The unclean spots come through to an old PCB etching solution. But for the illustration is enough.

The rework:

Now the holes for the components have to be drilled. The best way to do this is with a drill press and a 0.8mm drill.

Finally, the copper side is provided with a coating of solder varnish (contact chemical). This makes it easier to solder and the varnish protects against corrosion.

Now solder, and there is a clean circuit that is impressive.

 

 

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