Etching of boards with hydrogen peroxide and citric acid. How to create a printed circuit board using laser iron The easy way to etch printed circuit boards

Hello dear friends! At 5:30 in the morning, today I specially woke up early to write something useful. And yes, today is May 9 on the calendar, so I congratulate you on this great day, on Victory Day!

And Today we will talk about an etching solution printed circuit boards which is striking in its accessibility and simplicity. Yes, today we'll talk about how you can etch a board using hydrogen peroxide and citric acid, and a bit of salt.

What etching solutions exist

There are many different solutions for etching printed circuit boards, among which there are popular etching mixtures and there are also not very popular ones.

In my opinion, the most popular pickling solution in the amateur radio environment is ferric chloride. Why this is so, I do not know, maybe this is a conspiracy of sellers of radio stores who specifically offer ferric chloride and tactfully keep silent about the alternatives. And there are alternatives:

1. Copper sulfate etching with salt
2. Etching with ammonium persulfate
3. Etching with sodium persulfate
4. Etching with hydrogen peroxide and hydrochloric acid
5. Etching with hydrogen peroxide and citric acid

If you have any more options for pickling solutions, I would be grateful if you share them in the comments to this post.

What are the disadvantages of etching in ferric chloride

A solution of ferric chloride is good for everyone, it is not difficult to prepare it and the etching process usually goes lively. When cooking, it is very easy to deal with the concentration, which is called "by eye". Once prepared, the solution is enough for dozens of boards. But it has disadvantages that really interfere:

1. The solution is not transparent, which makes it difficult to control the process. You have to constantly get the board out of the pickling solution.
2. Ferric chloride solution stains plumbing very strongly. Each etching session ends with the process of scraping plumbing fixtures (sinks, bathtubs and everything with which the solution may come in contact).
3. Smudges clothes very badly. When working with ferric chloride, you should wear clothes that you will not mind throwing away, because the solution eats into the fabric very strongly, so much that it is almost impossible to wash it later.
4. The solution aggressively affects any metal present in the vicinity, even if stored in an unsealed container, the nearest metal objects can become rusty. The jar with ferric chloride was somehow closed with a metal lid (the lid was painted), after a couple of months this lid turned into dust.

How to etch boards in hydrogen peroxide and citric acid

Although I have always been an adherent of the conservative path, despite all the advantages of the FeCl3 solution, its disadvantages are gradually pushing towards the search for an alternative pickling mixture. And so I decided to test the method of etching boards in hydrogen peroxide and citric acid.

On the way home, I went to a grocery store and, in addition to food for a delicious dinner, grabbed 4 bags of citric acid, 10g each. each. Each bag cost me less than 6p.

I went to the pharmacy and bought a bottle of hydrogen peroxide, it cost me 10 rubles.

I do not have any project at the moment, so I decided to purely test the method, to understand what the whole point is. I found a piece of foil-clad textolite in my zagashnik and made a few strokes with a permanent marker. This is a kind of emulation of tracks and copper polygons, for experimental work it will go quite well.

The solution is not difficult to prepare, but it is important to observe the proportions. Therefore, pour 100 ml of peroxide into a plastic tray and pour 30 g of citric acid, Since I had 10 g sachets, I poured 3 sachets. It remains to salt the whole thing, put 5 g of table salt, this is about 1 teaspoon without a slide.

I noticed that salt can be added even more than is required, this leads to an acceleration of the process. Mix thoroughly. It is very important that you do not need to add water to the solution, therefore, for preparation, we choose such a container so that the solution covers the board, or we increase the amount of the solution, observing the proportions.

We put our "printed circuit board" into the resulting solution and observe the process. I want to note that the solution turned out to be completely transparent.

During the etching process, bubbles begin to emerge and the temperature of the solution increases slightly. Gradually, the solution begins to turn greenish - a sure sign that etching is in full swing. In general, the whole etching process took me less than 15 minutes, which made me very happy.

But when I decided to etch another board in the same solution, a bit larger than this one, everything turned out to be not so positive. The board was etched exactly by half and the process slowed down very much, slowed down so much that the process had to be completed in ferric chloride.

Apparently the power of the solution is enough for the time when there is a chemical reaction between hydrogen peroxide and citric acid. The process can be extended by adding and adding the required components.

Benefits of Hydrogen Peroxide and Citric Acid Etching

From the experience gained, it can be concluded that this method, like others, has its pros and cons, it has both its advantages and disadvantages.

Main advantages:

1. Easy accessibility - all components are easily found in the nearest pharmacy and grocery store.
2. Relative cheapness - all the components for preparing the solution are not expensive, less than 100 rubles. (at the time of this writing)
3. Transparent solution - the resulting solution is transparent, which simplifies the observation and control of the etching process.
4. Etching is fast enough and does not require heating
5. Does not stain plumbing

What are the cons

Unfortunately, in addition to all the advantages, this etching method has some drawbacks.

Cons of etching in hydrogen peroxide and citric acid:

1. Disposable solution - solution suitable for single use only, i.e. in the process of a chemical reaction taking place in it. It will not be possible to etch many boards in it; for each time you will have to prepare the solution again.
2. Expensive - not looking at the fact that all the ingredients are cheap, in the long term, the solution turns out to be more expensive than the same chlorine jelly. After all, for each new board, the solution will have to be prepared anew.

That is, in principle, all the disadvantages. In my opinion, this method of etching boards has the right to life and it will definitely find its supporters and admirers. And in some cases, this method may become the only possible alternative, for example, in a remote village with a pharmacy and a grocery store.

And on this I will round off. Outside the window, it has long dawned and it is time to prepare a delicious breakfast.

Once again, I congratulate you on Victory Day and wish you good luck, success and a peaceful sky over your head!

With n / a Vladimir Vasiliev

In the article we will tell you about the methods of making a printed circuit board and etching the board.

There are many ways to make a PCB. The main method that I personally use is making a board from foil-clad PCB (getinax), by drawing with a drawing pen and etching in a chemical solution. It so happened that I started drawing boards from the sixth grade of the school (by the present - from the fifth), when computers were the size of entire rooms. At that time I also "trained". Therefore, I draw the board on a sheet of paper in a cage faster than on a computer, using special programs. True, the most voluminous circuit board in terms of element base that I have ever drawn by hand was a board consisting of fourteen microcircuits and a couple of hundred simple elements.

Making a board by drawing a drawing with a drawing pen or, more often, in recent times, LUT (laser-ironing technology) and etching in a chemical solution consists of the following stages, the difference from other methods may slightly differ in the operations themselves and in their sequence:

1. Planning the placement of radio elements on the board and routing of conductors (tracks). Currently, there are many programs for the development of radio boards. It's easier to use them. You can engage in development without using special programs, but this requires some perseverance and many times more time. In this case, for convenience, the board is drawn on a sheet of paper in a cage, and for redevelopment, it is drawn anew;

2. A board of the required size is cut out of foil-coated PCB, or getinax. More convenient material is a textolite, it is essentially a multilayer fiberglass, on it and the foil holds better than on getinax. Getinax is a sheet material made of pressed paper impregnated with bakelite varnish. Getinax is a lower quality material than textolite, and has several properties that I personally do not like:

- may delaminate;

- printed conductors bounce off of overheating faster than that of a PCB, which makes it difficult to replace radio components without damaging the board in the event of their failure;

- there are cases of overheating of radio components, from which the radio board can be "smoked". The same happens when moisture gets into high-voltage circuits. Burned-out getinax, often turns into a conductor (something like graphite). The same happens with the getinax when moisture accidentally gets into high-voltage circuits. The latter can bring you enormous trouble;

But with all that, it's decently cheaper and is cut with scissors. This is useful when you need to make a fast one-sided board using SMD parts.

3. The ends of the board are processed from sharp corners and burrs with a file or sandpaper;

4. The cut-out board is wrapped in a sheet with a drawn board. With a thin core, light hammer blows, pits (marking) of future holes are made, in those places that were previously marked on the sheet;

5. In the marked places, holes are drilled for future radio components. For small parts - resistors, capacitors, thin-lead transistors, a 0.5mm drill is used, for thicker leads - a 0.7mm drill. Other sizes can be used if required. As a drill, it is more convenient to use a portable drilling machine, which can be purchased at a specialized radio store. You can also use a manual electric drill with a certain skill;

6. After drilling the holes, the board is sanded with sandpaper. All burrs formed as a result of drilling are cleaned off, and the foil is cleaned for further tracing and etching;

7. A drawing pen is made from an ordinary empty ballpoint pen refill. To do this, the rod is heated over the flame of a match (or lighter), and when the plastic melts, the rod is pulled out. After solidification of the plastic, the end of the reefer is cut to obtain a hole with a diameter of approximately 0.2 ... 0.4 mm;

8. A varnish (more convenient - nail varnish) 2 ... 5 cm in height is typed into the drawing pen, after which a printed circuit board is drawn: soldering pads are made around the holes, and printed wiring tracks are drawn between these pads. With a certain skill and using rulers as guides, the quality of the drawing may not be inferior to factory radio cards;

9. After the varnish dries, the unlacquered areas of the board are etched by placing the board in a solution of ferric chloride. At the same time, the copper of the tracks protected by varnish is not etched, and not the copper coating of the board covered with varnish, entering into chemical reaction dissolves in ferric chloride. To speed up the etching process, the solution with the board can be heated in a water bath, or simply put on a central heating battery;

10. After etching, the board is washed with water and with a cotton swab moistened with acetone or another solvent, the varnish is removed from the board, after which it is washed again under running water;

11. It is better to solder radio components using low-melting solder and flux - rosin dissolved in alcohol.

It should be added:

A disposable syringe can be used as a reefeder, while breaking the oblique cut of the needle, sharpen it so that there are no sharp scratching surfaces of the tip. Recently, there are many markers on the market, the dye of which is not washed off with water and gives a sufficiently strong protective layer, so they can also be used as a reefer.

Some craftsmen, after etching the board, also tinker. Tinning is done in one of two ways:

1. Soldering iron;

2. The iron tray is filled with Rose or Wood alloy. The alloy, in order to avoid oxidation of the solder, is completely covered with a layer of glycerin on top. For tinning, the board is immersed in the melt for no more than five seconds. The bath is heated with an electric stove.

Recently, the printer method of transferring the pattern of a radio card has become more and more widespread.

It consists in the following:

1. With the help of special programs, a radio board is designed and drawn;

2. A mirror image of the board is printed on a laser printer on a substrate. In this case, thin coated paper (covers from various magazines), fax paper, or film for laser printers are used as a substrate.

3. On the prepared board, the front side (picture) is applied a substrate and using a very hot iron "rubbed" against the board. To evenly distribute the iron pressure on the substrate, it is recommended to put several layers of thick paper between them. The toner melts and sticks to the board.

4. After cooling down, there are two options for removing the backing: either the backing is simply removed after transferring the toner to the board (in the case of film for laser printers), or it is pre-soaked in water and then gradually separated (coated paper). This leaves the toner on the board. After removing the backing, in those places where the toner is still separated, you can retouch the board manually.

5. The board is etched in a chemical solution. During etching, the toner does not dissolve in ferric chloride.

This method allows you to get a very beautiful printed wiring, but you need to get used to it, because it may not work the first time. The fact is that a certain high-temperature regime is required. There is only one criterion: the toner must have enough time to melt enough to adhere to the board surface, and at the same time, it must not have time to reach a semi-liquid state so that the edges of the tracks do not flatten. Removing the paper sheet requires some softening with water, otherwise the paper sheet may come off along with the toner. Drilling holes in the printed circuit board is carried out after etching.

PCB Etching

There are many compounds available for chemically etching copper from a printed circuit board. All of them differ in the speed of the reaction and the availability of chemical reagents necessary for the preparation of a solution. Do not forget that any chemistry is harmful to health, so do not forget about precautions. Here are the chemical solutions for etching printed circuit boards that I personally used:

1. Nitric acid (HNO 3)- the most dangerous and not popular reagent. Transparent, has a pungent odor, is highly hygroscopic, and also evaporates strongly. Therefore, it is not recommended for home storage. For etching, it is used not in pure form, but in a solution with water in a ratio of 1/3 (one part of acid to three parts of water). Do not forget that it is not water that is poured into the acid, but, on the contrary, the acid is poured into the water. The etching process takes no more than five minutes, with vigorous gas evolution. "Azotka" also dissolves the varnish, therefore, before using it, it is necessary to let the varnish dry well. Then, during etching, he will not have time to soften and lag behind copper plating... Precautions must be strictly followed.

2. A solution of sulfuric acid (H 2 SO 4) and hydrogen peroxide (H 2 O 2)... To prepare this solution, it is necessary to throw four tablets of hydrogen peroxide (pharmacy name - "Hydroperit") on a glass of ordinary battery electrolyte (solution of sulfuric acid in water). The finished solution should be stored in a dark container, not sealed hermetically, since gas is released during the decomposition of hydrogen peroxide. Etching time for PCB is in the order of one hour for a well-mixed fresh solution at room temperature. This solution after etching can be reduced by adding hydrogen peroxide H 2 O 2. Estimation of the required amount of hydrogen peroxide is carried out visually: the copper plate immersed in the solution must be repainted from red to dark brown... The formation of bubbles in the solution indicates an excess of hydrogen peroxide, which leads to a slowdown in the etching reaction. Precautions must be strictly followed.

Attention: When using the two previously mentioned solutions, all precautions must be taken when working with corrosive chemicals. All work must be done only on fresh air or under the hood. If the solution comes into contact with the skin, it must be washed immediately with plenty of water.

3. Ferric chloride (FeCl 3) is the most popular PCB etching reagent. In 200 ml of warm water dissolve 150 g of ferric chloride in powder. The etching process in this solution can take 15 to 60 minutes. The time depends on the freshness of the solution and the temperature. At the end of etching, the board must be washed with plenty of water, preferably with soap (to neutralize acid residues). The disadvantages of this solution include the formation of wastes during the reaction, which settle on the board and interfere with the normal course of the etching process, as well as a relatively low reaction rate.

4. A solution of sodium chloride (NaCl) and copper sulfate(CuSO 4) in water... 500 ml hot water(about 80 ° C) dissolve four tablespoons of sodium chloride and two tablespoons of powdered copper sulfate. The solution is ready for use immediately after cooling (when using heat-resistant paint, cooling is optional). Etching time is about 8 hours. To speed up the etching process, the solution with the board can be heated to 50 ° C.

5. A solution of citric acid in hydrogen peroxide (H 2 O 2). In a small bath (up to 100 ml), a printed circuit board is poured with a large volume of hydrogen peroxide, after which 1 tablespoon of citric acid is added there. After that, the process of etching the printed circuit board begins. It is actively accompanied by a change in the color of the liquid from transparent to blue. The edges are smooth and, if you first walk on the foil-coated fiberglass with fine emery, then everything is etched very evenly.

Using this method, I managed to get boards with the following parameters:

The gap between the conductors is 0.2 mm.

With a specified conductor thickness of 0.25 mm, in fact, it turned out to be 0.2-0.22 mm.

Dimensions of boards up to 100x200 mm.

If you need to pickle faster, you can add a pinch of regular table salt. It will speed up the process, but be careful: During the etching process, heat energy is released and usually the solution heats up decently. During my long-term practice of working with this solution, it blew up 2 times and "splattered" everything around. Of course, everything was rubbed off very quickly an ordinary rag with soda and no traces on clothes or things from it (unlike ferric chloride, it does not remain), but it is quite interesting to observe.

The average pickling time is 20-30 minutes.

I did not use other solutions for etching printed circuit boards. It is more pleasant to work with the last item, since the components can be obtained in any city.

If you need to do it efficiently

In principle, a printed circuit board can also be ordered at a factory specialized for their production. Of course, it costs more than you would make it yourself, but the workmanship will be many times better. If you have a lot of such prototypes, then I highly recommend watching a video on the production of a printed circuit board assembly immediately.

The point here is as follows. The factory takes money for 2 things: for preparation for production, during which it translates your files from printed circuit board to its standard and manufactures tooling, and for the manufacturing itself. The production itself is not expensive: factories buy blanks for radio payments in large volumes and the production itself is cheaper from them, but they charge an average of 2-3 thousand rubles for preparation. For me, it doesn't make sense to pay that kind of money for making one board. But, if there are 10-20 of these boards, then this preparation money is divided between all boards and it turns out to be cheaper.

Tahiti! .. Tahiti! ..
We have not been to any Tahiti!
We are well fed here too!
© Cat from the cartoon

Entry with retreat

How were boards made before in domestic and laboratory conditions? There were several ways - for example:

1. drew future guides with race fereders;
2. engraved and cut with cutters;
3. pasted tape or electrical tape, then the drawing was cut out with a scalpel;
4. made the simplest stencils with subsequent drawing using an airbrush.

The missing elements were completed with refeeding tools and retouched with a scalpel.

It was a long and laborious process, requiring remarkable artistic ability and accuracy from the "painter". The thickness of the lines could hardly fit into 0.8 mm, there was no repetition accuracy, each board had to be drawn separately, which greatly constrained the release of even a very small batch printed circuit boards(hereinafter - PP).

What do we have today?

Progress does not stand still. The times when radio amateurs painted PP with stone axes on mammoth skins have sunk into oblivion. The appearance on the market of generally available chemistry for photolithography opens up completely different prospects for the production of PP without metallization of holes at home.

Let's take a quick look at the chemistry used today to manufacture PP.

Photoresist

You can use liquid or film. We will not consider the film in this article due to its scarcity, the difficulties of rolling onto the PCB and the lower quality of the printed circuit boards obtained at the output.

After analyzing the market offers, I settled on POSITIV 20 as the optimal photoresist for home PCB production.

Purpose:
POSITIV 20 is a photosensitive varnish. It is used for small-scale production of printed circuit boards, copper engravings, when carrying out work related to the transfer of images to various materials.
Properties:
High exposure characteristics provide good contrast of transferred images.
Application:
It is used in areas related to the transfer of images to glass, plastics, metals, etc. in small-scale production. The method of application is indicated on the bottle.
Specifications:
Color: blue
Density: at 20 ° C 0.87 g / cm 3
Drying time: at 70 ° C 15 min.
Consumption: 15 l / m 2
Maximum photosensitivity: 310-440 nm

The instructions for the photoresist say that it can be stored at room temperature and is not subject to aging. Strongly disagree! It should be stored in a cool place, for example, on the lower shelf of the refrigerator, where the temperature is usually maintained at + 2 ... + 6 ° C. But in any case, do not allow negative temperatures!

If you use photoresists sold "on tap" and do not have opaque packaging, you need to take care of protection from light. It should be stored in complete darkness and temperature + 2… + 6 ° C.

Enlightener

Likewise, the most appropriate educator I find is the TRANSPARENT 21 I use all the time.

Purpose:
Allows direct transfer of images onto surfaces coated with POSITIV 20 light-sensitive emulsion or other photoresist.
Properties:
Gives transparency to paper. Provides transmission of ultraviolet rays.
Application:
For quickly transferring the contours of drawings and diagrams to the substrate. Allows you to significantly simplify the reproduction process and reduce the time NS e costs.
Specifications:
Color: transparent
Density: at 20 ° C 0.79 g / cm 3
Drying time: at 20 ° C 30 min.
Note:
Instead of ordinary paper with an enlightener, you can use transparent film for inkjet or laser printers - depending on what we will print the photomask on.

Photoresist developer

There are many different solutions for developing photoresist.

It is advised to develop with the help of "liquid glass" solution. His chemical composition: Na 2 SiO 3 * 5H 2 O. This substance has a huge number of advantages. Most importantly, it is very difficult to overexpose the PP in it - you can leave the PP for an unspecified time. The solution almost does not change its properties with temperature drops (there is no risk of decomposition with an increase in temperature), it also has a very long shelf life - its concentration remains constant for at least a couple of years. The absence of the problem of overexposure in the solution will allow to increase its concentration to reduce the time of PP development. It is recommended to mix 1 part of the concentrate with 180 parts of water (slightly more than 1.7 g of silicate in 200 ml of water), but it is possible to make a more concentrated mixture so that the image is developed in about 5 seconds without the risk of surface destruction if overexposed. If you cannot get sodium silicate, use sodium carbonate (Na 2 CO 3) or potassium carbonate (K 2 CO 3).

I have not tried either the first or the second, so I will tell you how I have been showing without any problems for several years. I am using a caustic soda solution in water. 1 liter cold water- 7 grams of caustic soda. If there is no NaOH, I use a KOH solution, doubling the concentration of alkali in the solution. The development time is 30-60 seconds with the correct exposure. If, after 2 minutes, the pattern does not appear (or appears weakly), and the photoresist begins to wash off the workpiece, it means that the exposure time has been chosen incorrectly: you need to increase it. If, on the contrary, it quickly manifests itself, but both the illuminated and non-illuminated areas are washed away - either the concentration of the solution is too high, or the quality of the photomask is too low (ultraviolet light freely passes through the "black"): you need to increase the printing density of the template.

Copper etching solutions

Excess copper from printed circuit boards is vented using various etchants. Among people doing this at home, ammonium persulfate, hydrogen peroxide + hydrochloric acid, copper sulfate solution + table salt are often common.

I always use ferric chloride in glassware. When working with the solution, you need to be careful and attentive: if it gets on clothes and objects, rusty spots remain, which are difficult to remove with a weak solution of citric (lemon juice) or oxalic acid.

We heat the concentrated solution of ferric chloride to 50-60 ° C, immerse the workpiece in it, gently and without effort drive it with a glass rod with a cotton swab at the end along the areas where copper is less efficiently etched - this achieves a smoother etching over the entire area of ​​the PCB. If the speed is not forcibly equalized, the required etching duration increases, and this eventually leads to the fact that in the areas where copper has already been etched, the undercutting of the tracks begins. As a result, we have not at all what we wanted to get. It is highly desirable to provide continuous mixing of the pickling solution.

Photoresist remover chemistry

What is the easiest way to wash off an already unnecessary photoresist after etching? After a lot of trial and error, I settled on plain acetone. When it is not there, I wash it off with any solvent for nitro paints.

So, we make a printed circuit board

Where does a high quality PCB start? Right:

Create a high quality photomask

For its manufacture, you can use almost any modern laser or inkjet printer. Considering that we are using a positive photoresist in this article, where copper should remain on the PCB, the printer should draw in black. Where there should be no copper - the printer should not draw anything. Highly important point when printing a photomask: you need to set the maximum dye flow (in the printer driver settings). The darker the shaded areas, the more likely you are to get great results. No color needed, a black cartridge is sufficient. From that program (we will not consider programs: everyone is free to choose himself - from PCAD to Paintbrush), in which the photomask was drawn, we print on a regular sheet of paper. The higher the print resolution and the higher the quality of the paper, the higher the quality of the photomask will be. I recommend at least 600 dpi, the paper should not be very thick. When printing, take into account that the side of the sheet on which the paint is applied, the template will be placed on the PCB blank. If you do otherwise, the edges of the PCB conductors will be blurry, indistinct. Let the paint dry if it was an inkjet printer. Then we saturate the TRANSPARENT 21 paper, let it dry and ... the photomask is ready.

Instead of paper and an enlightener, it is possible and even very desirable to use transparent film for laser (when printing on a laser printer) or inkjet (for inkjet printing) printers. Please note that these films have unequal sides: only one working. If you will be using laser printing, I highly recommend doing a "dry" feed of a sheet of film before printing - just feed the sheet through the printer, simulating printing, but not printing anything. Why is this needed? When printing, the fuser (oven) will warm up the sheet, which will inevitably lead to its deformation. As a result, there is an error in the PCB geometry at the output. When making double-sided PCBs, this is fraught with a mismatch of layers with all the consequences ... And with the help of a "dry" run, we will warm up the sheet, it will be deformed and will be ready to print a template. When printing, the sheet will pass through the oven for the second time, but the deformation will be much less significant - it has been checked repeatedly.

If the software is simple, you can draw it manually in a very convenient program with a Russian interface - Sprint Layout 3.0R (~ 650 KB).

On preparatory stage draw not too cumbersome electrical circuits very convenient in the also Russified program sPlan 4.0 (~ 450 KB).

This is how the finished photomasks look like, printed on the Epson Stylus Color 740 printer:

We print only in black, with maximum dye watering. Material - transparent film for inkjet printers.

PCB surface preparation for photoresist application

For the production of PP, sheet materials coated with copper foil are used. The most common options are with copper thickness of 18 and 35 microns. Most often, for the production of PP at home, sheet textolite (fabric pressed with glue in several layers), glass fiber laminate (the same, but epoxy compounds are used as glue) and getinax (pressed paper with glue) are used. Less commonly - sittal and polycor (high-frequency ceramics - used extremely rarely at home), fluoroplastic (organic plastic). The latter is also used for the manufacture of high-frequency devices and, having very good electrical characteristics, can be used anywhere and everywhere, but its use is limited by its high price.

First of all, you need to make sure that the workpiece does not have deep scratches, scoring and corroded areas. Further, it is advisable to polish the copper to the mirror. We polish not particularly zealous, otherwise we will erase the already thin layer of copper (35 microns) or, in any case, we will achieve different thicknesses of copper on the surface of the workpiece. And this, in turn, will lead to a different etching rate: it will etch away faster where it is thinner. And a thinner conductor on the board is not always good. Especially if it is long and a decent current will flow through it. If the copper on the workpiece is of high quality, without sins, then it is enough to degrease the surface.

Applying photoresist to the surface of the workpiece

We place the board on a horizontal or slightly inclined surface and apply the composition from an aerosol package from a distance of about 20 cm. Remember that the most important enemy in this case is dust. Every particle of dust on the surface of the workpiece is a source of problems. To create a uniform coating, spray the aerosol in continuous zigzag strokes starting from the top left corner. Do not use an excessive amount of aerosol, as this causes unwanted smudges and results in a non-uniform coating thickness that requires a longer exposure time. In summer, high ambient temperatures may require re-treatment or aerosol spraying from a shorter distance to reduce evaporation losses. When spraying, do not tilt the can too much - this leads to an increased consumption of propellant gas and, as a result, the aerosol can stops working, although there is still a photoresist in it. If you get unsatisfactory results with aerosol spray application of the photoresist, use a centrifuge coating. In this case, the photoresist is applied to a board mounted on a rotating table with a drive of 300-1000 rpm. After finishing the coating, the board should not be exposed to strong light. By the color of the coating, you can approximately determine the thickness of the applied layer:

• light gray blue - 1-3 microns;
• dark gray blue - 3-6 microns;
• blue - 6-8 microns;
• dark blue - more than 8 microns.

On copper, the coating color may have a greenish tint.

The thinner the coating on the workpiece, the better the result.

I always apply the photoresist in a centrifuge. In my centrifuge, the rotation speed is 500-600 rpm. Fastening should be simple, clamping is done only at the ends of the workpiece. We fix the workpiece, start the centrifuge, spray it on the center of the workpiece and observe how the photoresist spreads over the surface in a thin layer. By centrifugal forces, excess photoresist will be dumped from the future PCB, therefore I highly recommend providing a protective wall so as not to turn workplace to the pigsty. I use a regular pan with a hole in the bottom. Through this hole passes the axis of the electric motor, on which a mounting platform in the form of a cross of two aluminum rails is installed, along which the ears of the workpiece clamp "run". The ears are made of aluminum corners, clamped on a rail with a wing nut. Why aluminum? Small specific gravity and, as a consequence, less beating when the center of mass of rotation deviates from the center of rotation of the centrifuge axis. The more accurately the workpiece is centered, the less beating will be due to the eccentricity of the mass and the less effort is required to firmly attach the centrifuge to the base.

The photoresist is applied. Let it dry for 15-20 minutes, turn the workpiece over, apply a layer on the second side. We give another 15-20 minutes to dry. Do not forget that direct sunlight and fingers on the working sides of the workpiece are unacceptable.

Tanning of the photoresist on the surface of the workpiece

We place the workpiece in the oven, gradually bring the temperature to 60-70 ° C. We stand at this temperature for 20-40 minutes. It is important that nothing touches the surfaces of the workpiece - only touching the ends is allowed.

Aligning the top and bottom photomasks on the workpiece surfaces

On each of the photomasks (upper and lower) there should be marks according to which 2 holes must be made on the workpiece - to align the layers. The farther the marks are from each other, the higher the alignment accuracy. I usually put them on the diagonal of the templates. Using these marks on the workpiece, using a drilling machine strictly at 90 °, we drill two holes (the thinner the holes, the more accurate the alignment - I use a 0.3 mm drill) and match the templates along them, not forgetting that the template must be applied to the photoresist the side that was printed on. We press the templates to the workpiece with thin glasses. It is preferable to use quartz glass - they transmit ultraviolet light better. Even better results are obtained by plexiglass (plexiglass), but it has an unpleasant scratch property, which will inevitably affect the quality of the PP. For small PCBs, you can use the transparent cover from the CD packaging. In the absence of such glasses, you can use a regular window glass, increasing the exposure time. It is important that the glass is even, ensuring an even adherence of the photomasks to the workpiece, otherwise it will be impossible to obtain high-quality track edges on the finished PCB.

A blank with a photomask under plexiglass. We use the box from under the CD.

Exposure (flare)

The time required for exposure depends on the thickness of the photoresist layer and the intensity of the light source. POSITIV 20 photoresist varnish is sensitive to ultraviolet rays, the maximum sensitivity falls on the area with a wavelength of 360-410 nm.

It is best to expose under lamps whose radiation range is in the ultraviolet region of the spectrum, but if you do not have such a lamp, you can use ordinary high-power incandescent lamps, increasing the exposure time. Do not start illumination until the illumination from the source has stabilized - it is necessary for the lamp to warm up for 2-3 minutes. The exposure time depends on the thickness of the coating and is usually 60-120 seconds when the light source is located at a distance of 25-30 cm. The used glass plates can absorb up to 65% of ultraviolet radiation, so in such cases it is necessary to increase the exposure time. Best results are obtained with clear plexiglass plates. When using a photoresist with a long shelf life, the exposure time may need to be doubled - remember: photoresists are subject to aging!

Examples of using different light sources:

UV lamps

We expose each side in turn, after the exposure we let the workpiece stand for 20-30 minutes in a dark place.

Developing an exposed workpiece

We develop in a solution of NaOH (caustic soda) - for more details, see the beginning of the article - at a solution temperature of 20-25 ° C. If there is no manifestation up to 2 minutes, it is small O exposure time. If it manifests itself well, but useful areas are washed off - you are too clever with the solution (the concentration is too high) or the exposure time with a given radiation source is too long or the photomask is of poor quality - the insufficiently saturated printed black color allows ultraviolet light to illuminate the workpiece.

When developing, I always very carefully, effortlessly, “roll” a cotton swab on a glass stick over the places where the exposed photoresist should be washed off - this speeds up the process.

Washing the workpiece from alkali and residues of exfoliated exposed photoresist

I do it under water tap- ordinary tap water.

Photoresist re-tanning

We place the workpiece in the oven, gradually raise the temperature and stand at 60-100 ° C for 60-120 minutes - the drawing becomes strong and solid.

Development quality check

For a short time (for 5-15 seconds) we immerse the workpiece in a solution of ferric chloride heated to a temperature of 50-60 ° C. Rinse quickly with running water. In places where there is no photoresist, intense copper etching begins. If a photoresist remains somewhere by accident, carefully remove it mechanically. It is convenient to do this with a conventional or ophthalmic scalpel, armed with optics (glasses for soldering, loupes a watchmaker, magnifier a on a tripod, microscope).

Etching

We poison in a concentrated solution of ferric chloride at a temperature of 50-60 ° C. It is desirable to provide continuous circulation of the pickling solution. Gently “massage” the badly bleeding places with a cotton swab on a glass stick. If the ferric chloride is freshly prepared, the pickling time usually does not exceed 5-6 minutes. We wash the workpiece with running water.

The board is etched

How to prepare a concentrated ferric chloride solution? Dissolve FeCl 3 in slightly (up to 40 ° C) warmed water until it stops dissolving. We filter the solution. You need to store in a dark, cool place in a sealed non-metallic package - in glass bottles, for example.

Removing an already unnecessary photoresist

We wash off the photoresist from the tracks with acetone or a solvent for nitro paints and nitro enamels.

Drilling holes

It is advisable to select the diameter of the point of the future hole on the photomask so that it will be convenient to drill later. For example, with the required hole diameter of 0.6-0.8 mm, the diameter of the dot on the photomask should be about 0.4-0.5 mm - in this case, the drill will center well.

It is advisable to use drills coated with tungsten carbide: HSS drills wear out very quickly, although steel can be used for drilling single holes large diameter(more than 2 mm), since tungsten carbide drills of this diameter are too expensive. When drilling holes less than 1mm in diameter, it is better to use a vertical machine, otherwise your drills will break quickly. If you drill hand drill- distortions are inevitable, leading to inaccurate joining of holes between layers. Move from top to bottom on vertical drilling machine the most optimal from the point of view of the load on the tool. Carbide drills are made with a rigid (ie, the drill exactly matches the diameter of the hole) or with a thick (sometimes called "turbo") shank, which has a standard size (usually 3.5 mm). When drilling with drills with carbide spraying, it is important to firmly fix the PCB, since such a drill, when moving up, can lift the PCB, skew the perpendicularity and pull out a piece of the board.

Small diameter drills are usually inserted either into a collet chuck ( different sizes), or into a three-jaw chuck. For precise fixation, fixing in a three-jaw chuck is not the best the best way, and the small size of the drill (less than 1 mm) quickly grooves in the clamps, losing good hold. Therefore, for drills with a diameter of less than 1 mm, it is better to use a collet chuck. Just in case, purchase an extra set containing replacement collets for each size. Some inexpensive drills come with plastic collets - throw them away and buy metal ones.

To obtain acceptable accuracy, it is necessary to properly organize the workplace, that is, firstly, to provide good illumination of the board when drilling. To do this, you can use halogen lamp by attaching it to a tripod to be able to select a position (illuminate right side). Second, raise work surface about 15 cm above the table top for better visual control over the process. It would be nice to remove dust and chips during the drilling process (you can use a regular vacuum cleaner), but this is not necessary. It should be noted that the dust from fiberglass, formed during drilling, is very prickly and, if it comes into contact with the skin, causes skin irritation. And finally, when working, it is very convenient to use the foot switch of the drilling machine.

Typical hole sizes:

• vias - 0.8 mm or less;
• integrated circuits, resistors, etc. - 0.7-0.8 mm;
• large diodes (1N4001) - 1.0 mm;
• contact blocks, trimmers - up to 1.5 mm.

Try to avoid holes less than 0.7 mm in diameter. Always keep at least two spare drills 0.8 mm or less, as they always break at the very moment when you urgently need to order. Drills of 1 mm and larger are much more reliable, although it would be nice for them to have spare ones. When you need to make two identical boards, you can drill them at the same time to save time. In this case, it is necessary to very carefully drill holes in the center of the contact pad near each corner of the PCB, and for large boards - holes located close to the center. Lay the boards on top of each other and, using the 0.3mm center holes in two opposite corners and pegs, secure the boards against each other.

If necessary, you can countersink the holes with larger diameter drills.

Tinning copper on PP

If you need to iron the tracks on the PCB, you can use a soldering iron, soft low-melting solder, alcohol rosin flux and coaxial cable braid. For large volumes, tinning is carried out in bathrooms filled with low-temperature solders with the addition of fluxes.

The most popular and simple melt for tinning is the fusible alloy "Rose" (tin - 25%, lead - 25%, bismuth - 50%), the melting point of which is 93-96 ° C. The board is placed under the level of the liquid melt for 5-10 seconds using tongs and, after removing it, it is checked whether the entire copper surface is evenly coated. Repeat the operation if necessary. Immediately after removing the board from the melt, its remnants are removed either using a rubber squeegee, or by sharp shaking in the direction perpendicular to the plane of the board, holding it in the clamp. Another way to remove the remnants of the Rose alloy is to heat the board in an oven and shake it. The operation can be repeated to achieve a uniform coverage. To prevent oxidation of the hot melt, glycerin is added to the tinning container so that its level covers the melt by 10 mm. After the end of the process, the board is washed from glycerin into running water. Attention! These operations involve working with installations and materials exposed to high temperatures, therefore protective gloves, goggles and aprons must be worn to prevent burns.

The tin-lead tinning operation is similar, but the higher melt temperature limits the application. this method in the conditions of handicraft production.

Do not forget to clean the board from the flux after tinning and degrease it thoroughly.

If you have a large production, you can use chemical tinning.

Applying a protective mask

The operations with the application of a protective mask exactly repeat everything that was written above: apply a photoresist, dry it, tan, center the masks, expose, develop, wash and tan again. Of course, we skip the steps for checking the development quality, etching, removing the photoresist, tinning and drilling. At the very end, we tan the mask for 2 hours at a temperature of about 90-100 ° C - it will become strong and hard like glass. The formed mask protects the PCB surface from external influences and protects against theoretically possible short circuits during operation. It also plays an important role in automatic soldering - it does not allow the solder to "sit" on adjacent sections, closing them.

That's it, the double-sided PCB with the mask is ready

In this way, I had to make PPs with a track width and a pitch between them up to 0.05 mm (!). But this is already a piece of jewelry. And without much effort, you can make PPs with a track width and a pitch between them 0.15-0.2 mm.

I did not put a mask on the board shown in the photographs - there was no such need.

The printed circuit board in the process of mounting components on it

And here is the device itself for which the PP was made:

This is a cellular telephone bridge that allows you to reduce the cost of mobile communication services by 2-10 times - for this it was worth fiddling with PP;). The PCB with soldered components is located in the stand. It used to be ordinary Charger for mobile phone batteries.

Additional Information

Hole plating

At home, you can even metallize the holes. For this, the inner surface of the holes is treated with a 20-30% solution of silver nitrate (lapis). Then the surface is cleaned with a squeegee and the board is light-cured (you can use a UV lamp). The essence of this operation is that under the influence of light, silver nitrate decomposes, and silver inclusions remain on the board. Further, the chemical precipitation of copper from the solution is carried out: copper sulfate (copper sulfate) - 2 g, caustic soda - 4 g, ammonia 25 percent - 1 ml, glycerin - 3.5 ml, formalin 10 percent - 8-15 ml, water - 100 ml. The shelf life of the prepared solution is very short - you need to prepare it immediately before use. After copper deposition, the board is washed and dried. The layer is very thin, its thickness must be increased to 50 microns by electroplating.

Copper plating solution:
For 1 liter of water 250 g of copper sulfate (copper sulfate) and 50-80 g of concentrated sulfuric acid. The anode is a copper plate suspended parallel to the part to be coated. Voltage should be 3-4 V, current density - 0.02-0.3 A / cm 2, temperature - 18-30 ° C. The lower the current, the slower the metallization process, but the higher the quality of the resulting coating.

Fragment of the printed circuit board, where metallization in the hole is visible

Homemade photoresists

Photoresist based on gelatin and potassium dichromate:
First solution: pour 15 g of gelatin with 60 ml of boiled water and leave to swell for 2-3 hours. After the gelatin has swollen, place the container in a water bath at a temperature of 30-40 ° C until the gelatin is completely dissolved.
The second solution: dissolve 5 g of potassium dichromate (chromic peak, bright orange powder) in 40 ml of boiled water. Dissolve in low ambient light.
Pour the second into the first solution with vigorous stirring. Add a few drops of ammonia to the resulting mixture with a pipette until a straw color is obtained. The photoemulsion is applied to the prepared board in very low light. The board is tack-dried at room temperature in complete darkness. After exposure, rinse the board in low diffused lighting in warm running water until the unhardened gelatin is removed. To better assess the result, you can paint the areas with non-removed gelatin with a solution of potassium permanganate.

Advanced DIY Photoresist:
The first solution: 17 g of wood glue, 3 ml of an aqueous solution of ammonia, leave 100 ml of water to swell for a day, then heat in a water bath at 80 ° C until complete dissolution.
Second solution: 2.5 g of potassium dichromate, 2.5 g of ammonium dichromate, 3 ml of an aqueous solution of ammonia, 30 ml of water, 6 ml of alcohol.
When the first solution has cooled to 50 ° C, pour the second solution into it with vigorous stirring and filter the resulting mixture ( this and subsequent operations must be carried out in a darkened room, sunlight is not allowed!). The emulsion is applied at a temperature of 30-40 ° C. Further - as in the first recipe.

Photoresist based on ammonium dichromate and polyvinyl alcohol:
Preparing the solution: polyvinyl alcohol - 70-120 g / l, ammonium dichromate - 8-10 g / l, ethyl alcohol - 100-120 g / l. Avoid bright light! It is applied in 2 layers: first layer - drying 20-30 minutes at 30-45 ° C - second layer - drying 60 minutes at 35-45 ° C. The developer is a 40% ethyl alcohol solution.

Chemical tinning

First of all, the board must be pickled to remove the formed copper oxide: 2-3 seconds in a 5% hydrochloric acid solution, followed by rinsing in running water.

It is quite simple to carry out chemical tinning by immersing the board in an aqueous solution containing tin chloride. Tin precipitation on the surface of a copper coating occurs when immersed in a tin salt solution in which the potential of the copper is more electronegative than the coating material. The potential change in the desired direction is facilitated by the introduction of a complexing additive, thiocarbamide (thiourea), into the tin salt solution. Solutions of this type have the following composition (g / l):

Among the above, the most common solutions are 1 and 2. Sometimes it is proposed to use detergent"Progress" in the amount of 1 ml / l. The addition of 2-3 g / L of bismuth nitrate to the 2nd solution leads to the deposition of an alloy containing up to 1.5% bismuth, which improves the solderability of the coating (prevents aging) and greatly increases the shelf life before the components are soldered in the finished PP.

For surface preservation, aerosol sprays based on fluxing compositions are used. After drying, the varnish applied to the surface of the workpiece forms a durable smooth film that prevents oxidation. One of the popular substances is "SOLDERLAC" from Cramolin. Subsequent soldering is carried out directly on the treated surface without additional varnish removal. In particularly critical cases of soldering, the varnish can be removed with an alcohol solution.

Artificial tinning solutions deteriorate over time, especially when exposed to air. Therefore, if you have large orders infrequently, then try to cook right away a small amount of solution sufficient for tinning the right amount PP, and store the rest of the solution in a closed container (bottles of the type used in photography are ideal, which do not allow air to pass through). It is also necessary to protect the solution from contamination, which can greatly degrade the quality of the substance.

In conclusion, I want to say that it is still better to use ready-made photoresists and not bother with metalizing holes at home - you still won't get great results.

Many thanks to the candidate of chemical sciences Filatov Igor Evgenievich for advice on matters related to chemistry.
I also want to express my gratitude Igor Chudakov ".

After the printed circuit board drawing is transferred to the foil textolite with the help, it is necessary to etch the printed circuit board. Several recipes for etching printed circuit boards are described under the cat.

1. Method one - ferric chloride.

Ferric chloride is added to water in a ratio of 1: 3. To stir thoroughly.
The etching time depends on the temperature of the solution, the thickness of the copper and the "freshness" of the solution.
On average, from 10 minutes to an hour. When applying tracks with laser printer toner, do not heat above 45 ° C.
It is recommended to swing the board in the solution.

2. Method two - copper sulfate plus table salt.

Solution preparation - 200 ml. warm water, two tablespoons of table salt and a tablespoon of copper sulfate. The etching process can be quite lengthy.

Salt

For the normal course of the etching process, a significant excess of salt is recommended, heating the solution and wiggling the board in the solution.

3. Etching the printed circuit board in hydrogen peroxide plus citric acid.

Enough quick way etching the PCB at room temperature plus the availability of components.

Solution composition:
In 100 ml. Dissolve 3% hydrogen peroxide with 30 g of citric acid and 5 g of sodium chloride.

Salt can be given in excess.
Do not dilute the solution. The more distortion, the more intense the process will be.
But it must be borne in mind that the solution is disposable and cannot be stored.