3 ways to etch printed circuit boards at home

Etching circuit boards with hydrogen peroxide and citric acid

Author: Vladimir Vasiliev · Published on May 9, 2022 · Updated on August 25, 2018
Hello dear friends! It’s 5:30 in the morning, today I woke up early on purpose to write something useful. And yes, today is May 9 on the calendar, so I congratulate you on this great day, Happy Victory Day!

Today we will talk about a solution for etching 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 little salt.

Purpose and device

The development board for solderless assembly allows you to mount an electrical circuit and run it without using a soldering iron. In this case, you can check all the parameters and characteristics of the future device by connecting measuring and control devices to the board.

A breadboard is a plate made of a polymer material that is a dielectric. Mounting holes are drilled on the plate in a certain order, into which the leads of the parts - components of the future device - should be inserted.

The holes allow the connection of leads with a diameter of 0.4-0.7 mm. They are located on the board, as a rule, with a pitch of 2.54 mm.

To simulate the connections of the component leads to each other, the breadboard has special conductive plates that connect the holes in a certain order.

Typically, these connections are made in groups along the board along its long sides. There may be two or three such rows. These contact groups are used as buses for connecting power.

Between the longitudinal rows, the holes are connected by plates in groups of five. These plates are located in a direction across the board.

Near the holes in the places of future contacts, the current-conducting plates have design features that allow them to clamp and firmly hold the leads of the parts, while ensuring the presence of electrical contact. This is the meaning of installation without soldering.

Quality prototyping boards can be assembled and disassembled while maintaining a strong and reliable connection between parts up to 50,000 times.

Breadboards produced industrially and purchased in a retail chain, as a rule, have a layout of contacts and conductive connections between the holes.

What etching solutions are there?

There are many different solutions for etching printed circuit boards, including popular etching mixtures and some that are not particularly popular.

In my opinion, the most popular etching solution in the amateur radio community is ferric chloride. I don’t know why this is so, maybe it’s a conspiracy of radio store sellers who specifically offer ferric chloride and tactfully keep silent about alternatives. But there are alternatives:

1. Etching with copper sulfate and salt
2. Ammonium persulfate etching
3. Sodium persulfate etching
4. Etching with hydrogen peroxide and hydrochloric acid
5. Etching with hydrogen peroxide and citric acid

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

Printed circuit boards using a laser printer.

The method of manufacturing single printed circuit boards by transferring a design from a printout on a laser printer is becoming increasingly popular among radio amateurs. It is best to print on thin coated paper - it has less lint, a good result is obtained on sheets of the "Stereo & Video" magazine, as well as "self-adhesive" substrates and thermal paper for faxes (choose the side experimentally). In laser printers, you should enable the maximum toner supply mode (turn off the “economy” mode if it was turned on, set the contrast to maximum, etc.), and also use a path with minimal paper bending (this option is available in older HP LJ 2 models , LJ4, etc.). The board design must be “mirrored”; this option is available in the print menu of many graphics programs, for example Corel Draw, Corel Photo Paint, and when printing from programs that cannot “mirror”, it is necessary to use output to Postscript printers that have a mirroring option in the driver. Instead of outputting to a laser printer, you can use photocopying, but also in maximum contrast mode and onto thermal fax paper. When making two-layer printed circuit boards, to reduce heat shrinkage of the paper, it is recommended to “run” the latter through the printer empty (without printing the image) before printing the image. In addition, both sides should be on the same sheet to avoid severe misalignment due to different heat shrinkage of the paper. The degreased board is laid with the copper side up on a flat surface, with the resulting print on top, toner side down. This “sandwich” is pressed on the paper side with an iron (for 20 - 30 seconds), heated to the ironing temperature of crepe de Chine (ask the ladies). The iron should not immediately melt the image made by the laser printer. That is, the toner at this temperature should turn from solid to viscous, but not liquid. When the board has cooled down, you need to immerse it in warm water and hold it there for several minutes. As soon as the paper becomes limp (it will be visible), everything can be easily pulled off, the rest can simply be rolled up with your finger. Instead of water, you can remove the paper with sulfuric acid. If the tracks are greased, you carelessly removed the iron or placed a cold weight. If the tracks are missing somewhere, the iron is too cold. If the tracks become wide, the iron is too hot, or the board was heated for too long. If the board is double-sided, then first the paper printouts of both sides are aligned, in any free opposite places two technological holes are pierced with a needle, the first side of the board is “ironed” as usual, then it is drilled along the technological holes with a thin drill, and on the other side along them the gap is aligned with the paper printout of the other side. You can poison with ferric chloride (warm it up a little to speed it up) or with hodgepodge with hydropyrite. All this was used even on getinax, there are no peelings of the tracks, tracks up to 0.8 mm wide are normally made, and with some experience up to 0.5 mm. After etching, the toner is removed with acetone, nail polish remover or Flux Off spray. Drilled, trimmed and so on, as usual...

What are the disadvantages of etching in ferric chloride?

Ferric chloride solution is good for everyone, it is not difficult to prepare and the etching process usually goes quickly. When preparing, it is very easy to figure out the concentration, which is called “by eye”. Once prepared solution is enough for dozens of circuit boards. But it has some disadvantages that are very annoying:

1. The solution is not transparent, which makes it difficult to control the process. You have to constantly remove the board from the etching solution.
2. Ferric chloride solution stains plumbing fixtures very badly. Each board etching session ends with the process of scraping off the plumbing fixtures (sink, bathtub, and anything else the solution might come into contact with).
3. It stains clothes very much. When working with ferric chloride, you should wear clothes that you wouldn’t mind throwing away, because the solution eats into the fabric very strongly, so much so that it is almost impossible to wash it later.
4. The solution has an aggressive effect on any metal nearby; even when stored in unsealed containers, nearby metal objects may become rusty. Once I closed a jar of ferric chloride with a metal lid (the lid was painted), after a couple of months this lid turned into dust.

Assembling simple circuits on a breadboard

Let's try connecting a few elements and make sure everything works. To assemble these simple circuits we will use the elements:

Let's make the LED light up

Rice.
1 Schematic diagram. Assembling a circuit with an LED First, let's draw the circuit that we are trying to assemble. The meaning of the circuit is this: electric current passes through the LED and it lights up, while a resistor limits the current so that the LED does not burn out. Our version of assembly on a breadboard.

Rice. 2 An example of assembling a circuit on a breadboard.

Please note that it is convenient to connect power to horizontal rows, making them common + and -. These designations on some breadboards are just a hint for you, so it’s convenient to connect. Indeed, it is often convenient to have a common “bus” - a common wire with a plus and a minus. But this does not mean that you cannot connect something else there.

It will be interesting➡ What are the categories of premises according to the degree of danger of electric shock according to the PUE

Circuit with two LEDs connected in series and a button

Let’s complicate our circuit a little; now we’ll light two LEDs through a button. The button will allow us to close and open the circuit and thus control the inclusion of LEDs.

Rice. 3 Schematic diagram for exercise 2. Connecting two LEDs in series.

Try to assemble this circuit yourself. Below is our solution.

Rice. 4. Assembling a circuit with two LEDs on a breadboard.

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 me to search for alternative etching mixtures. And so I decided to test the method of etching boards in hydrogen peroxide and citric acid.

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

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

I don’t have any project at the moment, so I decided to purely test the method, to understand what the big deal is. I found a scrap of foil PCB in my stash and made a few strokes with a permanent marker. This is a kind of imitation of tracks and copper polygons; it will work quite well for experimental work.

Method of applying a design to a paper using a laser printer

I do everything much simpler: I take a blank and a simple Soviet eraser. I thoroughly wipe the entire board with an eraser. All oxidation is removed. Just in case, you can wipe it with gasoline (but I don’t do this, an eraser is enough). Then I take the thermal paper from the fax machine and iron it with an iron. It turns gray-violet. I insert this paper into the printer (I have an HP 6L and I don’t glue any paper for rigidity, I haven’t chewed it yet) and mirror print the board design. I put the paper on the paper and start fiddling with the iron. My power is at 3/4 of the maximum power. I iron for 3-4 minutes. Then I throw the workpiece into hot, warm water and wait 5 minutes for the paper to soften. Then I use a sponge or fingers to roll the paper off the board. Do not pick up the edge of the paper or tear it off; the tracks may come off along with the paper! Just roll it off the board. Next I core, drill, trim and etch. And the board is ready.

Advantages of etching in hydrogen peroxide and citric acid

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

1. Easily accessible - all components can be easily found at the nearest pharmacy or grocery store.
2. Relatively cheap - all the components for preparing the solution are not expensive, less than 100 rubles. (at the time of writing)
3. Transparent solution - the resulting solution is transparent, this simplifies observation and control of the etching process.
4. Etching occurs quickly enough and does not require heating
5. Doesn't stain plumbing

Scientists have figured out how to make semiconductors for electronics ten times thinner

The results of the study were published in the Journal of Alloys and Compounds. The size of electronics components is critical to its efficiency. The simplest example: the smaller the elements of a smartphone’s microcircuits, the higher the device’s performance and the lower the heat dissipation.

Today, the main material used to make semiconductor electronics is silicon. However, it itself has lower conductivity compared to other semiconductor materials. Obtaining the pure silicon needed to make devices is a difficult and expensive process.

In addition, further reduction in the size of the elements is already practically impossible, but this is precisely what is required to increase the speed of information processing, since the smaller sizes of semiconducting elements imply the possibility of using them in larger quantities at the same time.

Scientists from NUST MISIS, together with colleagues from the University of Nebraska, have figured out how to reduce the thickness of semiconductor components by 10 times.

To do this, it was necessary to abandon the already familiar silicon in favor of other materials - compounds of titanium and zirconium with sulfur (TiS3 and ZrS3). The use of titanium-zirconium alloys and pure sulfur as starting materials makes it possible to precisely control the properties of the resulting thin semiconductor tapes, which are then used in devices. However, the scientists were faced with a problem that other research groups had repeatedly faced before: why it was not possible to obtain the entire spectrum of compounds from pure ZrS3 to TiS3 in order to control the optical and electrical properties of these materials for effective use in semiconductor devices.

Scientists have found that the problem lies in the temperature at which the materials crystallize – 800°C. Using scanning electron microscopy, it was possible to see that, in addition to small “needle-shaped” crystals, large octagons - hexagons - are formed in the structure, violating the homogeneity of the materials.

It was decided to gradually lower the crystallization temperature and observe how the structure of the materials “behaved.” It turned out that if the solution solidifies at a lower temperature, hexagonal crystals no longer form, and the entire material consists of thin ribbons. Thanks to the layered structure of these materials, it was possible to obtain films with a thickness of only about 1 nm.

Next, scientists plan to continue experiments with titanium and zirconium: using different ratios of metals, combining them into solid solutions with sulfur and measuring the conductivity of the samples. In the future, this will make it possible to find optimal and stable combinations of materials with the highest degree of conductivity.

What are the disadvantages

Unfortunately, in addition to all the advantages, this etching method is not without its disadvantages.

Disadvantages of etching in hydrogen peroxide and citric acid:

1. Disposable solution - the solution is suitable only for one-time use, i.e. during a chemical reaction occurring in it. It will not be possible to etch many boards; you will have to prepare the solution anew each time.
2. Expensive - despite the fact that all the ingredients are cheap, in the long run 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's basically all the shortcomings. 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 be the only possible alternative, for example, in a remote village with a pharmacy and grocery store.

And with this I will wrap up. It’s already dawn outside and it’s time to prepare a delicious breakfast.

It depends on you, but my least favorite process in the manufacture of printed circuit boards is their etching. It doesn’t seem to be that complicated - I threw the board into a water bottle with ferric chloride, took it out after half an hour, washed it and it’s done. But storing and constantly pouring this LIQUID from a bottle into a bath is fraught with staining everything around: from hands and clothes, to walls, floor, table, cat... well, you get the idea. In general, it is better to do this dirty business in a specially designated place. Or switch to less dirty components, which is what I decided to try to do. Therefore, now we will consider the two most popular and cleaner compositions for etching printed circuit boards.

I just needed to etch three small single-sided boards, the pattern was transferred using LUT, roads 0.4 mm thick

1. Hydrogen peroxide + citric acid + table salt

This recipe is new and was first published here . This is probably the most affordable option for etching printed circuit boards; components can be easily obtained at the nearest pharmacy or store. The price of a 100 ml bottle of hydrogen peroxide is about 10 rubles; for an 80 gram package of citric acid I paid 23 rubles. And if you go to wholesale stores, you can generally buy citric acid for 100 rubles/kg, although in bags of 25 kg.

To prepare a solution, 30 grams of citric acid and a teaspoon of table salt are dissolved in 100 ml of 3% peroxide.

This volume, according to the author of the recipe, is enough to etch copper with an area of ​​100 cm2, but more often you have to prepare more solution, depending on the etching utensils and the dimensions of the board. The downside is that the solution cannot be stored for a long time, and if the boards are etched rarely, you will have to prepare the solution anew each time. At my place, I mixed 200 ml of peroxide, 80 grams of citric acid and two teaspoons of table salt.

2. Ammonium persulfate

This is also a relatively new method of etching, and we have only recently started selling jars of persulfate in radio stores. According to reviews from those who have already tried this method, it poisons well and, most importantly, does not leave walls and floors stained with rust, as ferric chloride likes to do. For a jar of persulfate weighing 250 grams I paid 150 rubles. According to the instructions, this volume is dissolved in 0.5 liters of water; after etching, the finished solution can be stored and reused.

The first two compositions turn out to be equally transparent and etching for both occurs with active gas formation. If you etch the board with the foil facing down, you will have to shake it from time to time to shake off bubbles from the surface.

When etching in persulfate, one unpleasant feature emerged: in addition to bubbles, some kind of hard transparent coating forms on the copper. Judging by the reaction formula below, the transparent coating is the ammonium salt of sulfuric acid (ammonium sulfate)

(NH4)2S2O8 +Cu → CuSO4 + (NH4)2SO4

This plaque is quite difficult to scrape off and naturally, the copper underneath stops being etched. I had to often take out the board and clean the copper from plaque, otherwise the board would be etched in pieces. I don’t know why this happens, no one has complained about it, perhaps this happens while the solution is fresh and the reaction is too intense. I'll see how the next boards are etched in the same solution.

3. Ferric chloride

And since I started comparing, I took a can of XJ at the same time. A method familiar to everyone who has made printed circuit boards at home. Knowing about the amazing ability of ferric chloride to spread everything around, I really didn’t want to even open a jar of this crap. But it was still interesting to visually compare the two new methods with what I have been using to etch boards for the last 10 years.

250 gr. a jar of HJ cost 120 rubles

For a small board, just a little solution is enough. Ferric chloride is good because it is easy to dose according to the color of the resulting solution; it should be the color of strong tea.

All three compositions begin to etch faster if you heat them to a temperature of 35-40 degrees, this can be done, for example, by placing the dishes in a basin or sink with hot water. In hydrogen peroxide and persulfate it is very good to observe the process, the compositions are transparent and you don’t have to take out the board to see how much unetched copper is left.

During the etching process, the color of the peroxide solution first turns green and then becomes increasingly blue. The color of the persulfate also changes to blue and the longer the etching goes on, the more saturated the color becomes. And the slurry with ferric chloride remains rusty in color, becoming darker

Results

Copper in the solutions considered is etched quite quickly. We had to keep the board in ammonium persulfate for the longest time, because we had to take the board out and remove plaque from the surface of the copper. In total, etching in peroxide took 15 minutes, in ferric chloride about 20 minutes, and in ammonium persulfate a little more than 30 minutes.

At first glance, all three boards were well etched, but when I washed them, it turned out that persulfate had gotten under the toner and eaten up half of the tracks! This is something I definitely didn’t expect.

In hydrogen peroxide (board on the left), as well as in ferric chloride, there are no such tricks. Although peroxide still produces a better result - the edges of the tracks, if you can see, are smoother (all three boards were rolled simultaneously on a laminator and from the same sheet, so we do not take into account factors such as the quality of rolling toner onto copper, it is the same for all three) .

To make the experiment complete, I decided not to pour out the solutions with peroxide and persulfate. I wonder if the peroxide will poison at least a month after mixing. Yes, and you need to achieve a suitable result from persulfate.

* * *

So, after a long pause of 2 months, I took out both solutions. They were kept under the bathroom, where it was dark and cool. I did not pour the solutions, I stored them directly in flasks, covering them with a rubber glove, in case the solutions began to release gas (I heard stories about jars in which the persulfate solution was stored that exploded). I did not observe any gas formation during storage, but a sediment containing persulfate formed at the bottom. The color of both solutions evened out and they became similar, if not for the sediment it would have been difficult to distinguish which was which.

And here is the sediment at the bottom of the ammonium persulfate solution. Blue crystals, Heisenberg would approve :) Or maybe not blue, but still beautiful in person.

I prepared two boards that the persulfate solution ruined for me last time (these are boards for a small amplifier based on the LM4871 chip)

The ammonium persulfate solution immediately got to work and began to etch the board with strong release of gas bubbles.

But the hydrogen peroxide solution, unfortunately, ran out of steam. He couldn't do anything other than lighten the copper on the board a little. The solution had to be poured out and etched in persulfate.

And this time there were no etched paths

In general, I was very pleased with the two new lineups. If ammonium persulfate is available in stores, it will be a good replacement for ferric chloride, although the difference in price is small. For better results, it would be a good idea to assemble an etching bath with rotaspray . Then the undercutting won’t be a problem and you can make the roads much thinner (again, without fear that they will end up at 0).

Well, as for the hydrogen peroxide solution, it is well suited for the role of auxiliary. In case you run out of persulfate, you can always mix peroxide with lemon; fortunately, these components are used in everyday life and can almost always be found in the kitchen cabinet or in the nearest store.

How have boards been etched in the past?

In the past, making a printed circuit board required a lot of effort. First, the diagram was drawn on paper, then holes were made in the workpiece, after which the tracks were transferred to foil PCB or getinax, using paint and varnish products. After the coating had dried, it was peeled off, and the board was immersed in a container with meadow for etching.

The hardest part was etching the board. Since ferric chloride-based meadow was used for these purposes. In the radio circle, such a remedy was not in short supply, but at home one had to look for an alternative, which most often was copper sulfate.

Processing the board carried another secret: the board was etched unevenly. Some paths were corroded, and in some places the surface was under-etched. All due to the inexperience of the craftsmen or repeated use of the puddle solution.

Preparation of fiberglass laminate and drilling.

Cut a piece of fiberglass to the size of the drawing. Remove burrs with a file. Place the design on the board, fold the edges of the paper and secure them to the back with tape or (preferably) electrical tape. Next is the drilling process. Yes, yes, right according to the drawing and without punching. An important condition for the drill not to lead is its “freshness”. However, you can understand what to expect from a specific drill by drilling a test hole on some scrap of fiberglass. The best solution to this problem is to have an appropriate drilling machine, even a homemade one. If a “motor with a drill” is used, as a rule, it is better to “punch” future holes. All holes, including mounting ones, are drilled with the same (smallest) diameter. Next, you need to check the drilling for “clearance” as there will definitely be undrilled holes. Drill more. After this, the board drawing is very carefully removed from the fiberglass (the danger is burrs from drilling). Next, the mounting and other large-diameter holes are drilled out.

After the operations have been completed, the surface of the board is cleaned with fine sandpaper. This process is necessary to remove burrs from drilling and for better adhesion of the design paint to the surface. If possible, do not touch the cleaned surface with your fingers to avoid leaving grease marks. After cleaning, it is necessary to degrease the board using alcohol (in extreme cases, acetone, but make sure that no white powdery stains remain). After this, you can only touch the end surfaces with your fingers.

How to etch a board correctly?

To make etching of the board with hydrogen peroxide and citric acid faster, you can use two containers. Simply place the smaller container of meadow into the larger container and pour hot water into it. This will speed up and strengthen the process.

Etching a board in a solution of hydrogen peroxide is done as follows: the board is placed in a meadow with the side on which the tracks are drawn facing down, so that the decomposition products easily sink to the bottom of the container. To ensure the reaction proceeds more evenly, the solution must be stirred lightly from time to time. The whole process takes no more than 10 minutes.

Another way to apply a design to paper using a laser printer.

Making printed material using a laser printer and an iron is a rather tedious process, but it gives a pretty good result if you practice a little.

1 . Carefully glue a sheet of fax paper (glossy side up) onto a sheet of regular paper (to compensate for the lack of faxing rigidity). For what? It is necessary to first run the paper through the printer/laser oven for shrinkage. To smoothly pull through the tract, simply iron the thermal paper on the sensitive side with an iron. 2 . Paper - take the base from self-adhesive paper, or thermal paper for faxing, definitely thermal paper, and prepared - first iron the sheets with a hot iron until flat (at the same time they will turn dark brown, then bluish-gray), fold them in this form for future use. Before outputting the board, run the sheet through the printer - for example, by printing a blank page. The minimum sheet size is ~6*12 cm for HP 5/6L. 3 . Print at maximum boldness, mirror image. printing and transferring to the blank can be up to a week apart, I haven’t tried it again (this is for those who don’t have a laser at home). 4 . Take the workpiece with a margin of 3-5 mm on each side. foil - lightly sand with zero polish and wipe. There should not be any harmful deposits such as white sediment from denatured alcohol. I use isopropyl alcohol or “galosh” (aka “lighter”) gasoline. 5 . Iron - with a normal, smooth surface. reheat in advance. Temperature - for waxing you need to select it more carefully (I have a display meter set to “artificial silk”), otherwise the impregnation will begin to transfer. for thermal paper - higher is possible. 6 . There should be no dust or any small things, neither on the foil nor on the paper. 7 . Make a sandwich - on a flat thick plywood (although I have 3mm paper), put a piece of thick cardboard, a blank board, blow off the dust, drawing, for thermal paper (it's thin) - also a piece of moderately thick paper, a hot iron. 8 . You begin to move with the iron, pressing with a force of ~5..10 kg/sq.dm. wait about two minutes for it to stick. 9 . Tilting the iron very slightly, you roll out individual tracks for a couple of minutes. It is very important here not to crush the tracks, and at the same time to weld them. From time to time you need to lower the iron to the entire plane so that the rest of the iron does not cool down. The thermal paper clearly shows the difference in welded and defective pieces. 10 . Well, you iron for another minute to clear your conscience and put the iron away. The sandwich cools and sections of paper between the tracks swell. We don’t wait for it to cool down, put the board directly under a stream of boiling water. eleven . Now the board - under running water and a piece of wet foam rubber, you begin to erase the paper. You cannot tear it off in large pieces or from dry foil. You need to remove clumps of paper from the foam rubber more often. We take the paper by the corner and tear it off. Then we remove the remains with our finger/rag/foam rubber. 12 . Use a new piece of sponge to wipe off the lint (as much as possible), and look at the wet pattern under a magnifying glass. if there are many defects, or they are located in inconvenient places - see point 1, with variations in parameters. 13 . Cover the reverse side with strips of wide tape and etch. It is possible even in boiling FeCl3

How can you tell if the board has already been etched?

In a hydrogen-acidic environment, the reaction proceeds according to the formula: Cu+ H3Cit +H2O2 → H[CuCit] +2H2O. Etching a printed circuit board in hydrogen peroxide can be considered complete if any reactions in the solution have stopped: it no longer hisses or bubbles.

The finished board is cleaned and washed with water. Toner or paint is washed off with acetone. After which the board is thoroughly wiped and degreased.

Important! Check the tracks for integrity after processing the board. A damaged circuit will not work.

As you can see, etching a board with hydrogen peroxide at home is not only possible, but also safe. It will not be difficult to find the necessary components for preparing the etching composition, and the process itself will take no more than 15 minutes. Today, any radio amateur, thanks to simple and accurate advice, will be able to experiment at home without harming himself or others.

Source

Drawing.

In our circles, of course, we argued a lot about the paint used and the technology for applying the paths, but I settled on what is described below. Drawing is done with nitro paint, with rosin powder dissolved in it (provides plasticity for correction for some time after drying and does not allow the paint to “lag behind” in the case of etching with hot solutions). Drawing is done with glass drawing pens (which are very difficult to find these days). In addition, it is possible to use as a paint, asphalt-bitumen varnish, dissolved to the desired condition with xylene. The bottle will last a very long time. It is possible to make drawing feeders yourself, with appropriate training, of course. To do this, you can take a thin-walled glass tube and stretch it over a flame (over a gas stove) and break it in the middle. Then “finish” the broken tip on fine sandpaper. Next, after heating over the same flame, bend the tip to the desired angle. Difficult!? In fact, no more than 5 minutes. You can also use disposable syringes for drawing. The varnish is drawn into a disposable syringe (1-2 ml) and a thin needle is inserted. Before installation, the needle must be processed with a file so that the edges are smooth (remove the sharp end). From the side of the piston, you can insert another needle to allow air to pass inside the syringe.

Before you start drawing the printed circuit tracks, you need to draw the mounting pads for soldering the elements. They are applied using a glass pen or a sharpened match around each hole, approximately 3 mm in diameter. Next you need to let them dry. After this, you need to cut them using a compass to the required diameter (I use a small compass-measuring device with a threaded distance lock (may professional draftsmen forgive me for this expression, I never knew its real name), one of the needles of which is ground into a flat cutter). Next, the trimmed excess is cleaned with an awl or scalpel. In fact, I use a recycled school utensil for these procedures. The result is smooth round areas of the same diameter, which can only be connected by tracks, according to the previously drawn drawing of the printed circuit board. Next, after drying, the second side is drawn. Then the tracks and errors are corrected using a scalpel. Moreover, it should be noted that in order to align the edge of the track, you must first trim the edge using a ruler (preferably a metal one), and then remove the excess by scratching. If you clean the path right away, then, depending on the degree of dryness of the paint, you can get “chips” even worse than the original ones. Check that the pattern on the board matches the pattern on the drawing.