Production of printed circuit boards LUT'om from A to Z

Good day! Among my friends there is an opinion that it is useless to produce printed circuit boards (PCBs) independently. Considering that modern components have gone far from DIP packages, it’s not worth trying to poison boards under them. Nevertheless, there is always a need for a quick assessment of a component, and there is no time to wait for a few days for the ordered board. And this is considering that the order for “several days” is expensive, for a one-time task.

In this article I want to set out a procedure that will allow you to quickly make PP for components in cases like TQFP-100, that is, with legs 0.2 mm and the same clearance, and at the same time minimize marriage.

Of course, this is a method of manufacturing boards only for prototypes, but it reduces the risks of making mistakes when creating the final device.

The network has a lot of articles and videos with similar tips, but as a rule there are not covered all the nuances of certain actions. Here I want to show the whole process, which at home will allow for an hour and a half to make an acceptable copy of the software.

Under cat details and traffic.

Minimum set of materials:


  1. Correct paper (below I will focus on the concept of "correct")
  2. Ammonium persulfate
  3. Pickling tank
  4. Skin "null"
  5. Brush (natural or fiberglass)
  6. Toothpick

And, of course, a laser printer and an iron.

I’ll show the whole process on the manufacture of software for the evaluation board of the ATxmega128A1U-AU chip (evaluation of the declared hardware crypto module, EBI and in general), and boards for connecting a 7-inch display to the STM32F407VE.

For evaluation boards I try to make wiring on only one side, where intersections cannot be avoided , I put a resistor with resistance = 0 and housing 0805, passing the road under it. If there are many intersections and you definitely need two layers, then I etch each layer on a separate textolite (then I connect it via VIA).

First stage

PCB preparation.

A single-sided textolite with a copper thickness of 17-35 μm is washed from the dirt with dishwashing detergent under warm water, then a drop of detergent is applied to the skin with P800 grain or less and the future board is ground until roughness is formed over the entire area. A moment with a skin is required! In this way, we will not overwhelm copper to holes, but we will ensure good adhesion of the toner. After grinding, the surface is washed with clean water, wiped dry and set aside to dry.

By the time of transfer of the layout, the textolite should be dry, free of oxides, greasy stains and noticeable roughness.

In one of the articles I saw a recommendation that the copper layer should be held in the sun, before the appearance of a bluish oxide film, in our case this is not necessary.

Second phase

Layout preparation.

For ATxmega128 I made such a wiring:


if necessary, then there is PDF .

On the board itself is xmega, an ft232 interface converter and an lp2985 stabilizer, as well as small things - a PDI, USB connector, LEDs for the entire port “B”. The board pattern is slightly different from what I will etch. Before printing added inscriptions and little things to complicate.

All roads are on the top layer (TOP), so we print the layout in mirrored form.

The presence of an “uneconomical” mode for bold printing in the printer is optional. I printed on different printers with default printing and there were no problems, except for one point: Brother printers (specifically HL-l2340 and HL-l2250) are very disrespectful about translating DPI to real size, so the picture may float in size , and this is critical when 1mm two roads should fit.

Now paper.

No glossy magazines and self-adhesive backing!

And even I refused the Chinese paper for LUT (too thin and wrinkled when printing) The
paper should be dense - at least 150g per square centimeter, should quickly stick when heated and not fidget under the iron, swell well in water.

The best option is glossy photo paper, not too good quality. Not “too good quality” it means neither premium nor LOMOND. That is, cheap glossy photo paper. In the photo above, one of these is also shown, there is also “Glossy Photo Paper”, produced under the brand name of a large computer equipment store, this is a clone of the one in the photo (it seems that they are from the same factory, but in different packages).

This paper immediately sticks to copper under the iron and does not move when ironing (matte paper does not contain a glossy layer and therefore does not stick, and hot toner is easy to grease), it easily leaves in warm water (unlike LOMOND and paper with a “premium” prefix )

So it's time to print. We print the layout, then, without touching the front side with our fingers, we trim the edges. and cook the iron.

Third stage

Translation layout.

You must first prepare a container of water in which the board will be soaked. I have the role of this capacity performs an ordinary basin. Hot water is poured (50 degrees, that is, so that the hand can’t stand it anymore), five liters, and a little detergent is dissolved in it (a little, this is a tablespoon).

And go to the iron.

We put the prepared textolite on a flat surface and cover it with a printed breadboard, iron it to the maximum temperature and iron it in the center line, and then from the center to the sides. At the first ironing, it is better to hold the printout so that it does not move. After the first ironing, a sheet of photo paper sticks to copper and you can no longer be afraid to move it with an iron. Now you can walk the nose of the iron along all the edges and places where the paper seems to go. Then thirty seconds just warm up the entire volume.

I could not refrain from showing the main character in an article about LUT:


After ironing, without cooling, we throw a fee of water. That is, without removing the paper, pick up the hot tweezers and put in a prepared container of water. 10 minutes soaking break.

Fourth stage

Paper cleaning.

After 10 minutes, remove the board from the water and remove the paper. No matter how long the board is in the water, all the paper will not lag behind. More precisely, the paper itself is without problems, but the glossy layer, which provided us with good adhesion, will remain in narrow places.

something like this:


In general, the toner holds very reliably, you can rub it with your fingers, an eraser or a sponge to wash dishes, but it is difficult to remove the gloss between the tracks, it is enough to let the board dry, as such places will be visible.

There are three ways.

  1. Soak the board in alcohol for another 10-15 minutes, the glossy layer will swell and rinse off with a soft cloth. This is not our way, in view of its sacrilege.
  2. Soak the board in the “anti-silicone” solvent, which is sold in hardware stores. I don’t know what is there as an active substance (it is not written on the bottle), but the glossy layer also swells and is removed, while the toner remains. This is an amateur method, the tool is quite smelly.
  3. And the third way is to remove it mechanically, which is not very long.

To do this, you need to wet the board back and remove the excess with a sharp object. It is best to use a sharp toothpick. Wet gloss can be removed without problems, and the toothpick tree does not take out the toner. I especially note that you can not use needles! Not because toner can be removed (it is then adhered well), but because iron leaves traces on copper. Yes! I’m shocked myself, I know that copper is softer than iron, especially stainless steel. But the fact is the place to be. Where the needle drove the copper is etched very slowly.

An example from practice:


After removing the remnants of the glossy layer, we wash the board with detergent, removing the “fingers”. Leave to dry.


Almost deliberately left several places where the gloss was not removed (then we will see that everything is not so scary).

Fifth stage


I poison ammonium persulfate, I won’t say that it is better than ferric chloride, it’s just dirtier than iron (well, yes, ammonium persulfate is bleach, what kind of dirt is it) and ferric chloride is harder to store - hygroscopic and, as a result, fuses into large pieces that need to be crushed .

Poison at a temperature of 40 degrees. For a board with copper 35mkm - 15 minutes, With copper 17mkm - 5 dashes 7 minutes. It is possible to etch about 20 minutes at room temperature 17 microns, 35 microns in theory 40 minutes, but I don’t remember that anymore.

At home, you can etch in any container, for this article specially poisoned in a regular plastic container, which imposes certain additional actions from the performer. But if PPs are made often, then you can fix yourself a bath for etching:


the main addition of which is a pump for mixing the solution, it exempts from “certain additional actions”. The pump needs a diaphragm, with a plastic membrane.
The one in the figure, bought in an online store for robocrafts.

Inside the capacity of the partition to accommodate several PP.


In the photo, two sides of the board under the STM32F407VE connected to a seven-inch display are etched.
Under xmega I will etch in open plastic.

We make a solution - half a liter of water plus 100-150 g of ammonium persulfate. In general, 250 grams per half liter is recommended, but in artisanal conditions, when the solution cools down and the water evaporates, crystals precipitate and firmly stick to copper, as a result of which are not etched points.
As I wrote above - the temperature is 40 degrees.

We throw the board into the solution and begin to mix the solution with a brush so that the etching proceeds uniformly. Also, with a brush, you can remove glossy-coated flakes from the board, if not all were removed during preparation.

I have a board with copper of 35 μm, after 10 minutes I can already see the textolite:


I wait another 5 minutes and everything is ready.

I must say that in the process of etching it is better to overexposure the board than not to contain it. And the extra time can be quite large. Once, when I saw an unfinished landfill, I threw the scarf back and forgot about it for about three hours, when I remembered, I thought that it had been corroded through and through. However, I did not notice a single etching:

this overexposure (already tinned):


So, we pulled out our board, washed it and looked at the light:


If you found excess copper, you can throw it back into the solution.

If all is well, then LUT is over!

We wash off the toner with acetone and tin it, if tinning is not provided in the near future, you can store the board without washing off the toner, it will be a protective shell.

Bottom line:


Above, I marked the places on the board where the glossy coating remained. Those places that the gloss closed hermetically (a corner on the board) were not etched there, where there are small overlaps between the tracks - everything is fine, the solution got there. If you use a container with a pump, then the glossy coating can generally not be completely wiped off, just the etching time is doubled.

A couple of phrases about tinning. Since LUTs are made temporary or for yourself, you don’t really need to bother with tinning (IMHO), you can just go with a soldering iron to those places where there will be soldering, and then varnish everything.

But if the components on the board are soldered or the board will be used for a long time, it is better to tin. Either go through the entire copper with a soldering iron, or if there is a hairdryer, then with solder paste.

I mix the paste with flux for about 1 part of the paste and 5 parts of the flux, cover the entire board and heat it with a hairdryer:


during heating, with a textolite brush (known as the “eternal brush”) I drive the solder to the edges of the board, there is no excess solder on the tracks with this method , and where it is not enough, you can drive from the edges. Not an air knife, of course, but also pretty neat.


The main problem when using solder paste is the extra balls that are stuck to the board. Here you can clearly see them in the photo:


Therefore, after tinning, the board should be thoroughly washed and wiped with a cloth moistened with acetone.

The plate was irradiated, now everything is for sure. Mounting. Verification:


The task has been completed. This board took no more than an hour (taking into account the photographing stages).

At the same time, the second board, or rather the two sides of one board, was etched. And if the first scarf was more for demonstration (it was possible to execute on the DIP adapter, rather than making arduins), then the second was needed for a specific purpose and weaving braids of wires on the adapter is not an option (and it’s not a fact that it doesn’t interfere with connecting via fsmc)

Two sides:


As you can see, I did not poison the two-sided textolite, undergoing the killer procedure of combining two templates at the stage of ironing. Better do it now.

We drill holes on the VIA for all the boards, take the legs from the resistors and 5 pieces, solder to one side, then string the second side on them, solder from both sides. All boards are combined! Now you can solder all the holes.

Something like this:


Everything is ready!

You must have noticed a strong marriage on one of the sides: The


paper after the printer is electrolyzed and collects everything. Especially hair, especially cat hair! So I did not finish.

And here is the culprit: It


controls all the processes that are running.

After restoring the track, the software is ready and the device is assembled:


True, it was just a temporary board - to check the connections, so that later they would be reconfigured humanly and ordered.

That's all. Good luck in your endeavors!

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