Making inscriptions using photoresist. Film photoresist. Making printed circuit boards at home. Negative sides of LUT technology

What do we need:

• Film photoresist negative (for example, in AliExpress)
• PC and (optional SL5-SL6)
• Transparencies for inkjet or laser printers (such as this)
• Printer (for the corresponding film - who has which)
• Foil fiberglass
• Paper (plain) and eraser
• Sharp object (needle, scalpel, etc.)
• UV lamp
• Soda ash (baking soda will not work)
• Smooth hands

So, a negative film photoresist is a photosensitive polymer material coated on both sides with a thin protective film (such a sandwich in Fig. 1). Exposure to light on it either destroys the polymer (positive photoresist), or, conversely, causes its polymerization and reduces its solubility in a special solvent (negative photoresist). During subsequent processing, etching occurs in the "windows" formed by overexposed (positive photoresist) or non-overexposed (negative photoresist) polymer regions.

For example, there is a ready-made layout of a certain device (let it be):

To make a printed circuit board, you must first make a photoresist photomask. For this:

1. we climb the menu "File" -\u003e "Print"
2. disable printing unnecessary layers
3. scale 1: 1
4. and put the checkbox "Negative" (if you forgot to put it and put it into print on the printer, you will have to reprint it) !!!
5. throw more paint onto the transparent film. Therefore, we climb into the printer settings and set:
   1. print quality: very high
   2. print type: black and white
   3. if there are other settings - see for yourself

We check points 2-4 again and send the template for printing (see the pictures below).

After - we check our template for transparency - the drawing should be clear and not transparent (if you can see everything through it - it's a bad thing - you can print it again or print a new one (by changing the printer's print settings))

Here's the result:

In the meantime, our template dries up (do not leave your prints on it), we will prepare the basis for applying the photoresist - PCB foil. To do this, the copper coating of the PCB must be cleaned and degreased: we take the correct size PCB and wipe the copper layer with an eraser in order to remove dirt from the copper. That's it, DO NOT touch this part of the PCB with your fingers! So that there are no gum particles left on the foil and again not to cover it with greasy hands, the copper should be slightly polished to a shine with paper (but NOT PRESENT!).

Next, we take our photoresist (the one that is the roll). Cut off the desired piece and hide the roll far away from the light (otherwise, over time, it may light up and the whole roll will disappear). You need to LITTLE pick up the matte protective film (it is located on the inside of the roll, see the figure) with a needle, for example.

Do not touch the part of the photoresist with which you are peeling off the film with your fingers, otherwise it will not stick to the copper.
Now, with a slight movement of your hand, we apply the photoresist to the board, press and gradually remove the matte film (photo). We carefully smooth out the whole thing (the photoresist should adhere all and so that without bubbles, etc., after smoothing, the board can be put between the pages of the book and pressed firmly)

While we were molding the photoresist to copper, our photomask managed to dry (hopefully). Now we apply it to the board with the photoresist (the side where it is printed, to the photoresist - if you did not print a mirror template). We align the template along the edges of the board and put glass on it (the template must be tightly pressed against the board, otherwise something that should not be illuminated may light up)
Now we put an ultraviolet lamp at a level of 10-15 cm above the board and light up our photoresist for about 7 minutes.

We remove the photomask and peel off the transparent film from the board (photoresist). This operation must be carried out carefully so as not to tear off the photoresist itself from the board.

Now we need to develop our photoresist. To do this, soak our board in a solution of soda ash for 30 seconds. With light movements of the toothbrush on the surface of the board, we wash off the remnants of the unlit photoresist (while dipping the board in a soda solution). When copper is clearly visible, rinse the board with plain water and let it dry out.

What problems can arise?

If the photoresist remains, where it should not be, then:

• Or overexposed with ultraviolet light,
• Or they made a bad photomask and through it the ultraviolet light illuminated everything
• The photomask was badly pressed against the photoresist (in this case, the tracks may be wider than necessary)

If the tracks themselves are torn off during the development of the photoresist, then:

• The photoresist does not adhere well to the copper -\u003e the copper is poorly prepared (oily, dirty, etc. or the photoresist is broken (I did not have this, but anything can be))
• Need EASIER rub with a toothbrush
• Overexposed the board in water (solution) - after all, the photoresist was not glued to copper on superglue.

Well, if the photoresist is completely washed off during development, it means that the UV lamp was not illuminated

And then everything is as in the scenario: ferric chloride ... we etch out ... wash off the remaining iron ... the photoresist can be removed with a knife, or with a solvent (which is much easier), or left as a protective coating for the tracks (so to speak).

The first time it may come out crooked, but with practice, mastery comes. Good luck!

I remember how at the end of the eighties, when I was in school, subscribed to the magazine "Young Technician" and there was a color music circuit in one of the rooms connected to the tape recorder "Electronics". How I fired up to collect it. With difficulty I found a getinax with copper, took a nail polish from my mother and carefully translated the diagram. Then after school I asked the chemistry teacher nitric acid, for which he was sentenced to the conclusion of the reaction on the board, and etched the circuit. On this it all stood up. There was nothing to drill holes for parts. The next experience came in the 2000s. I decided to master MK, armed myself with the book "Microcontrollers - it's just" Frunze and MK AT89C51. Then I printed the diagram on an inkjet, one could only dream of a laser, and pasted it on the textolite. Then he punched holes and drilled. Then he tore off the paper, cleaned it with sandpaper, and then drew a track with a marker. After a while, lasers dropped in price and I mastered LUT. Oh yeah, I just couldn't get enough of the quality of the boards. But soon I became too lazy to drill holes, only the AT90S8515 required forty of them and I decided to switch to surface mounting. All there would be nothing, LUT coped with a bang here too, but I somehow got acquainted with STM32 and ... TQFP100. Here LUT simply surrendered without a fight. And I decided to switch to a photoresist. I bought a five-meter sheet PF-VShch and started. Either the paths twisted, then nothing appeared at all, or even everything was washed away. In general, I exhausted the whole roll and nothing good happened. Either the hand is growing from the wrong place, or the photoresist is bad, in general I spat on this venture. But I recently saw an Italian photoresist "Ordyl alpha 350" on the Internet. Well, everyone is praising. I thought and thought and decided to try. I took out two rolls of five meters each, so it was cheaper and started. Here's what happened.
We take a textolite with dimensions larger than the future board by 10 millimeters and clean it. For these purposes, I use a chrome washcloth.

The plus is that it removes the oxide layer while not picking up like sandpaper. Then we wipe it with alcohol, acetone, solvent or wash it with soap, it's to your taste, as you like. Personally, I use a brake cleaning spray.

Knurling. Here I will dwell on in more detail. I don't know if the photoresist is too good or too new, but if you apply it to copper, you won't be able to peel it off. Grabs to death. I made the first attempt like this. Tore off the protective film from the edge. This one is matte. Then he applied it with a corner to the copper and gradually, pressing it with his finger, pulled out the film. It stuck well, but there was dirt and bubbles ... In short, I switched to the principle of toners. We take a two vat syringe and fill it with plain, cold tap water. Then we tear off the protective film completely. We hold the photoresist with one hand, with the other we pour water from the syringe onto the copper. The syringe is more convenient, since the copper is defatted and the drops roll down, and the syringe dispenses a little over the entire copper. After wetting, apply a photoresist. While the copper is wet, the photoresist freely crawls over it, and the water pushes out all the debris and air. And even if something went wrong, you can always tear it off the copper. After adjusting from the center to the edges, using a rubber spatula, without pressing, we expel the water. When all the water comes out, we begin to squeeze out the remnants with force, also from the center to the edges. The photoresist will start to knock closer to the edges. Nothing wrong. Pressing with a spatula from the center, it stretches quite easily and fits well.

After ironing, wipe it off with a napkin or toilet paper, it doesn't matter. The main thing is to wipe dry. We take a sheet of blank paper and fold it in half. Put textolite with photoresist between the halves and close this sandwich.

Well, here is someone like, someone with an iron, someone with a hairdryer, personally I am with a laminator. We heat the laminator at the highest temperature. After warming up, we send our sandwich there. Attention!!! If you send it to the laminator without a sheet of paper, then the pieces of photoresist, those that stick out outside the textolite, will be wrapped around the hot rolls and it will not be easy to tear it off from there.

I run it through the laminator twice in order to warm it up thoroughly. As a result, I get such a thing.

Template. There are three options here. The first is typography. Well, given her absence near my house, this option was immediately dropped. The second is printing on paper using a laser printer, then enlighten with a transparency. Well, I don't have this muck. And the last one is printing on film. The laser has given poor quality, or rather not bad, but rather transparent toner. Keep over acetone vapor ... No ice for two reasons. The first is that it stinks, and they will kick me out of the house, and the second is that now for some reason acetone has been replaced with some nasty thing that leaves drops of water after evaporation. Therefore, I switched to an inkjet. In addition, I have it sharpened for photos. The film "Lomond" was chosen for printing.

She has one drawback. The surface on which you need to print is rather sticky and any debris sticks to it, and this, as practice has shown, negatively affects the quality of the board. In short, if the distance between tracks is 0.2 - 0.1 mm, then a speck of dust can play a bad role and create a gap between tracks. Otherwise, this film makes great templates.

Oh yeah, I almost forgot. The template needs to be printed on the collar for eversion, that is, negative. Where to etch the copper black, and where to leave it transparent. And don't forget to mirror. The important thing is that the paint should lie on the copper, and not vice versa, paint up. In general, we put the template on a photoresist and all this under a UV lamp. I have so:

Here we will dwell in more detail. Lamp: Model ELSM51B-Color 20W Black. As seen in the photo, energy saving. Purchased from "Chip-dip" for 200r. The distance from the lamp to the PCB is 20 cm. Taking into account that the glass retains UV light, it is impossible to specifically stipulate the exposure time, since someone will tear off 6 mm glass from the sideboard, someone 3 mm from the entrance window. I bought in "OBI" a photo-frame made of dense wood measuring 300 x 200. The pieces of iron and cardboard went straight to the trash heap, and the glass 2 mm thick went to the clamp. I used the frame itself to stretch the mesh for applying a solder mask. But this topic is another article. So I have 2 mm glass. For the cargo I use two 7 Ah gel batteries. In this form, the illumination is seen exactly two minutes from turning on the lamp to turning it off. I do not warm up the lamp, since 20 watts is quite powerful. As a result, I get an overexposed photoresist. Another plus against ours, after development, the exposed areas darken and you can see what happens. Next, we prepare the bath. On a glass COLD !!! water half a teaspoon of soda ash. The water should be at room temperature. If you take a hot one, it will be like with our photoresist. All the tracks will fall off. After preparing the bath, we bathe the textolite.

If you help with a brush, the development will take less than a minute. As a result, we will get just such beauty.

We dry, we look. If something is wrong somewhere, we will rule. If you can't fix it, then we start all over again. Another plus against our photoresist. After exposure, we throw it into the soda ash solution for 30 minutes and the photoresist will fall off by itself. Domestic so I could not tear off, neither acetone nor soda. In short, I threw out the spoiled workpieces. After all the checks, we poison in a pickling solution. Here every man for himself. Some in acid, some in vinegar, I personally prefer ferric chloride. Preferably water, otherwise waterless, if you throw it into the water, there will be an explosion :)

Well, after etching, as always, drilling and applying a solder mask, but this is the topic of the next article.

Like with a photoresist and that's it, if you have any questions, write either in the comments or on the forum.
All good boards.


Andrey 04/05/13

Great article. I did everything as written, it worked the first time. Now someone else would write the same article about metallization :)

SergeBS 04.21.13

Some kind of game. 1. "In short, if the distance between the tracks is 0.2 - 0.1 mm, then a speck of dust can play a bad role and create a jumper between the tracks." The photoresist is negative (see below about the template). The speck of dust will not let the track light up and, as a result, the track is broken and not closed. 2. "I use two 7 Ah helium accumulators for the cargo." There is no HELIUM in the batteries, but there is GEL. And it is not at all necessary that there is gel in maintenance-free batteries. Gel batteries are rare. 3. "As a result, I get an overexposed photoresist. Another plus against our

SergeBS 04.21.13

Truncated comment. Okay. Let's repeat. Some kind of game. 3. "As a result, I get an overexposed photoresist. Another plus against ours, after development, the overexposed areas darken and you can look at what will turn out. Next, we prepare a bath. In a glass of COLD !!! water, half a teaspoon of soda ash. The water should be at room temperature. . If you take a hot one, it will be like with our photoresist. All the tracks will fall off. After preparing the bath, we bathe the textolite. If you help with a brush, the development will take no more than a minute. As a result, we are half

SergeBS 04.21.13

As a result, we will get this beauty. "We will not get NIFIGA. Before etching, you need to peel off the protective Mylar film from the surface of the photoresist. Regardless of the origin of the film photoresist. (Import or Russia). So this is:" Andrey 05.04.13 Excellent article. Did everything as written, it turned out the first time. "Lies. Miracles do not happen, it does not etch through the film. And if you tear off the film before exposure, the photoresist will stick to the glass. 4." Dry, look. If something is wrong somewhere, we will rule. If you can't fix it, then we start all over again.

SergeBS 04.21.13

Wonderful:). The photoresist flew off - pure copper remained - it's time to etch. Even if we assume a miracle that something (even soda, even ferric chloride) has crept through the unremoved protective film ... for the photoresist to fly off. About the explosion, a joke of humor, well, is completely out of place too. Someone can believe it. So this magnum opus must be edited. And in the future, do not write a review for yourself (this is about the mythical Andrey, who did as in the article and he succeeded :)). Read comments from bottom to top, "stitching" over identical pieces of text.

SergeBS 04.21.13

Total. CORRECT: 1. Negative template. You can use the laser. I have no inkjet - but everything is fine. 2. Peel off the bottom matte plastic wrap. 3. Glue and let lie under the load. 4. Highlighting - the template with paint (toner) to the photoresist.

SergeBS 04.21.13

5. After exposure - 30 minutes pause. Then we tear off the top shiny protective lavsan film and develop in baking soda. In a weak solution (citric acid - a teaspoon per glass) we tan the manifested. 6. In warm water we throw a little (so as not to boil) ferric chloride and poison in it.

SergeBS 04.21.13

7. Etched - in any alkali ("Mole" diluted 1:10 - 1:50 is that). In 10-15 minutes, the photoresist will fly off. 8. We wash with water (it is possible with liquid detergents). 9. We drill, tinker, solder the parts. Everything. In short, we do it according to the instructions ...

Alexey 04/21/13

Dear SergeBS 1 about the film. Describe its removal? Maybe you are offered to learn Russian, but how will you read an article, it is written in Russian. 2 With the battery, this is just a banter for the sake of writing. What's the difference than pressing. For example, I have replaced them now with two trances. And that there are few photos in the article. By the way, this board works and feels great. And in the end there is a section "Write an article", you write, and you will be criticized, then we'll see. And everyone can shout and throw mud.

Alexey 04/21/13

Oh yes, at the expense of the laser. Neither XP nor Xerox provide quality templates. I've tried everything. Especially if with a domestic resist, then it is stupidly illuminated as if there is no template at all. Maybe, of course, they sold me an old resist ... And even if, according to your scheme, to tear off the protective film and try to glue it, and then under the load.)))) Well, well.

Vitaly 05/14/13

Alexey, a very wonderful article. I have a great desire to do all this, to start with buying everything you need (if you can help with this, I will be very grateful). And what kind of inkjet printer did you use.

Alexey 05/14/13

At first I had an Epson Stylus CX4300 but the head on it dried up. I have now bought an Epson L110. It is designed for continuous use and the ink is poured from the side into flasks, not cartridges. According to my measurements, black paint is enough for 50 sheets of A4 solid fill. And of course ink is much cheaper. If you have any questions, write. I will definitely answer.

Mikhail 05/16/13

Hello. The article is actually good, this is me, as a person who has been making boards for more than 15 years. SergeBS, why are you broke? Write your article, business. : +) And I have one question for the author: could you tell us what settings you set on the Epson L110 to print a template? Sincerely, Mikhail.

Alexey 05/16/13

Hello Mikhail. In the printer properties, select the "Advanced Settings" tab. In the "Color Correction" section, check the "Settings" box. The "Advanced ..." button will appear by clicking on which the settings menu will appear. In this menu, the brightness is at a minimum, and the contrast and saturation are at the maximum. Yellow at maximum (yellow delays UV) and magenta with cyan at minimum. And here's another, uncheck "High speed printing". Look like that's it.

Mikhail 05/16/13

What material / quality do you choose? In general, it's interesting, it's simple, I now also use the L100, and on the contrary I removed the yellow one, otherwise it refuses to dry on the template (the film is the same).

Alexey 05/16/13

And there the quality is either automatic or manual. My material is just paper. Do they dry for a long time? What ink? Relatives, "Fool" or not original? It is important.

Mikhail 05/16/13

I have a lot of everything in the drop-down list. Normal, high, photo, best photo ... I am currently printing using Photo RPM (max dpi) with saturation up. Prints slowly, a bunch of passes, but the quality is perfect. Only here it is the yellow color that dries for a very long time. And the ink is native, which came in the kit.

Alexey 05/17/13

Well, in principle, this is the very thing. I set it up on the old one. How long do they dry? If 10 minutes, then you can roll the photoresist at this time. :)

Alexey 11/22/13

For some reason, in the space between the 0.1 0.2 mm tracks, the photoresist in soda does not come off well .. you have to hold and help with the brush longer and at the moment when this space is cleared, in other places with thicker tracks the pads are already pads and the tracks themselves fly off ..

Alexey 11/23/13

Try reducing the exposure time by 10-15 seconds.

Alexey (friend 02/17/14

Hello Alexey! Thank you for the article. It's funny, but now I'm making exactly the same board for exactly the same controller, but not 100 but 103 series. I am suffering with PF-VShch. And my problems are exactly the same as you described. I have already taken out a sheet of 30x50 (my board is 5x6cm, i.e. about 50 samples), but the result is zero. I don’t give up yet. There is no other FR in our city. :(

Alexey 17.02.14

MarioFly 09/08/14

"Another plus against ours, after development, the exposed areas darken and you can see what happens." Not after development, but after exposure.

Anton 11/04/14

Yes, thanks, I also suffered with this PF-VShch. I thought that everything, hands have grown to another place. And yet I took Ordyl on trial, so everything worked out right away. Even with a pattern with gaps (LED printer), it came out normally at minimum illumination.

Alexey 11/04/14

I give this PF-VSH in good hands))) a roll of 5 meters. True, the expiration date has already expired, but I think it's nothing ... My protective mask has expired as 2 years and nothing. So if there are those who want to try their luck with PF-VShch, write. And then it's like a suitcase without a handle, you don't need nafik yourself, but it's a pity to throw it away.

There are many manufacturing techniques printed circuit boardsavailable to amateurs. Each has its own pros and cons.
I've tried the following:

At the dawn of my hobby for radio amateurism, I made boards by drawing with an ordinary rod from a pen. A ball was squeezed out of the tip with a needle, and a good ruling pen was obtained. Next, a varnish suitable for viscosity was sucked in and tracks were drawn with this device. Pros- necessary equipment almost everyone has at hand, negligible cost of technology. Cons - no automation.

Then I got a laser printer and PCB routing software. Experiments began to translate the board drawing from a printout to a textolite. There are many nuances in the technology: the quality of the translation depends on the material and structure of the paper, the temperature of the iron, the material and temperature of toner baking, the pressure of the iron on the paper-textolite sandwich. As a result of research, I came to the following conclusion: the HP LJ 1018 printer, we print on thin coated paper, in my case it is the gutted magazine "Upgrade". We use only the original cartridge, no refills, because the toner density decreases. We skin the board with a zero, then we transfer the print with an iron, frying at maximum, through 2 sheets of A4. Finally, under warm water, erase the paper with your finger.
Pros of technology: minimal time between printing and receiving a payment, no chemistry is needed, there is an incentive to read magazines. Cons: instability of technology, dependence on many factors, the difficulty of obtaining large boards with small tracks - they will always peel off in places, you have to retouch the bald patch. With some "luck" you can ruin the surface of the iron. For stability of rolling, instead of an iron, you need an expensive laminator with temperature control, ordinary cheap ones do not warm up the board, the print does not even stick.

The last technology I mastered, which immediately showed a qualitative leap in the manufacture of boards - use of film photoresist...

Briefly, the technology looks like this: we make a transparent negative template with a board pattern, roll the film photoresist onto the textolite, run the sandwich through the laminator (or iron it with an iron) to fix it, put the template on the board, light it up with an ultraviolet lamp, peel off the polyester and develop it.

At first glance, it looks too long, but it is almost 100% compensated by the result. However, to get a stable result, you will have to spend a little.

First of all, I recommend purchasing laminator... You can roll the film with an iron, but as practice shows, due to the unevenness of the board and the surface, the photoresist often does not roll in here and there, and as a result, the subsequent peeling of the tracks in this place.

In METRO or AUCHAN, you can buy the cheapest laminator for 800-900r, and we don't need the best. Also, a laminator can be made from an oven from a printer or copier, but this is not for everybody.

Absolutely essential a printer... I use a laser, but inkjet will work as well. It is highly desirable to use cartridges for laser printers only "from scratch", filled, due to the worst parameters of the toner, do not provide the necessary contrast of the print, due to which "dancing" begins with a precise selection of exposure and development time. And this is an extra headache that spoils the joy of our hobby.

Glass for clamping. I gutted the sideboard. It is quite workable.

UV lamp... I use 11W, without a ballast, for a table lamp, but it is quite possible to use ordinary ones, "a la energy saving" with a base for a standard cartridge.

Still need film for printing on your type of printer, many of them are produced, for example, Lomond. I do not recommend ordinary paper with the use of various kinds of "clarifiers" due to the mass of negative reviews on the forums and the lack of transparency of the resulting nasty for ultraviolet radiation.

And, of course, the photoresist itself... I used LIUXI and PNF-VSH. Chemistry will require soda ash(in extreme cases, you can use food, but it will appear worse and longer) and some kind of alkali.

Photo roll for rolling

Photoresist roll, 30 cm wide

Cut off a piece of photoresist

The photoresist has one side made of lavsan (top), shiny, the other made of polyethylene, matte (bottom).

First of all, we print the template on film

It is necessary to print in a mirror image, since the side on which we are printing should be adjacent to the board when exposed to light. Some types of films are seen in the sins of shrinkage during laser printing, therefore, if you are not sure about the quality of the film, I recommend that you first run it through the printer by printing a "white sheet of word".

Ready template

Separately, I would like to warn against sticking anything into the laser printer - if the film is not designed specifically for laser printing, it can melt in the oven and wrap around the shaft, as a result of which you will, at best, get to replace the shafts and thermal film. If you can't wait at all, try first to drive away the unknown film, putting it between paper sheets and securing everything with construction (not film!) Tape. If it does not wrinkle and does not stick to the paper, you can use it.

Next, we need to roll the photoresist onto the board.

Pay attention to the lighting in the room. There should be no bright sources near the workplace. From experience, I can say that the resist does not particularly react to a ceiling lamp made of two 36w fluorescent lamps. First, we take a PCB blank of the required length. In its preliminary processing, opinions differ, some recommend degreasing with solvents, others, on the contrary, say that after the evaporation of the solvent, many impurities remain that only harm. I usually just sand it with zero (especially if the textolite is old) and wash it with soap. After processing with your fingers, it is no longer recommended to touch the board.

We tear off the polyethylene

The workpiece floats in the tray

We melt the photoresist

Smooth with a roller

We put the sandwich in a paper daw

Pull through the laminator (repeat 3 times!)

Finished workpiece

Next, we prepare a small bath of water, in which we will roll the photoresist onto the board. The bath must be pre-washed, because dirt, hair and other floating artifacts are contraindicated in our process - where they get. Next, we cut off the desired piece of photoresist and tear off the protective plastic film from the corner. Can be pinned, but I use sharpened tweezers for smd components.
Note that the film photoresist consists of three layers: transparent lavsan, through which the illumination is performed, the photoresist itself, and a matte polyethylene protective film. So it is necessary to tear off matte, do not confuse.
After the film has been torn off, we throw the board into a bath of water, then we put a photoresist film on top of it. Gently press it to the board and smooth it so that there are no bubbles. Then we take out what happened, put it on a rag and roll it out with a finger (preferably with a roller, I use a photo roller) this sandwich in order to finally expel the water from under the film. In principle, with some skill, you can roll it dry, but firstly, there is no dirt and dust under water (if the bath has been washed), and secondly, because of the stickiness of the photoresist, if the probability that the bubble formed in the center of the board is not can be ejected either with a roller or a laminator. You cannot tear off the film, so you only have one attempt at dry rolling.

Next, cut a piece of paper with a width slightly larger than the width of the board, and a length slightly more than double the length of the board. We fold it in half and put the board into the resulting "jackdaw". After that we stretch the sandwich through the laminator. You need to stretch it 2-3 times, otherwise the board does not have time to warm up normally. I do not recommend stretching without paper - the photoresist is a sticky thing, then you cannot scrape off the laminator.

So, we have got a blank, everything is ready for exposure

We put a magazine, rubber mat or some similar pad on the table. We put the board blank on it. On the template blank, with the printed side down. This is important, otherwise there will be side flares due to the significant thickness of the film and the refraction of the rays in it, as a result, thin tracks cannot be obtained.

Everything is ready for exposure

Highlight

Side view

We put glass on top of all this for pressing. It is imperative to press, otherwise, due to irregularities, some areas during exposure may blur, defocus, and we get a marriage. Place the UV lamp at a height of 20-30 cm above the board. Distance is also important from the point of view of side illumination, since the higher the lamp, the more perpendicularly the rays will fall on the template and less light will pass from the side under the track on the template. Naturally, if you are making a board with a track width of 0.8 mm, these recommendations may not be followed. But if you need 0.1 mm, then any little thing can ruin the case. Further exposure. I illuminate with an 11w lamp for 5 minutes. More powerful lamps will suffice to shine for a significantly shorter time.
In principle, with a good factory pattern, even prolonged overexposure will not spoil the case. But if you have a refilled cartridge or the printer does not provide a dense and contrasting template, you will have to experiment. If you don't light enough, the drawing will wash off during development, if you overexpose, the drawing will not appear at all, or, more often, there will be a coating of indelible photoresist between the tracks, which, when the board is etched, will appear as tracks glued together in a heap.

We got to development

Manufacturers are advised to show in soda ash. Typically, they do not deceive. I have also tried the usual one. It turns out, but the process takes longer and in the presence of small, about 0.2, distances between the roads, the underexposed photoresist may not dissolve. Concentration - a couple of tablespoons of baking soda per liter of warm water. Before bathing the board in the developer, do not forget to tear off the lavsan film from above. It makes sense to stir the solution, you can also wave a brush around the board to speed up the flushing of unpolymerized photoresist.

Dissolve soda ash

We show

Manifested

If you're lucky and everything worked out as intended the first time, you should have a beautiful board ready for etching. But everything can go crooked (at least when I started to master the technology, I made a lot of defects), then the fee before next try (as well as after etching) must be cleaned from the photoresist layer. You can peel it off with emery, but that's not sporting. It is better to use a solution of any alkali. On occasion, sodium hydroxide was lying around, and I wash it off, but it is quite suitable, for example, Mole, caustic soda and various Mr.Properties for cleaning the stoves from fat. We lower the board into this solution and after a few minutes the entire photoresist film gently slides off.

Storage

The photoresist can be stored in any place protected from light, for example, wrapped in a layer of newspaper. But it's better to come up with a cover for it.

I store in this tube

A photoresist sticks out of the tube, on the right is a plug from a bag wrapped with electrical tape

For this I use a piece of sewer pipe from the sink, which is sealed tightly on one side, and on the other, is plugged with a removable plug from a tightly crumpled bag wrapped in electrical tape. In such a tube it is also good to transport photoresit, without fear of wrinkling along the way.

Today I will tell you about the manufacture of a printed circuit board using film photoresist or the so-called photoresist technology for manufacturing printed circuit boards. Do not shout that LUT is cooler, cheaper and faster - I do not argue, but the photoresist has a higher resolution and is able to give results where LUT may not work. All of the following will apply to negative film resist. In my practice I use PF-VShch-50. The process of manufacturing a board using film photoresist can be divided into the following stages:

1) preparation of the board blank and photomask;
2) applying a photoresist to the workpiece;
3) illumination of the workpiece with photoresist through the template;
4) development of the board drawing;
5) etching the board.

We cut the workpiece from foil-clad material with an allowance of at least 5 mm to the main size on each side. We print the template on film for the printer that is at hand. I have a laser and I print on universal double-sided film for laser printers and copiers. Whoever has an inkjet, then accordingly we take a film for inkjet. When printing, in the laser settings, we select the maximum print quality, turn off the toner saving - the more there is on the template, the better. As a result, we have the following:

The printer is old and the cartridge has been refilled a bunch of times, so the print quality is poor. Therefore, the toner on the template is transparent enough, but we need it to transmit as little light as possible, i.e. it is necessary to increase the optical density of the image. For these purposes, there is a tool for increasing the optical density of the negative Density Toner, but it was not possible to find it and it costs decently. I decided to use acetone - it turned out to be more than enough for my needs: we moisten a piece of medical cotton in acetone, throw it into a glass jar, put the template inside the jar with a pattern, twist the lid and set it to heat.

Heating can also be carried out on a radiator or some other thread (depending on your imagination). This process requires control so as not to overexpose the template in acetone vapor, otherwise the entire pattern will drain to the bottom of the can. In the photo, a template that has passed a pair of acetone - it has become somehow more black and shiny, try it - the result will be on your face.

We proceed to applying the photoresist to the workpiece foil, for this we stock up on approximately the following tools:

We roll out a roll of photoresist and cut a piece with a knife along the workpiece with a small margin on the sides, because it will not work perfectly evenly.

Now we take the "zero" and under a stream of cold water we begin to clean the foil of the board blank from the oxide film. A sign of the absence of an oxide film is a uniform coating of the foil with a water layer and the absence of drops.

Now we separate the bottom (matte) film from the cut out piece of photoresist. This can be done with the tip of a cutter or with a needle. Separate the film approximately 5-10 mm wide and glue the photoresist to the workpiece so that there are no air bubbles.

Now gradually pulling out the film, roll the photoresist to the workpiece with a roller. After rolling, cut off the protruding sides and roll the workpiece in the laminator.

Now we proceed to the exposure (exposure) of the billet. I use a COMTECH CE ST 26 E27 BLACK lamp as a radiation source. At this stage, it is necessary to choose the right exposure time (see comments to the article). We put the workpiece on a hard, even surface, put a template on top and cover it all with ordinary window glass, and install a lamp on top.

We cover the workpiece with a book or other material that does not transmit light, turn on the lamp and let it warm up for a minute.

Remove the opaque coating and time it for normal exposure.

As soon as the time required for illumination has expired, turn off the lamp, remove the blank in a dark place and go to prepare the developer. As a developer I use soda ash (detergent), it is sold in household goods at a price of about 20 rubles per 0.5 kg. For cooking, take a teaspoon of baking soda and dilute with 1 glass of cold water.

Now we take out the illuminated workpiece, separate the upper glossy film, throw the workpiece into the developer and use three toothbrushes - a drawing of the future board begins to appear on the photoresist.

We continue to "clean" the future board until all the extra photoresist is washed off and we get this:

We wash our future board under cold water and throw it into the pickling solution to swim.

For etching, I use ferric chloride, and to speed up the process, I glue the board to a piece of foam with double-sided tape and lower it with the pattern down. In this case, it is necessary to check whether air bubbles remain under the board, otherwise they will not stain. After 10 minutes, we get the following result:

Now you need to wash off the remaining photoresist and here you can go in 3 ways:

1) toss the board in caustic soda (CAUTION! ALKALI! WORK IN GLOVES!);
2) boil the board in the solution in which it was developed;
3) toss the board into the solution in which the workpiece was developed.

The choice of method depends on the time it takes to make the payment. The longest is soaking in the solution in which it was developed (I throw it there overnight). Boiling in the developer takes about a couple of minutes. I don’t know the time for caustic soda, but they say that it is also very fast.
It remains to bring our board to the required size, tk. we made allowances on each side and we can drill and solder our device. But to give the board beauty and improve solderability, it is better to even tin the conductors. Someone with what, and I - with an alloy to Rose, as it turns out very quickly. For this I take the following ingredients:

Pour a glass of water into a bowl with a flat bottom and add a spoonful of citric acid (plays the role of a flux), throw the board there in the paths up and put a piece of Rose's alloy on top. We put all this on the stove and wait until the alloy begins to melt (it is better to hold the board with something).

The molten alloy is "rubbed over the board" (I use a brush with a piece of cotton wrapped around it). BE CAREFUL! STEAM CAN BURN YOUR HANDS! When rubbing, excess alloy is thrown into the water and only a thin shiny film remains on the conductors. We take out the board and rinse with water. Now you can drill and solder.

Some comments on technology:

1) The whole process takes about 1 hour.
2) When purchasing a photoresist, look at the manufacturing date. The shelf life is 9 months, after this period it does not stick well to the board. Store the purchased photoresist in a cold place (I have it in the refrigerator, it still sticks well, albeit expired).
3) You don't have a laminator to roll the photoresist to the workpiece? It doesn't matter - the iron will help. We turn on the thermostat to the 1st position and wait until the iron heats up. After heating to a certain temperature, the iron turns off, pull out the plug from the socket and put the board on the iron seam with the photoresist up, let the board warm up. We remove it and "from the heart" roll it with a roller.
4) When rolling the photoresist onto a wet workpiece and using a laminator, it is best to run the workpiece cold through the laminator to squeeze out the water. Otherwise, during hot lamination, water will evaporate and air bubbles will appear under the photoresist.
5) The choice of the exposure time of the workpiece through the template is as follows: A negative template with numbers from 1 to 10 is printed, applied to the board with the applied photoresist and every minute the exposure is covered with an opaque material, one digit at a time, starting from 1. After development, it will be seen how many minutes light up. I have a 26W lamp, the distance from the workpiece to the lamp is 12 cm, the glass thickness is 4 mm - the exposure time is 3 minutes, I tried it for 5 minutes - it also works. I take a photoresist from the same manufacturer - const time.
6) Rosa can be tinned with an alloy in glycerin, but you can get it from your family for the "fog" in the kitchen.
7) When soldering a tinned board with flux, it must be washed off immediately after soldering, otherwise the flux causes darkening of the Rose alloy.
8) The photoresist is not afraid of light from incandescent lamps, so you can work with light.

Greetings, dear friends! You are on the blog of Vladimir Vasiliev and it is early morning outside! This is all because I got up early to write a useful post for you, so let's go ...

In the last article, I wrote that the quality of the boards received by LUT-m ceased to satisfy me, so I'm going to move away from the popular LUT technology and switch to photoresistive technology. For this I am including a film photoresist. By the way, it is quite possible that an article will soon appear on my blog about how to properly make printed circuit boards using the photoresist method. But it will be later, and now I want to tell you my experience of using a photoresist, in particular, getting the right exposure time.

There is one subtlety about using a photoresist. The quality of the formed pattern on the photoresist depends very much on the correctness of the selected exposure time (exposure). I felt this subtlety on myself.

After the photomask has been prepared and the photoresist has been safely applied to the foil glass fiber laminate, it is time to find out the required exposure time. To do this, I formed a “sandwich”, covered the textolite with the applied photoresist with a photomask and put a sheet of plexiglass on top (in my case, it is a transparent cover from the CD box).

Next, a hypothetical exposure time for this sandwich was chosen - 2 minutes. For 2 minutes I turned on the ultraviolet lamp and began to wait with trepidation for the result. These 2 minutes passed quickly ... My first disappointment was that although I had an indicator photoresist, for some reason the purple outline of the drawing was extremely faded.

Well, further this beauty was expected by immersion in soda ash. The solution was a teaspoon of soda ash per liter of water. After washing in the solution, a second disappointment followed - if the pattern at the beginning of the washing still took place, then by the end of the washing (2-3 minutes) it was finally washed off. It's time to think ...

After analyzing my actions, I came to the conclusion that the weakest point in the chain of my actions was precisely the exposure time of the photoresist, and this time was insufficient ...

The exposure time cannot be somehow universal, because several floating factors appear here, including the quality of the photomask, the power of the UV lamp and its characteristics, the material of the pressure glass. All this can be very different and it is not surprising that when choosing one universal exposure time, the result will also be very different!

Based on the experience gained, I re-read a lot of information and found a very interesting trick with which you can quite accurately determine the required exposure time. I would like to note that this technique will only work if all these factors (UV lamp, photomask quality, pressure glass) are low.

In order to conduct this experiment and find out how long it takes to illuminate the photoresist, I suggest downloading the calibration photomask file. I found this file on one of the amateur radio forums.

There is only a fragment of the picture in the image, if you download a pdf file then there will be 2 rows of ten images.

To conduct this experiment, you will need the following tools:

1. Calibration drawing
2. Installation for exposure (or just a UV lamp)
3. A damper that is opaque to UV rays by the size of the photomask - it can be a strip of cardboard, opaque plastic, even a piece of PCB.
4. Timer - the phone perfectly copes with the role of a timer
5. Soda ash - sold in hardware stores and costs a penny

The essence of the experiment

We print our calibration drawing - this will be our photomask. Then we take our piece of foil-clad fiberglass with already knurled photoresist (if not already rolled, then roll it by running) and put it on the table with the photoresist up. Next, put the photomask with the printed side down, cover this bag with glass and press down well.

Weights can be used for these purposes, but I use paper clips. It should be noted that weights or clamps must not impede the movement of the valve. Yes, the next layer of our sandwich is a flap that should cover all the elements of the photomask except for the last one (for example, the 10th). One edge element of the photomask must remain open.

Thus, the nine elements will be closed by the shutter and therefore the UV rays from the lamp will not fall on them.

We place the Ultraviolet lamp above our composition at a distance of say 10 cm (at the moment this is not so important, but this moment can then be corrected according to the results of the experiment). We timed 5 minutes and turn on the UV lamp.

Every 30 seconds, we move the flap, thereby opening the next element of the picture. Thus, it turns out that the 10th element will receive the maximum exposure time, the 9th element will be exposed for 4 minutes 30 seconds, the 8th - 4 exactly, etc. The first element of the picture will glow for only 30 seconds.

After the end of the exposure, it becomes clear that the elements that were underexposed will appear the least. Elements that have received a sufficient dose of ultraviolet light will change their color to bright purple. At the same time, it should be noted that the areas of the picture covered by the photomask should not change their color. If this happens, it means that the pattern of the photomask is not dense enough and ultraviolet rays still fall on the photoresist. But even if your photomask is not perfect, all is not lost, you can find a compromise between under-exposed and overexposed areas. But the final decision will be made only after the development of the photoresist.

Photoresist development

The photoresist development stage has come. To do this, we dilute about a teaspoon of soda ash in a liter of water and stir well. And now we put our illuminated sandwich in this bath.

During the development process, periodically pull the board out of the solution and rinse it in cold running water. In this case, the situation must be kept under control. It is necessary to wait for the moment when the protected elements (the elements that were covered with a photomask) finally dissolve in the solution, but the illuminated areas will be clear and contrasting. Thus, we find the element that suits us the most. And since we know how long each element shone, we can easily determine the required dose of radiation.

For the purity of the experiment, it is worth repeating this procedure again and make sure that the result is repeatable.

After carrying out all this procedure, I found out that in my case the exposure time should be 4 minutes. Honestly, there were some flaws when applying a photomask. When the photomask was printed, it turned out to be surprisingly long (extended along the entire length of the A4 sheet). It was me who later discovered that the drawing was printed at a scale of 212%. When overlapping, I had to limit myself to 5 elements from the photomask line, since the pressure glass could not cover the entire area.

Although the photo turned out not very high quality, you can see from the image that elements numbered 1 and 2 are faded more than elements numbered 3 and 4. The exposure time of elements 3 and 4 corresponds to 4 and 5 minutes, respectively. Yes, as you can see, I moved the shutter every minute, the wrong scale is to blame.

Well dear friends, that's all for me, I wish you success in all your endeavors and be positive! Be sure to subscribe to updates and see you soon!