How to use a solder mask. What is the best solder mask color? Screen Tensioner

The quality of any homemade electronic device depends very much on how good it is.
was made (yes - a useful phrase, it's so clear! Well, yes .... But I need something
to begin?).
The printed circuit board plays a big role in this (this is if you have a not too simple design that
can and
do volumetric installation). The more complex the device, the more complex the PCB pattern, and the
better
it must be made. About one of the ways DIY PCB manufacturing speech
and go.

Foreword

All materials used in this article can be bought in our store

There are several ways PCB manufacturing at home. At the very beginning (this was when I studied at the school as an electronics engineer), I drew tracks with nail polish (very brutal printed circuit boards turned out), then I tried a waterproof marker (already better). But only when I mastered laser ironing technology(LUT) (and this happened relatively recently) I was finally able to get the quality of the boards that was pleasing to the eye. After all, I make electronic crafts purely for the sake of the process itself. Well, this is my hobby. And what is the interest in soldering something on a scary printed circuit board? But after a couple of years, this technology ceased to suit me. Although LUT has many advantages:

speed (with a printer - from printing to the start of soldering, I managed to achieve about 10 minutes);
simplicity (although you will have to pay for this simplicity with a good dozen unsuccessful takes at the very beginning of using this technology. That is, you need to “get your hand in”.)
good repeatability. (I got about 90% of all attempts. I did not include the first ten in the statistics!).

With the help of laser-ironing technology, it was even possible to apply inscriptions, which I did in some cases.
But LUT gave an accuracy of no more than 0.3 mm. This is a practical ceiling. I tried to make the tracks thinner, and I succeeded, although at the same time the rejection rate increased quite a lot. In general, I already dragged out the preface to the article, so let's move on to the actual solder mask.

What is a solder mask?

FSR8000- two-component composition sensitive to ultra-violet radiation. Has three states.
1. "Raw State". After the two components have been mixed. In this form, it can be washed off with either acetone or a solution of soda ash.
2) "Hardened State".
2a) Not exposed to ultraviolet light. Soluble with acetone and soda ash solution.
2b) After exposure to ultraviolet light, the mask becomes resistant to a solution of soda ash, but can still be washed off with acetone.
3) "Baked State". It is obtained after heating to 160 degrees, followed by exposure for several tens of minutes. Does not dissolve in acetone, has high mechanical resistance.
In simple terms, a mask is a protective layer that can often be seen on prefabricated printed circuit boards. Very often green. This article will discuss the non-standard use of this mask as a photoresist.
To do this, you need to use the first two states, i.e. with the help of illumination and subsequent development, obtain a pattern of conductors on the textolite. And after etching, wash off this pattern with acetone.
Then the mask can be used for its intended purpose, covering the area of the entire board with the mask, except for the pads intended for soldering parts. Then transfer the mask to the third state. And now about the same, but in detail and from photographs.

List of what you need for the PCB manufacturing process

- FSR8000(You can buy in our store)
Thermostat. Despite the formidable name, you can use a regular iron with the ability to adjust the temperature. You also need a thermometer (up to 160 degrees) to remember the positions of the regulator at 70 degrees and 160 degrees. After that, the thermometer, in fact, will no longer be needed.
. You can simply use an ordinary energy-saving lamp with a cold light. It's just that the exposure time will be very long. But it's safe.
Mesh frame. Frame with stretched mesh.). for a mask and can be purchased on our website, we also recommend reading the article
Photomask with a drawing of the board and the placement of contact pads. for photomask,
insulin syringes. Needed in order to accurately mix the components of the mask .
toothpicks. To stir the components of the mask.
For a uniform application of the mask on the textolite, we need: , credit card, piece of foam. I use a credit card (already unnecessary, of course).
For development we need soda ash. Look next to laundry detergents in stores.
Acetone. To wash off the mask after etching.
Capacity for developing (any plastic utensils)

The technological process of manufacturing a printed circuit board at home

Photomask(). It can be done in a printing house that has equipment for phototypesetting films. Often this service is not advertised by printing houses, as it is purely internal. But, as a rule, they agree to print your handkerchief drawings on phototypesetting film without any problems. The file format, the dimensions of the drawings must be clarified in a particular printing house.
To obtain a board pattern, the pattern must be inverted (white tracks on a black background). For a protective mask - straight (black circles on a white background) . Photoresist Ordyl Alpha 340

The photographs show the photomask itself. One side seems embossed, the other should be glossy and smooth.
It is important not to confuse the sides - the photo layer is on the side where the relief is.

Wooden frame (made of balsa, glued with low-viscosity superglue!) with a stretched baby bow.

We cut out the blank from textolite. We give some margin on the sides.

We clean the surface with sandpaper. No need to try hard, just remove the dirt. The mask has very good adhesion.

The photo shows a cleaned textolite. Metal shavings must be washed off with water.

An iron with a thermometer. It is not necessary to always control the process like this. Now I know the position of the regulator
for 60-80 degrees, and by setting it to this position, I am sure that I am getting the right temperature.
Be careful, the temperature of the iron should not be higher than 100!

We collect mask components in small syringes.

Everything you need to work
- mask components in syringes
- frame
- photomask
- toothpicks
- Squeegee rubber

We squeeze out the required amount of reagents onto the textolite.
For such a scarf, this is 3 ml of mask (green component) and 1 part of hardener (white component). Those. the proportion should be 3 to 1
.

Stir with a toothpick. We try to stir well, since a lot depends on the quality of stirring.

Mixed Uniform Mask

We press the mesh on top. Here, perhaps, it is worth saying that in some cases (especially when
when the mask is already expired) it is better to mix large portions, for several at once
handkerchief. Then put a frame with a mesh on the scarf, and on top of the mesh already apply the required amount of mixed
masks. Then the mesh will not allow dense (thickened) lumps of the mask to get on the textolite, thereby spoiling
the whole picture.

We distribute the mask over the textolite. The point is that the mask remains only in the cells of the grid. Then when removing
grids - we get an evenly distributed mask. Therefore, a piece of squeegee rubber (or a credit card)
we try to remove excess mask from the surface of the grid. Without fanaticism! Don't break the mesh

Result

Remove mesh carefully

The mask quickly spreads over the entire surface, forming a uniform layer.

Putting a handkerchief on the iron

We cover the scarf with something to protect it from dust. And we wait a few minutes (or tens of minutes).

In the meantime, we throw the grid with traces of the mask into soda ash.

It is important to catch the moment of almost complete drying of the mask. You can try to check the mask with your finger on the edge of the scarf
(where you left the tolerance. You left the tolerance?!). If, when swiping a finger, no remains on the surface
traces, while the mask slightly sticks to the fingers - this is what we need. Scarf with a mask with a cut-out pattern.

We impose a template with a photo layer to the mask and carefully smooth it to the scarf. DO NOT CONFUSE the side! If the surface
a little sticky - the template stays on the scarf without any problems. If the surface is already almost dry - it does not matter.
Try either moistening the surface with water so that the template sticks, or press the template against the handkerchief with something.
(you can attach it with tape. But be careful!) In general, the template should fit snugly against the scarf.

I put on the light. The exposure time is determined experimentally. I can tell my lighting modes:
70 (maybe even 80) minutes at a distance of 7 cm, under a 22-watt power saver. UV lamp will give much less
exposure time, but the time tolerances will decrease accordingly).

Preparing a solution for developing

Water at room temperature. Cleaned, soft. Dosage - experimentally, in the photo the dosage for
soft St. Petersburg water (As you may have guessed, the photos were taken by Termite). For hard water - soda should be
more. The solution should be slightly soapy to the touch. If there is too much soda, the development will be fast,
but at the same time, a slightly underexposed mask will “peel off” during development. And if there is too little soda, the development will be
very slow. Moreover, heating the solution will only interfere with development. After the time has passed, the necessary
for illumination - remove the film, and throw a scarf into the solution

Scarf in solution.

If everything is correct, then in a minute you should see a slight pattern of conductors.

When the handkerchief is fully manifested, wash it from the remnants of soda ash, put it to dry on the iron.

What happened.

One of the unpleasant features of the mask is underdeveloped areas.
On a dry handkerchief - they are very clearly visible as whitish spots. They shouldn't be! They won't give a solution for
pickling to get to the copper. Then we throw the handkerchief back into the solution, and lightly clean those areas with a cotton swab.
Again, rinse, dry, control. And if everything is in order, then ... We poison the scarf.

In the process of etching, we control that there are no air bubbles. Often they are between the tracks.

We poison, we poison ...

Here is what happened

Wash off the mask with acetone. You can check the scarf, ring for breaks and short circuits. For now we will
apply a protective mask, and then it will be very difficult to fix breaks, and especially short circuits.
Apply the mask template. The alignment accuracy can be checked by light (if the scarf is one-sided)

Again into the light (yes, yes, again for 70-80 minutes, if you don’t have UV. But you can make several scarves at the same time!)
Then into the development in the same solution of soda ash. Basically, it lasts a long time. Truth change everything
anyway, because in the green solution you can’t see the scarf itself, and how it is getting more and more beautiful

For example, I like to watch how shiny copper pads gradually appear on a green surface.

So, pros using this method on your own PCB manufacturing:

Very very technological and beautiful
High accuracy. 0.15 mm is not a problem. Two tracks between the legs of a DIP package? Trying hard is not a problem.
Almost 100% repeatability(of course, this is when you already know at what distance and how long to light up other small things that are determined experimentally on the first attempts to make scarves)
protective mask. This is a very good plus - after all, soldering with a protective mask becomes very simple - SMD components simply fall into place by themselves.

And now the cons.

A very long time. When using conventional energy saving devices - VERY LONG. But who is stopping you from making scarves in batches?
Photographic film is required. (You can, of course, use templates from the printer. But ..., honestly. I do not advise. Because then the tolerances for the exposure time become very, very small)

Safety engineering.

Keep in mind - in the description of the FSR8000, a lot of unpleasant things are written about the toxic properties of mask vapors. At least - work with an open window. And best of all - under the hood. Now, about my advice “touch your finger to see if it's dry” - it's better not to do it. If the mask gets on your hands, wash it off quickly.
Acetone. Also harmful. It dissolves fat, which means that something unpleasant can be done from subcutaneous fat. It is better not to allow prolonged contact.

Ferric chloride. It is better not to inhale its vapors. In general, I have the whole process on the balcony, with an open window. I go to the balcony only when my presence is necessary. And after the end - I ventilate it well.

findings

Craft DIY printed circuit board almost factory quality at home- it is possible, and not even very difficult! I would also like to master the quality of manufacturing vias ...

15.10.2015

A solder mask (Solder Resist or Solder Mask) is a mandatory heat-resistant protective coating for the conductive pattern of printed circuit boards. Purpose: protection of individual sections of the PCB from the adverse effects of flux and solder, as well as the influence of a humid environment and mechanical stress.

Type variety

Application features

The solder mask is applied to either one () or both sides of the PCB. Mandatory isolation is required, contact areas (under the output of the microcircuit, etc.) from conductive elements - conductors or transitional holes. The result is a reduction in labor intensity/soldering time.

If it is necessary to isolate adjacent contact areas, the cutout method is used (creating an area not covered with a solder mask layer). In this case, the size of the cutouts should be 100–150 µm larger than the total size of the contact area. The distance from one edge of the solder mask to the other edge of the contact area should be within 50-75 microns. The minimum width of the jumper - the area between 2 adjacent contact areas - 75 microns.

Color - red, white, green, blue, black, yellow or super white - is chosen by the customer. The LED industry uses super white/white soldermask color, in other fields green is the most popular color. In this case, it should be taken into account that the final color saturation of the PP is created not by the base material, but by the mask coating.

The process of creating a protective layer

The mask is applied through a stencil in the form of a grid (the size of one cell is 150 μm). Wet layer thickness: 30-35 µm. Then, the product is dried. Temperature in the drying chamber: no more than 75 ˚. Dried blanks are sent to the stage of photolithography - the combination of photomasks of masks with products - and high-power UV exposure. The final stage is the manifestation of blanks in solution (substance temperature 32-34 ˚).

Restrictions

When creating a thin jumper (less than 75 microns), it can be damaged during installation and disrupt the required adhesion to the PCB surface. As a result, the solderability properties of damaged contact areas are lost.
Lack of possibility to apply a mask on the terminal contacts of the connectors/test points.
When creating a protective layer on printed circuit boards with a lead-out pitch of more than 1.25 mm, it is allowed to get the solder mask on the contact areas only on one side and not more than 50 microns. And with a step of less than 1.25 mm - no more than 25 microns.
All vias that are subject to subsequent coating with a protective solder mask must be closed (tented).
Possible defects: the presence of areas with no protective mask - less than 0.2 mm 2 on 1 conductor and less than 2 mm 2 on polygon areas; the presence of minor delaminations (up to 0.25 mm); the occurrence of long tunnel voids.

Pros of using a protective solder mask

High chemical resistance . The mask protects against the manifestation of aggressive environments, oxidation of copper conductors.
Significant indicators physical stability . There is protection against scratches, mechanical impact.

The quality of any homemade electronic device depends very much on how well it was made. (yeah - a useful phrase, it's so clear! Well, yes .... But do I have to start somewhere?). The printed circuit board plays a big role in this (this is if you don’t have too much which you can do with volumetric installation). The more complex the device, the more complex the pattern of the printed circuit board, and the better it must be made. About one of the ways DIY PCB manufacturing speech will go.

Foreword

There are several ways PCB manufacturing at home. When I was just starting to master the manufacture of printed circuit boards (this was when I studied at an electronics engineer at school), I drew tracks with nail polish (very brutal printed circuit boards turned out), then I switched to a waterproof marker (the boards already looked much better). But only when I switched to laser ironing technology(LUT) (and this happened relatively recently) I finally started making printed circuit boards that are pleasing to the eye. My hobby is to design and manufacture various electronic gadgets. Is it interesting to solder something on a scary printed circuit board? But, after some time, this technology ceased to suit me. Despite the advantages of LUT as a technology for manufacturing printed circuit boards, there are quite a lot of them:

What is a solder mask?

FSR8000— two-component composition sensitive to ultra-violet radiation. Has three states.
1. "Raw State". After the two components have been mixed. In this form, it can be washed off with either acetone or a solution of soda ash.
2) "Hardened State".
2a) Not exposed to ultraviolet light. Soluble with acetone and soda ash solution.
2b) After exposure to ultraviolet light, the mask becomes resistant to a solution of soda ash, but can still be washed off with acetone.
3) "Baked State". It is obtained after heating to 160 degrees, followed by exposure for several tens of minutes. Does not dissolve in acetone, has high mechanical resistance.
In simple terms, a mask is a protective layer that can often be seen on prefabricated printed circuit boards. Very often green. This article will discuss the non-standard use of this mask as a photoresist.
To do this, you need to use the first two states, i.e. with the help of illumination and subsequent development, obtain a pattern of conductors on the textolite. And after etching, wash off this pattern with acetone.
Then the mask can be used for its intended purpose, covering the area of the entire board with the mask, except for the pads intended for soldering parts. Then transfer the mask to the third state. And now about the same, but in detail and from photographs.

List of what you need for the PCB manufacturing process

The technological process of manufacturing a printed circuit board at home

Photomask (phototypesetting film). It can be done in a printing house that has equipment for phototypesetting films. Often this service is not advertised by printing houses, as it is purely internal. But, as a rule, they agree to print your handkerchief drawings on phototypesetting film without any problems. The file format, the dimensions of the drawings must be clarified in a particular printing house.
To obtain a board pattern, the pattern must be inverted (white tracks on a black background). For a protective mask - straight (black circles on a white background).

The photos show the photomask itself for the printed circuit board. One side seems embossed, the other should be glossy and smooth. It is important not to confuse the sides - the photo layer is on the side where the relief is.
Wooden frame (made of balsa, glued with low-viscosity superglue!) with a stretched children's bow. In general, it is best to use special grids. I subsequently abandoned the bow - and switched to organza (it is looked for where all sorts of curtains and curtains are sewn on windows. For example, they gave me scraps of this organza for free)

We cut out the blank from textolite. We give some margin on the sides. You can not give a margin, but cut out a PCB blank of the right size right away, but then you need to make sure that the mask does not accumulate on the edge (i.e. try to evenly distribute it)

We clean the surface with sandpaper. No need to try hard, just remove the dirt - the mask sticks very well to the textolite.
The photo shows a cleaned textolite. Rinse metal shavings with water.
Iron with thermometer. It is not necessary to always control the process like this. Now I know the position of the regulator for 60-80 degrees, and by setting it to this position, I am sure that I am getting the right temperature. Be careful, the temperature of the iron should not be higher than 100! If you exceed this temperature, your mask will lose its ability to develop in soda ash.
We collect mask components in small syringes. Everything you need to make a PCB
- mask components in syringes
- frame
- photomask
- toothpicks
- a piece of foam
We squeeze out the required amount of reagents onto the textolite.
For such a scarf, this is 3 ml of mask (green component) and 1 part of hardener (white component). Those. the proportion should be 3 to 1.
Stir with a toothpick. We try to stir well, since a lot depends on the quality of stirring.
Mixed Uniform Mask
We press the mesh on top. Here, perhaps, it is worth mentioning that in some cases (especially when the mask is already with an expired storage line) it is better to mix large portions, for several scarves at once. Then put a frame with a mesh on the scarf, and apply the required amount of the mixed mask on top of the mesh. Then the mesh will not allow dense (thickened) lumps of the mask to get on the textolite, thereby spoiling the whole picture.
We distribute the mask over the textolite. The point is that the mask remains only in the cells of the grid. Then when removing the grid - we get a uniformly distributed mask. Therefore, we try to remove excess mask from the surface of the mesh with a piece of foam as in the photo (or a credit card). Without fanaticism! Don't break the mesh
Result
Remove mesh carefully
The mask quickly spreads over the entire surface, forming a uniform layer.
We put the future printed circuit board on the iron
We cover the scarf with something to protect it from dust. And we wait a few minutes (or tens of minutes). In the meantime, we throw the grid with traces of the mask into soda ash.
It is important to catch the moment of almost complete drying of the mask. You can try to check the mask with your finger on the edge of the scarf (where you left the tolerance. Have you left the tolerance?! Yes, by the way, if you didn’t leave it, it doesn’t matter — you can touch the mask where there will definitely not be a pattern. Yes, and for printed conductors - your fingerprints are hardly a hindrance). If there are no marks left on the surface when swiping a finger, and the mask slightly sticks to the fingers, this is what we need.
Scarf with a mask with a cut-out pattern.
We impose a template with a photo layer to the mask and carefully smooth it to the scarf. DO NOT CONFUSE the side! If the surface is a little sticky, the template stays on the scarf without any problems. If the surface is already almost dry - it does not matter. Try either moistening the surface with water so that the template sticks, or press the template against the scarf with something (you can tape it with tape. But be careful!) In general, the template should fit snugly against the scarf.
I put on the light. The exposure time is determined experimentally. I can tell you my exposure modes: 70 (maybe even 80) minutes at a distance of 7 cm, under a 22-watt power saver. The UV lamp will give a much shorter exposure time, but the time tolerances will also decrease accordingly).
We are preparing a solution for developing (in advance, we just threw a frame into it Water at room temperature. Cleaned, soft. Dosage - experimentally, in the photo the dosage is for soft St. Petersburg water (As you might have guessed, the photos were taken by Termite). For hard water - soda should be more. The solution should be slightly soapy to the touch. If there is too much soda, the development will be fast, but at the same time, the slightly underexposed mask will “peel off” during development. And if there is too little soda, the development will be very slow. Moreover, heating the solution will only interfere with development.

After the time required for illumination has passed, we remove the film and throw the scarf into the solution
Scarf in solution.
If everything is correct, then in a minute you should see a slight pattern of conductors.
When the handkerchief is fully manifested, wash it from the remnants of soda ash, put it to dry on the iron.
What happened. Clear PCB pattern
One of the unpleasant features of the mask is underdeveloped areas. On a dry handkerchief - they are very clearly visible as whitish spots. They shouldn't be! They will prevent the pickling solution from reaching the copper. Then we throw the handkerchief back into the solution, and lightly clean those areas with a cotton swab. Again, rinse, dry, control. And if everything is ok...
We weave a scarf.
In the process of etching, we control that there are no air bubbles. Often they are between the tracks.
We poison, we poison ...

Here's what happened.
Wash off the mask with acetone. You can check the scarf, ring for breaks and short circuits. After all, we will now apply a protective mask, and then it will be very difficult to fix breaks, and especially short circuits.
Already in principle - you can solder, but we have a mask! We need a protective mask! So we repeat the whole process. Application of components
Mixing and distribution
Drying This time it takes longer to dry. So that the mask does not stick at all. After all, now you need to very accurately combine the template with ready-made tracks, and when the template sticks to the mask, it will be very difficult to do.

Apply the mask template. The alignment accuracy can be checked by light (if the scarf is one-sided)
Again into the backlight (yes, yes, again for 70-80 minutes, if you don’t have UV. But you can make several printed circuit boards at the same time!) Then into the development in the same solution of soda ash. Basically, it lasts a long time. True, you still have to change, because in the green solution you can’t see the scarf itself, and how it becomes more and more beautiful
For example, I like to watch how shiny copper pads gradually appear on a green surface.
Result. A very beautiful printed circuit board, made by hand.
And the result is clear. Slightly missed the tracks
Next, dry the scarf. At the same temperature (60…80). This is necessary so that the water does not boil and the mask does not swell.
After that, we raise the temperature to 160 degrees, and dry the scarf for about an hour. And here is the result. Already cut, drilled, tinned and soldered Isn't it very similar to a printed circuit board made in some kind of factory?
So, pros using this method on your own PCB manufacturing:

Very very technological and beautiful
High accuracy. 0.15 mm is not a problem. Two tracks between the legs of a DIP package? Trying hard is not a problem.
Almost 100% repeatability(of course, this is when you already know at what distance and how long to light up other small things that are determined experimentally on the first attempts to make scarves)
protective mask. This is a very good plus - after all, soldering with a protective mask becomes very simple - SMD components simply fall into place by themselves.

And now the cons.

A very long time. When using conventional energy saving devices - VERY LONG. But who is stopping you from making scarves in batches?
Photographic film is required. (You can, of course, use templates from the printer. But ..., honestly. I do not advise. Because then the tolerances for the exposure time become very, very small)
Well, the most important thing: the FSR8000 mask is hard to get.

Safety engineering.

Keep in mind - in the description of the FSR8000, a lot of unpleasant things are written about the toxic properties of the mask vapors. At a minimum, work with an open window. And best of all - under the hood. Now, about my advice “touch your finger, is it dry” - it’s better not to do it anyway. If the mask gets on your hands, wash it off quickly.
Acetone. Also harmful. It dissolves fat, which means that something unpleasant can be done from subcutaneous fat. It is better not to allow prolonged contact.

findings

Craft DIY printed circuit board almost factory quality at home- it is possible, and not even very difficult! I would also like to master the quality of manufacturing vias ...

Many thanks to Termite for the provided photos, the very description of the technology (he was the first to try it out), and for the donated mask

Kind of like jewelry. It must be carried out very carefully so that the surface is not damaged. It is impossible to allow the formation of jumpers or bridges, spreading or sticking of drops of solder, its inhomogeneous accumulation.

Applying a solder mask can help to get the job done with a good result. In fact, there are two main functions of the compositions: protective and aesthetic. A beautiful board after processing is ready for high-precision soldering. Solder will only get to the required places of future contacts.

Printed circuit boards are now used everywhere. Everywhere they play a responsible role, ensuring the operation of complex electronic circuits. Nevertheless, according to the test results, the evaluation of the main characteristics, in accordance with GOST, two main classes of requirements for solder masks are distinguished:

for printed circuit boards of devices, computers that are not used in critical military situations, they produce class T products;
for use in circuit boards used at defense facilities, class H compositions are used.

Soldering points obtained with class H masks guarantee the absence of short pauses in work. Belonging to the class must be indicated by the manufacturer, must be taken into account by the consumer.

Application methods

Protective coatings for printed circuit boards can have different compositions and require application using different technologies. The classification of solder masks is based on this feature.

A layer on the surface can be applied in two ways:

stencils,
photolithographically.

Epoxy solder masks are used for screen printing. Initiate curing by heating or UV irradiation. The method is affordable, inexpensive, but requires the availability of screen printing stencils. The accuracy of applying solder masks leaves much to be desired.

The photolithographic method is otherwise called photoresistive. Currently, such means are predominantly used. Popularity is explained by the ability to create any drawings.

Photoresistive solder masks differ in consistency, number of components. Means with one component have a homogeneous composition. Two-component mixtures are brought to a homogeneous state during production.

Dry and liquid formulations

Dry solder masks are abbreviated as SPM. They are produced in the form of films of various thicknesses: from 50 microns to 10 microns.

Applying SPM is not easy. This requires equipment that performs vacuum lamination. The surface of the board must be thoroughly cleaned before coating, otherwise the film will not adhere well.

After vacuuming, the board should be exposed and developed. The developing composition may be organic or aqueous alkaline in nature. Often, soda ash is used to create an alkaline environment. The last stage is hardening. This is the name for the treatment of the board by heating or UV irradiation for the final formation of the layer.

Liquid solder masks are abbreviated LSM. They are applied in one of two ways.

When working on small series of printed circuit boards, screen printing is used.

During the production of large series of products, solder masks are applied using special equipment that creates a falling laminar “curtain”. Then exposure, development and hardening of the processed board are carried out.

With the help of an LPM and a stencil, a solder mask can be applied at home with your own hands. All operations are quite affordable and are regularly performed by craftsmen and amateurs.

Soldering with the smallest pitch becomes a real thing. The printed circuit board, previously protected by a mask, will be able to work for a long time and reliably.

Online stores sell one-component masks that harden when irradiated with UV lamps. The processing of the boards goes like this. A small amount of liquid soldering compound is applied to the center and sides.

Press down with a transparent hard film (lavsan or other) and rub with an eraser or press down with a thick glass.

The paste under the film should be evenly distributed in a thin layer, acquiring a light shade (usually light green). After that, the template is carefully applied.

Shine through with ultraviolet light for 40 minutes, remove the template and illuminate for another hour. The nuances of application may vary, but in general, the point is that the paste is evenly distributed and hardened.

The solder mask, or "brilliant green" as it used to be called, protects the printed circuit board during soldering, covering the conductors, preventing short circuits between the pads and protecting the fiberglass from overheating during installation. It used to be possible to make it only green. Many colors are now available. What color to choose? And does it matter what color of the mask is chosen?

Real life examples

We have a customer who orders a different solder mask color for each type of printed circuit board. It all started with shades of blue, red, purple, then black, white, now purple, turquoise, burgundy...

There is another customer - a huge enterprise with many departments. Each department chooses its own mask color. In my opinion, even every developer in this enterprise prefers its own shade. Is this good or bad?

In my opinion, this is not just bad - it is a disaster for the enterprise. And that's why.

1. Problems with input control

If a facility conducts incoming visual inspection of printed circuit boards, differences in mask color can lead to a significant increase in staff fatigue. Firstly, bright colors such as red or white are much more tiring for the eyes. Secondly, as the color changes, the saturation of the mask also changes, which means that it can be more difficult to distinguish the conductors under it and control their quality. Thirdly, the eye, accustomed to detecting defects under a mask of the same color, will not be able to find them with the same quality when changing colors.

2. Problems with installation and output control

Even greater difficulties begin with the final visual inspection after installation. Especially if the mask is black or white. The control of the presence of components turns into sheer flour. If such small components as 0402 are used, the quality control of their installation against the background of a dark or black mask can be several times longer.

3. PCB quality problems

The default mask color is green. Accordingly, each PCB factory has a stock of a mask of this color in stock. But as soon as the games begin with the choice of mask color and shade ("I, please, red, but not faded, but brighter ..."), the manufacturer is forced to select the desired mask either in their stocks or from the supplier of materials. And it may happen that the mode of dilution, application or curing of this mask is slightly different from the standard one. And here the loss of quality of the mask coating is possible. So changing the color of the mask for large batches should be done with caution, try samples first.

4.. Problems with the appearance of printed circuit boards

I strongly advise against using a white mask. After installation in the oven, it acquires a "icteric" shade.
I do not recommend using a red mask. The difference in shades is too noticeable, and when making repetitions, you can get a shade that does not match the boards of the previous launch.
Black and blue boards look good, but, as I said, they are much more difficult and longer to control visually.

Matte and glossy

A glossy mask is more comfortable and scratches are less visible on it. Boards with a glossy mask look more elegant.
PCB technology makes a green glossy mask by default.

In some situations it is necessary to apply special colors (for example, matte black is used in traffic lights to reduce glare, and white is used in illuminators to increase light output). In such situations, the choice of a non-standard color or matte / glossy is quite justified.