There are many colors of the electronic circuit board on the market, which one should I choose? Do these colors have special symbols and meanings in the industry? Will the color of the solder mask and screen printing affect the function of the PCB? What is the reason for the solder resist falling off of my electronic PCB board? Today, the editor is here to summarize, to tell you the mysteries of solder mask and screen printing.

What Is The Use Of Solder Mask in PCB

The solder mask layer is a solid-colored protective film formed by the welding resist after high-temperature baking or ultraviolet curing on the PCB circuit board. We usually distribute it on the printed PCB board where no soldering is needed to protect the non-solder parts from solder. It is the permanent protective film of the circuit board, which has the function of preventing the wire from being scratched.

The deposition or diffusion of solder on the non-solder area during component soldering is also a function of preventing a short circuit between wires during soldering. Also, the solder mask has the features of anti-moisture, anti-chemicals, heat resistance, insulation, and beautiful appearance.

Solder Mask Ink

For example, thermosetting solder masks usually made by mixing a certain proportion of welding resist and strengthening agent. According to customer needs with a certain amount of toner. However, the PCB produced by this ink has problems with oil leakage and jump printing, and the appearance is not good. Therefore, at present, most factories are using liquid photo-imaging solder resist ink with better effect.
Common Solder Mask Ink brands include Tamura DsR2, TaiyoPSR, Cotes XV, Toyo K, Gin Hwa DSR, and Lea Ronal, Danachm, and other company products, two-component, these models have been UL certified. Usually green, but also yellow, black, white, and different colors. Asian products are shiny, while European and American products are mostly matte

Silkscreen Ink

Silkscreen ink thermosetting type is two-component, such as British Coateskspl hardener SP1606, Gin Hwa-ML411 hardener SM 502, etc. are white, Coates Ksp4, HYsol5002BR, etc. are yellow.

The mixing ratio of the principal-agent and the hardener is 100: 8, 19: 1, 100: 6. Before use, you need to mix according to the information provided by the supplier carefully.

After curing the characters, pass the UV curing machine, usually three 80w lamps. Harden, the bell silkscreen, only needs a few seconds.

Because light-solid character inks are slightly yellowish, some discerning customers stipulate that characters must use thermosetting white inks. We use silkscreen to display the position of components, and white figures are in most use. If it is white ink, black, red, yellow characters are the more common matches.

Why Does the PCB Solder Mask And Silkscreen Fall Off

Many reasons cause the solder resist to fall off, which may be due to improper storage, but process factors cause most of them. From the perspective of the process, roughly divide it into these situations:

1. Before curing, the proportion of solder resist is unreasonable, or the quality of the solder resist is not right, resulting in weak adhesion.
2. The pretreatment before curing is not in place, resulting in excessive impurities on the surface of the board. After curing, there are bubbles and contaminants between the solder mask and the board surface, and the stroke is layered.
3. Ink thickness is too thin, easy to scratch, and fall off. Solder mask Insufficient curing time causes incomplete adhesion.

How To Solve The Problem Of Solder Mask Peeling Off

1. Change to the appropriate ink.
2. Add pre-treatment process of the solder resist and improve pre-treatment process.
3. Use the correct temperature and time to increase the amount of exhaust air.
4. Adjust the dosage or use other additives.

Editor, why do some of the circuit boards I purchase appear to be unclear and easy to fall off?
The reason for the silkscreen shedding is very similar to the reason for the dropping of the solder mask. The process may have the following problems:

1. The incorrect mixing ratio of Silkscreen ink hardener leads to insufficient adhesion
2. Less baking time, the short character hardening time
3. Too much solder resist ink hardener, too hard solder resist after forming causes the screen printing to fall off
4. The solder mask is not hardened in time, resulting in insufficient adhesion of characters

Optimization Measures

1. Choose high-quality brand inks and carry out ink debugging according to the ratio recommended by the supplier
2. Adjust the baking time
3. Calculate the proportion of hardener for solder. Resist ink to make the characters have the best adhesion effect.
4. Increase the quality inspection process of the solder mask, strictly control the baking time and hardening degree of the solder mask, and attach the silkscreen.

There are 27 conventional solder mask and screen printing problems and solutions. I have put them together and put them in the form of the link below. If you need it, you can click to download it.

Why does Apple use black PCBs?What is the difference between green and blue mask? Does the color of the solder mask have any special meaning or function?

Not only the black electric board in the iPhone is black, but the core circuit boards of many high-end brands are black. There are many sayings in the world that some electronic parts shipped in mobile phones need to enter in the dark state. is this real?

The answer is of course no. Under normal circumstances, the supplier does not recommend the selection of black solder mask, because the black solder mask oil causes the entire board to be black, it is difficult to see the circuit, the appearance inspection of the board factory, and the later product debugging and maintenance will not be small Impact, so the cost of black ink will be slightly more expensive than other noise.

But because of this, black ink often represents a symbol of high-end PCB boards, a confident display of its products, and the protection of its technology. This type of color will be used more on some computer motherboards, graphics cards, and development boards. It gives a thick and calm feeling in the hand.

For example, ASUS used it on the motherboard in the early days, while other brands are still green. Because the black appearance is not natural to check, the after-sales repair will be troublesome, and the cost is high, which requires the PCB quality to be very good. The ASUS motherboard uses black, in addition to showing its excellent quality and reliable after-sales, it can also enhance the brand Product image.

Now more and more brand manufacturers are also aware of this type of problem, and they will also put forward relevant requirements for the PCB solder resistance color of some products.

Why PCB Board Will Use Different Colors

The three colors of green, black, and white all have their specific application reasons. Other colors such as red, yellow, and blue have no particular application reasons, and they may base on personal aesthetic preferences. Some companies may use different colors to distinguish the boards of different grades of products, such as green low-end, red mid-end, blue high-end, and so on. Some companies will also define the blue board as the board in the trial development period. We set the means of different color PCBs, and the color itself has no particular function.

We use most of the colors other than green on the PCB of finished product transactions. Unique colors will make the appearance of the circuit board, such as the motherboard and graphics card, without a casing more attractive and attract buyers. The customer can not see the PCB inside the shell, so whether the color is okay. So whether it is from the practicality or cost considerations, basically use the most conventional green.

Taking the double panel of FR-4 PCB as an example, the same 10cm² PCB, Matte black PCB, is 34 $ more expensive than green solder mask PCB.
Standard solder mask colors currently on the market include light green, sun green, dark green or matt green, red, blue, white, black, yellow, etc.

Conclusion

With so many introductions, I believe everyone understands. The solder mask color itself has no meaning, and if you have a purpose, you give it. It may have a little effect on the exposure process of the electric board, but it will affect the overall quality, and we can almost ignore it.

If there are no special requirements, it is recommended to use a green solder mask, at least to save costs. If you pay attention to the beauty of the PCB or want to sell branded semi-finished products, then choose the color you like. Remember to keep your eyes open, select the solder mask ink brand before putting into production, do an excellent job in processing pre-treatment, and debug the solder resist and control the process. Get rid of the problems of solder resist and screen printing.