How to use green Soldermask in pcb fabrication.
As we know that printed circuit boards are the building blocks of electronic devices. It is not wrong if we say that the electronic industry is relying on the quality of printed circuit boards in order to provide better functionality and performance. Now let us move forward with the fact that the printed circuit board is something we need to understand first if we are talking about electronics. Maybe you have seen one in your computer or other commonly used gadgets. What color came to mind? Let me guess! Is it a green board we usually see on our computers? Yes! Printed circuit boards are usually designed in this color. Although there are many other colors available, a vast majority of circuits are designed in green color.
There are a number of reasons for choosing green and we will discuss it further.
But before that let us make one thing clear. The green color of the PC board doesn’t mean that it is green all the way through. It is the outer part that is visible. And that other part is the solder mask of the circuit. So now we have another point. If you want to understand the color philosophy of the circuit, you need to understand what solder masking is. And why it is needed in the circuit.
In the manufacturing process of printed circuit boards, the copper circuitry is etched on the glass fiber interior. This circuitry helps the circuit in avoiding short circuits and soldering errors. The hue of the solder mask is used to protect that copper circuitry and it is the reason that the printed circuit board looks green. But the green color can be modified according to the need and to differentiate multiple printed circuit boards. For example, there is variation in the circuitry of colors provided by design companies. Black, blue, green, and red is provided as standard and commercial color for the solder masking. The electrical traces inside the board are shielded from contamination and moisture with the help of the solder mask.
Moreover, it helps in regulating the process of molten solder flux. There is a plain drab and yellow core of the conventional FR-4 circuits. But there is a variation for the solder masking. We have a number of colors available for solder masking such as white, black, blue, red, and yellow and usually decided during the PCB design portion of the job. Moreover, it is interesting to know that many uncommon colors are also in the hue list such as purple, orange, smooth, red, etc. similarly most combined colors are also available as an extravagant for the boards. So now when we have known that the number of choices is available then the question is even more strongly that why green? Or you can simply say why green is preferred when we have other choices too.
Now we are going to see the reasons why green is the most commonly used color for the solder masking of the printed circuit boards. There are a number of reasons, and we will see the important ones.
In the early era of technical constraints, humans were controlling the quality of the circuit manually by verifying the board. So, many factors explain the green color of the PCB. As we have discussed before the green color means only the exterior of the printed circuit board. This does not mean that the inner PCB would also be of the same color. The exterior sheet is solder masking.
There are a number of factors that affect the copper traces present inside the circuit board such as oxidation, humidity, contamination, and FOD. The solder mask is the role that reduces the chance of these effects on the circuit board. Now let’s see the reasons for overlying the green sheet over the exterior sheet of the printed circuit board.
Colors may relieve you or exhaust you depending upon their tendency to affect your sight. It may exhaust your min dot work on tiny circuits. But it is proved by psychologists and neurologists that the spectrum of green color has a relieving and smoothie impact on your body and mind. The green color may help in relieving tiredness and fatigue. Squinting at the tiny circuit is difficult but green wavelength has relaxing effects on the body, so it is easy to work on this layer.
Moreover, it is medically proved that the human eyes and cones are most sensitive to the green color. It is easy to distinguish green color as the eyes are robust to green color. Therefore, the traces, empty areas, silkscreens, electrodes, pads, and printings have greater contrast especially during the pcb assembly process. It is easy to detect the flaws in the outer layer if one looks simply at the outer layer. This is easy because of the color contrast used in the outer layer. If you compare the green color solder mask with others such as white, black, red. You will notice that it is easy to distinguish spots in the green color because of high contrasts. Although there are a number of techniques that are being used for spot detection such as flying probe technique and automatic optical inspection. These techniques are highly effective in spotting errors. But the technical reason for using green color remains the same.
R&D is preferring green color for making high-quality solder mask oils because of the typical convention of using green hues. The functionality of the resin is impacted in the duration and the actual environment by organic chemical pigmentation. When the demand is reaching the limitation then there is no restriction for choosing a pink board. But the fact is, no other color in the aesthetic palette possesses the qualities same as green color. Moreover, the solder mask dams of 0.1mm can only be produced reliably by commercial green color. On the other hand, 0.12mm can be achieved by red, blue and yellow.
Additionally white and black can produce 0.15mm dams. Solder mask dams play an important role in fine pitch components and integrated circuits. Both ICs and fine pitch components are essential in shielding solder masks from forming.
It is also interesting to know that chlorine is the basis of the green color in the green solder oil. Halogens are made in PCB substrate when chlorine is combined with bromine. Halogens have a severe impact on health and also affect the environment if disposed of inappropriately. But you can also go for halogen-free solder masks as they are also available in the market. But you have to switch to some other color for a halogen-free solder mask.
Silkscreen techniques are used when we need to apply solder masking. Across the screen mesh, a large glob of oil is dragged. There is a circuit board underneath which is sent for the curing and another board is pulled under the solder mesh. But there is a pause if you want to apply another color. Because for this purpose you need to wash the silkscreen in order to remove excess oil from the solder mask and then you can apply a new color. Moreover, you need a silkscreen station for each color.
The cost of the circuit board would be affected if you are changing color, increasing the thickness of the board, using multiple pictures, and increasing the number of possible combinations. The wastage of material would also be increased in this way. If the industry is not refusing to take your circuit board, even then you are paying more than your budget in this case which is of course not a good choice. But you can save your cost if you are going for the commercial green colors and their features. Moreover, you should also keep in mind that making a new solder mask that is visually appealing, cures well, applies, and adheres well and a good insulator is not an easy process at all. For your special request such as for matte color, you need to pay an extra amount.
So, there are a number of choices available for you to consider in the case of the colors of the printed circuit board. Every color has its pros and cons. Commonly green is preferred because of its efficiency over other colors but you can choose as per your need.
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