Why are circuit boards mostly green? See what these 20+ engineers have to say

Why are circuit boards mostly green? This is a detail that power engineers rarely think about. Today on Zhihu, I saw that more than 20 engineers gave some answers. Let's see what each engineer said.

Point 1

It is mainly coated with a layer of green solder resistant oil to form a solder resistance layer. Like first picture on 1st floor, this is a board without solder oil. It must be a board engraved by hand.

Solder oil is applied to surface of printed circuit board to protect circuit on board as much as possible from short circuits by foreign objects. wire is not easy to fall off (some exposed pads are easy to fall off, with a layer of solder mask, it is not easy to fall off).

Now there are not only green solder resistant oils on market, but also other colors such as red and black.

Point 2

Subject question I think test subject knows colors of other solder resistant paints besides green oil, blue oil, oil, black oil, black matte oil, purple oil, red oil, green matte oil, sun green are commonly used. etc. What is difference between these inks? I think it's mostly a matter of cost. For green ink, for Nanya, largest ink manufacturer in China, total price is about 80 1 kg, while same ink such as Green Sun and Green Matte, price ranges from 150--250. Of course, there are also cheaper blue matte inks. The price is about 60 1 kg. But main issue is that high-precision printed circuit boards still need manual alignment operations. , Other inks Color is simply too easy to cause defects for human manipulation. (Leveling is soldermask step, which is to wash away unwanted soldermask with liquid medicine. The erosion accuracy here must be supplemented by a manual leveling operation, so I won't go into details.) So, there will be more rework. This is really a big test for manufacturers. . So cost is biggest reason.

Third paragraph

In response to question above why most solder masks are green, I looked at technical documentation of some Fab manufacturers, ink suppliers and online prices for various colors of ink and came to following conclusions:

(1) Green ink can achieve less error, smaller area, and higher accuracy. Below is an interception of a white paper on company's Fab capabilities.

You can see from whitepaper that green, red, and blue have higher design fidelity than other colors. In test IC board I designed earlier, pin to fanout distance of some devices is 6 mils, as shown in figure below, so first three colors are most appropriate in this case. Maybe because design of IC Test Board often challenges Fab's limits, so I've never seen colors other than green, blue, red, and of course absolutely no other colors (I just haven't seen it).

(2) Compared with inks of other colors, green ink has better performance. The following figure shows specification table of Sun Ink product.

From above information, it can be concluded that green has better performance than other color systems, especially plug hole green color characteristics, which can be better implemented in design of IC test board, and plug holes are mainly used. They will be from hundreds to thousands. Combined with Fab technical paper above, it becomes clear why green can be produced with high precision, which is also determined by characteristics of green.

(3) I have checked a lot of websites for solder resistant ink prices, but I have not come to conclusion that green ink is cheaper than other color inks, but I think that green ink should be cheaper than other colors. After all, demand for green ink is larger, larger supply naturally lowers costs.

Summarizing: from manufacturer's capabilities to green oil's own characteristics and cost considerations (although there are no data for this article, I believe they should be available if it is not possible to consult manufacturer of plant). and characteristics of circuit board itself, green ink is used more and more than absolutely. If there are errors or omissions mentioned above, please point them out and we will make progress together.

Point Four

Well, real question is why most of them are green, which means subject knows there are other colors. Why can't everyone discuss why? I will be a curious child. Everyone discussed what green layer is (solder mask, green oil) and what it is for (to prevent short circuits caused by solder paste contacting copper surface during soldering).

The three major questions of life: who am I (solder resistance), where do I come from, and where am I going (solder resistance) have been completely eliminated. Let's talk about origin and composition (in fact, now is not a revolutionary era)

First of all, main main ingredient of green oil is resin + green paint. Of course, because resin is not born green, picture above (thanks to Du Niang)

Then green paint doesn't need picture above, does it? Simply put, this is mixing resin with paint, and then turning it into green oil (the production process is omitted here)

You have to ask, why add paint? Since resin is a translucent product, if you do not add color, it is very difficult to see if there is a solder mask on copper plate. If you cannot see it, how to go online for production? Especially when you rely on visual inspection at an early stage, inspectors at control station will work hard with you.

Finally it's easy to check color and it's ready to go online and play on board

Well, actually, I never answered why there are more green ones. But smart friends probably found that first employees were more visual. My teacher from childhood said that green is good for eyes and relieves fatigue. With such a heavy workload every day, eyes of production staff need protection (in fact, I hope they can work harder and make fewer mistakes in a less fatigued state, evil capitalism). This is one of reasons why green is main reason.

The second reason. Let's get back to cost. Well, yes, I buy, and cost is very important. Since green is main color in production process, purchase volume of natural green paint will be larger, it can be argued that purchase cost of green paint will be lower than other colors. At same time, using same color ink in mass production can reduce cost of line replacement.

The third reason is directly related to second reason. In order to reduce costs, many green oil producers will mass-produce green green oil. If you need other reds, oranges, yellows, blacks, blues, indigos and purples, you can mix other colors based on existing green oil. You see, you need to add extra paint and you need to add money. There will also be customers with special needs, and quantity is very large. In this case, manufacturer can also choose red, orange, yellow, black, blue, blue and purple paint directly when adding paint.

It is thanks to these three reasons that green has become main color scheme for printed circuit boards. There is also PCB research and development, and I complained that if green oil turns black, performance will drop and impedance will not be as good. But it hasn't been studied or compared and I don't think it would be a reason to go green mainstream so I removed it from reason.

Regarding price of green paint and price of other color paints, I also want to know because my PCB supplier said that green oil supplier didn't tell him. . .

Okay, let me start here, if you have anything to add please let me know, especially price and material cost analysis related to printed materials.armor.

Fifth paragraph

There are several opinions on this issue:

1. Generally speaking, all products at level of electronic boards must go through process of board manufacturing and chip placement. In process of making board, there are several processes that must go through yellow light room. The visual effect of greenery in a room with yellow light is better. Some, but not main ones.

During SMT soldering, tinning, patching and final AOI inspection are required. All of these processes require optical positioning and calibration, and a green background color is better for instrument identification.

2. Red, yellow, green, blue and black are common. Because of problem of craftsmanship, verification of many lines still depends on what workers see with their own eyes (of course, most of them use flying probes now). My son, this is a very tiring job. Green is relatively least harmful to eyes. Therefore, most of them use green.

3. The blue and black color is because they are alloyed with cobalt and carbon, respectively, and have a certain conductivity, so there is a risk of short circuit. The green PCB is more environmentally friendly and does not emit toxic gases when used in a high temperature environment.

4. Since about 2007, people have been paying attention to PCB color, mainly because high-end boards of leading manufacturers such as ASUS and MSI use black PCB color, so people slowly think that if PCB color is black, it should be high class. After that, more and more manufacturers began to use a black coating of printed circuit boards - one can say that such an inexplicable phenomenon was caused by an inexplicable reason. No one has ever said that color of PCB is black, which means that quality of motherboard must be good. This is entirely due to misleading product caused by first-line brands using black to indicate product positioning. It is true that black PCB can really show its technical strength, because black PCB is most difficult to see wiring, so both design and after-sales service will suffer unprecedented cost pressure, and board manufacturers with strong technical strength use black printed circuit board. fee. color tone is not because black can improve performance of motherboard. From perspective of rational analysis, it is also known that color itself cannot improve performance of board.

5. No reason, but it was used all time.

Item 6

First level answer. There are many different colors of ink, some green, some black and white. The most intuitive difference between colors is price! Green oil is cheapest and most common on market.

Second level answer. FR-4 is also called plastic. plastic! Because plastic is cheap, there are many printed circuit boards on market that are made from plastic.

However, plastic plate does not dissipate heat well, which can lead to safety violations and seriously affect life of electrical appliances.

Now! With advent and popularization of ceramic PCBs, more and more LEDs and sensors are now using ceramic PCBs. That is, in future you will see a white ceramic substrate.

However, ceramic circuit boards are mainly used in high-tech industries and products, it depends on whether you are ready to disassemble electrical appliances!

Item 7

The green part is called solder, and its components are resin and pigment. The green part is green pigment, as well as various other colors that are no different from decorative paint. Assembly solder is pasty and flowable before it is printed on PCB. Once printed on PCB, it must be "cured" at end, allowing resin to solidify when heated. The purpose of a solder mask is to protect PCB from moisture, oxidation, and dust. The only place not covered by a solder mask is usually pad where solder paste is applied.

Item 8

Solder resistant green ink is cheapest and most mature in the industry. And many other colors!

Item 9

In addition to price, viscosity of solder mask of these colors is also different. Green is smallest, red, yellow and white are slightly larger, and black is largest. On a high-density PCB, distance between pads and pads is very small, and width of solder mask is smaller. When using a soldermask for screen printing, less viscous soldermask oil is easier to apply to PCB. Therefore, sometimes a printed circuit board that can be made in green cannot guarantee quality of soldermask if you change color. . .

Tenth point

Look at opposite example

Point Eleven

Surface layer is solder resistant to prevent short circuit caused by solder paste contacting copper surface during soldering. Green is just a color with added pigment. It used to be green. The color was mainly chosen by buyers It seems that Apple is very fond of black color.

Item twelve

Green is like a protective layer. Protect circuit from short circuit. Also available in red. You can see that many computer motherboards are painted with red protective paint. The first board 1l is not painted with protective paint. This board is mostly experimental. Rarely used in real production. It's easy to make a short circuit.

The thirteenth paragraph

Colours other than matte are no longer charged.

Item fourteen

Color refers to color of top layer of insulating oil, there are many kinds, most common are red, yellow, green, blue and gray. Due to problem of craftsmanship, checking many lines still depends on how workers see with their eyes (of course, most of them now use flying probes to check) It is very tiring to constantly look at board with strong eyes, and green is relatively Least harmful to eyes .So most of them use green. I think this explanation is more plausible.

Item 15

Solder oil seems to cure with light at a certain wavelength, perhaps green is more likely to absorb light at that wavelength. So production precision is relatively high and can be widely used, but color definitely does not match black, and purple is more perfect than green.

Sixteenth point

Green oil is commonly used for bulk products with value in mind. The test board is used by our company to use yellow as a label. Red Oil is a pilot product. Fuel oil is a high class product and expensive for same circuit.

The seventeenth point of view

Just because green ink is cheapest, there are many colors: white, yellow, black, blue, indigo, etc...

Item 18

The green board is cheapest, followed by blue one. The black board seems to be most expensive. If there is not much difference in performance, of course choose cheapest one, but green board looks a bit low and blue one looks advanced. a bit.

Item nineteen

Green is more stable, mature and versatile than other colors. Except in special cases when it comes to optics (for example, black to reduce reflections), green is recommended.

Item 20

On boards with a low raftYou can use solder mask in different colors. But green is cheapest type of quote for most PCB manufacturers. There are often manufacturers who make a development version in red, blue, black, and other colors. There are also manufacturers who use colors to distinguish between different phases.

Viewpoint Twenty-One

Homemade PCBs use green solder mask oil to protect track, to prevent track corrosion in natural conditions, or prevent solder from contacting track during solder wave soldering to cause a short circuit. Of course, for us hobbyists After learning technology of homemade soldering masks, gold content of self-made circuit board will be higher and more advanced.