PCB Tech - Why are printed circuit boards (PCBs) mostly green?

Why are printed circuit boards (PCBs) mostly green? This is a detail that a power engineer rarely thinks about.

The first point of view is to apply a layer of green solder mask to form a solder mask. Like the first picture on the first floor, it is a board without solder mask. This should be a board corroded by hand.

The solder mask oil is applied to the surface of the PCB board 1 to protect the circuit on the board from short-circuiting by foreign objects, 2 to cover the copper wire above, so that the copper wire is not easy to fall off (some exposed pads are easy to fall off, some After the solder mask, it is not easy to fall off).

Nowadays, there are not only green solder masks but also other colors such as red and black.

Viewpoint 2 Question of the subject I think the subject knows the colors of other solder mask inks. In addition to green oil, there are also commonly used blue oil, butter, black oil, black matte oil, purple oil, red oil, and green matte. What is the difference between these inks such as Green Sun? I think the main problem is the cost.

For the largest domestic ink manufacturer Nanya, the general price of green ink is around 80 1KG, while the price of similar inks such as Green Sun and Green Matte The price between 150-250 of course also has cheaper blue matte ink, the price is around 60 1KG, but the main question is that now high-precision PCB boards still need manual alignment operations, other ink colors It is too easy to cause defects for manual operation. (Alignment is a step of solder mask, which is to wash away the unnecessary solder mask with chemical water. The accuracy of the erosion here needs to be completed by manual aligning operation, and I will not elaborate on it.) As a result, there is a lot of rework It is a big test for manufacturers

In summary, cost is the biggest reason

Point of View 3 Regarding the above question, why most soldermasks are green, I searched some Fab manufacturers, ink suppliers' technical documents and online quotations for various color inks, and came to the following conclusions:

(1) Green ink can achieve smaller error, smaller area, and higher accuracy. The following is the interception of a company's Fab capability technical document.

It can be seen from the technical documents that green, red, and blue have higher design accuracy than other colors. The distance from pin to fanout via of some devices in the IC Test Board I designed before is 6mil, so in this case, choose the front Three colors are the most suitable. Perhaps it is precisely because the design of the IC Test Board often challenges the extreme capabilities of Fab, so I have never seen other colors other than green, blue, and red, and of course there are absolutely no other colors (I just didn't see it).

(2) Green ink has better characteristics than other color inks.

From the above information, it can be concluded that the green color system has better characteristics than other color systems, especially the green plug hole characteristics. It may be better to experience the plug hole in the IC Test Board design. Basically, the plug hole will be several hundred to There will be thousands of them. Combined with the technical documentation of the Fab above, it is also clear why green can be made with high precision, which is also determined by the characteristics of green.

(3) I checked a lot of solder mask ink quotation websites, and did not come to the conclusion that green ink is cheaper than other color inks, but I believe that green ink will be cheaper than other colors. After all, there is more demand for green ink. With larger shipments, it is natural to cut costs.

To sum up: from the ability of the PCB manufacturer to the characteristics of the green oil itself to the cost considerations (although this article did not find the data support, it is not possible to consult the fab manufacturer) and the characteristics of the PCB board itself, the use of green ink is more than absolute.