Green Circuit Boards
Date: Fall 2013
A student asked me why most of the components in a computer are green. Hopefully, you will give us an answer. My husband said it was probably easier to see the copper tracings on green, but he said he had worked on brown printed circuits before, so his answer may not be correct.
Thanks for the question. I am not sure. I suspect the green color is due to either the dyes used or the type of plastic used in the circuit board. However, I have seen other colors of circuit boards. In fact, I remember assembling some simple circuits myself using brown boards.
I hope this helps.
Great question. The green color you usually see on a PCB (printed circuit board) is the "soldermask", a lacquer-like finish that controls where the solder goes (e.g., prevents solder-bridging between adjacent pads/pins) and can prevent corrosion on bare copper conductors. For very low-tech boards soldermask is omitted to save cost, and in such case you will see the plain laminate material, which can range from brown to pale green, depending on type.
I have watched for years the debate about "why green", and to my best understanding the simple reason is that it was originally the easiest to use. Photo-imagable green soldermask was easy to expose, the resultant material was much more durable against solvents and high soldering temperatures, the resolution was sufficient to provide image detail, it provided a consistent visual contrast sufficient for text identifiers (traditionally printed in white) to be readable, and it was easy to see where it had been applied (compared to clear soldermask, e.g.) . As a result, green became the most common color, which made it also the cheapest and fastest option. For example, some low-cost printed circuit board fabrication shops to this day only offer green, because any other color would unnecessarily complicate their process. You might also ask why tennis balls are yellow, and bicycle tires are black. They do not have to be, but they usually are.
Today, green is still the default for the above reasons and for reasons of tradition, but the quality of alternate colors has gotten much better and costs are increasingly comparable. As a result, it is a little more common to see black, white, clear, blue, and red. Nevertheless, as a coworker of mine expressed it, "no one ever got fired for using green."
The circuit board laminate you refer to is a type called "FR-4". The
green color is simply traditional, and was originally used to make the
laminate more attractive. Without the added color, FR-4 laminate is a
very unattractive "dirty" light brown in color.
Note that FR-4 laminate is available in several colors (notably red), but
the traditional green color is most commonly used. Note that the color
has no function other than aesthetics.
I am an electrical engineer who works with circuit boards on a routine basis.
Circuit boards in relatively expensive products such as computers are usually made of a fiberglass-epoxy laminate referred to as FR-4. This material is usually translucent, although copper conductors which are plated on the laminate are opaque. For some reason this is usually green in color, however I have worked with some which were blue or red. Some companies may use different colors to differentiate a prototype from a production circuit board, however I think that green is most common only by way of convention and because we engineers usually do not care much about the color. These circuit boards will usually have copper plated conductors at least on both sides. In some products they may have many layers of copper and epoxy fiberglass bonded together into a rigid board.
Circuit boards in some lower cost products (such as a cheap "transistor radio") may be of a phenolic material which is usually brown or tan and is opaque. Compared to FR-4 laminate, phenolic is not as strong and is more brittle. These will usually have copper plating on only one side.
Some circuit boards are flexible and are made on thin high quality plastic film. These are usually brown and translucent.
My answer is not so scientific, but it is based upon many years of experience.
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Update: November 2011