● Old Military Requirements
● Mixture of Yellow and Brown
● Right Contrast with White Legend
● Most Visible Color to Human Eyes
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Soldermask is functionally the "mask layer" that defines the size and location of all of the solderable surfaces of a PCB. This layer allows the other conductors of the outer layers to remain isolated from solder during assembly processes.
For many years the only soldermask color you could see on a printed circuit board was green. Why Green Soldermask is only soldermask color at the early time? Why didn't we start with blue, yellow or red soldermask? There are several possible reasons for reference.
1) It goes back to the old military requirements, that the soldermask must be green.
2) Soldermask is green because when it was originally produced, the base resin was brownish yellow in color and the hardener was very muddy brown and when you mixed them together you got green. Also, laminates at that time were mostly green. So it was easy to accept the idea of green soldermask as well.
3) That particular shade of green produced the right contrast with the white legend ink while being tested under all types of adverse conditions.
4) Green has been proven to be the color most visible to the human eye.