This is the best response received when this question came up on the DC list
last year.
Jeffrey A. McGlaughlin
Sr. PCB Designer
Battelle Memorial Institute
Columbus Ohio
[log in to unmask] <mailto:[log in to unmask]>

<<snip>>
DC Members,
I talked to a couple of retired experts (my brothers )  and this is what
they had to say....
First my brother John:
My theory is that the color green preserves the solder coating on the board
from breaking down, a lot like the color brown on beer bottles keeps the
beer fresh.  I could give you a long theory to go along with that, but I
need to delve into the color brown right now.
and from my brother Joe:
(p.s. shows where the brain in the family is....)
I thought that everyone knew the answer to this question.
The green color of soldermask was chosen after extensive testing by the U.S.
military at the National Materials and Procurement Center in Cedar Bluffs
Virginia in late 1954. According to Colonel Robert Bright, Public Liason
Officer, the particular shade of green was found to provide the maximum
contrast to the white silkscreen ink under all tested adverse situations
while still allowing a clear view of the underlying circuitry. Every other
color tested failed to provide the required contrast under conditions of low
/ high illumination levels and various colored light sources.
The quantity of Printed Circuit Boards purchased by the Defense Department
established a "de facto" standard which most vendors began to follow. Usage
of other colors is permitted for prototype and or pre-release boards.
Hope this clears this matter up.

Karl

        -----Original Message-----
        From:   Arturo Aguayo [SMTP:[log in to unmask]]
        Sent:   Wednesday, 16 February, 2000 03:14
        To:     [log in to unmask]
        Subject:        [TN] Why are soldermasks green?

        I was recently asked by a college student working on a research
project,
        "why are printed circuit boards green?". The short answer to that is
that
        they are green because of the soldermask color. Which led to the
next
        question "is there a reason why soldermasks are green?" To this
question I
        had no answer and therefore turn to this forum to see if anybody
might know
        the reason (I wouldn't want a student to not graduate because of
me).

        regards
        Art Aguayo



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