From: ulan@ee.ualberta.ca (Dale Ulan)
Subject: Re: Why circuit boards are green?
Nntp-Posting-Host: eigen.ee.ualberta.ca
Organization: University Of Alberta, Edmonton Canada
Lines: 28

kuusama@kaarne.cs.tut.fi (Kuusama Juha,,,VTT,) writes:

>Not that the question is anything important, but I am still curious:
>Why is that almost all printed circuit boards are green? I have seen
>a few blue ones, but no red, yellow, company logo etc. Is there a
>technical reason or could it be that the marketing "geniuses" have
>not tought about it (yet)?

The green layer is a solder-mask, and is used to make a finished board
look neat, and to avoid solder bridges, especially when using wave
soldering (or any other mechanized approach). I've seen red mask,
but most that I've seen are green.

A bakelite board will look brown in colour, and, if the solder mask
is put on, looks like a brown board with green 'paint' on either side
(or just one side) of the board.
A fibreglass board will look green from the side, because the green
solder-mask makes the board appear that colour. If you got a fibreglass
board with no mask, it would be a whitish-grey colour.
Teflon boards do exist, as well... but I'm not sure about that one.

I'd guess the stuff they invented for solder mask was green, so they're
not about to change. Also, any change in any chemical probably requires
a better than normal cleaning of the machines that make boards. A lot
of companies do not make their own boards... they ship them to a real
boardhouse.