I quite like the reason Bob gave. Solder mask is green so as to blend with the light greenish colour of the
printed circuit board before masked. The light greenish colour of the printed circuit board if my memory
does not failed me comes from the combination of the resin and epoxy being used. The percentage between
them and also the woven glass cloth give a slightly different colour.

Maybe there are other reasons too. This is just my little contribution :)
Regards.

Bob Landman wrote:

> My educated guess would be that as green is easier on the eyes (the photopic
> curve peaks in the green as human evolution goes back to sea creatures and green
> light penetrates water farther than any other part of the spectrum (why that is
> so is due to the shorter wavelengths being scattered (blue and vioiet) which is
> why the sunset is red (shorter wavelengtns scatter) and longer wavelengths
> (orange, yellow, red and IR) are absorbed more.   That is also probably why
> fiberglass PC boards have become standardized as green (they were also available
> in blue and I never liked them as the blue was not translucent so it was more
> difficult to inspect them).
>
> Interesting question.  Look forward to more answers!
>
> Bob Landman
> H&L Instruments LLC
>
> ----- Original Message -----
> From: Craig Lang/AEC <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: June 14, 1999 10:47 AM
> Subject: [DC] Origin of green??
>
> > Hello all...
> >
> > Often wondered about this and never had the umph to find out until
> > prompted
> > by a bet.  Yes I guess it does take money to get such crazy quests
> > started,
> > but here it goes....
> >
> > A majority of the solder-mask used on PCBs is green.....why?
> >
> > Now I've seen blue, red and even a goldish-yellow but why does green
> > seem
> > to be standard.  And since this is a bet, technical explanations are
> > necessary.
> >
> > I'll save my committed wager theory until I get a few ideas on this.
> >
> > Thanks
> > Craig
> >
> >
> > --
> > Craig M. Lang, Engineer
> > Applied Electro-Optics Corporation
> > [log in to unmask]
> >
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