From: zlau@arrl.org (Zack Lau)
Subject: Re: Why circuit boards are green?
Organization: American Radio Relay League
Lines: 64

In sci.electronics, swanee@megadata.mega.oz.au (Geoff Swan) writes:
>
>Rubbish. The reason for the colour of the boards depends on the solder

The May 1993 cover of QST has a picture of three different boards without
any solder mask (you can tell from the copper colored traces). The box
labeled 2304 transverter has the brown teflon/glass board, while the one
in the center has the grayish board exposed.  On the left is some 
fiberglass board that looks green to me.  I see no reason
for putting solder mask on circuit board used for box covers :-).

I wonder if any manufacturer actually puts a solder mask on their
low noise microwave preamps?  Often, microwave circuits have odd
bits of wire/foil/metal attached to wherever/whatever is necessary
to make the unit work properly (this is a commercial product?).  A
solder mask would certainly make doing this tougher, never mind 
the finding something that minimally degrades the circuits.  (Q dope
for coils *does* not improve the Q--it just holds things together with
minimal loss).

Zack Lau  KH6CP/1

Internet: zlau@arrl.org           "Working" on 24 GHz SSB/CW gear     
			          Operating Interests: 10 GHz CW/SSB/FM
US Mail: c/o ARRL Lab				       80/40/20 CW
	225 Main Street		  Station capability: QRP, 1.8 MHz to 10 GHz
	Newington CT  06111	               modes: CW/SSB/FM/packet
						      amtor/baudot
Phone (if you really have to): 203-666-1541

Zack Lau  KH6CP/1

Internet: zlau@arrl.org           "Working" on 24 GHz SSB/CW gear     
			          Operating Interests: 10 GHz CW/SSB/FM
US Mail: c/o ARRL Lab				       80/40/20 CW
	225 Main Street		  Station capability: QRP, 1.8 MHz to 10 GHz
	Newington CT  06111	               modes: CW/SSB/FM/packet
						      amtor/baudot
Phone (if you really have to): 203-666-1541

>mask that is used. Older boards (bakelite and phenolic) rarely used
>a solder mask (these boards are not suited well to automatic stuffing
>and soldering techniques) and hence are the colour of the compound
>used to make them. These days boards are made of fibreglass for most
>general purpose uses and have a solder mask applied to them to prevent
>close traces shorting to one another during soldering (and also to prevent
>the decomposition of traces under harsh environments). The light and dark
>green boards ofter seen have a "dry film" mask applied to them (usually
>applied as a complete film photographically produced). The blue (and red
>or orange) boards are a two-part epoxy or a liquid-imageable resist
>formulation and are applied in a different manner. There's a lot of info
>about the pro's and con's of each, but that's another story...
>
>    Sla/n go fo/ill,
>                    Risky B.
>--------------------------------------------------------------------------
>Geoff Swan (research & development)   _--_|\         swanee@mega.com.au
>Megadata Pty Ltd                     /      \ 
>2/37 Waterloo Rd, North Ryde,        \_.--._/               +61 2 805 0899
>NSW 2113, Australia.                       v          (Fax) +61 2 887 4847
>
>
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