From: [EMAIL PROTECTED]
Date: Fri, 26 Aug 2005 22:23:20 +0000
.047" (actually 3/64") Copper Clad Laminate is an industry standard thickness
and when you include plating (typically <.0005") and solder mask, the board
thickness will increase .002" - .003".
It may be an industry standard, but it is not that easy for the
hobbiest to find stock in that thickness. At least, I did not find
any in a great deal of google searching on PCB mail order companies.
A typical 1/16" board (our typical thickness) measures .0645" or
.065" depending
on where you take your measurement. I am not sure why people have had a
difficult time finding this (3/64") stuff, but it is quite common.
It does not appear to be commonly available at the mail order places
available to hobbyists. Or if it is, those places don't come up on
Google very readily. Now, most of the PCB build houses will do
3/64" if you want it, but they'll also charge an arm and a leg for
the service--i.e. their regular price plus some surcharge for the
"non-standard" thickness.
If the only
standard stock was 1/16", imagine how thick a 16 layer board would be! We
have 4 layer boards which are 1/32" total.
Yeah, I just picked up some .010 and .016 stock as well, but I'm not
sure how one laminates separate layers into a single board either.
Regarding the photo-resist. I "think" our local board house purchases their
laminate pre-coated... We used to purchase it that way when we made one-off
prototypes. You could certainly (using a silk screen) apply
(liquid) resist over
your track & pad areas, but this method is not common these days (the screens
stretch and there are definite registration issues).
I definitely want to use a photolithographic process, not silk
screening, so the photoresist needs to be applied to the board.
Hmmm. I wonder if I could get a spin on agent like they use on
silicon wafers.... Anyway, I've never seen .047" board anywhere
pre-coated. It may be available on the wholesale level, but I've yet
to see it available for purchase to the general public. I'd be happy
to be shown wrong here with an affordable example... :-)
Designing a SIMM should be fairly simple, but tooling costs would
kill you unless
you had a fair number of buyers. I believe it runs us something
like $500.00 for
an initial production run of 5 flats (roughly 64 sq. in. each)...
The regular services are too expensive as you mention. Once one buys
a couple of hundred boards, the unit cost gets down to $6 - $8 per
board, depending on the specifics, but that isn't really supportable
for this kind of tinkering.
This varies from place to place, but that's in the ball-park for most
places' regular service. 4PCB.com (Advanced Circuits) is the most
commonly known affordable proto-type service. There are others with
a variety of options. I have used Sierra Proto-Express in the past.
They have a "No-Touch" service where they run your boards, pretty
much without looking at what files you've sent them.
So for about $100 one can get two ~8" X 10" two-layer boards (not
sure about the exact dimensions anymore) and I'm pretty sure there's
nothing stopping one from putting several repeats of the same board
on the design files one submits. The proto service won't do the step
and repeat for you, and they won't cut the boards apart for you, but
they'll probably build the design you submit if it meets their
specifications otherwise.
Sierra includes front & back green solder mask and one side silk
screening in their proto service. They also have a four layer proto
service for about $150.
The catch is that all these affordable proto services are for .062"
board only. They won't do the proto in .047" board.
I use Osmond PCB to produce Gerber and Drill files from the Mac.
Osmond was a free download when it was in beta testing (for several
years) but it recently became actual pay software.
<http://www.swcp.com/~jchavez/osmond.html>
So the regular board service is too expensive. The Proto Service
only builds .062" board. It's hard to find (at least for me) .047"
stock.
I've found some interesting offers on Ebay from a couple of Chinese
PCB houses and one of them will do 200 sq. in. of board with solder
mask and silk screening for about $130. The 200 sq. in. can be one
or several boards. For an extra 10% they'll do .047" instead of
.062". However, in my emails to them, their responses have been so
difficult to understand, that I fear I could never communicate any
problems to them if there were issues with their service.
Because I'm still looking for work (I'm not seeing any economic
recovery) funds are really tight. So, if I can do it affordably,
I'll build a couple of boards myself to test my designs and if
they're good, then give the Chinese place a try. 200 sq. in. will
get me about 50 boards for a unit price of about $3 per board.
Fifty is a reasonable quantity and even if there's little or no
market, $150 is an absorbable loss. Plus it will be fun.
But to build a few boards myself, I need to find a way to do
photoresist on copper clad board which is not precoated.
Jeff Walther
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