4 Oct
1999
4 Oct
'99
11:08 a.m.
--- CLASSICCMP(a)trailing-edge.com wrote:
In the past few months, I've been heavily involved
with upgrading
some CAT scanners that date from the late 70's...
The PC boards that make up the backprojector make use of a unique
technology: the PC boards themselves are just plain old two-layer boards,
with the actual PC traces carrying only power and ground. All the actual
wiring is done by fine machine-laid wiring between pads, with all
the wire layers "potted" in a plastic compound.
The last design a former employer did was with a technology derived from this,
Augat's Unilayer. We sent them gerber plots and a couple of weeks later (for
an outrageous sum of money), we got back ten VAXBI 68010-based communications
boards. Our break-even cost on a custom 10-layer (yes... DEC specified ten
layers) was in the neighborhood of 20-25 boards. We never sold out of these
VAX-BI units, so it was a worthwhile way to go.
The actual construction was of two "decals" with embedded wires. Once spun,
they were laid onto a perforated board and tacked down to small solder pads
next to the holes, most of which had spring inserts in them. One defective
board turned out to be a missing insert, thus, no electrical contact between
pin and wire. A quick fix. We did re-work these - there was one ECO of a
cut and a 1" jump. No fun, even with the microscope.
I still have the boards. One of these days, I'll scan them in with the
rest of our DEC<->IBM product line (PDP-11/04's in the *real* old days,
custom 68K boards to the end in the 1990's).
-ethan
=====
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