On Sat, 20 Sep 2014 18:25:05 -0700, John Larkin
wrote:
You didn't literally need a UV light. A 250-watt warehouse-type
mercury vapor lamp, maybe 6 feet above a table, worked fine.
Yep. That should work. Some detail and alternatives:
http://unblinkingeye.com/Articles/Light/light.html
How we got to the plywood and glass kludge was almost predictable.
Someone defined the need. Management declared that there was no
money, floor space, staffing, etc. Irritated engineer throws
something temporary together to be used only until the necessary
money, floor space, staffing, etc are found. However, since the
temporary kludge worked reasonably well, the crisis had been averted,
and the kludge become permanent.
Moral: If it works, it's permanent.
I found one of my layouts from 1985:
http://802.11junk.com/jeffl/PCB-Layout/
It's a light pen interface card for the IBM PD as a 16 bit ISA card. I
did a lousy job and am not very proud of it. However, it does show
what was typical of 1970's PCB layout technology. If anyone wants
details or more drawings, please say something as all of this is going
into the trash in a few daze.
Ooh, curved traces. I was taught to never do that, on the theory that
the tape would eventually creep in the corners.
That does happen if one stretches the tape when laying a trace. It's
especially bad with narrow traces. Traces will move, especially if
the layout is left in the sun. I used a rubber roller from my wet
photography kit, to flatten the traces and make sure they're properly
stuck to the mylar. (Incidentally, note that I used acetate instead
of mylar in the above layout. Not a good idea and I forgot why I did
it).
For RF, rounded corners are a problem due to impedance bumps. Sharp
corners are equally bad due to reflection problems. The compromise is
a chamfered corner (mitered bend):
http://www.microwaves101.com/microwave-encyclopedia/480-mitered-bends
which unfortunately also makes a tolerable fuse at the bend.
However, the above PCB is not an RF board. Instead, the problem was
the cheap wave solder machine that we were using at the time. Somehow,
it often managed to burn or scrape off the solder mask on sharp corner
bends. The result was usually an impressive solder bridge at the
corners and a tedious touchup job. I was never able to determine the
cause, so it was circumvented by using radiused bends and liberal
trace spacing.
I know companies that define "breadboard" "prototype" "beta"
"pre-production" "pilot production" and "production". And use all of
them. Takes them years to finish anything.
I had a weird situation at 3 consecutive companies. After the usual
extremely long management inspired delays deciding if the company
should work on a given product, a schedule was created, usually by the
engineering manager. Invariably, there was not enough time to work
through a proper design. For example, one project that took about 8
or 9 months from conception to delivery, only allowed 2 weeks for the
initial (paper) design. Everything else was allowed a fairly normal
period (breadboard, testing, FCC certification, compliance testing,
fixture construction, prototype run in manufacturing, etc). In
effect, the design was mostly frozen two weeks after the project
started. Little wonder we needed a full prototype in order to find
the inevitable design errors. If we had time to have done a more
rigorous design, much of the subsequent fire drills could have been
avoided.
They assume the first few
iterations will have errors, so they do.
As I previously noted, my attempts to do one product perfectly the
first time, failed because the PC fab house reversed the component and
circuit sides of the PCB.
Lesson learned: Trust but verify.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558