John Larkin wrote:
On Sun, 07 Oct 2007 09:28:27 -0700, Joerg
wrote:
John Larkin wrote:
On Fri, 05 Oct 2007 18:21:24 GMT, Joerg
wrote:
Rich Grise wrote:
On Thu, 04 Oct 2007 00:00:26 +0000, Joerg wrote:
Eeyore wrote:
Joerg wrote:
I'll second John's and Rich's comments. Besides rounding you might want
to consider flaring the traces into the pin header vias. I think
layouters call that "drop". That way there could be less stress fractures.
Teardrop. It's astonishing how many good practices of old have been lost as a
result of CAD layout.
There was once a Marconi (Instruments) IIRC guide to pcb layout from the early
days of tape-up. It covered all these subtleties. I've seen excerpts but never
the actual publication.
I HAVE seen foil fractures where a thin trace enters a pad resulting from rough
handling, rework or whatever. Tear drops reduce such stresses hugely. It's basic
engineering.
PADS IIRC is the only package I've seen that has a teardrop function built in as
standard.
Eagle can do that as well AFAIK. But I never do layouts myself.
A lot of layout is common-sense and it gets violated a lot. Why on earth
everyone thinks right angle looks more cool that round traces I will
never understand. And then the stuff breaks.
Right angles are much more "modern" - like chrome-and-glass furniture as
opposed to art deco. ;-)
They're also easier to tape up. ;-)
I've always belonged to the group of round-tapers ;-)
I was taught to never bend tape, because longterm it would be under
tension and ooze around on the mylar and change clearances. Ditto to
not make 90 degree bends. So it was
Make 90 deg junction
Overlay diagnonal tape into the corner
Xacto trim, trim, trim, trim.
Oh man, we never had to do that. We had Symbol sheets that also came in
a "trace pattern" edition. IIRC it was from a company called LetraSet.
But this was in Europe, no idea if they were for sale here. However,
this stuff was IMHO freaking expensive.
Here it was Bishop Graphics. Excellent stuff, but expensive, and now
and then the sales guy would hint that you'd better buy your blueline
supplies from them too, if you wanted your tape and pads to be
delivered. When CAD came along, everybody gave them the finger, and
they're gone.
I don't miss sending art out to be photographed, either. Lorry Ray was
good, though.
I've never seen a LetraSet rep. I bought that stuff via special order
through the book store in town. That company wasn't really specialized
in layouters, they catered more to sign makers. Their letter and symbol
sheets were really handy for creating professionally looking front panels.
I sure don't miss manual taping, or slide rules, or typewriters and
carbon paper, or wire-wrap, or thru-hole boards. There's not much I do
miss from the olden days. We are incredibly more productive now.
Wire-wrap was IMHO the pits, I never allowed that on any of my designs.
But I helped others a lot finding sub-optimal wraps and stuff. The slide
rule is still frequently used here. Very handy if you want to whip up a
filter from catalog parts or from parts you find in a client's parts bin.
I wrote a little LC filter de-normalization program (free for the
asking) that makes it fairly easy. Look up a prototype in Williams,
plug that in, and fiddle with terminations and cutoffs until you
stumble onto a set of values that you can get. Then run LTspice and
see how it will look.
I'd be interested. "jsc AT ieee DOT org" is shorter to type than my biz
email.
I use routines like Aade but mostly just the old slide rule. Goes like
"Ok, we've got 1.2uH, 2.7uH and 4.7uH available here plus the E12 series
for caps, lets see how we can get into the ballpark with that". I am a
bit worried about my Williams, the pages are beginning to turn yellow.
--
Regards, Joerg
http://www.analogconsultants.com