Re: gnarly PCB

On Fri, 12 Apr 2024 13:42:20 -0700, john larkin <jl@650pot.com> wrote:

On Fri, 12 Apr 2024 12:13:08 -0700, boB <boB@K7IQ.com> wrote:
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On Thu, 11 Apr 2024 06:54:47 -0700, John Larkin
<jjSNIPlarkin@highNONOlandtechnology.com> wrote:
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On Thu, 11 Apr 2024 09:13:26 +0200, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote:
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On 11-04-2024 03:31, John Larkin wrote:

 
https://www.dropbox.com/scl/fi/fiy73ou127rd5hi23jkw9/P948_A6.jpg?rlkey=symijy4b0veq1s5ho982r0sa0&raw=1
 
My layout guy is struggling with this. Actually, he seems to be
enjoying it.
 
It has two D25 connectors, 130 relays, 49 polyfuses, and the usual
FPGA and such. 8 layers, four of which will be 2oz copper.
 

It's a big PCB for sure.

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Yes. It is supported on the ends.
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https://www.dropbox.com/scl/fi/43dl9eoja8gr0j0wqox56/P940_FA_2.jpg?rlkey=n3s4ycq3cpnxwx7d6l8jbxm50&dl=0
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One customer wants to fly it and is rightly concerned about vibration.
I'm working on that.
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The Brat put up our new web site yesterday, and it includes the public
announcement of our modular power system.
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https://www.highlandtechnology.com/Category/MPS
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The P940 system originated when a customer, on a zoom call, said "we
hate power supplies."
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Nasty layout program, looks like it's from the 90'ties

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It has pads and traces. Don't all layout programs do that?
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Switch to Altium?

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It's PADS. We've been using it since the dos/floppy disk days. It
works fine. I don't like the color scheme that my guy uses; we change
the colors before we release the boards.
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The schematic editor is excellent. It actually understands
connections.
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Very pretty with all those layers/colors !
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Just put enough standoffs to hold it and should be fine.
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Be careful of big ceramic SMT caps next to flex points.
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boB

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It's supported on the ends and is very flexy.
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My plan is to add rubber weatherstripping strips to the chassis bottom
and to and top cover, to damp resonances.
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This feels good, nice and snug.
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https://www.dropbox.com/scl/fi/gifrf8h2j3ldnlv8azfsv/BWS_in_P940_chassis.jpg?rlkey=9mfy323fj2l0gr579c2ockfic&raw=1
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https://www.dropbox.com/scl/fi/u9u5zb7wq22y6vvuh2isf/BWS_D_on_cover.jpg?rlkey=ynwn6yt3maeh094q8uyd48g9n&raw=1
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This will go in a "flying test bed", basically an old 747 with three
original engines and one DUT. Vibration will be mild, nothing like an
F35.

Even so, beware.  Those cards _will_ flex badly, and destroy the card
to card connectors first.  Fretting, maybe fracture.  Depends.  The
card may be OK, but it too will fail eventually.  BTDT.  Or rather, I
got the fixup job, in the 1970s.

Later, I've seen fretting due to cooling-fan vibration and tin-plated
connector fingers destroy a midi-computer in the 1990s.  Which is why
people don't use tin plated connectors (even with some anti-whisker
lead alloyed in) in such applications.

The two bumper weather strips don't look to be enough, especially when
the top and bottom sheets flex outward.  But edge clamps screwed to
those sheets could work.  Or some kind of crossbars passing between
the circuit cards from top sheet to bottom sheet.

Joe Gwinn