David,

Hi and thanks for the info.  Yes, there is circuitry onboard however, the
area of compression is an isolated 1 inch circle on one edge.  The potential
problem is the small size of compressed PCB (not much glass-epoxy to
dissipate the energy) and if the base material degrades as a result of
repeated compression.  And I don't believe it matters if the material is or
isn't slightly compressible as long as it's consistent over time.

-Ron

-----Original Message-----
From: David Cary [mailto:[log in to unmask]]
Sent: Friday, April 06, 2001 12:58 PM
To: [log in to unmask]
Subject: Re: [DC] Substrates


Dear Ron King,

"King, Ron" <[log in to unmask]> on 2001-04-04 11:48:26 AM
...
> redesign a piezo wafer and PCB
> sandwich that will be compressed in order to get a force reading.  We are
> currently using FR-5 and the substrate appears to be holding up however,
we
> have not done a micro section.  My question is:  What substrate would
offer
> the most resistance to compression in the Z axis without being too
brittle?

I take it what you really want is something that will last the longest under
many cycles of high load. (Does it matter whether the substrate is slightly
compressible ?)

FR-4 is pretty strong stuff (glass fiber and epoxy). I find it hard to
believe
that you could apply enough force to damage it if the force is properly
spread
along the top and bottom surfaces.

But if you want to go for overkill...

Some PWB boards are mostly solid metal, with a very thin (typically ceramic)
insulator:
  Thermal Clad
  http://www.bergquistcompany.com/thermal/tclad.htm

  "NAVSO P-3651: Thick Film Ceramic Boards w/ Leadless Components Tech
Process
Guidelines"
  http://www.bmpcoe.org/guideline/books/3651/

  http://www.thermagon.com/

Do you actually have any components on these PWBs ? I would like to learn
more
about piezo connections and interfaces. (Although I use them to measure very
small loads).

--
David Cary

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