Dan,
sounds like a case for ceramic substrates, like Alumina or Aluminum
Nitride (AlN). Extremly low CTE, inert to humidity, rigid, cheap and can
be processed by several american companies. And if they need
multilayers, you can give them LTCC. E.g.
http://www.mskennedy.com/store.asp?pid=7943&catid=19680
Inge

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dan Skweres
Sent: den 13 augusti 2007 21:25
To: [log in to unmask]
Subject: [TN] Another Request.

Fellow Technetters,
I have another request from a customer that I do not have an immediate
answer(s) for. Once again I was hoping that with the wealth of knowledge
you collectively have that perhaps you could assist me in assisting my
customer. They need a circuit board that...

  a.. Will reside within a float assembly of a gyroscope. 
  b.. The environment will consist of hydrogen with trace helium. 
  c.. A concern is the moisture absorption or adsorption, the
hygroscopic properties, of the circuit materials used in the stackup. 
 They're searching for materials with extremely low coefficients of
hygroscopic expansion and contraction, CHE and CHC.  The board needs to
maintain stable electrical, mechanical and dimensional properties. Is it
generally better to go with a rigid design rather than a flex design
when concerned with the affects of ambient moisture?

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