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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