[SI-LIST] Re: PCB materials, solders, and components for VERY HIGH impedance applications

  • From: Mike Brown <bmgman@xxxxxxxxxx>
  • To: Steven Waldstein <swldstn@xxxxxxxxx>
  • Date: Sun, 22 Aug 2010 19:56:24 -0500

Steve, many years ago (45+), Milgo Electronics used G10 boards with a 
bake and a wax-like impregnation to achieve 1e12 ohms surface R, for 
boards used in a high-performance analog computer.  Special cleaning was 
also involved.  I was only peripherally involved, so I don't know the 
process details, and memory may mislead after so long.  Point being it 
can be done with enough attention to detail.

I suspect that there are better materials for such an application today, 
but I've never had to achieve anything like that kind of performance in 
my recent experience.

Regards

Mike
- - - - -
Steven Waldstein wrote:

>To all,
>
>I'm wondering if anyone has experience with PCB boards for very high
>impedance application (i.e > 100 GOhm). I'm learning about Isolation
>Resistance on capacitors and realizing that surface mount capacitors
>might only offer ~ 1e9 ohms of isolation. I'm now beginning to think
>about PCB materials as well. What kinds of leakage is there on FR-4?
>Do I need to worry about this as well. I also have been told that the
>right solders and fluxes need to be used as well along with good
>baking to ensure all trapped moister, which can lower the impedance,
>is used as well. Anyone have any experience with these as well and can
>recommend the proper types. Any and all help is appreciated.
>
>The application is a sensor that has a very low capacitance for AC
>coupling, a very high impedance input is used to ensure a very low
>highpass corner.
>
>Thanks in advance for any help
>
>Steve
>  
>

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