For a really, really hi-Z circuit, discard the PCB paradigm. Use PTFE standoffs to hold a wire in air, and a flying connection to the transistor or IC lead. This connection should also be in air rather than involving a PCB pad. Same trick at the input connector. Put a shroud over this path to prevent resistance lowering dust accumulation and electrostatic charging from air circulation. Make it from plastic if capacitance has to be minimized but if so use a high resistivity anti-static formulation lest the shroud itself become charged. Orin Laney On Sat, 21 Aug 2010 17:18:19 -0400 Steven Waldstein <swldstn@xxxxxxxxx> writes: > 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 > -- > Steve Waldstein > E-mail: swldstn@xxxxxxxxx > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject > field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > List technical documents are available at: > http://www.si-list.net > > List archives are viewable at: > //www.freelists.org/archives/si-list > > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > > > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu