Thanks for your responses so far - I have read alot of articles as such ... For the most part I see a lot of good practices... I'm hoping that Ansoft can bring to light the more analytical approach to many trade offs to attain the desired goal. This is what I found out so far: 1) clean is essential. 2) can't mask vapor deposition paralene coating - guard ring masking is pretty hard to do (I don't know why masking will help....please shed some light on this) 3) baking the boards after assembly increases volume resistivity 4) I wish i understood why the guard ring works - in my mind its' a common practice, but..... 5) using other material other than FR-4 increase the volume resistivity - see Rogers Corp 6) distance between electrodes is better... 7) looking for a cost effective solution - teflon is too much / plus it's a soft material / need something rigid like fr-4 8) slots are great , cost of pcb increases I think some should write a program for use in battery applications and hi-z amplifiers Keith Kowal www.product-designs.com > Date: Fri, 19 Nov 2010 05:35:07 -0800 > From: weirsi@xxxxxxxxxx > To: epd2001usa@xxxxxxxxxxx > CC: si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Re: Guard Rings ... DC > > Keith there are articles on this sort of stuff from the makers of very > input impedance amps: ADI, TI, NS, LTI, etc. The trade-off with > conformal coating is that the coating will give you a lot more leakage > than a clean, dry PCB. If the board can be kept clean and dry then > avoid the conformal coat. There are other tricks that have been > previously mentioned involving packaging the Hi Z amplifier off the PCB > using PTFE stand-offs and such. > > Steve > keithK EPD wrote: > > I am dealing with DC ! so, some of my questions are not for the entire High > > speed audience, so I apologize > > > > I have a 4 gig ohm electrode/electrodes(s) ..... my electrode spacing is > > 0.230" and my socket has a 0.175" diameter / 4 layer > > > > I haven't seen much lit on the subject - > > > > PCB material / voids / components / etch width to the 1 resistor into the > > opAmp / given 0.060" / slots req'd > > what does conformal coating do for me.... > > > > comments, pointers to white papers, etc are welcome. > > > > > > Keith Kowal > > > > www.product-designs.com > > > > ------------------------------------------------------------------ > > 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 > > > > > > > > > > > -- > Steve Weir > IPBLOX, LLC > 150 N. Center St. #211 > Reno, NV 89501 > www.ipblox.com > > (775) 299-4236 Business > (866) 675-4630 Toll-free > (707) 780-1951 Fax > > > ------------------------------------------------------------------ > 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