[SI-LIST] Re: Guard Rings ... DC

  • From: keithK EPD <epd2001usa@xxxxxxxxxxx>
  • Date: Fri, 19 Nov 2010 09:16:14 -0500

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
> > 
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> 
> -- 
> Steve Weir
> IPBLOX, LLC 
> 150 N. Center St. #211
> Reno, NV 89501 
> www.ipblox.com
> 
> (775) 299-4236 Business
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