Noticed any recent bare PCB leakage problems?

Hi,

Has anyone noticed a recent increase in board leakage in FR4 Double sided boards? We have some high gain preamps that have worked for 8 years no probs, then found leakage on boards from an Aussie and a Malaysian supplier. This first happened around November.

Reply to
Geoff C
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Are you saying that your circuit boards have incontinence issues (like Phil ;-) or are you suggesting that the dielectric constant of FR4 material is no longer as constant as you would like?

Should a high gain preamp design be so reliant on substrate material properties that manufacturing variations can adversly effect the circuit performance?

More info pls. Is it a matching issue, stripline calcs are no longer valid or dieletric losses are making your preamp not such high gain?

You say leakage, so I assume you are not flashing an LED with a 555, but perhaps a little faster. FR4... not above 1GHz if you can get away with it.

Testing the boards is the only option and make sure there were no component / supplier changes around about the same time.

Matching / Q gone out the window.... I hate it when that happens.

cheers, GtG

Reply to
Greg the Grog

What values are we talking about here?

I find it hard to believe that a bare PCB could have leakage that low to be a problem, even with very high value impedances (100Mohms+). Are you sure it's the bare board and not a board loading/washing contaminant?

Dave :)

Reply to
David L. Jones

He said high gain, not high frequency.

I would be interested to know exactly what 'high gain' means.

With 8 years of success, I would be looking at manufacturing/components before blaming the substrate.

Reply to
The Real Andy

This can be a problem with some opamp circuits: Nat Semi suggests lifting one IC leg into the air and wiring the components in air.

Reply to
Mark Harriss

"Greg the Grog" wrote in news:L8XPf.1951$ snipped-for-privacy@news-server.bigpond.net.au:

Frequencies are low, 100 Hz samplin and sqare wave, sensitive to a few kHz and DC. I measured the baord with a Kiethley electrometer and it is >

100Gohm but I will test more rigorously next week. Yesterday I drilled the PCB and air connected the opamp node, and all was OK. The f/b R is 10 meg, input is photodiode ground connected. Opamp is OPA404. Sure, FR4 is not always suitable for high gain, but I would rather stick with low cost FR4 and air connect the 4 connections to the node. The board has worked fine for 8 years. Different suppliers no prob. No known component changes. All contending components were swapped b/n a good and bad board but prob followed PCB. Bottom line is I have a fix. I will crunch numbers next week. Good to have a solid explanation, but at least production is running. BTW, tried baking and solvent cleaning, and latest baord had guarding artwork on the sensitive node. Of course, this only works for surface currents.
Reply to
Geoff C

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