[SI-LIST] Re: PCB Leakage Currents

Chris,
   I saw something like this when I was a test engineer .  My experience 
lead back to the fabrication of the board in the socket area.  If the 
clearance is not large enough sometimes the etch does not remove all the 
copper.  The leakage path is usually lateral along the board surface or 
between the PCB layers.
   That being said, Have you looked at an unpopulated board?  200nA may be 
component leakage?  I would recommend you look at all the components on the 
board and make sure that you do not have a leakage path though them.  Also 
if that does not work, try thermally imagining the board, the area of 
leakage will show up as warmer then the rest.

Good luck
-Ed Sayre





At 08:55 AM 4/20/2005 -0700, Christopher.Jakubiec@xxxxxxxxxxxx wrote:
>All,
>
>I am currently working with a PCB DUT board that interfaces to an ATE
>(tester).  I am using this board along with a single socket to measure
>power MOSFET DC characteristics.  The PCB is a simple 4 layer board that
>routes the force/sense resources of the tester to the MOSFET socket.  I
>currently do not know the exact layer stackup of the board since I
>merely created the schematic, and the layout was done elsewhere.  I do
>know that there are a set of force and sense traces on the board for 5
>individual tester resources.  1 resource connects to the gate, 3
>resources to the drain, & 1 resource to the source(source is also tied
>to ground).  There are also some digital traces on the board that bring
>digital power for the EEPROM and the relays, and these have tantalum and
>electrolytic capacitors included.  Everything on the board, analog and
>digital are using 1 single point ground.
>
>My problem is when I am trying to measure off-state leakage from drain
>to source of the MOSFET (Vgs =3D 0V, Vds =3D 55V), I measure >200nA of
>current before I even put the device in the socket.  When I repeat the
>measurement with a blank PCB board I measure 20nA, so I don't believe
>that it is coming from the tester or cables.  The tester resource that I
>am using for the measurement has accuracy & resolution <100pA.  Any
>ideas of where this 200nA leakage current may be coming from?
>
>Thanks,
>
>Chris
>Infineon Technologies
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