[SI-LIST] Re: PCB Leakage Currents
- From: "Kai Keskinen" <kalevi@xxxxxxxxxx>
- To: <Christopher.Jakubiec@xxxxxxxxxxxx>, <esayre3@xxxxxxxx>
- Date: Sun, 24 Apr 2005 17:03:06 -0400
I encountered this problem when a customer had asked for solder containing
water soluble flux. The manufacturing people said the solder would be OK in
their process. They did not account for the fact that they would have to
adjust their process to wash the boards after reflow. The flux residue
absorbed water and caused the 5M Ohm to 100M Ohm resistances between -48V,
return, and ground similar to what your are seeing. Once we had the boards
washed, the resistance became essentially infinite.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of
Christopher.Jakubiec@xxxxxxxxxxxx
Sent: Friday, April 22, 2005 12:16 PM
To: esayre3@xxxxxxxx
Cc: si-list@xxxxxxxxxxxxx; Christopher.Jakubiec@xxxxxxxxxxxx
Subject: [SI-LIST] Re: PCB Leakage Currents
I appreciate all of the input from the list. I have discovered one
thing upon further probing with a hand held DMM. As I mentioned
previously I have several DC power supplies that are routed to the board
as well (+24V, -24V, +5V, +12V, -12V). When I measure resistance
between these DC traces and the trace to the MOSFET drain pin, I am
observing between 10M-ohm to 50M-ohm. There is supposed to be no
physical path between the digital and drain pin traces. This connection
between the 2 appears capacitive because I can watch the resistance on
the meter rise and then ultimately go infinite (open circuit). =20
Also, I don't believe that I am dealing with contamination, since this
is repeatable on 2 of the same boards that were manufactured 6 months
apart.
Thanks,
Chris
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Ed Sayre III
Sent: Wednesday, April 20, 2005 1:13 PM
To: Jakubiec Christopher (IFNA AI QM CM)
Cc: si-list@xxxxxxxxxxxxx
Subject: [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=20
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=20
between the PCB layers.
That being said, Have you looked at an unpopulated board? 200nA may
be=20
component leakage? I would recommend you look at all the components on
the=20
board and make sure that you do not have a leakage path though them.
Also=20
if that does not work, try thermally imagining the board, the area of=20
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=20
>(tester). I am using this board along with a single socket to measure=20
>power MOSFET DC characteristics. The PCB is a simple 4 layer board=20
>that routes the force/sense resources of the tester to the MOSFET=20
>socket. I currently do not know the exact layer stackup of the board=20
>since I merely created the schematic, and the layout was done=20
>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=20
>the gate, 3 resources to the drain, & 1 resource to the source(source=20
>is also tied to ground). There are also some digital traces on the=20
>board that bring digital power for the EEPROM and the relays, and these
>have tantalum and electrolytic capacitors included. Everything on the=20
>board, analog and digital are using 1 single point ground.
>
>My problem is when I am trying to measure off-state leakage from drain=20
>to source of the MOSFET (Vgs =3D3D 0V, Vds =3D3D 55V), I measure >200nA =
of=20
>current before I even put the device in the socket. When I repeat the=20
>measurement with a blank PCB board I measure 20nA, so I don't believe=20
>that it is coming from the tester or cables. The tester resource that=20
>I am using for the measurement has accuracy & resolution <100pA. Any=20
>ideas of where this 200nA leakage current may be coming from?
>
>Thanks,
>
>Chris
>Infineon Technologies
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