[SI-LIST] Re: How to solve short circuit issues in high dense pcbs
- From: Doug Smith <doug@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 01 Nov 2011 18:56:33 -0700
Here is another idea which I have used back at Bell Labs years ago:
* Use a current limited supply and raise the current to the point where
youcan see the hot spot on the board with a camera that can detect surface
temperature. I remember back at Bell Labs we had to literally fill the
camerawith liquid nitrogen for it to work. Much easier today.
* Start with a low current and work up while watching the thermal image.
Itworked well for us.
Doug
On 11/1/11 3:20 PM, Pommerenke, David wrote: Danny, Use magnetic field
tracking. A method is to take a signal generator and a power amplifier and
apply a low frequency to the PCB. You may need an Ampere or so. The
frequencydepends on the bulk capacitance, select the frequency as high as
possible, but low enough such that the current flows through the short, not
via the large capacitors. Next you need a magnetic field probe useful for
that frequency. A Hall effect sensor, a GMR sensor (check NVE's offerings)
works pretty well. Attach a narrow band amplifier behind the magnetic field
sensor, tuned to the frequency you are using (like 10Hz), then begin
searching the board for areas with strong magnetic field. You can try DC
current, but the magnetic field of the earth is kind of strong, so you will
have to use an on/off method to see changes in teh field between having DC
current and having no DC current. David Pommerenke
________________________________ From: si-list-bounce@xxxxxxxxxxxxx[1] on
behalf of Danny Damhave Sent: Tue 11/1/2011 1:31 PM To:
si-list@xxxxxxxxxxxxx[2]Subject: [SI-LIST] Re: How to solve short circuit
issues in high dense pcbs Hi Kiruba If not already done it is also a good
idea to check the orientation of all the ICs and that all land patterns for
the ICs are correct (right pitch etc.) I have seen both causes shorts. BR
Danny Damhave On 31/10/2011, at 09.01, rskiruban wrote: Hi All, One of my
board having a short circuit (Zero Ohms) across a power supply (That supply
connects to thousands of decoupling capacitors and 44 BGAs) and Ground. Is
there any method to identify the route cause for the short without removing
any components? Note: #### 1. The board is not yet powered on. 2. It was
verified that the PCB doesn't contains any short across supplies before
boardassembly. Thanks and regards Kiruba Sankar Project leader Hardware
Design &Development Email: rskiruban@xxxxxxxxxxxxxxxxxx[3] web:
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