[SI-LIST] Re: How to solve short circuit issues in high dense pcbs
- From: steve weir <weirsi@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 31 Oct 2011 01:21:56 -0700
Apply power using a high current capable supply set to 0.15V or less at
the board connection and slowly increase the current while observing any:
1. FLIR image for hot spot.
2. Voltage drops by region.
3. Manual temperature monitor by region.
The idea is that you do not want to forward bias any ESD protection
diodes. If you have a hard short somewhere 0.15V will be plenty to
drive many Amps into the board.
If you use your head, you can decide different points to apply the
external power as an aid in localizing the problem.
Your alternative is to attempt to use a TDT or VNA w/ low frequency
capability to localize the short. The better that your power system is,
the harder it will be to use a TDT or VNA to locate the problem. This
is further complicated by the difficulty of getting a clean launch.
However, the TDT/VNA approach can be useful if you probe from the middle
of each edge of a power polygon extent while observing from the opposite
edge ( assuming that you can get to it) and compare the measurements.
This kind of "quadranglization" can provide clues as to what kind of
short you have: localized or distributed.
The most likely problem is solder shorts with the BGAs, or cracked
capacitors due to poor solder processing, or counterfeit parts.
However, your board could also have warped during soldering, and/or
process chemicals wicked causing a short between Vdd and Vss planes.
Steve.
On 10/31/2011 1:01 AM, 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 board assembly.
>
>
> Thanks and regards
> Kiruba Sankar
> Project leader
> Hardware Design& Development
> Email: rskiruban@xxxxxxxxxxxxxxxxxx
> web: www.datapatternsindia.com
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--
Steve Weir
IPBLOX, LLC
150 N. Center St. #211
Reno, NV 89501
www.ipblox.com
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