[SI-LIST] Re: How to solve short circuit issues in high dense pcbs
- From: Alfred Lee <alfred1520list@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 31 Oct 2011 13:22:30 -0700
>2. Voltage drops by region.
Just a data point. We used 6-digit DVM to measure uV. Standard 3.5-digit DVM
is not accurate enough.
Regards,
Alfred
steve weir <weirsi@xxxxxxxxxx> wrote:
>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
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