Re: Processor wirh Vdd-Vss Short

Dec 05, 2007 3 Replies
J



>> Hi All,
>>
>> I had a tray of 3v processors back from the boad loader and 20 of about
>> 80 had a dead short between Vdd and Vss (3ohms).
>>
>> Any idea of what could of caused it?
>>
>> ESD?
>>
>> Board loader improper handling?
>>
>> Vdd Transient on power?
>>
>> Any ideas and experinces you have to share would be apprecicated
>>
>> Joe
>
> Counterfeit part?
>
> --
> Tim Wescott
> Control systems and communications consulting
>
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>
> Need to learn how to apply control theory in your embedded system?
> "Applied Control Theory for Embedded Systems" by Tim Wescott
> Elsevier/Newnes,
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Hi Tim,



I had consider this but - Source has been identified from official distributor of the micro and ins a seal vacum pack.



Joe


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J

Hi scott,

3ohms was the max resistance measured a few were 1 ohm - both polarities.

I used the term "dead short" loosely as the meter accuracy is _+ 1ohm - also allowing for lead resistance.

Joe

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J

Hey Jim,

Thanks for your input,

Boards come back from board loader - first power up the the 3v regulator starts to shut down (~ 100mA)

V/I curve ===> good idea

I wish I had one of those good USB microscopes!

Regards Joe

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J

So how do you know it is the processor, and not a solder or etching bridge ? Drop the supply a little, so things do not fry, and you can do a voltage profile along the traces with a millivoltmeter. That shows where the current is actually going, before you remove anything. It can help find errant 'shorts'. These boards were bare-board tested ?

Check the package markings carefully - it is the package detents that matter, not the direction of the brand markings.

-jg

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