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May 2009

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Subject:
From:
Steve Gregory <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steve Gregory <[log in to unmask]>
Date:
Fri, 1 May 2009 06:56:45 -0500
Content-Type:
text/plain
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text/plain (63 lines)
Hi Wee Mei!
 
Sorry it took me so long to get your pictures posted, but Homestead was
down for server maintenance yesterday. I have your pictures posted now:
 
http://stevezeva.homestead.com/files/Q55-_burnt_site.JPG
 
http://stevezeva.homestead.com/files/Q55_-_remove.JPG
 
http://stevezeva.homestead.com/files/Q55_-_close_up.JPG
 
Yep, looks like some of the metal vaporized...pretty high temperature!
 
Steve

________________________________

From: Lum Wee Mei [mailto:[log in to unmask]] 
Sent: Wednesday, April 29, 2009 8:35 PM
To: Steve Gregory
Subject: Is fusing current current?


Dear All,
 
An engineer was trying to probe for a signal while he accidentally slip
the probe pin and has it shorted between the MOSFET metal tab (power
output) and the exposed area fill ( Chassis GND) beneath it. Ooop, up
come the smoke and a small burnt site. The MOSFET is removed and found
to be still functioning. The questions are :
 
1. To have the copper area blown up and fused look like we need a very
high temperature. If that is the case, why we do not see any damage to
the laminate epoxy glass fibre. We have a previous case, where the trace
burnt and curled up and the laminate epoxy glass fibre burnt and become
brittle.
 
2. As this PCBA is already fully populated and the damage does not seem
bad, I was thinking or just sealed teh exposed laminate with epoxy,
mount back a good part and use the PCBA as it is. Can I do that? or it
would be good to re-mount the whole PCBA?
 
All the PCBAs are made from Nelco-4000-11.
 
Your kind opinion is greatly appreciated.
 
Steve : Would appreciate you can upload this pic for me and forward to
TechNet for discussion.
 
 
Thanks and Regards,
~ Wee Mei ~

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