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Subject:	Problem With PCB Opens - Another case study
From:	Lum Wee Mei <[log in to unmask]>
Reply To:	TechNet E-Mail Forum.
Date:	Tue, 16 Dec 2003 08:04:42 +0800
Content-Type:	text/plain
Parts/Attachments:	text/plain (41 lines)

Hello there!

SInce we are at this topic of open circuit on PCB, I like to bring up
one more case study.

I have some assembled boards, tested functioning and went through ESS.
They are put aside and after some times, the engineer wanted to donwload
a new firmware through the molex pins on the board. Oop, the software
cannot get through. He take the meter and measure the connections
between the molex pins to the IC chip and found them open. He touched up
the solder joints at this molex connector and found it open. Then later,
the connections are found to be opened again. All the connections are in
the inner layers - 3 layers from top. Soldering of the molex connector
is from the bottom - 8th layer. Other molex connectors along the same
axis have not problem including the same connectors on other boards.

What has been done : we take measurement on the connections. There are
connections from the IC chip to the vias but found open circuits from
vias to molex connector. It is surprise to find all the 5 connections
opened while the ground and supply connections are intact. The signal
traces are of 5 -6 mils.

What could be the root cause of such defect? Anyone want to try? Can
X-ray surface the open circuit?

Note : No cross-section is allow on this assembled faulty board as it
will be used.

Regards,
Wee Mei

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