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January 2005

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Subject:
From:
"Braddock, Iain" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Braddock, Iain
Date:
Wed, 5 Jan 2005 08:05:43 +0000
Content-Type:
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text/plain (128 lines)
A couple of years ago we had a similar problem that proved to be a right
PIA.

Not quite the same connector but sounds like similar problem; due to tight
test parameters we had lots of failures, quite often at full EPU assembly
stage so rectification was a costly job!

Eventually identified the problem as being the product of wave soldering,
the flux was vaporising (RMA) and wicking up the connector pins.  The only
way to spot the ultra fine coating was to make / unmake a mating connector
and look for the witness under a Mantis but even then it needed almost a
trained eye to spot it, in fact the person best placed to spot the problem
was the test engineer..........who wasn't very happy being used as goal
keeper.

The fix was to place mating slave connectors to the boards prior to wave
soldering (which req'd cleaning periodically!), this helped a lot but the
only wave to eradicate the problem completely was to clean the boards post
soldering using Ultra-Sonics......fortunately the boards were motherboards!

Hope this helps.

Regards,
        Iain.

-----Original Message-----
From: Dave Seymour [mailto:[log in to unmask]]
Sent: 04 January 2005 07:09 PM
To: [log in to unmask]
Subject: [TN] flux wick-up?


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We had a batch of boards with high fall out. Below are a couple of
statements
from the CM building our cards. The socket mentioned below is a 370 pin CPU
ZIF
socket with a locking arm. We have manufactured this double sided
SMT/Through
hole mix card for 4 years.

My questions are,

Is there such a thing as "flux wick-up"?

Is the hole supposed to stop flux from getting onto the top side of the
PCBA?


I figured that flux is supposed to go up into the PCB hole ( and maybe even
getting into the socket contact area) to prepare the hole for soldering.
Then
the cleaning operation washes away any residue.

Any comments or help would be appreciated.

Thanks
Dave Seymour


>From CM:
"On a failed board we reviewed CPU sockets and removed the lid off the
socket
and viewed the gold contacts under a microscope and found some evidence of
contaminants/foreign matter on the gold contacts. "

"Got 23 CPU sockets from Stock and removed lids and there was no
contaminants found on sample of 4 parts."

"MFRG's data sheet and hole pattern recommendation is .030" 2 plc's = 0
tolerance.
Fab DWG shows hole dia to be .033" +.004 -.001.
Board hole dia is oversized compared to mfgr recommendations. "

"Can this possibly allow flux to wick-up?"

"We are continuing to investigate the findings and working to
determine what the contamination is...."

--
Dave Seymour, CID+
Catapult Communications Inc.
800 Perimeter Park Dr, Suite A
Morrisville, NC 27560

Direct: (919)653-4249
Main: (919)653-4180
Fax: (919)653-4297

[log in to unmask]

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