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March 2007

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TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Fri, 9 Mar 2007 12:27:09 -0500
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TechNet E-Mail Forum <[log in to unmask]>, "Kolmodin, Todd" <[log in to unmask]>
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I concur with Kerry.  That is definitely a test probe mark. It most
likely was done by a rigid probe during bare board test at the PCB Mfg
site.  Usually the aforementioned spring probes would not cause this
unless the spring probe was bent or damaged.  The picture shows a common
witness mark from a probe that either was bent in the fixture or was
stuck by some other means.  The board was definitely overcompressed.

Todd
 

------------------------------------

Todd L Kolmodin

Service/Quality Manager

Mania Technologie Inc

Forest Grove, OR

[log in to unmask]

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kerry McMullen
Sent: Friday, March 09, 2007 9:17 AM
To: [log in to unmask]
Subject: Re: [TN] whodunit?

Seen that before.  That is the test point indent from a bed of nails 
bareboard tester.  The force is too great.  This can also be caused by
too 
many test points in the fixture and the operator not being able to dial
in 
the force required to make all the probes achieve good contact. 

Kerry McMullen
Principal New Product Mfg. Engineer
LTX Corporation
825 University Avenue
Norwood, MA 02062-2643
(T) 781-467-5468
(C) 508-631-1832
(F) 781-461-0993



Steve Gregory <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
03/09/2007 11:48 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Steve Gregory <[log in to unmask]>


To
[log in to unmask]
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Subject
Re: [TN] whodunit?






Hi Graham!

Got a picture of your "Whodunnit" up, it's at:
http://stevezeva.homestead.com/files/whodunnit.JPG

Sure looks like a probe mark to me...a chisel type tipped probe. Here's
one they call a "Flux Buster":
http://www.isiconnectors.com/mfrs/idi/catalog/so25.jpg
Looks like it would leave a similar mark...

-Steve Gregory-

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins
Sent: Friday, March 09, 2007 9:40 AM
To: [log in to unmask]
Subject: [TN] whodunit?

Hello Technet!
I've got a mystery today.  A colleague showed me a board, it's got some
unique damage on it.  It is the only one of maybe a thousand identical
assemblies, the rest do not have this damage.

Throughout the bottom side of the board there are damaged through-hole
pads.  The damage is an impact hole, where something triangular in shape
has in some cases literally punched through the pad.  In some cases
there is a lighter mark on the pad and/or on adjacent solder mask.  The
damaged pads are scattered throughout the board, they aren't restricted
to one area.  In some cases where there is damage there is visible
exposed copper.

Some facts
1) the board went through our assembly process without incident until
inspection
2) no unusual equipment malfunctions have been reported recently here -
so I don't think it is something we did.
3) The board is received with HASL finish on the pads, and is wave
soldered.
4) In all cases the damage is at a through-hole pad, some overlaps the
pad onto bare FR4/solder mask, but in all cases the damage at least
touches a pad.
5) the board also has SMT parts on the bottom side, we glue parts on and
wave solder attach them.  No damage has been identified on these pads.

I'm concluding that:
 - we don't have any equipment capable of doing this type of damage to a
PWB with such precision.
 - because there is exposed copper, whatever happened likely took place
after HASL coating.

At this point my theory is that the electrical test at the PWB shop did
this, but it's a theory.  Can you PWB guys advise, is this possible? 
Where else would something triangular have the potential to whack the
pads?

As I said already, it's only one - but I hate an unsolved mystery! 
Please help.


regards,

Graham Collins
Process Engineer,
L-3 Communications Electronic Systems Inc.
Halifax
(902) 873-2000 ext 6215

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