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March 2007

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Subject:
From:
Colin McVean <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Colin McVean <[log in to unmask]>
Date:
Fri, 9 Mar 2007 16:13:53 -0000
Content-Type:
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text/plain (129 lines)
There are some unique shapes on test probes on fixed bed of nails type
testers such a cone points, crown points, round points etc but all
designed to lightly penetrate oxide layers etc when bare board testing. 

Most, if not all, flying probe testers use probes terminating in a sharp
point. It's also unlikely that a flying probe machine can exert that
sort of force to damage the pads to the extreme that you describe. It
may be possible this effect is from the post testing fault diagnosis,
which can be performed by hand with a tone tester.

Pictures of the defect would be helpful  

Colin W.T. McVean M.Inst.C.T
Production Manager
 
Artetch Circuits Ltd  (www.artetch.co.uk)
Direct Dial      01903 712926
Switch Board  01903 725365
Skype: colin.artetch
 
P Before printing , please think about the Environment 
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Roger Stoops
Sent: 09 March 2007 15:44
To: [log in to unmask]
Subject: Re: [TN] whodunit?

Do you perform FCT or ICT in-house?
Is assembly wave-soldered or reflow w/manual soldering?

First guess would be a problem with flying-probe tester probe...

Roger

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins
Sent: Friday, March 09, 2007 10:40 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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