Hi,

Just some ideas:

If the bare boards were tested I assume any missing plating would result in
open vias and test failures. Were they bare board tested?

Take a few boards and heat the heck out of them with a hand iron and SAC305
solder. How long does it take to dissolve out the copper? Is that number
anywhere close to your process time? Perhaps you have some holes with only
electrodes-less copper and the though holes were never plated up correctly.

Bob K. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tom Burek
Sent: Wednesday, July 27, 2011 7:57 PM
To: [log in to unmask]
Subject: [TN] Missing PTH Barrels in Connector

Hello,
I have a PCA that hand solders 6 connector pins to an 4 layer PCB assembly.
The finish on the PCB is Lead Free HASL (SN100CL) and the solder used to
hand solder the pins is SAC305.  The hand soldering is performed as a
secondary assembly operation after reflow.
What happens to some of the assemblies, but not all of them, is that the
solder will wick straight up the pin, thereby not allowing a Solder joint. 
 The pin can be pulled right out of the hole, revealing a PTH with no inner
barrel.
Completely wiped out as if it was never there in the first place.  This
phenomenon is not present on every PCB or every pin of the same connector. 
 The PCB's are part of a multi-board panel.

As far as I know the PCB started out with a barrel, but I cannot rely on
this being the case as I do not believe the technician checks 100% of the
PTH's prior to inserting the pin. 

Am I looking at excessive heat causing complete Copper Dissolution of the
PTH barrel? 
or
A PCB that may not have a barrel in every hole, part of the PCB fabrication
process?
or
Any other suggestion as to which direction to head would be appreciated.

Thanks in advance.
 

Tom Burek, CID+



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