Good Morning Wee:
                                Some fluids can wick up a small orifice
easier than a larger one due to the capillary action. Water will climb
the walls of a thin glass tube but as the tube gets bigger in diameter,
gravity or the weight of the water will overcome the capillary action or
affinity between the water molecules and the glass. Some materials such
as Teflon (hydrophobic) do not allow this action to happen. The heavier
the fluid or more viscous the harder for it to climb the walls. So use
30 to 35 second Zhan cup #2 coating to initial coat the areas in
question, wait 15 minutes for the coating to skin and plug small
orifices, then coat as you normally do. To mask the sockets I found out
that ESD safe masking tape (paper) works better and easier to use
because that tape does not have memory (stays in whichever shape is
folded), do not bake after taping.
        Regards,
        Ramon
                  
         

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wee Mei
Sent: Sunday, July 10, 2005 7:46 PM
To: [log in to unmask]
Subject: [TN] Coating seepage through PTHs vias

Hello,

 I am trying to resolve the probelm of coating seepage into connector
sockets (forbidden). While most of the cases can be due to oversight,
there are observations that PTH vias directly beneath these connectors
actually allow the coating to seep through to the other side of the
board. I was wondering how via of 0.3mm can have such impact. From the
many observations, not always do we have coating seepage over due to
0.3mm via. I was wondering whether the coating volume concentrating at a
location especially with these vias around could be the most possible
cause. If not, what could be the likely causes.
Your expert advice would be greatly appreciated.

Thanks in advance and regards,
Wee Mei

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