In the past, we have experienced the same phenomenon.  As Ramon pointed out, capillary action will cause the coating to seep through the via and into connectors and other "keep-outs" causing rework or scrap at a late stage of assembly.  We often use a peelable solder mask to avoid this (where we can't demand solder filled holes).  As with all solutions, this causes new problems.  It requires a step to put it on and one to take it off after coating and a time allow the stuff to harden after application before coating.

George

-----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

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
 at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------