Are these boards Immersion Tin? We had a similar problem with some Tin PCB's
where the Tin chemistry was being left behind in the tented vias and then
erupting during reflow. Check with PCB supplier.

Mark

===== Original Message from [log in to unmask] (TechNet E-Mail Forum) at
3/05/05 16:40
>Greetings Tech netters,
>
>
>
>            In the past we've had problems with tented vias not completely
>tenting and trapping liquid.  The liquid would boil and find its way to
>the surface of the board.
>
>
>
>While this looks similar these vias were not tented.
>
>
>
>
>
>http://www.texas-gold.org/PCB/
>
>
>
>Al Onderick
>
>National Instruments
>
>
>---------------------------------------------------
>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
>-----------------------------------------------------

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