Susan is right in that it takes a complete disconnect for an open to occur.
Voids are another issue from an open condition.  Like Susan I would suspect
the bare board or the component it self.  There was an article sometime last
year in one of the SMT magazine about which is better an open or a short.
It was interesting is the idea of which is better since we do not want
either.  It was based on controlling your processes.  Years ago I remember
discussion on voids in connection being not necessarily bad since if and
when a crack would start to occur it would propagate along the connection
until it found a void at which time it would stop.  A new crack would have
to then to start in lieu of the first crack going all the way.  More
critical with SMT joints and that is what lead to the discussion.  Never
heard whether this theory when anywhere and I guess that is why there is no
discussion in the specs or standards about this.  I believe Labs and other
organization studying solder joint strength, intermetalics, etc like NASA
has Xray solder joints for years and have found voids in through hole
connections. I believe this is true of connector cups studies.  Jim Raby of
Soldering Technology International could give you some great history on this
subject.  I know I went off in another direction but maybe some others can
add to this or dispute any of what I said.  Again voids inside the joint
should not cause an open unless complete discontinuity has occurred.  Jon

 -----Original Message-----
From:   Thomas Han [mailto:[log in to unmask]]
Sent:   Monday, October 16, 2000 4:49 PM
To:     [log in to unmask]
Subject:        [TN] voids in BGA

Hi all,  Customers are finding some opens in the PBGA(292 pin 1.27pitch)
that we installed for them.  X-ray shows good even reflow, but has some
small voids in some of the connections.  The gentleman that took the xray
for us tells me that the voids are caused by moisture in the paste, but
that shouldn't cause opens.  We are running an OA process, and the BGAs are
processed thru PnP and forced convection reflow.  I have increased the ramp
temp and that didn't seem to help.  The profile looks good with reflow of
about 55sec(time above 183C) with max temp at 225C.  The whole profile is
about 4.5min.

Any input is greatly appreciated.

Tom

----------------------------------------------------------------------------
-----
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF TECHNET
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
----------------------------------------------------------------------------
-----

---------------------------------------------------------------------------------
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF TECHNET
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------