Where do I start?  Does anyone know of any good sources for obtaining
information on the pro's and con's of different vent patterns and of how to
apply them?  Does such info exist other than in the minds of process
engineers?

We generally apply a staggered dot vent pattern to all open areas of the
panel.  We are currently manufacturing a 0.040 8 layer board using 0.005
core, utilizing the following layup

 TOP - Component Side     ----------
                                       ///////   .005 Core H/H
  LAY_2 - Signal              ----------
                                       \\\\\\\\   2x106 prepreg
  LAY_3 - Signal              ----------
                                       ///////   .005 Core H/1
  LAY_4 - Plane               ----------
                                       \\\\\\\\   2x106 prepreg
  LAY_5 - Plane               ----------
                                       ///////   .005 Core 1/H
  LAY_6 - Signal              ----------
                                       \\\\\\\\   2x106 prepreg
  LAY_7 - Signal              ----------
                                       ///////   .005 Core H/H
  BOT - Solder Side        ----------

Cap construction (as opposed to foil lamination) used for this build because
of blind vias between layer 7 and 8.

We were seeing some irregular movement after pressing to which we attributed
to resin flow.  On some technical advice from our laminate supplier we
removed a good majority of the vent pattern retaining only what amounted to
approx .75" wide border around the panel with similar .75 band splitting the
panel horizontally and a .5" band splitting the panel vertically.  The panel
is 18x24 so the vent pattern basically splits the panel into quadrants, each
quadrant containing a 1.7x2.6 memory board.  I know this is difficult to do
without graphics (darn listservers!).

What we saw after pressing these panels was an improvement in the movement
in that we now had a more symmetrical movement about the center of the
panels but a significant increase in panel warpage (no real warpage issues
when using our conventional vent pattern placement).  We pressed one book
with 5 panels and saw some panels warp about the x-axis, some about the
y-axis, one was reasonably flat.

I would appreciate any insight into the general usage of vent patterns and
the pros and cons of the t=different pattern styles, ie dots vs starburst.
I would also be interested in opening a dialogue with any knowledgeable
individuals specifically relating to our problems with this particular
board.

Regards
John Parsons



---------------------------------------------------
Technet Mail List provided as a free 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/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------