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
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