Ken

In my past life experiences, I have found the following a successful sequence
to follow:
1.  Once layout design is complete, have a conversation with your fabricator
to discuss the quantity per panel they can produce versus the quantity YOU
want to see in the array structure for assembly. (If possible, before the
final dimensions are locked in, have this discussion with fabricator to
adjust individual board size to maximize panel usage, maybe an 1/8th inch
smaller perimeter would produce one more array per panel.)
2.  If you specify a certain quantity in the array (say 2 up) and you require
side rails for handling, the discussion should focus on "does this maximize
panel usage at the fabricator?"
3.  I have generally sent the one up Gerber to the fabricator, and asked for
suggestions to maximize array needs vs panel efficiency.  The fab house might
suggest smaller side rails, 3 up array instead of 2, of other options to get
more per panel.
4. The quantity per fab house panel will be dependent on the panel size they
use in their processing.  Your ultimate goal is to have an array produced
that meets YOUR needs for assembly, but also maximizes the panel efficiency
during board fab.
5.  If you source the fabrication from multiple vendors, you MAY have to
execute this process again IF the panel size to be processed is different,
resulting in a different panel efficiency (translation = $)
6.  Finally, once the array formatting has been decided, negotiate with the
fabrication house to prepare the ARRAY file to send to your stencil
fabricator to insure an exact match to the arrays to be produced.  ( I have
had difficulty in the past with sending the 1-up Gerber to the stencil house
and asking them to step the pattern into an array I THOUGHT I was getting,
only to find out there were small dimensional discrepancies resulting in an
unusable stencil because it didn't match the array.)  Most stencil
fabricators can turn the stencil quick enough to deliver it while the boards
are being fabricated.

The secret to success is COMMUNICATION - between layout designer, assembly
processing requirements, board fabricator, and stencil fab house.  The
assembly process considerations should carry the most weight.

my two cents worth....  hope it helps

Regards,

Pat Kane
Contamination Studies Laboratories

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
##############################################################