Hi Bob,
I have a lot of experience with both approaches to arrays using v-score and
tabs.  As you point out, there are many variables but none insurmountable.
The first thing to consider is how to depanel the boards without
overstressing the circuit card assembly including solder connections and
components near the board periphery.  There is equipment and techniques
available that can depanel v-scored arrays and tabbed arrays.  Some
limitations may be present regarding the proximity of components to the edge
of the card while depanelling.  How heavy is the assembly fully populated?
The answer to this question may provide the answer to tabs or v-score.
V-score is typically less expensive than tabs, but I would definitely seek
inputs from your fabricator.
The other consideration that you mention is the use of rails on your array.
This is dependent on the equipment and processes that you employ, again with
respect to the distance from the card edge to components and their
pads/termination areas.  Rails may be required for clearance on tooling and
pallets, dependent on the placement/insertion equipment and if you have a
variable width chain conveyor on your reflow oven.
Fiducials should not be required on the panel in addition to fiducials
present on each board -- typically you have one pattern placement program
that you will step and repeat for population, unless you choose to populate
the entire panel as a single board, yet additional fiducials are not
required given your panel size.
Hope this helps.

Steve Sauer
Mfg Engineer
Xetron Corporation


-----Original Message-----
Subject: [TN] Panelized Boards


I have a 3.5" x 5.5", .063" thick board we will be building in somewhat high
quantities (3,000+/month). This size board is just on the edge as far as
having to put it into a basket to run through our in-line aqueous cleaner to
keep it from moving around. I do not want the operators to have to put this
many boards in baskets during production runs. So, my thoughts have turned
to panelizing these boards, perhaps in a 2x2 arrangement. This would go
through the cleaner with no problem. I do not have a lot of experience in
the best designs for panels. What are the advantages/disadvantages between
v-score and tabs? If using tabs, how many are required to maintain the
rigidity of the panel during reflow? Does there have to be a border around
the boards? Are fiducials required on the panel in addition to the fiducials
already on the individual boards? Any other issues I may have missed?

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