Ted,
I ended up creating a separate panel layout drawing whereby I dimensioned
the overall panel, vertical distance between boards, horizontal distance to
inside rail, and maximum incursion into the board outline from the drilled
low stress mousebite breakaway tab hole pattern. I located and dimensioned
the tabs. Then I went back to the design and double checked to make sure
the tab locations would not impinge upon any circuit pattern features.
I put a note that panel tooling holes were to be located and sized at shop
option. One shop might use 3 0.140 holes 0.200 in from each edge and one
corner with no tooling hole, another shop might use 4 0.156 holes 0.250 in
from each edge on every corner, etc.
I'm leaving the fiducial locations to shop option as well for the same
reasons as above.
This is a long thin board which requires hand soldering of metal endcaps on
both ends, so I left considerable room on the ends of the boards for that
gang-soldering secondary op. The board is 0.093 thick, and we scored the
prototypes, but that did not work well, so we chose to route and tab the
production boards.
Thanks for the input!
Gary
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Ted
Tontis
Sent: Wednesday, August 23, 2006 3:18 PM
To: [log in to unmask]
Subject: Re: [DC] Breakaway tab specification
Gary,
Communication with the assembly house is crucial when designing
assembly panels, they are a valuable resource use them. That being said
communication with your assembly house throughout the design process is
key in reducing your time to market.
Here are some of the things I look at when designing an assembly
panel. Just remember that if you change your assembly panel you will
have to order a new stencil. If you need to use an electroform stencils
or need two stencils it can get pretty expensive.
1. Connectors/components hanging over the edge of the board must have a
large enough rail to accommodate the assembly equipment being used. Also
you want to route under all components hanging over the edge. This will
help keep the rail from making contact with the component when the
boards are removed.
2. The assembly rails must have fids. Check with your assembly house
they may have default fid sizes that the screen printer is set at and
have preferred fid locations.
3. Talk to the assembly house to find the optimal directions the boards
should be placed. Ideally you would like to be able to take the assembly
panel right to wave without having to use a solder pallet. (If the
boards are in the correct orientation they can minimize solder bridging
in the wave.)
4. When designing assembly panels remember the force needed to insert TH
components. Some components that have positive locking pins can require
a lot of force to insert them. This not only can break the assembly rail
but can flex the assembly panel. BGAS, fine pitch solder joints can and
will fracture if the panel is too large for the force needed to insert
the connectors.
5. Add a note to the manufacturing/ assembly panel drawing "The use of
dots to copper balance the assembly rails is strictly prohibited" Your
assembly house will thank you for that one.
6. V-Score note V-Score Top and Bottom (leaving .5mm (.020) web of
material). I would send you the drawings but they would just get removed
from the ipc mail server.
7. Typical routed with mouse bites (Route is 2.4mm(.093)wide, 5mm(.193)+
router bit, web, 1.27mm(.050)pitch for the mouse bites, 4 holes
.9mm(.036)+/- .08mm(.003)non-plated holes.)
>From my experience if a board is square v-score is the least expensive
and most reliable way to go, next would be routed tab with v-score. This
gives the assembly a nice clean look with the added benefit of not
having to file the edges down, last would be routed with mouse bites.
Good Luck in your design
Ted T.
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