A Default CDF VME Board Geometry

1. Murphy, S. Truitt

This document describes a standard VME board geometry for use in Mentor Graphics. The board geometry is found in /nfs/voyager/l2/parts/RELparts/geometries/pcb_geoms/boards and is called cdf_vme_board. A picture of this board geometry, along with a description of its features follows.

The board geometry has five items that are pre-placed. This means that as long as you use the proper LMS geometries and assign a pre-determined reference value, the part will automatically be placed in the proper location on the board. The five parts are the VME P1, P0 and P2 connectors, and the two discharge strips that go along the top and bottom edge of the board. A list of the released geometry names and required reference values follows.

Other features that are included on the board are the holes for the board stiffener, tooling holes for contract assembly of through-hole parts, global fiducials for contract assembly of fine-pitch surface mount parts, and holes for mounting the front panel.

The board stiffener is a long piece of metal that is screwed to the board at seven locations along the top of the VME connectors (see attachment). This holds the edge of the board that plugs into the crate rigid, to reduce the risk of bending pins on the backplane connectors. Four of the seven screws that hold the board stiffener in place use holes already on the board. The two screw holes for P1 and the two screw holes for P2 are used for the stiffener. There are three additional holes that need to be on the board. There are two just above P3 and one at the bottom inside corner of P3. There are placement and routing keep outs around these three holes. The keep out for the screw heads (the screws are inserted from the back of the board) are on Signal layer 8. If you have a different number of signal layers, you will need to move this keep out to your bottom routing layer.

The tooling holes for through-hole assembly are .125 diameter drill holes located in the top left and bottom right corners of the board. These drill holes have a power keep out and a large placement keep out surrounding them. You can place surface mount components and via holes within the placement keep out. If you are not having your board contract assembled, or if you are but you are not having them install any through hole parts, you can delete this feature entirely.

There are six global fiducials on the top and bottom of the board, along with placement and routing keep outs. These are used by vision alignment systems when placing fine pitch surface mount components. There are three of these fiducials on each side of the board, in the top left, bottom left, and top right of the board. The actual fiducials are nothing more than pads added to the top and bottom layer of the board. If your board is not being contract assembled (or only one side is) you can delete the corresponding fiducials.

The holes for the mounting of the front panel are along the top left edge and bottom left edge of the board. They are the drill holes closest to the front edge. These holes have a power keep out and are required in order to attach a front panel.