I've not been very interested in designing cases for most of the stuff I sell in the Tindie store. But I think the GPSDO really ought to have something.

Dave Jones made a video once showing off extruded aluminum cases. He also had the great idea of making front and back panel bezels out of PCBs. I've combined both of those pieces of advice and now am aiming to go with an extruded aluminum case with a PCB front and back panel.

By making the panels out of PCBs, not only do I get to design them with CAD software I already know well and use, but I can do all sorts of drilling and even milling of odd size holes as well as silkscreened text. Lastly, I can leverage the copper plating to either make pretty designs when combined with the solder mask or for shielding.

The tricky part of the operation is lining everything up, going only from the various design drawings.

The first step is to redesign the board to fit in the case properly. For extruded cases, the width of the PCB is critical. Moreover, the PCB will fit inside a pair of channels on opposite sides of the extrusion, so there's going to be a "keepout" area inside of which you should not run any traces or place any parts. The risk of anything other than groundplane being inside those channels is that if the soldermask is abraded when inserting or removing the board, you could easily create an intermittent short. In addition, if you have an existing design (as I did), you need to move parts that are intended to poke out of the chassis to the two "short" ends of the board. In this case, the LEDs and their light pipes needed to move to the front bezel from their former position on the side.

The next step is designing the replacement bezel PCBs. That begins with creating the correct outline, which you can simply copy from the design drawing of the case.

After that, the next critical part of the design is establishing a line on the bezel that represents the top surface of the board when everything is put together. If you're going to attempt to allow parts on the board to poke out of the bezel, then the placement of this line will be critical to getting it right. The best way to proceed with that is to measure from the center. This is because the bezel sits in a plastic channel of sorts and that means measuring from the edge won't work.

In EAGLE, the best way is to make a vertical center line of 0 with on the tDocu layer, and another horizontal line representing the top of the PCB.

In my case, I have to make 3 holes for LED light pipes, three "double-D" shaped holes for panel mount BNC connectors, a "single-D" (with a flat spot) hole for the SMA antenna connector and a hole positioned so that it's directly adjacent to the board-mounted power jack. The odd shaped holes are relatively easy to design with the arc and line tool. Make the outline with a 16 mil line in the Dimension layer and the fab will route the hole out.

Another trick is to use the two copper layers as shielding. To make this work, make a polygon covering the whole board and then copy it, moving the second to the bottom layer. Drop a via somewhere on the board and set it to the same name as the two groundplanes. That will electrically connect the two. I put some polygons on the back of the board surrounding the connector holes. This will expose the copper to the back of the connectors, bonding them to the shielding. I also added a ring around the two screw holes on the front, so that the screws will (at least ostensibly) bond the front surface to the extruded aluminum. Since the connectors all have grounded bodies, the result will be that the whole enclosure is grounded except for the three small holes for the light pipes and the hole in the back for power.

As I write this, I haven't ordered all of these boards yet. I'm waiting for the enclosure to arrive in the mail tomorrow. I've printed paper copies of the layout and will trim them out with an XActo knife and test fit them. I've already verified the spacing between the BNC jacks and the spacing of the light pipes that way.