Assembly and Removal of a ROD onto/from a Hub Module ------------------------------------------------------ Original Rev. 30-Oct-2019 Current Rev. 8-Nov-2019 This note is a description of installing a ROD onto a Hub Module and a short description of removing a ROD from a Hub Module. Installing ROD onto Hub: ------------------------ Keeping in mind all of the mechanical and electrical safety issues for the cards I have used the following procedure to install the ROD onto a Hub: - Make a final visual inspection of both cards especially the areas that will not be visible once they are mated. - Remove the FPGA Heat Sink from the ROD. The standoffs that hold the Heat Sink must remain on the ROD. - Verify that the screws going into these standoffs are tight from the bottom side of the ROD because there is no access to them once the cards are mated. - Mount the MiniPODs on the ROD and install their mounting screws from the bottom side of the ROD. I have always air hosed out both the board and MiniPOD MegArray connectors before installing the MiniPOD onto a board. It is probably best not to install the ROD Fiber Optic Ribbon Cable at this time. - The above steps have the ROD ready to install. With its FPGA Heat Sink removed the force to mate the big 400 pin MegArray connectors can be placed directly onto the ROD's MegArray connectors from the top side of the ROD. Thus there will be no bending of the ROD or significant forces in its FPGA BGA connections or other components. - The issue now is to support the Hub directly under its big MegArray connectors so that there is no force put into the Hub circuit board that will bend it or crush any of the small components on the bottom side of the Hub. - To support the Hub I have placed two stiff box-board platens directly under the Hub's MegArray connectors. These box-board platens are slightly larger than the foot print area of the MegArray connectors. I have just taped them in place with thin Scotch tape. The intent is that these box-board platens are soft enough to absorb any small irregularities in the Hub pcb and thus provide a uniform supporting force directly under its Hub MegArray connectors. These box-board platens were in the plastic sack along with the platens to use with the arbor press. - To keep these platens from sinking into the somewhat elastic anti-static mat I have placed in aluminum plate under them. This plate was also in the sack with the other platens. This plate is about 1" larger in both dimensions than the area taken up by the two box-board platens under the MegArray connectors. I also hold this aluminum plate in place with Scotch tape. - The thickness of the plate was picked so that the bottom of the bottom side components on the Hub was just slightly above the anti-static mat, so that no force is placed on these components when the ROD and Hub are pressed together. The intent is that all upward force that supports the Hub is placed directly under its two big MegArray connectors. - Once everything is set I have only then removed the MegArray connector Dust Caps, air hosed out these connectors, and then pressed the ROD and Hub together "rolling" the connectors together length wise as described in the MegArray documentation. All compression force is directly above and under these MegArray connectors. - The ROD and Hub are held together with M3 hardware: screws, nuts, washers, and nylon spacers (4mm). At least one of these spacers must be in its approximate position before the cards are mated or you can not get it in place. You can look at one of the Hub-ROD pairs to see which spacer needs to be in place first and how the hardware is put on. I try to make sure that all of this hardware is reasonably well tightened up as we do not want anything falling off with the cards in operation. - Washers are used under the screw head and under the nut to prevent them from cutting into the Hub or ROD pcbs. The 4mm spacer is made of nylon for the same consideration. I do not know how much relief is used on the ROD around its holes for these mounting screws so the intent is to be careful not to risk cutting into the pcbs. On the Hub the copper pads and tunnel for these mounting screw holes is tied to its internal ground planes. On the ROD this copper is floating. Thus these mounting screws do not provide a ground connection between the cards. - Re-install the ROD's FPGA Heat Sink. In the RODs that I installed I found the top of their FPGA and Heat Sink bonding surfaces to be dirty and needed to clean them to get a good thermal connection. Ed uses an elastic TIM material for thermal bonding on the ROD. - Record the serial numbers of the ROD-Hub that have been attached. ROD Remove/Install: -------------------- Remove ROD from Hub: I have never removed a ROD from a Hub. I would contact Ed to discuss this. It sounds like a good topic for a quick video meeting with Ed vs a long email. Besides the mechanical and electrical safety issues for the cards I think that there are 2 other general guidelines: - If the force to separate these connectors can be placed close to the connectors then it will minimizes how much area of the cards is subjected to a bending moment. - From the MegArray connector documentation (on the Hub web site) they suggest "pealing" the connectors apart length wise - i.e. not trying to separate them starting along their broadside edge.