Assembly of MiniPODs onto Hub Modules ----------------------------------------- Original Rev. 30-Oct-2019 Current Rev. 1-Nov-2019 This note covers the topics: gluing the Heat Sink onto the MiniPOD, installing the MiniPODs onto the Hub Module, installing the fiber optic ribbon cable Prizm connector into the MiniPOD, and routing the ribbon cables on the Hub Module. Gluing Heat Sink onto the MiniPOD: ---------------------------------- - The thermal epoxy that I have used for mounting the MiniPOD Heat Sinks (and other electronics assembly work) is Wakefield Part No 155 available from Newark as their Stock No. 00Z743. - This epoxy has a limited life once the tubes are opened. It has a pot life of only 2 or 3 minutes once mixed. It is very toxic to fish (and amphibians I think) and some what to people before it is cured. I have used it with gloves and in a fume hood. Mike or Reza can arrange for the proper disposal of any left over material. - Because of the limited pot life, in the beginning, I only assembled the Heat Sink onto one MiniPOD with each batch of epoxy that I mixed. Once I was practiced I could just do two MiniPODs with each epoxy batch and still be comfortable that the epoxy was making a good bond. - Before working to install the Heat Sink I've made sure that the MiniPOD's rubber Dust Cap is fully and tightly inserted. - To get the best possible epoxy bond to the metal body of the MiniPOD and to the anodized Heat Sink I have kept these parts as clean as possible (no finger prints) by wearing gloves. - For assembly I have buttered all surfaces of the MiniPOD body and Heat Sink that come into contact Except for the Heat Sink surface that wipes down over the ends of the rubber Dusk Cap on top of the MiniPOD. This un-buttered Heat Sink surface is still glued by the epoxy that it contacts on the MiniPOD body. The intent is to keep the rubber Dust Cap (and all of the area around the Prizm optical connector port on the MiniPOD) free of epoxy. - To push the MiniPOD and Heat Sink together I have used about 25 lbs for 10 or 15 seconds. Obviously one does not want to push on the MiniPOD's MegArray connector as that would damage the insides of the MiniPOD. I made a fixture to support the MiniPOD by just the perimeter of its metal body while I push down on the Heat Sink. - This thermal epoxy takes a good 24 hours to cure. Once it is cured I visually inspect the assembly, chip off any runs or loose blobs of epoxy, verify the the rubber Dust Cap is fully inserted, and then air hose off the assembly. Installing MiniPODs onto the Hub Module: ---------------------------------------- - After removing the 81 pin MegArray Dust Caps on both the MiniPOD and the Hub Module pcb, I air hose out these connectors to make sure that nothing is trapped in them during assembly. The intent is also to remove any dust/lint from the MiniPOD that may fall into its optical Prizm connector when the fiber optic ribbon cable is installed. - The metal alignment pin on the bottom of the MiniPOD and the two plastic keys in the MegArray connectors define the proper orientation of the MiniPOD to install it onto the Hub. The MiniPOD metal alignment pins are different for Transmitter and Receiver MiniPODs. - Insertion of the 81 pin MegArray connectors is rather straight forward. The low pin count makes the insertion force low enough so that with care you can feel for any miss-alignment of the connectors before pushing them together. - Insert the two screws from the bottom of the Hub pcb that hold the MiniPOD down on the pcb. These are M1.6 x 0.35 philips head machine screws that are selected to be as long as possible and still fit into the threaded part of the mounting holes in the metal body of the MiniPOD. Fully tighten these screws to minimize the chance that they will vibrate loose and fall out. Installing the Prizm Optical Connector into the MiniPOD and routing the Fiber Optic Ribbon Cables on the Hub: ------------------------------------------------------- - Installing the Prizm optical connector into the MiniPOD is described in the MiniPOD documents that we have on the web. A basic point is that this optical connection must be kept free of dust and dirt or else it will not work. This optical connection is supposed to be done in a clean room. - The Molex fiber optic ribbon pig-tail cables that are used on the Hub have a stiff plastic label on the ribbon that wraps around the ribbon multiple times and makes the ribbon very stiff in just the area where you need it to bend. I have very carefully removed this label and then cleaned any remaining adhesive from with ribbon with alcohol. It takes some minutes to carefully remove this label without stressing the ribbon cable. - Because folks may want to make a careful study of the light loss in the L1Calo fiber optic system I have kept the Test Sheets that come with all of the FO ribbon cables and written on them the Serial Number of the Hub on which the ribbon was installed, the MiniPOD (Tx or Rx) that the ribbon is connected to, and the date that the ribbon was installed. I currently have all of these Test Sheets for the Hubs and HTMs. I've passed to Philippe all of the Test Sheets for the 24 CMX cards. - With the MiniPOD as clean and dust free as possible, I remove the dust cap from the ribbon cable Prizm connector while holding and keeping the optical face of this connector pointing down to minimize the contamination that it picks up. Then I remove the rubber dust cap from the MiniPOD. The cable Prizm connector aligns via two pins with the MiniPOD and then snaps into place. Typically I snap the end of the Prizm connector where the cable exits into place first and then the length wise opposite end. - To fully and tightly re-install the MiniPODs rubber Dust Cap it is often necessary to manually push its multiple dust screens forward so that they fold into place while pushing the Dust Cap down into the MiniPOD optical opening. - The intent of the selected FO ribbon routing path on the Hub is to minimize the sharpness of the bends, minimize the blockage of cooling air flow, and hold the ribbon in place so that it does not vibrate. - The FO ribbons are held in notches in the Hub FPGA Heat Sink by two small spots of RTV. This is enough to hold them in place but still provides an easy way to remove these ribbons if necessary. Which ribbon is on top (Tx or RX) as they go though the FPGA Heat Sink notches is important and it must be correct or else the two ribbons will need to cross over each other at other points in their route. - The FO ribbons route between the large filter inductor and electrolytic capacitor for the 1.8V FanOut power bus. Again a spot or two of RTV can hold the ribbons in place at this location. - Before installing the ribbon MPO connectors into the backplane optical connector we snap an extraction handle onto the cable MPO connector. Without this extraction handle it takes a lot of digging to unplug the cable MPO connector from the backplane optical connector. - Where the ribbon MPO connectors plug into the backplane optical connectors the coil of ribbon can be trapped under the cable exiting the MPO to hold the coil in place. - Obviously the two FO ribbon cables on the Hub must be routed to the correct backplane optical connectors. - The correct routing of the Hub FO ribbon cables is shown in the following photo on the web: https://web.pa.msu.edu/hep/atlas/l1calo/hub/hardware/photos/Hub_Board/ file: 2019_Feb_20_Hub_SN09_with_ROD_SN04_top.jpg