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added fall 2009 end of semester update
****Finding AMP6 using the PDF bookmarks shows the prototype amplifier layout that resolves mismatched footprint issues (indicated in green in the image farther up on this page).
****Finding AMP6 using the PDF bookmarks shows the prototype amplifier layout that resolves mismatched footprint issues (indicated in green in the image farther up on this page).
== Fall 2009, Mid-Semester Update ==
== Fall 2009 Work ==
=== Mid-Semester Update, 11/12/2009 ===
We now have one fully working prototype of the SiPM Digital Control Board, and the SiPM Amplifier Board is currently being manufactured and assembled by Sierra Circuits, Inc. The backplane design is nearly complete and will be going out for quoting within a week.
We now have one fully working prototype of the SiPM Digital Control Board, and the SiPM Amplifier Board is currently being manufactured and assembled by Sierra Circuits, Inc. The backplane design is nearly complete and will be going out for quoting within a week.
*The SiPM amplifier (analog) board project will give an error message that it was unable to find "Test PCB.PcbDoc". Please ignore this. The file was intentionally omitted to prevent confusion, and is not related to the actual design.
*The SiPM amplifier (analog) board project will give an error message that it was unable to find "Test PCB.PcbDoc". Please ignore this. The file was intentionally omitted to prevent confusion, and is not related to the actual design.
*The backplane project will give an error message that it was unable to find "Backplane_New.PcbDoc". Please ignore this. The file was intentionally omitted to prevent confusion, and is not related to the actual design.
*The backplane project will give an error message that it was unable to find "Backplane_New.PcbDoc". Please ignore this. The file was intentionally omitted to prevent confusion, and is not related to the actual design.
=== End of Semester Update ===
This semester, a lot of progress has been made on the tagger electronics. The digital control board is now onto revision 2.0, the amplifier board is in production, and the backplane is awaiting completion of the purchase order for production to begin. It is exciting to say that the bulk of the work is now finally complete. Remaining for the spring are the tasks of testing the amplifier board, and seeing that everything fits into the backplane. Here are some details about what I accomplished this semester, as well as links to the most recent project files.
==== Digital Control Board ====
The semester began with the digital control board prototypes sitting on lab bench waiting to be tested. My job was primarily to design the boards, not to debug them, though I still played an integral part in the testing process. We were all relieved that none of the boards appeared to smoke immediately when we first applied power, though there were a few confusing problems that had to be sorted out. Most of these problems are described in detail on the [[Digital control board debugging notes]]
page. More or less, we had to solder a pin that wasn't connected, replace the crystal oscillator with a CMOS oscillator, and rewire few traces that had were accidentally connected to pins intended for other signals. I won't repeat all of the changes we made here since it would be redundant to the page that already discusses it, but the important part is that we have one board that is fully operational, and the version 2.0 schematics/layout reflecting all these changes are complete. I anticipate that production of the version 2.0 boards will occur at the beginning of the spring 2010 semester.
There is still one lingering problem with the digital board design that has not yet been resolved, however. Even after all of the version 2.0 changes were made to the version 1.0 boards, only one of the three boards produced actually functioned properly. For a reason unknown to us, two of the boards ended up with their digital to analog converters burning up and smoking. We thoroughly reviewed the schematics and the layout, and found nothing miswired. Furthermore, we analyzed the placement of the ball grid array DAC to the best of our ability, and determined that a misalignment of balls is not the cause of the failure. All of our power supplies are stable, properly decoupled, and grounded as called for by DAC's manufacturer. Currently, the best hypothesis for the failure of 2 of the 3 DACs is that one or more of the absolute maximum ratings must have been exceeded at some point during the assembly process. Analog Devices lists fairly specific specs with small tolerances relating to maximum temperature and the length of time which the DAC may spend inside a reflow oven. We have run into some difficultly trying to find out from the boards' assembler whether they followed the published specs for the assembly process, but we intend to keep trying until we get an answer.
==== Amplifier Board ====
Throughout the summer and the beginning of the fall semester, I completed the design for the SiPM Amplifier Board, version 1.0. All 30 channels have been implemented along with their summing circuits. As I mentioned in the mid semester update above, this board is being manufactured and assembled by Sierra Circuits, Inc. Some unexpected setbacks occurred in the assembly process that delayed the boards somewhat, but I believe everything is now on track for delivery of the finished product before the start of the spring semester. A number of problems relating to minimum quantities of parts, as well as part naming conventions have now been resolved, and the assembly process should be complete in several weeks.
==== Backplane ====
The backplane design, version 1.0, has also been completed. Sierra Circuits will be manufacturing the backplane, which we will assemble ourselves. The backplane is a particularly intersting PCB from a manufacturing standpoint, because it is designed to be completely light proof. Since the backplane is the only material standing between the whole of Hall D and the inside of the tagger microscope dark box, opacity of the board is particularly important.
Most PCBs with internal copper layers are already fairly opaque, because the copper blocks light from transmitting through the FR-4 and prepreg. Through hole components do not particulary compromise board opacity, because they are plugged with component pins and solder. What does have a greater affect on the opaqueness of a board, however, is the thermal reliefs by which through hole pins and vias connect to internal plane layers. These reliefs are designed to aid in the soldering process by minimizing the amount of copper that is directly connected to the plating in the hole. A typical relief consists of four 7-10 mil traces connecting the hole's plating to the internal plane. The plane itself remains about 20 mil away from the hole, to prevent conduction of heat during the soldering process. Unfortunately, this means that there is a small gap in which there is only FR-4 to stop light from passing through the board. Since FR-4 is transparent, this poses a problem for our design. We were able work with Sierra Circuits to come up with a board design that includes an internal layer of special black FR-4 to prevent light leakage through the heat reliefs. While this is certainly not a standard feature, Sierra was confident that they could implement it for us, and we look forward to testing the boards' opacity in the spring.