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| felix_ | getting some sleep was a good idea... routing the fpga and its decoupling capacitors is quite doable; managed to squeeze nearly all required capacitors beneath the fpga without needing some special pcb manufacturing process | 14:06 |
|---|---|---|
| se6astian | excellent! | 14:12 |
| felix_ | when this board is ready and tested, doing a high speed hdmi board shouldn't be much effort | 14:12 |
| se6astian | is 0402 instead of 0201 parts doable? | 14:13 |
| felix_ | routing the 3rd and 4th gtp pair will be annoying, but still seems to be possible | 14:13 |
| felix_ | uh | 14:13 |
| felix_ | some capacitors could be changed from 0201 to 0402, but definitely not all | 14:13 |
| felix_ | the capacitors on the vcco rails can basically all be replaced with the bigger ones. for vccaux and vccint the bigger size would be a bit of a problem; for the gtp ones both size and increased indictivity would be a problem | 14:19 |
| felix_ | so should i use 0402 parts where it's possible and leave the rest 0201 or should i try to minimize the number of different parts used? | 14:21 |
| felix_ | (i usually tend to optimize for the latter) | 14:22 |
| Bertl | I think both is fine, the idea behind se6astian's question was to avoid 0201 completely, which is probably not doable at all | 14:24 |
| Bertl | so don't worry too much about 0402 vs 0201, both are fine | 14:25 |
| felix_ | ok | 14:25 |
| felix_ | i wonder why xilinx recommends 100n capacitors for the gtps when there are 470n ones available in the same package; with todays mlcc capacitors the main part of the indictivity come from the package | 14:26 |
| Bertl | didn't you say xilinx recommends 470n yesterday? | 14:27 |
| felix_ | xilinx recommends 470n for the non-gtp rails | 14:28 |
| se6astian | for assembly with our pick and place machine 0402 is doable, 0201 probably isnt | 14:28 |
| Bertl | ah, I see, well 100n (from the construction) will be better at higher frequences | 14:28 |
| Bertl | (less layers) | 14:28 |
| se6astian | so if there is space and if it doesnt make routing harder 0201 -> 0402 | 14:29 |
| felix_ | in the same package it shouldn't make that much difference, butsince i don't really have the tools to simulate the frequency behaviour of the whole system, i just go with the recommendations | 14:29 |
| felix_ | ok, will do. have only placed and not routed most of the capacitors, so changing the package isn't much hassle | 14:30 |
| felix_ | can't get rid of all 0201 packages though | 14:31 |
| se6astian | thats ok | 14:33 |
| felix_ | what's the biggest package i can put on the bottom side? 0201 and 0402 probably won't be a problem, but would 0603 still be ok? | 14:34 |
| felix_ | all bigger capacitors can be easily put on the top side | 14:35 |
| Bertl | I think it is more a question of height than package size | 14:36 |
| felix_ | hm, is height the problem and not how heavy the parts are per area that they are soldered onto? | 14:37 |
| felix_ | i wonder what will still work reliably with your soldering process | 14:38 |
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| felix_ | i reduced the number of 0201 parts on the opposite side of the fpga to 5 | 22:15 |
| Bertl_oO | great! | 22:20 |
| felix_ | haven't looked at the capacitor placement near the sdi chips and the clocking chip, but i probably don't need that many 0201 parts there too | 22:20 |
| * Kjetil was handsoldering 0402 today.. It's small enough allready :P | 22:21 | |
| felix_ | was a really good idea not to use the fpga package with 0.8mm pitch... ;) | 22:21 |
| Kjetil | heh | 22:22 |
| Bertl_oO | well, you definitely want to have a stereo microscope for 0201 or smaller, but with that it's not really hard to do | 22:27 |
| Bertl_oO | 0402 is a piece of cake with the right equippment | 22:27 |
| felix_ | especially when using solder paste and stencil | 22:35 |
| felix_ | soldering 0201 by hand is rather meh, but with stencil and paste it's ok | 22:35 |
| felix_ | sure, a machine can do that better than me, but still ;P | 22:36 |
| Bertl_oO | usually it can't | 22:36 |
| Bertl_oO | all the PnP machines I saw so far had way worse quality than what I solder by hand ... sure, they are usually faster than I am :) | 22:37 |
| Bertl_oO | so faster? yes, definitely! better? I doubt it. | 22:38 |
| felix_ | ok. i only saw the product in the end and not right after it was placed and not yet soldered | 22:52 |
| * felix_ prefers to outsource that sort of stuff | 22:52 | |
| felix_ | the fpga and the capacitors http://i.imgur.com/2IS2RTu.png mostly unrouted, but all placed | 22:57 |
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