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| Critique my first PCB |
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| carl0s:
Hi. I'm looking for opinions or advice on my PCB layout. It's simply an adapter for the STM32L4R9I-DISCOVERY board to allow me to use a large round Panasys MIPI LCD display. It is to go in place of the supplied MB1314 AMOLED smartwatch daughterboard. So it has a backlight LED driver, basically following the datasheet circuit diagram, and then just tracks between the connectors. Both clock and DSI are high speed differentials. Annoyingly the P/N of the differential pairs always seemed to need to cross over each other! On the big connector they are side by side, but as the LCD panel's connector is double row, they are opposite each other instead! Things I thought about: * I could have made use of the bottom layer for more than just one big ground fill. That could have made it much easier to route the tracks. I was trying to keep it simple though and wasn't sure if that was a good or bad idea. * Number of vias to the ground layer.. too many? not enough? I suppose once I have one in my hand I will have a better idea of size and where I could have gone bigger or smaller. I will do a print out as well. I started with the ST schematics, just so I could get the big Samtec connector. That's why it still has their logo on it, and is named 'copy of mb1314' :-) Here's a PDF: http://www.internetsomething.com/lcd/pcb/PDF.pdf The rest (gerbers etc) can be downloaded from this directory: http://www.internetsomething.com/lcd/pcb/ and here's 3D pictures: Any obvious total fails? Other suggestions? |
| ataradov:
1. It is probably better to have some of the traces go on the bottom layer rather than have them snake around between the pins of the connector like this. 2. Purely aesthetic: I'd use only 45 degree traces. 3. Pour solid ground on the top layer as well. And more ground stitching can't hurt. Especially close to those ground pins next to the differential lines |
| carl0s:
--- Quote from: ataradov on May 19, 2018, 06:43:44 pm ---1. It is probably better to have some of the traces go on the bottom layer rather than have them snake around between the pins of the connector like this. 2. Purely aesthetic: I'd use only 45 degree traces. 3. Pour solid ground on the top layer as well. And more ground stitching can't hurt. Especially close to those ground pins next to the differential lines --- End quote --- Thanks. I have to admit, it was a lot harder than I expected. I started along merrily and then one track would be unroutable and I'd have to un-do it all and move components. One minute the LCD socket was below and the next it was above. Turning the backlight driver chip around multiple times, etc. I suppose I just thought that routing on both layers would be too much for me to try to deal with for my first time. Plus I was battling with not knowing how to use the program (Altium) that I borrowed. I think I might want to look at KiCad or Allegro as I have found a few things frustrating (length tuning being awkward, moving objects with tracks connected, erm, highlighted/unhighlighted toggle not actually reflecting what's on screen.. ). |
| ataradov:
Sometimes it is easier to go back and redo the whole board with your new knowledge after you've struggled though the first one. I would try to route all differential signals on one layer and actually keep the traces parallel for as long as possible. Then route remaining pins that can be routed cleanly on one side. A then move the rest on the other side. Right now there is not a whole lot of point in your length matching, for example. |
| carl0s:
--- Quote from: ataradov on May 19, 2018, 07:03:03 pm ---Sometimes it is easier to go back and redo the whole board with your new knowledge after you've struggled though the first one. I would try to route all differential signals on one layer and actually keep the traces parallel for as long as possible. Then route remaining pins that can be routed cleanly on one side. A then move the rest on the other side. Right now there is not a whole lot of point in your length matching, for example. --- End quote --- Hmm but the differential pairs are side by side on one connector, and top and bottom on the other. Unless I was to put the smaller LCD connector on sideways? How come there's not much point to the length matching? Is it not about time delay? |
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