alextie
Newbie
![Newbie level 4](/styles/images/ranks/blevel1.gif)
Hello everyone,
This is my first Raspberry Pi project where I had to face HDMI layout guidelines, so my question is, if anyone has issues with my design (I would call myself quite a PCB design beginner anyway). As you can see, the HDMI connector is mounted onto the same layer as the RPi CM3, so if I want to avoid crossing 8 traces on 8 layers, I have to wrap around traces to connect from the other side of the contacts. I‘ve recently learned about matching signal lengths, therefor 3/5 and 8/10 rules for chamfers and avoided 90° degree angles when doing so. I took into account the minimum spaces between the differential pairs and a short and continuous return current path on the GND layer (I plan to do them even shorter by milling the orange vias to GND in the picture). My suspected problems though:
-Is there any chance, that my meandering trace matching pattern works as an antenna? Because it looks just like one (I don‘t think so, because for a maximum HDMI clock rate of 165 MHz it would need an antenna with a length of about 1,8m, right?).
-Some online guideline said something about 7,8mm clerance to surrounding traces and parts, so what about the 5V trace, the LEDs and my screen interface?
-I want to avoid buried and blind vias. So there are some vias which I have to guide from top to bottom layer just between the differential pairs. Any issues with that?
-I somewhere read, that whenever line-to-line-spacing changes, there will be unwanted impedance changes as well. When you look onto the red lined box, over a quite great distance this spacing changes unsymmetrically and skew. Any problems with that?
-Does the general rule count, the wider the trace, the better? Traces are 0,2mm and vias 0,3mm and quite big compared to other projects. Any negative effects on impedance as well?
-I'm stitching through the GND layer twice per trace, any issues with that?
A lot of questions, but it will gain a lot of knowledge for me if answered. Thanks in advance!
Regards, Alex
This is my first Raspberry Pi project where I had to face HDMI layout guidelines, so my question is, if anyone has issues with my design (I would call myself quite a PCB design beginner anyway). As you can see, the HDMI connector is mounted onto the same layer as the RPi CM3, so if I want to avoid crossing 8 traces on 8 layers, I have to wrap around traces to connect from the other side of the contacts. I‘ve recently learned about matching signal lengths, therefor 3/5 and 8/10 rules for chamfers and avoided 90° degree angles when doing so. I took into account the minimum spaces between the differential pairs and a short and continuous return current path on the GND layer (I plan to do them even shorter by milling the orange vias to GND in the picture). My suspected problems though:
-Is there any chance, that my meandering trace matching pattern works as an antenna? Because it looks just like one (I don‘t think so, because for a maximum HDMI clock rate of 165 MHz it would need an antenna with a length of about 1,8m, right?).
-Some online guideline said something about 7,8mm clerance to surrounding traces and parts, so what about the 5V trace, the LEDs and my screen interface?
-I want to avoid buried and blind vias. So there are some vias which I have to guide from top to bottom layer just between the differential pairs. Any issues with that?
-I somewhere read, that whenever line-to-line-spacing changes, there will be unwanted impedance changes as well. When you look onto the red lined box, over a quite great distance this spacing changes unsymmetrically and skew. Any problems with that?
-Does the general rule count, the wider the trace, the better? Traces are 0,2mm and vias 0,3mm and quite big compared to other projects. Any negative effects on impedance as well?
-I'm stitching through the GND layer twice per trace, any issues with that?
A lot of questions, but it will gain a lot of knowledge for me if answered. Thanks in advance!
Regards, Alex