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PCB design practices

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OM222O:
Hello
I have seen these 2 PCB design practices used extremely often!
1) A ton of vias on the edge of the PCB connecting 2 ground planes
2) Crosshatch ground plane instead of a solid one

you can clearly see them in dave's latest teardown video as well:
vias on the edge (and even in the antena lines!):


crosshatch ground plane:


I'm not sure what the purpose of these 2 practices are. I had a guess that vias protects the edges of the PCB so they won't come off easily in case of some damage or a bad cut on the PCB. (Apple products, especially macbooks use ridiculous amounts of vias on the board edges) most people say it's for better grounding but that wouldn't make a ton of sense as the edges are the furthest apart for any signal to travel to. If they wanted grounding, they would have placed a lot of vias all across the the plane, not just the edge! Also I read about the crosshatch planes and everyone seems to say they are "a thing of the past" and solid planes are better, although I haven't seen a single product from microsoft that uses a solid ground plane ... If you have any thoughts or a definite explanation as to why these methods are used, please share it down below.

station240:
The vias spread over areas is called "via stitching", very common when there are power/ground planes/traces on two sides.
Serves to electrically bond the two areas.

Rarer but still common is via stitching around edges/mounting holes, done for mechanical reasons. Prevents the PCB substrate (fibreglass) from being compressed.

Bud:
Via stiching is to improve grounding properties at RF frequencies and for shielding purposes as well as to reduce RF emissions from board edges.

asgard:
One other important practice applies to RF and microwave designs, especially around the antenna assemblies.  Because of VSWR it is important to reduce as much as possible the parasitic coupling of from high-speed signals.  One approach is understanding that if we treat such signals traces as planar waveguides then two things must happen.  The other layers on the board must not have any active signal or copper under the waveguide, while surrounding the trace with via-stitched ground planes on all the layers.  It also can help if we use star-layout techniques to limit signal interference within the ground plane adjacent to the waveguide. Here is a datasheet that recommends such things for a WiFi module that I have been looking at (Cypress AN-91445):

https://www.cypress.com/file/136236/download

OM222O:
I think the mechanical reasons that station240 brought up would make more sense as again, the vias are mainly on the edges, not a specific trace or area. Also a laptop such as a macbook isn't a WIFI/RF module (they have seperate wifi cards and whatnot). but I'm guessing it will help with grounding or shielding signals that are near the edge naturally which makes sense. what about the crosshatch ground planes though? any specific reason for those? They still seem to be really popular

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