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Platform forum

NotSoFast , 01-06-2025, 11:11 AM

So, I'm trying to do this project on 2 layers. And Im already violating the 'as few ground plan tracks as possible' rule of thumb.
The SPI bus for the flash here will be running at 8MHz.
Opinions on the degree of routing on the bottom plane?

QDrives , 01-06-2025, 04:49 PM

Placing the components is the most important step. Good placement will reduce signal crossing.
The pitch of the bottom package is so big, that a trace might fit between the pads.
With both these, you may be able to completely eliminate the need for the bottom layer.

NotSoFast , 01-06-2025, 05:52 PM

And what is the consensus on routing a signal beneath the IC itself? I googled around and just wasn’t sure if it would be appropriate for any of the pic signals to go underneath the ic

NotSoFast , 01-06-2025, 05:53 PM

And routing in between the pads also wasn’t something I was sure about. But as long as I meet the tolerances that’s considered OK?

QDrives , 01-06-2025, 09:26 PM

What kind of IC is it that the traces going beneath it would cause a 'malfunction'?
"Tolerance" is not so much the right word. Fabricators have specifications as to the minimum track width and spacing for a given copper thickness.
If that allows you to route between the pads and it is ok to route below the component, than go ahead a route between the pads.

NotSoFast , 01-07-2025, 12:06 AM

In this case it’s just a flash device. I wasn’t sure if routing a spi line at 8mhz underneath it would cause interference if some sort. Maybe that’s a non issue.

QDrives , 01-07-2025, 12:28 AM

Are you sure that it is the right package?

NotSoFast , 01-07-2025, 01:28 AM

Uh oh… I was sure until you asked that question. I’ll have to review the footprint tomorrow. Doesn’t look that glaringly off?

QDrives , 01-07-2025, 03:34 AM

Few components have a 1.27mm pitch. Ones that come to mind are opto-couplers.

NotSoFast , 01-07-2025, 10:36 PM

Confirmed! Hopefully.

Robert Feranec , 01-08-2025, 08:00 AM

is not easier to route it if the tracks would go under the flash? by going under, you will re-order the routing

NotSoFast , 01-08-2025, 10:36 AM

It definitely would have been easier. I just didn't know if that was a valid way to route or not.

NotSoFast , 01-08-2025, 10:36 AM

It sounds like the consensus is that it is valid to route underneath the IC...

Robert Feranec , 01-08-2025, 11:55 AM

yes, you can route tracks under chips

NotSoFast , 01-08-2025, 01:21 PM

Great news. Thank for the tip.