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ZaMoRaK , 08-13-2025, 01:36 PM

Hello everyone, I am currently workng on a MPU based custom board. For prototyping/development purposes, I would like to add a breakaway section which will have SDCard and USB connectors for embedded development. Once the development is completed, the breakaway section will be removed. I am planning on using Tab Routing. My concern is that once the breakaway section is removed, there could be short-circuits on the remaining parts of the board. There will be traces(USB2.0, SDIO) routed on the breaking point. Since I also need a reference plane below those traces, breaking from that point could cause additional stress(Since I will have to break the copper plane on the breaking point as well) on the main board. What are the general guidelines to follow during the process? How can I successfully seperate two boards with minimum negative effects?

QDrives , 08-13-2025, 02:25 PM

You would need to saw them apart, otherwise the stresses on the copper might cause a lot of damage further in the board.
The copper will be exposed to the atmosphere so this will probably cause problems on the long run (like moisture getting into the board.)

ZaMoRaK , 08-18-2025, 10:15 AM

Hello @QDrives, thanks a lot for the response. In the STM32 Nucleo board, they do have a breakaway section onj which they implement the onboard STLINK structure. The breakaway section does have traces on it and there doesn't seem to be a problem after breaking that part. Considering that they made vast amount of sales on Nucleo boards, wouldn't many users face the moisture problem you explained above?

QDrives , 08-18-2025, 01:03 PM

No, because the vast amount of users do not break the Nucleo boards apart.
And if they do, they know it is just a development board.
None of the (3) Nucleo boards I have, have a break-away debugger.

Mini , 08-18-2025, 03:13 PM

Maybe you mean discovery board? All nucleo boards have break away option to my knowledge. At least every of mine have it and I have a lot of nucleos.

QDrives , 08-18-2025, 04:05 PM

**My** boards look like depicted here: https://www.st.com/en/evaluation-tools/nucleo-h753zi.html
**Not** like depicted here: https://www.st.com/en/evaluation-tools/nucleo-h743zi.html

Mini , 08-18-2025, 04:36 PM

Oh yeah, I forgot they have some Nucleo-144 which are like that.

QDrives , 08-18-2025, 06:11 PM

Not just the 144 pins, this 64 pins(?) too https://www.st.com/en/evaluation-tools/nucleo-c071rb.html

But yes, all my Nucleo boards are newer than the ones with the break-away section.
Perhaps that too is the answer to your question - there were problems with it.

Mini , 08-18-2025, 06:41 PM

To be honest I have one similar on desk as well. Yeah newer ones seems to be solid. But not all for some reason. I have also nucleo-C031C6 on desk and that is break away version. So I guess they use both versions.