Row & Column Short When Closing Case – Need Insulation Advice!

[Zestfully4]

I have built a custom keyboard (not the designs, these are open-source) and have a problem with a row and a column shorting out, causing a switch to simulate a perpetual key_down event.

This is caused by screwing in the controlled to close the case. Upon my inspection it must be the row, not the column ribbon cable, maybe touching one of the switch pins of a switch on the row. The column (C3) and row (R2) that are shorting out are at completely other sides of the controller.

The controller must be inserted in a way that the ribbon cables are flush against the PCB in order to screw it in, and when it's not screwed it, the issue does not appear; just trying out various placements of the ribbons without any extra insulation did not work, and it's not future-proof.

See pics for a visual. The switch in question is C3R2 and I know this is a short because there is continuity between the row switch pin and cathode of the diode, which is column (these are marked in the picture). Here are the PCB files: https://github.com/Bastardkb/Skeletyl-PCB-plate/tree/main/flex/customs.pretty

I'm looking for your suggestions. I think of placing some insulating material between the PCB and the ribbon cables, perhaps taping insulation tape onto the cables and switch pins themselves, but are open to other suggestions!

 

[Tony Stewart]

Use Kapton Tape for now.

It seems twist and warp may exceed strength limits on some joints and maneuverability issues need to be wired out.

 

[ahsrabrifat]

Since the issue happens when screwing in the controller, it’s worth checking if any small exposed copper on the PCB is making unintended contact. A bit of tape or conformal coating on the PCB itself may also help.
Conformal coating is a protective non conductive dielectric layer that is applied onto the printed circuit board assembly to protect the electronic assembly from damage due to contamination, salt spray, moisture, fungus, dust and corrosion caused by harsh or extreme environments. It is usually used in products that are used in outdoor environments where heat and moisture are prevalent. Coating also prevents damage from rough handling, installation, reduction of mechanical and thermal stress. It also prolong the life of the product during its operation. For more info regarding this type of coating, you can see here: https://www.pcbway.com/project/share/Conformal_Coating_Of_Printed_Circuit_Board_Assembly.html