Is there any limitations to adding stiffeners on a flex pcb? I am making a flex PCB and I want to know if you can or cannot add a stiffener adjacent to the layer (in my case the back layer) that has copper (ie needs to be free of copper or any vias)? I imagine the answer would be no since stiffeners are usually just added after the fact and glued on?

 

Not really, the main thing though is picking the correct thickness of the flex and the thickness and type of the stiffener. That will come into play when you're assembling your product especially if space is constrained. Some companies prefer metallic vs FR4 (completely up to you though) but in either case I don't see a problem with it. If you're using conductive adhesive though, then yes you may have a problem especially if the copper underneath is not masked.

Now, if you're saying you want to add stiffener to both the top and bottom side, that would be a bit more tough. This is more of a DFM conversation with your flex vendor to see if they're able to do it. I know a few that you can talk to get an idea.

 

Sounds feasible....I asked my vendor and he just sent me back a note saying "just make sure your drawings match your intent".

Thanks!