Today’s electronics continue to get smaller in size but with increasing design complexity. More and more, PCB designers are using rigid-flex printed circuit boards to carry-out these high complexity design requirements.

Rigid-flex printed circuit board
When working on the rigid-flex PCB Layer stack-up, an essential factor to consider is the stresses that flex board experiences due to bends and curves of the PCB.

So, use these 4 tips to help you create a stack-up for a robust rigid-flex PCB:

1. Proper anchoring – you need to ensure that vias don’t fatigue or peel as a result of repeated use. So, use a minimum diameter of 10 mils for vias that are in the flex portion. And, to obtain a wide via anchoring to the polyimide surface, increase the overall diameter by another 10 mils.

2. Enhance structural integrity – route traces to the via using teardrops, which expand the copper so that we end up with a more structural connection to the via itself. You’re reinforcing that copper area, again to minimize fatigue and potential cracking over time.

3. Keep the distance – when placing a via in a rigid section, keep it a minimum of 50 mils away from the edges of the flex board. The reason for this is that you can get instability in the materials right at that very edge where there is a transition. The 50 mil gap ensures better material reliability after completion of the drilling process.

4. Blind & buried vias – keeping the flex portion free of blind & buried vias will avoid manufacturing issues and improve signal integrity.

Rigid flex-rigid PCBs can add a considerable amount of functionality, flexibility, and overall packaging reduction to a PCB design and the right PCB stack up will advance you toward an optimized design.