Standard flex PCBs bend but don't stretch. This wearable application needed electronics that can elongate with body movement without cracking traces.
The Solution
Rigid component islands connected by serpentine copper traces on a stretchable substrate. The serpentine geometry acts like a spring: as the substrate stretches, the traces unfold rather than strain. FEA modeling optimizes the balance between stretchability and overall size. Component islands are stiffened with FR4 backing to protect solder joints from flex stress.
Results
Survives 30% elongation over thousands of stretch cycles with no trace failures.
How it stretches without cracking
The traces unfold instead of straining. Components sit on stiffened islands where the solder joints never flex, and the serpentine copper between them behaves like a spring, with the geometry set by FEA to balance stretch against size.Stretch against size. A straight trace takes the full elongation of the substrate and passes the fatigue limit of copper within a few percent. A serpentine turns most of the stretch into bending, and the taller the meander the less strain reaches the copper, but the more board length every connection uses. The FEA work found the smallest amplitude that keeps the peak strain under the limit at 30%.
Have a Similar Challenge?
Stretchable PCB design with FEA validation is part of the practice.
