Flexible substrates are not a problem - the industrial solution is polyimide (Kapton) or just really thin FR4. The problem is inflexible components. As soon as you bend a curved surface attached to a small flat rectangle (IC), it pulls at the joins.
You might get better results with bare die+wirebonding, then encapsulating with slightly flexible epoxy. That would allow the bondwires to flex and take up the bending. Doesn't help with the discrete components or the battery.
You might get better results with bare die+wirebonding, then encapsulating with slightly flexible epoxy. That would allow the bondwires to flex and take up the bending. Doesn't help with the discrete components or the battery.