Now let's see what kinds of ICs are being used:

Nordic nRF51422 low power RF SoC. Used for Bluetooth LE.

Cypress CY8C20767capacitive touch controller.

Maxim 14676B wearable charge management IC.

Assumed to be an ARM Cortex-M microcontroller. Freescale, the manufacturer, is no longer in business, as it was purchased by NXP recently - this makes it hard to look up the marking.

There are all kinds of test points visible on the back. Garmin must do a pretty thorough QA.

Looking side-on, you can see that the flex circuitry is sandwiched between two sets of rigid PCB.