Extended Data Fig. 6: Assembly of back-mounted devices.

a, Cover the BM module and probe with PI shadow mask with contact pads exposed. RIE process removes the parylene coatings on contact pads, allowing future electrical connections among these components. b, Solder the probe on soft interconnection traces (left). Verify the electrical connections by powering the µ-ILED with multimeter (right). c, Solder the soft interconnection traces on the BM module to complete the assembly. d, Encapsulate the solder joints with epoxy. The joints include the back side of the probe’s flag (top left), top side of the ends of soft serpentine traces (bottom left), top side of the probe’s flag (top right) and back side of the ends of soft serpentine traces (bottom right). e, Use a sharp tweezer to dip Ecoflex droplets on the top side of serpentine traces followed by thermal curing. Then dip PDMS droplets on top side of the BM module and back side of probes (the side with the tungsten stiffeners) followed by thermal curing. f, Similar dip coating process with PDMS droplets is applied at the back side of the BM device including the back side of the electronic module and the front side of the probes (with µ-ILEDs). Scale bar, 5 mm.