Substrate for a two-terminal device

A substrate 602 for a two-terminal electronic device e.g. optoelectronic device. The substrate comprises at least one series of grooves, each groove 604 comprising a groove base 650 at a first depth and first and second opposing groove faces extending between a proximal end and a distal end. The substrate also comprises at least one channel 606 comprising first and second opposing channel faces, spaced apart by a channel width at a second depth, and a channel base 654 at a third depth. The channel transects at least one series of grooves. The third depth is greater than the first depth, and the third depth is determined by the channel width and a coating angle relative to an axis normal to the groove base. A shim for embossing a surface of a UV (ultra-violet) curable coating to form a substrate for a two-terminal electronic device is also disclosed.