I have a project I'm working on that is so tightly packed that I'm totally out of room. I could save the whole thing by slapping a bunch of surface mount LEDs (30 of them) on the back of a (non-surface mount) 28-pin ceramic package in my circuit and wiring them to the device's pins.
I've tried a few things without success, like gluing the LEDs in place and running very fine wire to the solder points on the surface mount LEDs and soldering them in place. The solder breaks down the glue (crazy glue almost works, but one way or another, the solder won't bond to the top of the contacts on the LEDs.)
I have copper tape that I've tried X-Acto-ing traces out of, but the soldering iron breaks down the adhesive and the whole assembly disconnects itself.
I've even tried conductive glue and conductive pens. They have such hit-or-miss impedance properties that the LEDs don't light evenly. One will be many times the brightness of another.
If I could afford the space, I'd just slap a PCB on there and call it good, but I really need the LEDs right on the back of the IC. I can fill in with epoxy after the fact to keep everything protected and in place.