I'm using a large area of sticky tape, which holds these little devils so well you can also deconstruct and repair structures that would just fall apart. Careful modular construction prevents most of the problems anyway.
I spent quite a lot of time trying out various sticky surfaces. Double-sided tape is great as a working surface. It isnt too sticky, but it melts under the iron and tacks onto the LEDs making them sticky once soldered. The solder also tins it, which may or may not be useful.
I also tried Kapton, which was a dream compared to soldering on double-sided tape because it doesnt melt, and neither does the glue on it. However, the solder has a slight tendency to bead on the glue and leave edges on the wires but it doesnt actually tin it.
Last of all I tried metal tape. This is absolutely perfect, doesnt wrinkle or shrink even under abusive desoldering and the glue repels the solder in beads. I just layout a surface with double-sided tape and put a patch of ali tape inside it, glue upwards.
I took the cube apart so I could make it smaller after it occurred to me that the wire could also be used to line them up laterally.
So I made a guide, which worked really well. I just taped down the far ends and let the tape's glue hold it in place properly. Finally I added a patch of ali tape glue-down to rest my fingertips on while soldering under magnification. It doesnt stick that much, but it is enough to be annoying after a hundred times or more. ;-)
And finally, to form the wires properly I added a tiny jig the sits on the LEDs, lines them up correctly and provides a neat grid to run them over.
Simply bead and solder the top end, then press it into the grooves and remove the jig to solder the dips to the cathodes leaving clear loops over the anodes, which are all connected to the horizontals.
The above grid measures 9x8mm and is 2mm tall, making the completed device 9x8x8mm.
I am however running out of LEDs, they do not like being repeatedly heated and I have now got some dead ones, and one the contact stripped off. Any more problems from here on in, and I'll have dead pixels in the finished cube. However, I am witing on an order 0f 0402s to replicate this cube using double-sided LED banks so it is visible 360 degrees. Currently it is not visible from the back, as these LEDs are solid based.
The resulting room gained by using a device half the size will be lost by using two of them, and allowing a little more wiggle room for the wiring underneath, so the new version will be bicolour as well as 9x8x8mm.
The current cube is just Plexed, the LEDs go from anode to cathode in a grid. The new one will be Charlie-Plexed, which adds a new dimension to the code too. By switching the LEDs between red and blue using PWM, I can generate purple...