My first prototype has been made without soldering jig. It works, but looking from a close range you can see the component does not have a perfect alignment.
For now, I tested the following material:
-Marble is not that good. Even with a good polish, solder then to stick to it.
-PTFE (teflon). I could not find some 0.5 or 1mm teflon sheet, so I tested with PTFE thread seal tape wrapped on some 2mm aluminum bar. It works: teflon stick a little bit to solder, but is easy to remove with tweezers. But my 2mm aluminum bar does not have sharp enough corners. Since the components are so thin (0.5mm for the resistors I bought, leds are even thinner) I would need a really sharp corner with thin ptfe tape to get a really good result. Anyway it is working.
-I've been given some 1mm polyimid (kapton) sheet. That seems to work fine but kapton is so slippery... I need to find something to hold the parts of the jigs in place. High temperature glass glue would be fine but mine is too old and I don't want to buy tome more. I could make holes and use 2x2mm metal cylinders to fix the sheets, but polyimid sheets are not easy to buy and I may try to find something else for this tutorial. I ordered adhesive polyimid tape to give it a try.
-Microscope slides can be a good alternative to marble (1"x2"x glass), I'll try to buy some next time I go near a lab supply shop.
-Wood is not that bad, but you have to find a particular piece of wood that will not wrap when put in oven at 280°C for one minute.