UV-sensitive negative photoresist with 50µm resolution?

[mavey]

Hello,

I'd like to pick your brains regarding your experience with super-fine detail etching using a negative photoresist.

I built a laser positioning system with a 405nm UV-blue (Blu-ray) laser head for automated direct printing of PCB (i.e. not etching/milling). The laser exposes the UV-sensitive layer after which the PCB is etched as per usual. The PCBs I use in this process are standard FR4 with thinner Cu plating (18µm, i.e. ½ oz), but I'm having a real difficulty finding a reasonably priced photoresist capable of such resolution. The etching process itself is not a problem since the thin plating in combination with a rapid etching technique allows for short enough times that almost all resists survive undamaged.

In my desperation, I've been coming up with even such exotic notions as dusting the PCB with a thin layer of fine laser toner and having it laser-melted onto the board. That one has yet to see the light of day, but it may illustrate how badly I need your collective expertise!

Thanks!