Domestic PCB process tracks closer than 10 mil in Rogers substrates

[alan.bain]

My "domestic" PCB process cannot cope with parallel track spacings of less than 10 thou.  It is mainly intended for Rogers PTFE substrates as for FR4 JLCPCB or equivalent is easier (and makes nicer looking boards).  I'd like to improve it.  The back is always a groundplane.

Process is
o) Drill vias 0.4mm by hand on high speed machine using the drill location plot
o) Conductive ink in vias
o) acid copper plate for 20min
o) Two laser printed negative mirror layers on 80gsm tracing paper lined up on light box (visible) and taped together
o) Dry film photoresist laminated onto board at 120C
o) UV exposure in the usual "Mega" box. Step wedge shows an exposure of 60s-90s for ideal density, but I find that the black of even two laser printed layers means this is too long and close tracks fuse. For fine detail maybe 15s plus a second exposure after development.
o) Sodium carbonate developer until uncovered copper clear
o) Second UV exposure (if development right, there will be no blue on the copper)
o) Ferric chloride etch in usual heated bubble tank (Mega) at around 45C
o) KOH strip

I suspect the limiting factor is the lack of a proper photoplot or rather the poor density blacks. But in thinking of fixing this it seems that it might be easier to plot directly on the film before lamination to the board.  I sort of want a "UV laser printer".  I'm sure I'm not the first one to want one of these....

Alan