Storm Circuits made a lot of HDI PCBs this year. we have good capability now.
Here is an example for HDI 2+N+2 quick turn in 10 days.
PCB Spec:FR4,TG170 .Shengyi S1000-2 material,
Copper thickness 1OZ, min hole 0.1mm, min trace/space 0.1/0.1mm
finish the PCB in 10 days.