HDI Dielectric / Prepreg
A thin prepreg layer is the most common HDI substrate. It provides good reliability, process-ability and reasonable cost.
Typical thickness of prepreg HDI layer is 60u +/-20u. Typical laser hole diameter (drilled top) is 100 - 150u.
Another option is RCCu (Resin coated copper foil) which is used in applications that require extremely good drop test performance. Aspocomp has process capability for halogen-free RCCu and stock of 50,60 and 75u RCCu. Please check case by case the availability of RCCu.