Are RoHS compatible PCBs also halogen-free?
No, not necessarily. The RoHS directive prohibits two bromided flame retardants, PBB (polybromided biphenyls) and PBDE (polybromided diphenyl ethers). What is normally used in PCBs is a bromided flame retardant called TBBP-A (Tetrabromobisphenol A).
Do the RoHS or WEEE directives require the PCB to be marked?
No, but for practical reasons PCBs that have lead-free HASL should be clearly marked stating their RoHS compatibility due to the risk of confusion with leaded HASL.