According to an article in Design News sister publication Electronics Weekly, adjustments to comply with RoHS is causing problems with some components. Certain types of devices housed in plastic packages were originally designed for safe exposure to temperatures that 30 to 40 degrees (C) lower than the 260 degrees (C) considered to be the benchmark for lead-free processes.
The higher temperatures can cause plastic bodied devices to deform, melt or burn, so changes in mold compounds may be required to bolster heat resistance. More robust and resilient compounds are often more expensive than the standard temperature versions they are replacing.
For certain sizes and formats of liquid electrolyte capacitors, compliance to RoHS creates some particularly serious challenges. Because of their construction, these devices sometimes require more characterization and changes to their construction than other types of components.
Another issue is that RoHS compliance has pushed the obsolescence of many older parts. This is especially true for certain ICs, and also for capacitors and other passives.