Don't know much about Pb-free technology, but this refers to a more environmental friendly way of making and soldering ICs...
Rail-to-rail refers to either input, output or both capability of the opamp. Let's say you have a rail-to-rail output opamp and you power it at 5V and ground, then the opamp will be able to output a voltage near to 0 or 5V. Regular opamps can't get nearer than around 1.5-2V from the supply voltage.
Pb-free means the compositions of package material is prohibited to include
Pb.
Lead free means one type of package which is without foots out like a centipede.
search 'what is lead free' on google. i'm not sure about hebu's definition since lead means both foot and pb, i guess lead free refers to plumbum free.
Standard solder is a combination ot Tin and Lead. IC pins are coated with solder in order to make them easy to solder to the board. Lead is bad for the environment so the move is away from lead. When they say an IC is lead free, it means the solder on the pins doesn't contain lead. It is RoHS compliant.
toonafishy is right...The reason to use lead is because the
soldering temperature is lower. However, with ROHS
(lead free) compliance devices they will have to withstand
a higher temperature in the soldering process
search 'what is lead free' on google. i'm not sure about hebu's definition since lead means both foot and pb, i guess lead free refers to plumbum free.