> Exists precision resistors with accuracy +-0.5%, or even 0.1%, but high precision applications, typically used some very different technologies. For example, are high quality multi-turn variable resistors, laser cut resistivity pads, created with high cost materials or even rare-earth materials.
Most modern resistors are of either a thin-film type, with sub-micron-thin layers of nickel directly sputtered and onto a ceramic body, or a thick-film type, with a metal oxide/ceramic paste applied and baked onto the ceramic body.
The process window is aimed at a target, but binning operations after production are all that separate precision resistors from cheap resistors.
If you sputter on a little too much nickel, or your paste isn't quite as conductive after baking as you hoped, you just sell that one as a 10% or 5% resistor.
If you get lucky, and produce one that is within 0.01% of an E96 resistor (which might even happen while aiming for an E12 resistance!), you sell it as a precision unit.
Agreed that these aren't that important in most modern designs.
> binning operations after production are all that separate precision resistors from cheap resistors
Absolutely, no.
Cheap resistors not only have low precision of marking. They also suffered from many other issues.
Examples of cheap resistors issues: they have large temperature coefficient; they change resistance permanently on overheat and when under high voltage; they aged fast and this mean, their resistance permanently change; they usually have large parasite inductance and also they usually have coil structure, and under high voltage happen leak between turns.
High voltage, in this case, mean just about 100Volts.
A single measurement does not a 0.01% resistor make. When you want that kind of tolerance, drift and aging properties are hugely important and the resistor is not going to be constructed the same way as your bog standard $5/reel 1% resistors.
Most modern resistors are of either a thin-film type, with sub-micron-thin layers of nickel directly sputtered and onto a ceramic body, or a thick-film type, with a metal oxide/ceramic paste applied and baked onto the ceramic body.
The process window is aimed at a target, but binning operations after production are all that separate precision resistors from cheap resistors.
If you sputter on a little too much nickel, or your paste isn't quite as conductive after baking as you hoped, you just sell that one as a 10% or 5% resistor.
If you get lucky, and produce one that is within 0.01% of an E96 resistor (which might even happen while aiming for an E12 resistance!), you sell it as a precision unit.
Agreed that these aren't that important in most modern designs.