Resistor Binning and Unusual Distributions Explained


I read about a little quirk related to binning resistors in a comment on this recent question.

Some manufacturers will sell, for example, 1% and 5% resistors that are really made in the same batch. When the resistors are being sorted by value, the more accurate ones are put into a 1% category and sold for a slightly higher price, and the less accurate ones are sold as 5% resistors.

This method of sorting guarantees that 5% resistors running through this process will never be within 1% of their nominal value. In other words, a 1 k\$\Omega\$ +/- 5% resistor would have a resistance in the range [950, 990] or [1010, 1050] – but never [990, 1010].

Does this actually happen? I guess that the parts are still what you're paying for, but it seems really odd that a 5% resistor would have 0 probability of being within 1% tolerance.

Best Answer

The point is that it might happen.

The right way to look at this issue is to never assume anything about the distribution of error within the specified tolerance band. Always assume the distribution will be the most inconvenient for your design, because you don't know that it isn't.

Speculating on how something behaves beyond the tolerance specified in the datasheet is pointless and will only get you in trouble.