AFAIK, it used to be that parts binning was used to sort parts by tolerance. So the 5% bin wouldn't include <1% parts because those were already selected into the 1% bin in the factory and so on. Is it still like this?
Mostly, no. Nobody except for expensive precision resistor companies are actually measuring resistors more than statistically.
The resistors are manufactured so that they are "guaranteed by manufacturing" such that the outliers are 1%, 5%, 10%, etc. And they do statistical checks on batches, but not really looking for the 10% outlier (which is stupendously rare and very difficult to catch) but looking for slight drifts off nominal (which are much easier to spot) which would result in more outliers than expected.
As such, if you measure resistors, you tend to find that you get really close to nominal--much closer than you would expect for 10%, say. Resistors are so cheap that binning simply doesn't make economic sense.
Is this how LEDs are binned as well, or are they powering each node on the wafer before packaging? They're orders of magnitude more expensive than resistors, so I figure they might...
There are all kinds of crazy parameter variations in optoelectronics. I understand that resistors are really close to nominal because the manufacturer's ability to tune the process controls are so much better than the standard 5% and 10% bins, but it seems that LED manufacturing is way more difficult and they can't always tune the process to get exactly what they want.
I saw a video from the WS2812 factory and from what I remember all of the LEDs were tested individually on the die before assembly. I don’t know if that’s typical but those are pretty cheap for what they are.
They should still bin, so that each individual resistor gets the highest price possible by the virtue of its classification, even if the binning is costly.
Not if the additional cost is more than the additional revenue.
Let's assume that without binning you get 20% over cost of manufacturing. If it costs 5% more to bin-check all resistors, and you wind up selling 1% of them for an additional 100% mark-up:
No bin Bin
Cost to mfg: $ 1.00 $ 1.00
Cost to bin: .05
------ ------
Total cost $ 1.00 $ 1.05
Base price $ 1.20 $ 1.188 (99% sold at base)
Premium price 0.00 $ 0.022 (1% sold at un-binned cost x 2.2)
------ ------
Total revenue $ 1.20 $ 1.21
====== ======
Profit $ 0.20 $ 0.16
It depends on the component and the company/process. Laser trim time for thin film is a significant cost-driver, so if possible you want to aim for a specific value and reject or bin-sort the rest out. My company only makes 1% tolerance resistors by laser trimming.
you can't always bin a ±5% resistor as a ±1% resistor if its value tests within ±1%, because, as i understand it, a ±1% resistor often needs to be ±1% over its temperature range, working voltage range, and lifetime, so it has to be made differently than a ±5% resistor
if your temperature range is -40° to 85° and your resistance is +0.9% off nominal when measured at 22°, your temperature coefficient of resistance would need to be under +16 ppm/° to ensure that it was still below 1% even at 85°. a more typical tcr for ±5% thick-film resistors is +250ppm/° (see, e.g., https://www.vishay.com/docs/51058/d2to35.pdf) and so there is no hope of binning such a resistor as a 1% one
aging is another source of component value error that can prevent binning (the component value drifts over time, usually proportional to the square root of its age), and some kinds of resistors also have a significant voltage coefficient of resistance (mostly semiconductor types like carbon-film and the antediluvian carbon composition)
these phenomena sometimes lead designers to use expensive tight-tolerance resistors (±0.01% nowadays, 50¢–250¢ each) even in circuits that can easily be calibrated to handle component value error, just to keep the calibration from going off due to temperature or aging and to improve linearity
disclaimer: i'm not an electrical engineer, i just play one in ngspice
The resistors are manufactured so that they are "guaranteed by manufacturing" such that the outliers are 1%, 5%, 10%, etc. And they do statistical checks on batches, but not really looking for the 10% outlier (which is stupendously rare and very difficult to catch) but looking for slight drifts off nominal (which are much easier to spot) which would result in more outliers than expected.
As such, if you measure resistors, you tend to find that you get really close to nominal--much closer than you would expect for 10%, say. Resistors are so cheap that binning simply doesn't make economic sense.