How do part manufacturers process deal with component tolerances? - Page 1
Forum section: electronics / projects

author: MoighonFweeman
author_rank: Contributor
timestamp: March 17, 2015, 09:10:35 pm
content: This is something I'm a bit curious about, and since I don't know anything about what exactly goes on in the chinese companies where everything in the world is made, I thought I'd ask.Sorry if the thread subject isn't clear. Allow me to elaborate.Say we have a hypothetical manufacturer. They sell 5% and 1% tolerance resistors. What if this manufacturer were to simply manufacture 5% resistors, and then test all the resistors that came off the line, and then sell the ones within 1% tolerance as such, and then sell the remainder as 5% tolerance?Because if that were the case, even if a consumer were to purchase a ridiculous amount of 5% tolerance resistors from said manufacturer, absolutely none of those resistors would be within 1% tolerance. None.So does this kind of thing happen? Would it even be beneficial for a manufacturing plant to do this? Obviously resistors are (literally) a dime a dozen to manufacture, but perhaps with other, more difficult-to-manufacture components...Once again, just curious.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 17, 2015, 09:30:23 pm
content: Perhaps a couple of possible reasons, but the most likely is that, if you're going to the trouble of measuring all your resistors, you're adding a constant cost to both your 5% and 1% products. The 5% are needlessly made more expensive. Maybe you sell them at a loss and mark up the 1% more to compensate, but the fact remains, the total has risen.Whereas, as far as I know -- the machines which make resistors are laser trim systems, which do measure the resistor as it's being trimmed, but, trimming takes time, and precision especially so (go slowly, use a weaker or tighter beam, etc.). To generate different tolerances, you simply crank the dial "faster" or "slower". Now your 5% (or even 10%?) parts are insanely cheap, just as they should be; and your 1% parts are made only with a modest increase in cost, and no additional measurement step or binning process.Tim

author: wraper
author_rank: Unknown
timestamp: March 17, 2015, 09:31:27 pm
content: If some binning occurs, less graded parts can easily be within better grade specifications. If there are too many of best grade parts, manufacturer will simply bin better parts to crappier grade. It is driven not by how many of the best grade parts can be made but how much demand there is for specific grade.

author: amyk
author_rank: Super Contributor
timestamp: March 18, 2015, 01:08:42 am
content: Dave has done a video on this:http://www.eevblog.com/2011/11/08/eevblog-215-gaussian-resistors/

author: cosmicray
author_rank: Frequent Contributor
timestamp: March 18, 2015, 01:11:46 am
content: When I have measured a few hundred resistors coming off a reel marked 5%, the majority of them seem to be within the +/- 2% area. I assumed that the manufacturing process was one that caused the values to distribute in a bell curve (i.e. there will be a few outliers, but they will still be within the 5% range). This may be highly dependent on the manufacturer tho.

author: free_electron
author_rank: Super Contributor
timestamp: March 18, 2015, 05:04:13 pm
content: resistors are made for 2%. if it turns otu better it ends up being 1% , if it turns out worse it ends up being 5%production processes are so controlled they can make 2% parts with high yield

author: georges80
author_rank: Frequent Contributor
timestamp: March 18, 2015, 06:54:01 pm
content: Binning has been going on for a long time, it is a byproduct of making 'real world' components. There is a spread due to manufacturing process. The manufacturers aim for a sweet spot for the production run and then bin as needed based on market requirements, .e.g. speed, tolerance are the simple ones. Things like LEDs have colour temperature, forward voltage, lumens/watt etc etc.Binning for speed is common place - hence the top end processor speeds are the most expensive due to a) they can charge what the market will pay and b) the quantity of ou=tperformers is relatively small versus the peak of the bell curve.This is nothing to do with components being made in China etc, it's just the way engineering deals for production runs with yield/performance variations of the various key parameters that sell the product.cheers,george.

author: calexanian
author_rank: Super Contributor
timestamp: March 18, 2015, 07:57:31 pm
content: Dont forget that time is a factor as well. In some components characteristics change over time. that % tolerance is over the expected life of the part during normal usage. A 5% 100k resistor may be spot on 100K when you buy it. After years of use and thermo cycling and what have you of normal abuse you should expect that part to not have drifted more than 5% over that time. Generally speaking with metal film and even carbon film resistors they are better than spec and are pretty stable these days.

author: SeanB
author_rank: Super Contributor
timestamp: March 18, 2015, 08:07:28 pm
content: I have some NOS carbon composition resistors that have all aged up with time. Some are still barely within the 5% tolerance range, but most are between 5 and 10% up in value. Pretty good though for resistors that originally were made as a rod with pressed in leads that then were coated in wax impregnated powder. I even have some 5R resistors that only have a green band, so they are 20% resistors. I used them as 8R dummy loads for 0.5W work.

author: calexanian
author_rank: Super Contributor
timestamp: March 20, 2015, 02:36:59 am
content: Quote from: SeanB on March 18, 2015, 08:07:28 pmBake them to drive off the moisture and they will change. many companies would heat the boards, then coat them with wax to keep the moisture from getting back in and making things noisy.