Manufacturing Process of Resistor - Page 1
Forum section: electronics / general

author: onemilimeter
author_rank: Frequent Contributor
timestamp: February 21, 2011, 05:05:05 pm
content: Resistors are graded with different tolerance, e.g. 10%, 5%, 1%, 0.1%, 0.01%, etc. Do you think resistors with different tolerances are manufactured with different processes? Or, all resistors are manufactured using the same process and they're sorted to be in different tolerance classes.

author: Zero999
author_rank: Super Contributor
timestamp: February 21, 2011, 05:36:43 pm
content: Good question.I know that carbon film resistors only come in 5% tolerance or worse because they're inherently exhibit poor drift and stability characteristics so there's no point in making them any better.At the low end, i.e. 1% and 0.1% probably not, there's just better process control on the narrower tolerances but the really good resistors probably use different processes entirely and are binned. It also wouldn't surprise me if some manufactures sell 1% resistors as 5% so they can shift more stock.

author: Unknown
author_rank: Unknown
timestamp: February 21, 2011, 06:46:51 pm
content: Quote from: Hero999 on February 21, 2011, 05:36:43 pmMore accurate resistors often also have a lower tempco and drift, so I doubt that it's just binning.Quote from: Hero999 on February 21, 2011, 05:36:43 pmSome chinese vendors also sell 5% resitors as 1%.

author: onemilimeter
author_rank: Frequent Contributor
timestamp: February 21, 2011, 08:30:44 pm
content: Quote from: alm on February 21, 2011, 06:46:51 pmDigikey also did that... as shown by Dave in one of his videos.

author: onemilimeter
author_rank: Frequent Contributor
timestamp: February 21, 2011, 08:32:30 pm
content: Is it really matter to have resistors with very low tolerance (e.g. 0.1% or 0.01%) in circuit design? For example, in designing a differential amplifier...

author: Neilm
author_rank: Super Contributor
timestamp: February 21, 2011, 08:35:21 pm
content: Manufacturers of some of the lower tolerance resistors will laser trim the resistor. This is particularly noticable on precisiion high power thick film resistors.Neil

author: Simon
author_rank: Unknown
timestamp: February 21, 2011, 09:02:43 pm
content: Quote from: onemilimeter on February 21, 2011, 08:32:30 pmit depends on what your doing and the acuracy you want. If your playing with audio you will be happy with 5% usually. If your making some test equipment or some other precision circuitry you will want as low as you can afford and unfortunately no money can buy 0%

author: allanw
author_rank: Frequent Contributor
timestamp: February 21, 2011, 09:10:29 pm
content: In differential amplifiers you'll want both halves of the circuit to match up as best as possible to maximize the differential gain, so better tolerance resistors are obviously better. However at a certain point other errors will have a bigger effect. You could put your circuit in a SPICE simulator and play around with tolerances to see what effect it'll have.

author: tecman
author_rank: Frequent Contributor
timestamp: February 21, 2011, 09:17:00 pm
content: Most resistors are graded after they are made. Some manufacturers only do a sample check of each batch as a check on tolerance bands.As stated, carbon film are generally restricted to 5%. Better than that is the realm of metal film. By keeping the deposition process under tight control, the tolerance band can be predicted to a tight value. Thus the batch sample testing is statistically significant and is most often used.Laser trimming is generally the realm of less than 0.1% and although a fully automated process, it adds significantly to the cost (relatively speaking).paul

author: Zero999
author_rank: Super Contributor
timestamp: February 21, 2011, 09:21:20 pm
content: Quote from: Simon on February 21, 2011, 09:02:43 pmIt depends on the part of the amplifier. For example if it's an op-amp pre-amplifier with a gain of around 20 it doesn't matter but if it's part of a bridged amplifier it might be more critical to minimise the DC in the speaker coil, which is bad.Also be careful as lots of cheap and nasty 5% resistors are noisy carbon film which is bad, unless you're building a valve amplifier lol.

author: Simon
author_rank: Unknown
timestamp: February 21, 2011, 09:22:18 pm
content: Yea, these days I aim for 1 or 2% resistor by default

author: onemilimeter
author_rank: Frequent Contributor
timestamp: February 22, 2011, 12:14:59 am
content: Quote from: allanw on February 21, 2011, 09:10:29 pmI read this as well somewhere. Is there a way to get around this design issue without the need of "tight tolerance" matching resistors?

author: Simon
author_rank: Unknown
timestamp: February 22, 2011, 06:30:10 am
content: not really, say you use 5% resistors, you have two gain feedback loops and usually they are matched, say on one feedback loop you have a resistor that is +5% and the other is -5%, that's a 10% drift in your desired value, now suppose it works out that one branch goes +10% and the other -10%, you now have a gain different in the circuit of 20% from the intended value. It's up to you wether that is acceptable or not.

author: Unknown
author_rank: Unknown
timestamp: February 22, 2011, 06:32:55 am
content: Quote from: onemilimeter on February 22, 2011, 12:14:59 amSure, just lower the CMRR requirements. The tolerances for matching are proportional to the CMRR.

author: Zad
author_rank: Super Contributor
timestamp: February 22, 2011, 05:43:45 pm
content: I am designing some test gear at the moment, for the majority of components absolute tolerance isn't vital but I have been quite surprised how cheap 1% resistors are. If I go for 0603 (urgh, I hate anything below 0805) then they are generally between 1.1 and 2.3p (£0.011-£0.023) each for quite obscure E192 values. It is amazing how many inaccuracies you can calibrate out with some smart software.1% seems to be the "new" 5%. Having said that, I did some spot checks on (new, big brand name) 5% and 10% components the other day, and the majority were better than 1% tolerance, which might imply that they weren't tolerance binned.

author: onemilimeter
author_rank: Frequent Contributor
timestamp: April 06, 2011, 01:38:31 am
content: Resistor sorting machinehttp://www.electrosort.com/chip_resistor_sorter.htm

author: AdShea
author_rank: Contributor
timestamp: April 06, 2011, 03:01:54 am
content: If you go for the really high precision (and yes, sometimes you do need it) they laser trim each one and have fancy parallel paths on the film.http://www.vishaypg.com/docs/63113/z201.pdfWe're using some of these in my lab because they're about the highest precision and absolutely the best stability you can get without building it yourself or buying crazy one-off equipment.

author: onemilimeter
author_rank: Frequent Contributor
timestamp: April 06, 2011, 08:35:06 am
content: Quote from: AdShea on April 06, 2011, 03:01:54 amThanks. By the way, how much does this high precision resistor cost you?

author: AdShea
author_rank: Contributor
timestamp: April 06, 2011, 05:05:05 pm
content: It's about 20USD each on digikey.