How to buy electronics components in bulk  at the  lowest price? - Page 1
Forum section: electronics / general

author: ocset
author_rank: Super Contributor
timestamp: May 04, 2019, 08:52:44 pm
content: Supposing an electronics design/manufacture company has a portfolio of some ten light consumer electronics products which each sell in the 10’s of thousands each and every year.Now suppose that the products all contain some relatively common components like the following ceramic capacitors and resistors…..components to these specs are made by multiple manufacturers, and each one goes under the guise of multiple different part numbers…..Capacitor ceramic, 470nF, 50V, X7R, 0603Capacitor ceramic, 100pF, 50V, X7R, 0805Capacitor ceramic, 100nF, 630V, X7R, 1812Capacitor ceramic, 1nF , 250VAC, Y2 rated, 1812, X7RCapacitor ceramic, 10uF, 35V, X7R, 1210Capacitor ceramic, 1.5nF, 630V, X7R, 1210Resistor, 5k1, 1210, 1%, 0.33WResistor, 0R22, 2010, 1%, 0.75WNow, the company must source these components so that the PCB assemblers can populate the boards. The prices of all the above components are highly volatile, changing dramatically by the minute almost. So how does the company ensure that it always buys each of the above types of components at the cheapest price?......1…Must the company employ specific staff whose job it is to spend the whole day on electronics component websites and keep watching all components till the wanted ones fall cheap, then they buy them?2…..Or is it best for the company to simply employ a distributor to source the components at the cheapest price?...ie, give the distributor the BOM and let them do all the sourcing?3…..Or are there software programs which can be programmed to monitor the component internet sites and see when the components fall cheap, and then buy them at the required quantity automatically?….or else the software could send a message to someones phone to say that the components wanted have suddenly fallen cheap?4…Or don’t bother with any of the above?….and instead just have one part number for each of the above types, and just keep buying them and rely on the fact that on average, you’ll get a pretty good bargain?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 04, 2019, 11:03:20 pm
content: It must be either a very good design or a very bad design, to be able to use ANY capacitor that claims those ratings (if they be rated correctly at all).Namely that X7R has a severe loss of C under DC bias, which varies between parts.The standard responsible approach is to maintain a list of qualified vendors and parts, with sampling to ensure in-spec product is being delivered.The same process can be applied to bargain-basement Chinese suppliers but the qualifying and sampling process is onerous, probably full acceptance testing. Test the approval samples, test the first delivered production reel(s), continue testing at least samples from each reel in production thereafter.Even worse if you need all this done IN China. It's still absolutely possible -- most production is done this way -- but you need to create a structure of accountability (rewards for quality, punishments for failures), enforced with frequent inspections from your company, or on-site management. Sampled testing of finished articles (potentially as detailed as testing individual components removed from boards), in trusted (stateside?) facilities, should still be done.There is, of course, every option inbetween. You can engage a domestic CM with a Chinese factory and entrust sourcing and production to them. Test and approve the finished articles. It won't be as cheap as the full China experience but far more economical overall in those quantities.Tim

author: nctnico
author_rank: Super Contributor
timestamp: May 05, 2019, 12:28:22 am
content: I usually don't specificy specific brand / part numbers for X7R capacitors unless their minimum value is really critical. Same for resistors. Just be sure to derate for worst case.Also be aware that a manufacturer can make a part perform worse at some point. You order the same part but number but suddenly you get something different. Happened to me with an A-brand manufacturer of ceramic capacitors.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 05, 2019, 05:41:04 am
content: If the minimum value isn't "critical" then why are you using a capacitor at all!It may be only a few cents BOM cost, but it's a semantically important question. How many capacitors do youreallyneed, asks Mr. Muntz?Note there's more priority for bypass caps in 2-layer PCB designs (where VCC is routed). Whereas with planes available, you may need just a few over the whole thing, despite dozens of logic chips drawing power from it!Tim

author: nctnico
author_rank: Super Contributor
timestamp: May 05, 2019, 01:06:56 pm
content: Quote from: T3sl4co1l on May 05, 2019, 05:41:04 amWell, it is assumed that the capacitor will behave at least as good as the worst specification. For example: the capacitance of a 100nf 50V X7R capacitor won't be 0 at 3.3V. You can easely turn the argument around: do you want a design which fails when the assembler loads a different type (with the same nominal value /voltage rating) of decoupling capacitors? Ofcourse this depends on production volume as well but saving a few cents while taking a 6 digit dollars financial risk doesn't make sense.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 05, 2019, 02:44:42 pm
content: I wouldn't expect a "100nF 50V", say 0603, capacitor to drop by ~90% at 3.3V, no.But I know better than to leave that open for abuse.What if they simply give youthe wrong part, period?You'll never know until you test them, or the product fails. Maybe your product never fails, and they charge you for all those extra capacitors you've not actually been needing all along. (Again, not that, say, a 1nF X7R is any more than a pittance cheaper than a 100nF. My point is about the opportunity in the first place, not the degree to which it might occur.)The more usual case is having a design intent for x uF, but it ends up x/10 at operating voltage because characteristics suck. And maybe that's x/20 or x/4 between different sources, and you won't know and it'll probably fuck up your, say, supply compensation or something, because you can't predict that at design time.Most design cases just need x uF, period, under whatever conditions are relevant. The above is the rookie mistake; having learned this lesson, the veteran might count on the characteristic of a particular part to be, say, -70% at 30V, so using 3.3 times "more" of them to compensate. But that strategy also fails, in precisely the same way, if the characteristic ends up different from the design value.I'm not sure what thought process would lead you to expectanydesign to work with thewrong partsplaced. What's different about a capacitor, versus a resistor, or a logic IC? You can't exactly replace a NE555 with a uA741, yet you're suggesting an error of comparable magnitude should be somehow acceptable.Pray tell, Mr. Babbage, if the wrong numbers are put into the machine, does the correct answer still come out?(Mind, specific to capacitors, this doesn't even mention the subtle differentiators -- reliability factors like AEC-Q200, flex term, fail-open, floating-metal types, and so on. These are even more insidious as you basically have to section and micrograph the part to figure out what it is, or endure huge field failure rates from poorly trusted supply chains!)Tim

author: sokoloff
author_rank: Super Contributor
timestamp: May 05, 2019, 02:48:58 pm
content: Quote from: treez on May 04, 2019, 08:52:44 pmThis is not a reasonable goal, especially for a company making only a few 100K units per year.Reliable sourcing is much, much more important than absolute lowest price, IMO. If you relax the constraint to get the cheapest price, a lot of the game becomes a lot easier. You can stock parts to prevent production outages. You can buy from only reputable distributors. You can spend way less staff time on sourcing.Quote from: treez on May 04, 2019, 08:52:44 pmYou could, but if that staff costs $100K extra, you've eaten into a lot of your "savings".4…Or don’t bother with any of the above?….and instead just have one part number for each of the above types, and just keep buying them and rely on the fact that on average, you’ll get a pretty good bargain?Bargain is represented by your lines never stopping because they're out of parts and your finished good not failing QC or being returned by customers.