Sometimes I don't understand part pricing.  Take FJH1100, the $8 signal diode. - Page 1
Forum section: electronics / general

author: JoeN
author_rank: Frequent Contributor
timestamp: January 12, 2017, 07:49:30 pm
content: Maybe the experts here can tell me what makes this part so special it can sell for $8?http://www.mouser.com/ProductDetail/Fairchild-Semiconductor/FJH1100/https://www.fairchildsemi.com/datasheets/FJ/FJH1100.pdfThe manufacturer's claim to fame is a 3pA reverse leakage. But some other parts have the same spec for far less like the NPX BAV199 which claims the same level of leakage current. These are five cents each, dirt cheap, in quantity.http://www.mouser.com/ProductDetail/NXP-Semiconductors/BAV199215/http://www.mouser.com/ds/2/302/BAV199-840428.pdfHow does Fairchild "get away" with pricing a small signal diode like this? What am I misreading? Thanks if you can make me understand.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 12, 2017, 08:07:57 pm
content: There is a big difference between 3 pA typical and 3 pA of maximum reverse current. The testing for low currents takes quite some time and thus adds costs. Also the plastic case is usually cheaper than glass - though not that much.Though I still don't see a reason for $8. Sometimes it is just a last batch of a type that gets expensive.

author: wraper
author_rank: Unknown
timestamp: January 12, 2017, 08:51:51 pm
content: Quote from: JoeN on January 12, 2017, 07:49:30 pmReally? One has 3 / 10pA max leakage current spec, another 5nA, although at much higher test voltage but nonetheless.

author: dmills
author_rank: Super Contributor
timestamp: January 12, 2017, 08:59:24 pm
content: Yep, and sometimes that **REALLY** matters, see also the LSK389 jfet, something else you only design in if you really need the performance.Another possibility is that they are locked into making this thing by some contract with a defence supplier (An industry where updating an old design can take a years worth of really boring pointless paperwork), in this situation you do not want to change **anything** and $8 for a diode is completely insignificant if annoying.I for one love companies that make the obscure, even if they charge for it, because sometimes you really need a 3pA diode or a 10G Ohm 1 % resistor or something else weird, and cost is not that important.Regards, Dan.

author: JoeN
author_rank: Frequent Contributor
timestamp: January 12, 2017, 08:59:33 pm
content: Quote from: wraper on January 12, 2017, 08:51:51 pmWell, the Fairchild part doesn't have a graph like NXP. That 3pA "max" number is at 25°C only, you get to guess how badly it derates above 25°C because they won't tell you. If it is anything like the NXP part, it derates quickly. The only thing we "know" is that the 3pA reverse leakage number is "max" for Fairchild and "typical" for NXP at 5V and at 25°C.

author: wraper
author_rank: Unknown
timestamp: January 12, 2017, 09:05:45 pm
content: Quote from: JoeN on January 12, 2017, 08:59:33 pmBecause FJH1100.pdf is not a full datasheet.

author: JoeN
author_rank: Frequent Contributor
timestamp: January 12, 2017, 09:13:33 pm
content: Quote from: wraper on January 12, 2017, 09:05:45 pmFairchild seems to disagree with you. I cannot find a more detailed datasheet.Product page:https://www.fairchildsemi.com/products/discretes/diodes-rectifiers/small-signal-diodes/FJH1100.html"Download FJH1100Datasheet"https://www.fairchildsemi.com/datasheets/FJ/FJH1100.pdf

author: wraper
author_rank: Unknown
timestamp: January 13, 2017, 01:31:54 am
content: Quote from: JoeN on January 12, 2017, 09:13:33 pmOften such "Download datasheet" button means downloading 5 page "datasheet" for very complicated IC, which is not much more useful than nothing at all. While real datasheet is something like 500+ pages which you can get only under NDA.

author: orin
author_rank: Frequent Contributor
timestamp: January 13, 2017, 06:37:25 am
content: Quote from: wraper on January 12, 2017, 08:51:51 pm"At a much higher test voltage..."They are not comparable with the given datasheets. You can't compare 5nA maximum at 75V reverse voltage with 10pA maximum at 15V reverse voltage.However, given the price, if you are prepared to test them yourself, the BAV199 looks pretty good.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: January 13, 2017, 02:57:11 pm
content: Hmm, I am familiar with both FJH1100 and BAV199 as we use both in the equipment we make at my workplace. There are differences and sometimes you have to pay a premium for the FJH1100 and tolerate it's problems, such as a strong light sensitivity. For a start, I can recommend to look at theBAV199 datasheet from ON Semias that one contains a graph with actual measurements of a reverse current vs voltage.CheersAlex

author: wraper
author_rank: Unknown
timestamp: January 14, 2017, 12:46:33 am
content: Quote from: Alex Nikitin on January 13, 2017, 02:57:11 pmAccording to the datasheet it should not be light sensitive unless body coating is damaged.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 14, 2017, 01:59:51 am
content: Quote from: orin on January 13, 2017, 06:37:25 amSure you can!Sort of.Diode leakage varies relatively little with reverse voltage. Maybe a factor of 10x between 10% and 100% of Vrrm. That's a huge difference compared to the 500x between diodes! (Which is reasonable for, say, the difference in leakage between 25C and 85C or more. Leakage does vary strongly with temperature!)"Sort of", meaning: They don't give a curve of reverse current versus voltage or temperature. So it's unclear how this diode was actually designed: is it a high voltage diode like 1N4148, selected and tested for one parameter (current at a mere 15V)? Or does it actually break down at low voltages, using a very different die?QuoteJFETs have long been used as low leakage diodes (for N-ch, use G for anode, tie D+S together as cathode). The downside that the channel resistance is a big factor: it more or less adds in series with the diode junction; and the gate current limit is always tiny (a few mA). They're often specified as well as the FJH1100 (~pA), yet cost mere pennies.Supposedly, a lot of BJTs have excellent leakage characteristics (B-C junction; tie B to E), particularly small junction RF transistors like BFR92. But again -- you have to test and select the parts yourself if you need guaranteed low leakage, not just "typical" performance.Tim

author: edavid
author_rank: Super Contributor
timestamp: January 14, 2017, 02:12:27 am
content: Quote from: T3sl4co1l on January 14, 2017, 01:59:51 amHave you priced a PN4117 lately? $2.29 each from Mouser.(P.S. The FJH1100 is only $5.05 at Arrow.)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 14, 2017, 02:53:39 am
content: Okay, not ALL JFETs cost pennies...Tim

author: David Hess
author_rank: Super Contributor
timestamp: January 14, 2017, 04:19:23 pm
content: Quote from: JoeN on January 12, 2017, 08:59:33 pmWe also know that the BAV199 is 5nA maximum at 25C so it is potentially 3 orders of magnitude worse than the FJH1100 maximum of 3pA at 25C. No leakage versus temperature graph is needed because PN junction leakage roughly doubles every 10C. (1)As Kleinstein points out, the difference is testing. Time spent on the test fixture costs money and low leakage current tests take lots of time.A good example of this is the National Semiconductor $0.83 LMC6081 and $5.76 LMC6001. They are the same part but the former is 10fA typical and the later is 25fA maximum at 25C. These articles suggest that the testing time at this level is a full minute which is consistent with the roughly 10 cents per second cost that I remember and the price difference between the LMC6081 and LMC6001:http://electronicdesign.com/test-amp-measurement/whats-all-teflon-stuff-anyhowhttp://electronicdesign.com/test-amp-measurement/whats-all-femtoampere-stuff-anyhowMany common small signal transistors have leakage in the picoamp range but their specification will be something like 25nA, 50nA, or 100nA maximum because that is what the ATE (automatic test equipment) can quickly measure and for their intended use, that level of guaranteed leakage is all that is required. At 10 cents per second of test time, not much time is available to test a 6 cent 2N3904.(1) Back when I was working on low leakage integrators that had to operate at high temperatures, I ended up using bipolar super beta 308 type operational amplifiers like the LM11 (50pA maximum at 125C) and graded CMOS amplifiers like the LMC6081 (10fA typical at 25C and 4pA maximum at 85C) instead of other CMOS and JFET amplifiers because starting from say 10pA, the later devices had too much leakage at high temperatures and tests found the rough doubling of leakage every 10C rule was pretty close. Analog Devices and Burr-Brown had JFET input electrometer amplifiers which would have worked but they were more expensive than grading LMC6081s.

author: jaromir
author_rank: Unknown
timestamp: January 14, 2017, 04:35:51 pm
content: Quote from: David Hess on January 14, 2017, 04:19:23 pmI'm curious - is this somehow typical rate per test second? What about more complicated silicon devices, like MCUs?Sometimes I wonder how on earth could they sell MCU for less than 50c per piece (and much cheaper in volume), when just the functional tests have to take "very long". I assume they load FLASH with simple program to exercise all the peripherals, that has to take a while (hundreds of miliseconds) at much more convoluted testers.

author: orolo
author_rank: Frequent Contributor
timestamp: January 14, 2017, 04:39:47 pm
content: Quote from: edavid on January 14, 2017, 02:12:27 amMMBF4117 is only 0.128 euro for a hundred pieces at mouser. Another caution with JFETs as diodes is the exponential temperature-leakage dependence. MMBF4117 goes from 10pA at 25ºC to 25nA at 150ºC.

author: rstofer
author_rank: Super Contributor
timestamp: January 14, 2017, 05:29:41 pm
content: Quote from: jaromir on January 14, 2017, 04:35:51 pmAll of which is why they invented JTAG! This was a way to test complex devices like MCUs.

author: David Hess
author_rank: Super Contributor
timestamp: January 14, 2017, 05:56:16 pm
content: Quote from: jaromir on January 14, 2017, 04:35:51 pmThis would only be for simple analog devices like diodes, transistors, and operational amplifiers.QuoteBIST (built in self test) is a major feature of complex logic devices an especially things like processors and memory. There is no way to supply all of the test data patterns through the pins in a timely manner so internal structures to generate and verify them are included.Part of this process includes activating redundant circuits like spare rows of memory to replace faulty ones. I read that one of the things that led to low yields resulting in high costs on the AMD K6-3 processor was lack of enough spare L3 (update: L2) cache rows.I wonder how they test OTP (one time programmable) devices though.

author: jaromir
author_rank: Unknown
timestamp: January 14, 2017, 06:39:17 pm
content: Quote from: rstofer on January 14, 2017, 05:29:41 pmBut still, this takes time, which is very valuable in manufacturing. And not all MCUs do have JTAG interface.Quote from: David Hess on January 14, 2017, 05:56:16 pmThat makes sense, thanks. The BIST is used along with specific program in FLASH to exercise it, which is erased after tests?

author: Kleinstein
author_rank: Super Contributor
timestamp: January 14, 2017, 06:56:03 pm
content: The costs for testing also depends on the type of testing done. More simple tests for large quantity devices like the 2N3906 can use more special, less capable tests. This still makes the low current tests rather expensive as they need time and high quality test equipment and those super low leakage diodes are not high quantity.Anyway there is not that much logic behind some of the semiconductor prices - some are just expensive because they have no reason to sell them for less. Also quantity and the factories that are used can be a big factor.

author: edavid
author_rank: Super Contributor
timestamp: January 14, 2017, 07:08:15 pm
content: Quote from: David Hess on January 14, 2017, 05:56:16 pm"OTP" EPROM based devices can be tested and erased before they are encapsulated.True OTP devices have spare cells for testing, but they can't be completely tested, so invariably have higher field failure rates than other devices.Good reason to avoid them if possible.

author: David Hess
author_rank: Super Contributor
timestamp: January 14, 2017, 08:49:37 pm
content: Quote from: jaromir on January 14, 2017, 06:39:17 pmI do not know the details but that would work. Or a separate ROM or state machine is included to run the test vectors using the BIST structures.I remember discussions about this problem in trade magazines in connection with the increased size of DRAM chips. For a while BIST was a major new feature in cutting edge integrated logic chips but I assume it is too common now to bother advertising.

author: Hypernova
author_rank: Unknown
timestamp: January 14, 2017, 11:07:05 pm
content: Quote from: David Hess on January 14, 2017, 05:56:16 pmMany OTP are just EEPROM without a local erase circuit. I have also heard from someone where they once were developing with some OTP MCUs. They just go to specialists that decap and window the chips and erase them with UV during development.

author: EEVblog
author_rank: Unknown
timestamp: January 14, 2017, 11:23:18 pm
content: This is what I like to see, a nerd fight over diode specs

author: Benta
author_rank: Super Contributor
timestamp: January 14, 2017, 11:58:06 pm
content: QuoteFirst, Fairchild is now ON Semi, but let that lie.What you need to understand, is how semiconductor companies (and other industries) do "Portfolio Management".There are several ways. direct "obsoletion" is one. But there might be a couple of major customers using the part, so in order to keep them satisfied and feeling secure, the part stays in the official portfolio, and these major customers will still get the parts at reasonable price until a redesign can be made.But ON/Fairchild wants to discourage everyone else from ever designing with this part, because it WILL be obsoleted at some point.So: the easiest way of doing this is simply pricing it out of the market.This is done by all manufacturers, and if you run into a part with outrageous pricing: start redesigning right now.Just for reference: I've worked in semicondutor marketing for over 25 years now. I know the mechanisms.QuoteGood one. In this case it's not about specs, though...

author: SeanB
author_rank: Super Contributor
timestamp: January 15, 2017, 09:40:42 am
content: Transistors and the like is simple to test, you do a basic function test. Apply eg 30v to collector, measure current after 1us, if the current is under 2 LSB then pass. Then apply 10uA to base, check collector voltage, with current limit of 1mA, is under 5V then pass. 2 checks, gives a good confidence the transistor has both no leakage and some gain. Otherwise any test fail then put the red dot of death on it. If you are binning them for gain groups, then after moulding you simply do the gain test again, and use a comparator and a resistive load to sort into the typical 3 bins of sub 100, 150 to 300 and over 250 bins. The overlap is simply because you will have devices that are close to the edges, so rather put them in a lower bin instead, so the higher value parts are not going to be rejected for suboptimal gain at the customer incoming QC verification. Unsorted parts are then either the whole batch or those that were not the desired gain grouping, giving some interesting spreads on the parts. You saw that with the resistors Dave tested a reel of, where there was a gap in the middle where the close tolerance parts were selected out of the run, leaving the outliers only.The rest of the type tests are sampled, not production line things, done on a random selection off the final part, typically the first few out the moulding and the last few. As the transistor dies are very often using the same mask sets for many transistors, with the only difference being things like gain, voltage rating and the actual package used, you often find a die that had the single 5 on die tests that were used to determine what transistor they were going to be ( one per quadrant, one in the middle, do a breakdown voltage test and actual gain taking sub 2 seconds per device, then select the generic ATE pattern of 10 per second for the rest) then it is marked as appropriate, or they just mark the whole lot with the desired lower rated part number and let it go at that.Thus you find transistors with Vceo max of 30V that actually will all break down only over 120V, as this is larger, but the die was not scheduled for the higher voltage part, or it was uncut inventory and an order for the lower part was needed, and using the stock wafer was an easy way rather than an unscheduled run. Tthey just make the stock up later, adding to the end of the line schedules for a run of the wafers. That way the silicon fab is always busy, and they always have stock of the cheap low cost parts.Diodes the same, just a per wafer reverse voltage test, then a single forward conduction test, a reverse leakage test at some value, and slice and package the working ones. Or even just do no test, and check the final product only, with a line which has had a long run, and where the quality control has enough confidence in the stability of the line to be confident they all will work. that then only means a sample check on breakdown, and a single forward conduction test on all to see they were packaged correctly. You rely on the QC history of the line, and the incoming material non variability as part of the process, so the result is the same wafer after wafer.The voltage marking is either the binning, or more likely with diodes a per order mark, if the customer wants a 1N4001 you simply mark the 1N4007 parts you know the line always makes with the 1N4001 and send out, or you have a wafer on hand which is not 1N4007 breakdown and use that.Parts you are going to obsolete, and price increasing, is simple. You have a 5 year supply of wafers in stock, and the line is going to close, so you have already told the large volume purchasers the part is going EOL, and have done the last final buys for them, and are saving the last batches of wafers for the announcement of EOL to the smaller markets, where the volume will use up that last batch in the ordering for them, making you a nice profit on the line as it is closing out.

author: karoru
author_rank: Regular Contributor
timestamp: January 16, 2017, 01:49:31 am
content: Quote from: wraper on January 13, 2017, 01:31:54 amHow much I love these datasheets where 4/5 consists of title, RoHS disclaimer, copyright and big picture of component reel with all dimensions:)

author: edavid
author_rank: Super Contributor
timestamp: January 16, 2017, 03:29:06 am
content: Quote from: SeanB on January 15, 2017, 09:40:42 amNot exactly, since 1N4001-1N4005 are PN, and 1N4006-1N4007 are PIN.

author: donmr
author_rank: Regular Contributor
timestamp: January 16, 2017, 05:33:10 pm
content: Quote from: rstofer on January 14, 2017, 05:29:41 pmWhat makes the difference is automatically generated scan testing. JTAG may be used to configure this but typically most of the IO pins are converted to clock and data signals that feed bit patterns into the part and collect the results. The data patterns are generated from the design data (logic gates) and a lot of computer power goes into optimizing them to get the best fault coverage in the shortest time.Also a lot of built in self test (BIST) is used, especially for memories.