Why are BJT's shipped in anti static bags? - Page 1
Forum section: electronics / beginners

author: antenna
author_rank: Frequent Contributor
timestamp: October 12, 2022, 06:01:02 pm
content: I get being careful with insulated gate devices, but I am curious why some BJT's, diodes and jfets come in anti static packaging even though they dont have insulated gates. Are normal diode junctions also sensitive to static discharge? I've always stored my BJT's in normal plastic pill bottles and never used a wrist strap with them, and I've never had one suddenly quit working like a cmos IC can. BJT's can be avalanched with high voltage, and as long as the current is low, it doesn't seem to ruin them, so what am I missing?

author: RoGeorge
author_rank: Super Contributor
timestamp: October 12, 2022, 06:13:52 pm
content: Deciding which components must get an antistatic bag and which ones may not would be a burden in itself for resellers, then keeping separated inventory and stock for each kinds of bags would be annoying even for manufacturers, then all the possible errors, and so on. The bag itself doesn't add much to the entire cost, so why optimizing about that. Too much hassle for no gain.Just put them all in antistatic bags.

author: ledtester
author_rank: Super Contributor
timestamp: October 12, 2022, 06:18:19 pm
content: As RoGeorge said, it's simpler to use one kind of packaging for all components.It also indemnifies the distributor/manufacturer from claims that the item was damaged from improper packaging.I've even received tactile switches in anti-static bags.

author: edpalmer42
author_rank: Super Contributor
timestamp: October 12, 2022, 06:58:55 pm
content: Any device that has a voltage rating can be damaged by ESD, including things like BJTs, diodes, and even precision resistors. Worse than being destroyed, it can be damaged to the point where it fails after a year or two instead of lasting for two or three decades.Back in 1983, HP published an excellent article on the subject.http://hparchive.com/Bench_Briefs/HP-Bench-Briefs-1983-03-05.pdfEd

author: Twoflower
author_rank: Frequent Contributor
timestamp: October 12, 2022, 07:17:56 pm
content: ESD damages not just happen on gates of FETs. That can happen also on other parts, even on Resistors:https://www.rohm.com/electronics-basics/resistors/chip-resistor-failure-modes. As soon as the charge is above a breakdown level it there's a chance that for a short period of time a current flows which might harm the device. Maybe not fatal but one or more parameters will change.Given, due to the high resistance of the gates they are especially sensitive to build up charges. But what do you think happens to a diode with a rated voltage of 1000V sees a charge of 10000V? It probably will arc somewhere between the terminals or damage the PN structure.A container or package that can't dissipate charge might build up a potential relative to the environment. The parts within are probably happy as all terminals are roughly at the same potential. If you now pick a device at one terminal with a conductive tweezer at environment potential that terminal will discharge to environmental potential while the others only can equalize to that charge via the device. Zap!In most cases for non commercial cases that risk is acceptable. But Mouser&Co send devices to commercial customers as well. And they can get easily pissed if their product fails and it turns out due to an ESD stressed part.

author: antenna
author_rank: Frequent Contributor
timestamp: October 12, 2022, 07:26:12 pm
content: I didn't realize it was such a serious issue until now. I saw the pictures in the HP manual linked above and that Rohm site is interesting too. Thanks!!!

author: Benta
author_rank: Super Contributor
timestamp: October 12, 2022, 08:18:08 pm
content: Seriously?You expect a warehouse worker to study every part and say:"Oooh, this is static sensitive, it goes into this bag. But this is a BJT, it goes into a different bag."I don't think so.

author: james_s
author_rank: Super Contributor
timestamp: October 12, 2022, 08:31:39 pm
content: I've had switches and batteries and stuff like that come shipped in antistatic bags before, it's just easier to use them for everything than to figure out what parts need them.

author: David Hess
author_rank: Super Contributor
timestamp: October 12, 2022, 09:22:04 pm
content: The base-emitter junction of a small signal bipolar transistor, and a JFET gate, can be small enough to be damaged by ESD when the junction suffers reverse breakdown. For a JFET this will result in high gate leakage or destruction. For a bipolar transistor, leakage may be increased and hfe lowered if it is not destroyed.Besides that, it may not make sense to have "not anti-static" bags for parts where it will not matter, although in the past I have seen power devices packaged in normal bags. Note that there is a difference between anti-static and ESD protection bags.

author: exmadscientist
author_rank: Frequent Contributor
timestamp: October 13, 2022, 06:19:16 am
content: The warehouse system tells the picker which of the several available types of bag to use. Many parts are just miscategorized.For BJTs this is pretty understandable, if often wasteful. To receive TVS diodes in the heavy ESD protection bags... that will never cease to be hilarious

author: Stray Electron
author_rank: Super Contributor
timestamp: October 13, 2022, 01:15:00 pm
content: Quote from: RoGeorge on October 12, 2022, 06:13:52 pmThis. I worked for a very large US contractor and EVERYTHING there was stored and shipped in anti-stat bags and in anti-stat tote bins. Even things like paper work, bare connectors, wire, optical lens and nuts, bolts, screws and washers. It's easier and cheaper to stock and to use only one type container than several different ones and also no-one can make a mistake and put static sensitive parts in a non-ESD safe package.I'll add this: The management of the co that I used to work for took ESD so seriously that they made everyone in the company take, and pass, an ESD awareness course once per year regardless of their actual job.

author: TimFox
author_rank: Super Contributor
timestamp: October 13, 2022, 01:54:50 pm
content: As discussed above, it is simpler to stock only one type of plastic bag.My favorite shipment in pink anti-static bags was a batch of 1/4-20 UNC stainless steel bolts--I don't want to see the ESD that could damage them.

author: bostonman
author_rank: Super Contributor
timestamp: October 13, 2022, 02:52:15 pm
content: QuoteLooks like the original question was answered, but I wanted to add that I too went through ESD training at a previous job. Although the person who taught the course didn't know anything about electronics and managed to convince upper management for him to do the training (probably to justify his position), as with any meeting/training, we always learned something; we even had a cool video on static electricity.From my understanding, it's not necessarily the charge you put into a device, it's the discharge rate that shocks the internal structure. So if you carry a device, it builds a charge based on humidity, material differences, etc... After you touch something at a different potential, let's say 0V, and the 1000V that built up as a result of ESD instantaneously discharges causing damage to the device; whether blowing it up immediately or weakening it.Personally, I should practice ESD at home, but I almost never do. I will try placing things in static bags when moving them around, and have laid out an ESD mat, but ESD practices is tough.We also treated unpopulated PCBs as static sensitive which was ridiculous.On another note, I remain baffled why DigiKey will use such a large box and lots of shipping material to ship one or two small static bags worth of devices. When I unroll the packaging material, I must have three-feet for only ordering maybe two surface mount parts with a quantity of five each.

author: Stray Electron
author_rank: Super Contributor
timestamp: October 13, 2022, 04:12:57 pm
content: Quote from: bostonman on October 13, 2022, 02:52:15 pmI've wondered the same thing about Amazon. This week we received a short length of bead chain, enough to fill a penny match box, but in a box the size of a shoe box. I suppose the same situation applies, namely it's cheaper to use a standard size box (and to waste 99% of it's capacity) than to stock an assortment of sizes.

author: bostonman
author_rank: Super Contributor
timestamp: October 13, 2022, 04:57:18 pm
content: I fully agree that using standard sizes is cheaper, but, if we are trying to save the planet, seems a shoebox sized box and three-feet of packaging materials to ship ten SMT components is a waste.It's one thing they ship using this much material, but multiply that the numerous people who order product from them.

author: IanB
author_rank: Super Contributor
timestamp: October 13, 2022, 04:58:27 pm
content: Quote from: Stray Electron on October 13, 2022, 04:12:57 pmWe can also think about this from the shipping perspective. Carriers need a package that is large enough to handle. If you tried to ship a matchbox by UPS it would probably fall through a crack somewhere and get lost. So there is probably a minimum convenient size of shipping box.In some cases, I've noticed sellers will ship small parts in a padded envelope by USPS, but this may not be convenient when a vendor has a contract with a dedicated carrier.

author: bostonman
author_rank: Super Contributor
timestamp: October 13, 2022, 05:04:38 pm
content: You bring up a good point.I've received envelopes for components before and think to myself, the carrier (someone other than USPS that needs to make a special trip to my house) must be frustrated having to transport an envelope rather than something that looks more serious like a box.

author: Zero999
author_rank: Super Contributor
timestamp: October 13, 2022, 07:37:41 pm
content: Quote from: edpalmer42 on October 12, 2022, 06:58:55 pmYes, BJTs are static sensitive, especially the smaller ones.Another big reason for using ESD protective packaging, for parts which genuinely don't need it, such as electrolytic capacitors and bog standard resistors is, it can be taken into areas where ESD sensitive parts are being handled. One can buy many ESD proof items, from clothing to stationary and tools.

author: David Hess
author_rank: Super Contributor
timestamp: October 13, 2022, 08:41:50 pm
content: Quote from: Zero999 on October 13, 2022, 07:37:41 pmAnything with a small enough junction can be damaged simply from the heat which is released. Power bipolar transistors are basically immune to ESD, and already operate at low hfe so damage to the base-emitter junction which reduces hfe is irrelevant. The oxide insulator of a MOSFET is especially vulnerable.Quote from: bostonman on October 13, 2022, 02:52:15 pmI'm aware of four effects:1. A small junction can be damaged by localized heating. Avalanche rated parts are fabricated so that the junction is uniform and heating will take place across the entire junction.2. A PN junction forced into reverse breakdown creates hot carriers which can damage the junction. This is responsible for the loss of hfe and increased leakage in a bipolar transistor.3. Oxide insulators can break down becoming leaky or even a short.4. Metalization can be destroyed.

author: Zero999
author_rank: Super Contributor
timestamp: October 13, 2022, 09:42:00 pm
content: Quote from: David Hess on October 13, 2022, 08:41:50 pmThe same can be said for diodes, SCRs and TRIACs, rated to more than a couple of amps.

author: coppice
author_rank: Super Contributor
timestamp: October 13, 2022, 09:55:42 pm
content: If you decap an IC, bipolar or MOS, which died from a static discharge, the results can be very hard to work out. You''d expect to find the physical damage around the I/O ring somewhere, but its often deep in the chip, far from the pin or pins which took the discharge.

author: EPAIII
author_rank: Super Contributor
timestamp: October 14, 2022, 07:06:00 am
content: More likely shortcomings of the shipping clerk than any company policy. They get paid to do things FAST, not well. And I am sure that management and some supervisors can claim a big share of the blame.(It took me a few minutes to clean up my original and much more insulting version of that answer.)Quote from: bostonman on October 13, 2022, 04:57:18 pm

author: tooki
author_rank: Super Contributor
timestamp: October 14, 2022, 06:45:45 pm
content: Quote from: Benta on October 12, 2022, 08:18:08 pmOf course not. It will be predetermined, and the workers use whatever they’re told to use. I imagine that nowadays, they have a handheld device of some sort that not only tells them what item and how many, but precisely what packaging type to use, what warning labels to apply, etc.

author: james_s
author_rank: Super Contributor
timestamp: October 17, 2022, 02:09:10 am
content: Quote from: TimFox on October 13, 2022, 01:54:50 pmI can see some potential value to that. The pink bags do not shield static, they just don't generate static. If you're handling static sensitive parts then it would seem prudent to use bags that don't generate static to pack the non-sensitive parts that may be in close proximity to the sensitive stuff.