Life lenght for underpowered/unpowered LEDs and passives - Page 1
Forum section: electronics / projects

author: daqq
author_rank: Super Contributor
timestamp: July 30, 2015, 09:31:19 pm
content: Hi guys,Is there any way to calculate/guess if an LED (or other parts, lower tech - not microcontrolers) is likely to fail in 10-20-30 years of service? Assuming it will run at, say, 10% of its nominal power.Also, do LEDs, PCBs, misc passives have "shelf lives"? As in - a product is assembled, tested, and lays unpowered (in a sealed enclosure) for a decade or two and then you just plug it in and turn it on with no problems?I know that avoiding electrolyte caps might be good for this kind of situation, but other than that is there any critical thing that would prevent longevity?Thanks,David

author: daqq
author_rank: Super Contributor
timestamp: July 30, 2015, 09:39:07 pm
content: Note: By failing I mean stops working totally - not "output light intensity drops 30%" or "resistance shifts by 500ppm".

author: tautech
author_rank: Super Contributor
timestamp: July 30, 2015, 10:06:37 pm
content: Good manufacturers list in datasheets a MTBF, normally in a measurable unit, hrs, yrs, or operational cycles.

author: amyk
author_rank: Super Contributor
timestamp: July 30, 2015, 11:32:14 pm
content: Regular (phosphorless) LEDs like red, green, and blue will last essentially forever if not overdriven. For white LEDs, they'll gradually turn blue over time as the phosphor degrades.An example of LEDs that have reached 30 years and are still functional would be the ones in early computers. Basically, anything made before 1985 and has a LED, probably still has a working LED.If you mean whether today's cheaply produced LEDs will last... that's a different matter. The wire bonding might fail early, but the die itself will probably still be OK.

author: Circlotron
author_rank: Super Contributor
timestamp: July 31, 2015, 12:34:35 am
content: I have read about lead free solder growing whiskers over an extended period of time and eventually causing shorts.A historically useful generalization supported by Arrhenius' equation is that, for many common chemical reactions at room temperature, the reaction rate doubles for every 10 degree Celsius increase in temperature.https://en.wikipedia.org/wiki/Arrhenius_equationso keeping the temperature low sounds like a good idea.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 31, 2015, 04:15:06 am
content: Quote from: tautech on July 30, 2015, 10:06:37 pmBut also within some performance spec, i.e.: a 10% degradation in output, etc.Which is exactly what the OP doesn't want. Go figure that manufacturers are more picky than that!As mentioned, roughly speaking, it's an exponential tradeoff, usually something like double life every -10C or whatever. But that assumes there are no lower temperature breakpoints in play; typically, at high temperatures (accelerated life tests), only one is dominant, and the failures at lower temperatures and (potentially exponentially) longer time scales, are unpredictable.Fatigue and wear factors are often dominant. If the light is being used for stroboscopy in an industrial fixture, how many billions of cycles might it go through during that 30 year lifespan? Are the wire bonds up to that? If it's a street lamp, how long will it survive under varying temperature cycles, and the frequent incremental ingress of moisture, electrolytes, dust, abrasives (sand, snow on the wind) and etc.? If it's powered by electric mains, how vulnerable is it to electrical transients of very infrequent magnitude -- should it withstand direct lightning bolts? Because it might be required to, if it must survive 30 years in any location, hilltop or valley!Many possible factors at play, when you get into deep life expectancy ranges like this (or beyond).Tim

author: coppice
author_rank: Super Contributor
timestamp: July 31, 2015, 04:29:43 am
content: Quote from: amyk on July 30, 2015, 11:32:14 pm30 year old LEDs are generally still working, but are quite dim compared to when they were new. If you need a particular level of output from an LED, rather than just something that lights up, you have to consider its lifetime quite carefully.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 31, 2015, 04:52:50 am
content: Quote from: daqq on July 30, 2015, 09:31:19 pmAs for these examples:Vintage electronics -- poor quality parts notwithstanding -- are generally good to go, and we have a modest history of dusty-old-garage parts that illustrate this. Minding that the most common garage specials were consumer gear, which fall prey to those very morbidities: wax-paper and electrolytic capacitors, carbon composition resistors, transformers and inductors glued with wax and varnish that has since turned to dust; etc.Examples of good stock:- Wirewound and metal film resistors. Mind possible corrosion on open type wirewounds such as variable ceramic tube/bar types and potentiometers/rheostats. Modern parts might be vulnerable only due to their small stature, i.e., thin film being what it is and all. Doesn't take much to corrode through, or vaporize with a transient, or crack through due to thermal or mechanical stress.- Ceramic capacitors (type 2 dielectric -- Y5P or up) do age over time; check values against tolerance. Chip caps are vulnerable to thermal or mechanical stress, and reliable parts are available with "flexible" terminations, or with attached leads / leadframes.- Vacuum sealed anything, including tubes/valves, which are good, out of the box, for dates going back to their very invention. If the seal was good once, it's probably good for more than a century.- Inductors and transformers, especially varnished (versus wax or tar dipped) or hermetically sealed (assuming they've not been abused in life or corroded in storage, and you don't mind the probable class A paper insulation -- UL had different standards back then..). Core materials don't really age, at least not to an extent that's really important (the aging of type 2 capacitors is analogous to a reduction in initial permeability affecting laminated iron and ferrite cored transformers, but not inductors using gapped cores).- Semiconductors (diodes, transistors, etc.), especially ceramic body or metal can, hermetically sealed types (going back to their invention in the 40s and 50s), as well as the better formulated plastic packages (I don't think I've heard of any problems with modern materials, which have been more or less modern since the 70s and 80s). Modern, low voltage, high frequency and high complexity parts are not stable, thermodynamically speaking, hence the low temperature ratings (silicon with ~30nm doping features simply can't be heated much above 100C for very long, or it will pretty soon cease to be the circuit it was fabricated to be). Higher pitch and higher voltage parts (like good old fashioned CMOS or TTL logic families, and contemporary ASICs, PGAs, MCUs, etc.) are much more stable (indeed, they had to be, as processing temperatures in the 300C range were used for diffusion doping). This is, in effect, a small part of why modern satellites and space probes don't have big, fancy processors in them (the second most important part being, they just don't need that much processing power -- and the first most important part being, anything new isn't space qualified -- paperwork and stuff!).- Connectors, switches, relays: give or take tarnish/corrosion, or inferior plating materials. Beware whiskers on pure-tin, silver and zinc platings; likewise, beware lead content on solder-plated types. Best quality parts with precious metal plated contacts (or for power switches and relays, usually a whole silver contact pad) always have, and always will, do the best.- PCBs: old stock is probably phenolic paper, which may be moisture sensitive, and may have corroded over time. (Even so, most PCB'd radios and TVs that need parts replaced, are still serviceable without lifting traces.) Much of anything from before the 60s was point-to-point wired anyway, so this doesn't matter much, looking back into history. Expect modern glass epoxy materials to last for ages, and be relatively resistant to corrosion (but do mind that a layer of conformal coat is advisable if exposure to cat piss or other contaminants is a possible requirement..). PCBs can also be fabricated from ceramic, in which case it's usually laser etched, with semiconductors mounted directly, and called a hybrid.- Protection devices: MOVs are wear items. As far as I know, this isn't a physical attribute, but part of their nature as a conspicuous, sacrificial element. They take more damage on large transients. TVSs and thyristors, I think, are unlimited, as long as they are operated within their (nominal, not one-time surge) ratings. Thermal fuses: these things are bad enough on their own; I wouldn't think they are, say, space-worthy. Possibly there are similar devices which are space qualified, I don't know. That would be the place to look. Regular fuses: works once then that's it. Duh?So, under conditions of "sealed, unpowered", making the obvious substitutions to the worst components, even a very ordinary consumer circuit should be able to last, heck, half a century is probably quite reasonable!Tim

author: daqq
author_rank: Super Contributor
timestamp: August 07, 2015, 09:47:06 am
content: Thank you very much for your wisdom guys! I'll take it into consideration, report in 50 yearsQuoteInteresting... Could it be that if I just let a 15nm (or any future tech) device just lay there for a decade under normal conditions, it will diffuse into a silicon blob?

author: tszaboo
author_rank: Super Contributor
timestamp: August 07, 2015, 11:11:05 am
content: LEDs for me are considered as plain semiconductors. The brightness dissipates over time, but otherwise if they are driven correctly there isnt anything to be broken. Unless moisture eats away the lead or something.About shelf life, as far as I understand normal plastic packages are moisture sensitive, they soak up, and when you try to solder it, it evaporates rapidly, breaking stuff. They say, heat it up to 90 degrees for a day, and you are fine.Resistors have sulfur contamination.Capacitors dry.Cables and other rubbery-plasticy stuff may react to anything.So, the same way electronics doesnt really work in the gigaherz region, it doesnt work in the nanoherz region (30+ years) unless specifically made for it

author: wraper
author_rank: Unknown
timestamp: August 07, 2015, 11:29:06 am
content: Quote from: coppice on July 31, 2015, 04:29:43 amI don't think so at all. Rather LEDs of those days initially were very dim compared to the modern ones.

author: Circlotron
author_rank: Super Contributor
timestamp: August 08, 2015, 03:01:26 am
content: I have a smoke alarm on the ceiling outside the bedroom. It has a green led that has been running 24/7 for 21 years. When it was new it was bright enough to see your way in the dark for a short distance. Nowadays, or should I say nowanights, it is nowhere near as bright. Maybe half or less.

author: German_EE
author_rank: Super Contributor
timestamp: August 08, 2015, 08:14:13 am
content: It has been my experience that old red LEDs turn pink over time and old green LEDs turn yellow. There are some elevator installations from the 1970's with LED status panels that are still running.