How to find the life expectancy of an electronic device? - Page 1
Forum section: electronics / projects

author: Sai teja
author_rank: Regular Contributor
timestamp: March 12, 2018, 01:57:32 pm
content: Hello, Currently we are developing a product and our development phase is completed. We will go into production soon. Before that, I would like to know the life time expectancy of electronics in my product. By lifetime expectancy I mean the duration before which electronics go non-functional.Please help me in this regard.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: March 12, 2018, 02:24:40 pm
content: Quote from: Sai teja on March 12, 2018, 01:57:32 pmThe MTBF of a device is done by testing, testing again and more testing. The MTBF is for the entire device, not just individual components. I am sure their will be more comments from more qualified folks.MTBF = Mean-Time-Before-Failure

author: CopperCone
author_rank: Super Contributor
timestamp: March 12, 2018, 03:05:59 pm
content: Some parts have mtbf in datasheets, like dc dc converters. Companies like analog devices have mtbf for things like opamps in certain packages.Usually these numbers are very good but obviously do not account for transients, running at maximum limits and power cycling, etc.I think that you will find putting together an accurate statistical model without your own data will prove difficult.You can generate some kind of expectationbut working in a factory i found failures to be all over the place.Things like mechanical damage and bad interconnects were leages more common then electrical faults.When i did see electrical faults it was either obviously shoddy components not specified well (i.e. high current dc switch) or damage on things connected off the board where it was determined the cause of failure was external energy.But you do have black swans like emi filters from stauffer or tthe capacitor plague....Power electronics and sensor interfaces are where your analysis efforts would be best placed.

author: james_s
author_rank: Super Contributor
timestamp: March 12, 2018, 04:25:46 pm
content: It depends on a huge number of factors. Generally speaking, electrolytic capacitors are the thing I see fail most often with time or hours used.

author: iMo
author_rank: Super Contributor
timestamp: March 12, 2018, 06:31:17 pm
content: Except pre-programmed obsolescence the components with the lowest mtbf used in your product give you the number. Those parts with lowest mtbf are firstly the mechanical parts (relays, switches, mechanical encoders, connectors, sockets, etc.), then the parts with volatile chemicals inside, ie. capacitors (aluminum, tantalum), LCD displays, batteries/accumulators, and then any devices/components working at "higher" temperatures, voltages, currents..

author: rfeecs
author_rank: Frequent Contributor
timestamp: March 12, 2018, 07:18:44 pm
content: There is a very well established process for predicting reliability of electronic equipment. Most military, aerospace and telecommunications contracts require a reliability prediction or guarantee of Mean Time to Fail (MTTF).The process involves listing all the component parts and their stress levels (voltage, current, power dissipation, etc.) Then a calculation is made to predict the MTTF.Some references:Wikipedia:https://en.wikipedia.org/wiki/Reliability_prediction_for_electronic_components"Reliability prediction basics":http://www.reliabilityeducation.com/ReliabilityPredictionBasics.pdfYou might want to look up MIL-HDBK-217 "Reliability Prediction, Electronic" and Bellcore/Telecordia.Most companies accomplish this task by hiring a consultant, giving him all the numbers, and he runs a computer program and provides you with a reliability prediction report.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: March 12, 2018, 08:28:15 pm
content: Naturally all this is worthless unless you're building in quantity and following procedures to the letter every single time. The numbers tell you nothing about a small sample and if anybody anywhere in the build process, including the supply chain, doesn't follow procedures, all bets are off. That's why space programs and the military are so procedure-centric.

author: splin
author_rank: Frequent Contributor
timestamp: March 12, 2018, 10:07:58 pm
content: I remember reading an article by HP many years ago, probably from the HP journal, about their examination of failure statistics which concluded that the vast majority of failures were systematic faults such as design issues, manufacturing process problems (eg. poorly trained operators), apparently insignificant changes in the manufacturing processes of components supplied by third parties etc. Failures were rarely due to random and wearout failures, meaning that MTBFs were pretty much worthless.Problems included overstressed plastic knobs/switches in scopes weakning over time due to heat or ozone exposure and overheating failures due to inadequate thermal designs etc. Some of these, such as excessive temperatures can be predicted and avoided, but there are many failure modes which are much harder to predict - perhaps potting/insulation breakdown in high voltage areas. Sure they might be similar to previous designs but perhaps the voltage is a bit higher, and/or the chemical composition(s) have changed slightly for cost or regulatory reasons or the cooling airflows are slightly different allowing more dirt, smoke etc to be deposited in a critical area. Extended and accelerated testing, if you have the time and money to do it, may not reveal any problems and it may be a few years before large numbers start to fail in the field.A big problem is that the life cycle of many designs/technologies/components is too short these days to be able to collect the relevant statistics. Obviously you can learn from previous problems and try to avoid them in new designs but that is likely to be sufficiently different to make many of the previous issues irrelevant. Excepting Dave's favourites including keeping electrolytics away from heat sources, Silastic and proper mounting of TO-220s etc!I used to work for a telecoms company where 5 9's reliability was taken seriously. I was told a story about one of our products, telephone exchanges which were built into air-conditioned shipping containers. These were sold in the Middle East to accomodate burgeoning demand until permanent facilities could be built. Failures started to occur and an engineer was sent to investigate who discovered that transistors were falling off the PCBs and could be found at the bottom of the racks!It transpired that the TO-18 metal can parts (similar to BC109s) were manufactured with gold plated legs, but it was known that gold can embrittle solder joints. Thus, to improve reliability the plating had to be chemically stripped from the Kovar leads which were then tinned (I don't know if the manufacture or a third party did this). All very well, except that it left a small part of the lead next to the glass hermetic seal untinned, probably to avoid damaging the seal from thermal shock. Kovar is Nickel-iron and it rusts...An air conditioned environment in the desert should be one of the driest places on the planet so it was a bit of a puzzle as to what was going on until the engineer happened to arrive on site early one day and discovered that the local maintenance employees, on arriving at work in the mornings, would plug their kettle(s) in inside the container, because there was power available, and as often as not would forget to turn them off turning the exchange into a steam room!No amount of component MTBF stats and studying pretty bathtub curves help you foresee these sorts of scenarios (albeit a rather extreme example). It would be interesting to know NASA's, and other high reliability industries including the satellite business's take on random/wearout versus systematic failures. Typo: systemic -> systematic

author: David Hess
author_rank: Super Contributor
timestamp: March 13, 2018, 12:20:56 pm
content: Quote from: rfeecs on March 12, 2018, 07:18:44 pmBob Pease called MIL-HDBK-217 out as an example which is just completely wrong in some aspects. Does adding protection networks decrease reliability? According to MIL-HDBK-217 it does.I could not find a copy of the article Pease cites but I did turn this up:https://www.nap.edu/read/18987/chapter/17

author: julianhigginson
author_rank: Frequent Contributor
timestamp: March 13, 2018, 01:12:58 pm
content: MTBF absolutely *does not* equal life expectancy of a product.Your best bet is to look a the kinds of parts that wear out quickly (electrolytic caps? built in batteries? mains protection parts) and do a lifetime analysis on those, based on actual measured currents and voltages and an understanding of the kinds of conditions they will see in use..

author: joeqsmith
author_rank: Super Contributor
timestamp: March 17, 2018, 01:08:26 am
content: May be of interest:https://www.eevblog.com/forum/chat/mil-hdbk-217f-mtbf-and-reliability-rant/msg1375658/#msg1375658I wrote some software using IBM BASIC on a PC for 217 to help speed things up.We later had purchased some software that helped automate some of it.Memory may not be there but it seems the automotive group / IEEE started to move away from 217 ground mobile and created PREL. PREL it seems was based on using their actual field failures.