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Electronic components aging

Discussion in 'Electronic Design' started by Piotr Wyderski, Oct 15, 2013.

  1. Speaking of high reliability... I think that it is often
    a somewhat neglected issue, so I start this thread as a
    mean to collect *practical* observations for people who
    care about long MTBF. In other words, "if I had to build
    a device which should last 50 years, I would... what?"

    Resistors (if not overloaded): immortal

    Ceramic capacitors: as above
    Tantalum/nobium caps: ?

    Electrolytic caps: disaster area

    Transistors, diodes and ICs: the silicon die should not
    degrade, but how about the endurance of the resin?
    At least some early Polish ICs had problems here:
    the thermal coefficient of the casing was not well-matched
    and power cycling finally broke the bonding wires.
    There were some moisture absorbtion problems, too.
    Is it still an issue?

    BGA: it can be expected that thermal cycling will
    eventually destroy the balls, as there are no "springs"
    to absorb thermal stresses. Gull wings are much better here.

    FR4: ?

    Soldering: the EU has done a lot in order to make
    the newer devices not very reliable as a consequence
    of the RoHS directive. I see nothing wrong with the
    old SnPb joints, the old boards look healthy.

    Conformal coating: ?

    Wires: ?

    Please add your comments.

    Best regards, Piotr
     
  2. Boris Mohar

    Boris Mohar Guest

    Optocouplers
     
  3. With the best will in the world, there is no electronics based technology
    that will last that long. It is hard enough doing designs that are required
    to have a life of 20 or 25 years with minimal (no) maintenance. After that
    time the equipment is replaced in major refurbishment programmes.

    Any component that relies on the long term stabiliity of chemistry will
    degrade and fail eventually. Even in the mechanical world metals like Iron
    and Stainless Steel will change over time.

    Only in software can you achieve really long lifetimes (if you are careful
    about your design) but then what would you have left to run it on?

    --
    ********************************************************************
    Paul E. Bennett IEng MIET.....<email://>
    Forth based HIDECS Consultancy.............<http://www.hidecs.co.uk>
    Mob: +44 (0)7811-639972
    Tel: +44 (0)1235-510979
    Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
    ********************************************************************
     
  4. Uwe Hercksen

    Uwe Hercksen Guest

    Hello,

    they are almost immortal if there are no fast and frequent and large
    temperature changes and if oxygen has no access.

    Bye
     
  5. Guest

    One way of examining this is to look for cards returning from systems
    replaced by modern systems.

    Look for the date codes (YYWW) for the youngest chip on the card to
    get some idea when the card was made.

    While it might be hard to get such information from companies active
    in the industrial technology field for decades, you might be convinced
    them to use allow such figures "how good devices we are (still ??)
    making" to be published.
     
  6. Large soldered connections on PCBs. Things like high current
    transformer tags and automotive-grade interconnectors. The pads always
    seem to develop circular cracks and go intermittently O/C.
     
  7. Guest

    That means one thing: Plain Old Relays. How long can sealed relays be expected to last, if we only fire it up occasionally? Perhaps one in weeks.
     
  8. RobertMacy

    RobertMacy Guest


    Would designers of those Jupiter/Staurn satellites, etc jump in here? Give
    back to the community. Their stuff works ten years and upwords of 25
    years. Be great if they wrote a little history of the 'battles' one must
    embark on and the design philosophy required to overcome THOSE reliability
    obstacles.
     
  9. Guest

    But they don't have the same enemies: Air and Water. Space might be easier to deal with than mother Earth.
     
  10. Be careful about using terms like MTBF unless you know the actual
    definitions. Often it applies only to the bottom of the bathtub curve,
    so infantile failures and wear-out are not considered. IOW, a part
    with a 20 year MTBF could legitimately wear out in a few years (if it
    even lasts the first month).
    Not my experience. Resistors that get warm and resistors that are
    stressed by high voltages (especially large DC voltage) often die
    early. Surge damage (often limits are not specified) can occur on
    stuff connected to the outside world (eg. induced currents from
    lightning strikes).

    Resistors run at < 10% of rating and low voltage can pretty much be
    ignored, IME.

    Trimpots and trimcaps are pretty good too (unless abused).
    Pretty reliable, not as good as unstressed resistors.
    Don't know. The niobium oxide ones are claimed to use the new "no
    burn" technology so presumably they'll spontaneously burst into flames
    less frequently.
    Expect to replace them after 5 years to 50 years, depending on how
    much heat they see (internal and external) and other factors. But
    they're quite _reliable_, they just have a limited and fairly
    predictable life, like electromechanical relays. It's pretty much
    impossible to make a mains-powered device of any usefulness without
    electrolytic caps, and there is a lot of experience with their
    reliability- eg. my HP 333A distortion meter is loaded with them
    (maybe 50+) and it still works fine after maybe 40-45 years.

    Lack of electrolytic caps can lead to extreme design choices that may
    negatively affect reliability.

    Inductors made from fine copper wire can be unreliable.
    If they're stressed, they can die early, sometimes very early.
    Moisture can hurt them. Temperature cycling can make them die very
    early- some early SSRs would die in months from thermal cycling if you
    ran them at the worst-case duty cycle. Power semiconductors are almost
    always stressed and can die early or later from thermal cycling. Parts
    run at too high internal current densities can die from
    electromigration, especially if hot. Radiation can kill them or cause
    degradation or latch-up. Sometimes they're damaged in assembly and
    expire later.

    LEDs and optocoupler LEDs degrade, especially if run hot and/or near
    their current limits. I would guess photodiodes with plastic lenses
    degrade if exposed to UV. Switches wear out, relays wear out.

    Probably, but less so.
    RoHS solder probably doesn't help.
    Solder joints can be bad, can get cracked etc.
    What does failure of conformal coating look like?
    Need to be treated carefully to avoid fatigue failures due to
    vibration or other flexing, but very reliable if properly used. Crimp
    connections are usually quite good if done right.

    Sensors are frequently a problem, mostly due to their operating
    environment.

    Connectors, due to corrosion and abuse. Especially if they're soldered
    to a board (and especially^2 if they're SMT and not mechanically
    isolated from abuse).

    Anything on a panel or connected to the outside world in any way is an
    opportunity for idiot-proofing to be tested.
     
  11. RobertMacy

    RobertMacy Guest


    they do have vibration, extreme temperature ranges, many temperature
    cyclings, and probably radiation hardening [which can be considered simply
    as accelerated testing on earth?]

    probably no water, smog, or dust though. Remember all those plastic IC's
    that died when shipped from Silicon Valley in the north flown down to Los
    Angeles in the south and the packages 'sucked' in smog during pressure
    change from descent of the airline carrier. Later the smog simply 'ate'
    the IC's up. Were those Fairchild's or National's first attempts at
    plastic packaging?
     
  12. They're okay for bypassing power rails if you have a local regulator
    that limits current (and if you derate the voltage).
     
  13. Tim Williams

    Tim Williams Guest

    My opinion on capacitors:
    - Definitely avoid electrolytics
    - Tantalums are, at *best*, dubious.
    - Ceramics don't die, but they do vary with temp, voltage and age.

    I have some old equipment with them and none are toast (my Tek 475,
    whereas the electrolytics are all dried up), but that's just one case.

    The main hazards are excessive voltage, and current spikes; they will be
    more reliable under conditions where this is controlled. For instance,
    using 16 to 25V rated caps on a 5V rail, and supplying each subcircuit
    from a current limiter (since a small bypass cap looks like a grain of
    sand against a heavy source, even if that source is current limited).
    Tantalums have also been made with internal fuses: of course, you need to
    accommodate failure in your design, which begs the question, why did you
    bother installing it in the first place?

    - Ceramics are more-or-less forever, but they do change. A typical X7R
    (and I won't even consider any worse grade) is +/-10% at room temperature,
    but can be -20% at rated temperature (I think??) and -50% at rated
    voltage. The derating is therefore similar to tantalums: pick 3x more
    voltage rating than you need. High-Q ceramics also age, where the value
    simply drops over time, while under polarization I think. I forget if
    this is included in the rated tolerance, or if it's additional as well.
    (Drops of -50% aren't uncommon, but I don't recall if that's Z5U or what.)
    So the challenge is, desigining your circuit to accommodate a wide range
    of capacitance while meeting guaranteed performance.

    Gold standard would be using C0G where possible (essentially an ideal
    capacitor at most frequencies, and AFAIK, stable under all conditions), of
    course, these are bulky and expensive. Definitely worth considering for
    the smaller timing and signal filtering components (say, anything up to
    10n, maybe even 100n).

    - Resistors: carbon composition can age a bit, especially under heavy
    load, but with those pretty much history these days, that's not a problem.
    :) I don't know of any issues otherwise. General advice applies, don't
    overheat them (as much for their own sake as for the sake of stuff
    nearby).

    - Generic silicon thoughts: I don't know that modern molding materials
    (i.e., since, say, the 60s or 70s?) are a problem (at least over here?
    :) ). Plenty of equipment survives from those days, including power
    amplifiers, for instance, that see wide temperature swings.

    - BGAs: I don't think these are actually a big problem. If leaded solder
    is used (reball if necessary?), cracking balls isn't a problem. The chip
    can also be underfilled with resin, encapsulating the balls and gluing the
    chip down. Pains could also be taken to minimize flexural stress on the
    chip and board (a good idea around any large or brittle device), say with
    stiffening frames or strategic routes through the board.

    With the amount of consumer stuff since RoHS, you'd think we'd have seen a
    lot more examples of tin whiskers -- apparently it was all hot air, and
    the processes turned out much more reliable than anyone expected. Yes
    there have been notorious cases of cracked balls: Xbox's Red Ring of Death
    for one, but that's a thermal issue at its root. It's characteristic of
    the process, but not one that is commonly seen under normal operation (of
    suitable vibration and temperature conditions).

    I also heard QFPs can be more failure prone, I guess because they have so
    damn many leads and not much solder to hold them down? Only example I
    have is a computer from 1987, which contains PLCC and TQFP gate arrays,
    but old logic like that never sees strain or temperature cycling, so it's
    a bad example.

    - Wiring -- do what the aerospace people do: use teflon wire, and lots of
    ties. I suppose I wouldn't mind PVC wire myself, but it probably will go
    brittle after long enough. Of course, you can't clamp or pull teflon too
    tightly either, because it cold-flows! Vibration and stress is the killer
    on connections, so keeping all that neatly secured will go a long way.

    Now, all of that said -- plenty of consumer electronics have demonstrated
    a life time over half a century, at not much above ambient temperature --
    but guaranteeing an MTBF of the same isn't so easy. The best approach is
    going to be finding mil-spec components, ceramic body packages where
    possible, and doing what the avionics people do, massive loads of ceramics
    to replace electrolytics. Gold plated everything is quite typical. Mil
    spec doesn't seem to have any problems with FR4 (heck, even old consumer
    phenolic from the toob days remains mostly intact, and there's no kidding
    about temperature cycling there). Controlling temperature is the other
    killer; excessive heatsinking isn't a bad thing!

    Tim
     
  14. Robert Baer

    Robert Baer Guest

    * Only if leaded and mounted according to NASA - leads having graceful
    hook-like "loops" to relieve stress. Then wrapped around turret for
    mechanical reliability, and as a final step soldered for electrical
    reliability.
    Oh, yes..100 percent test values BEFORE using as you might find the
    one in a million that is almost shorted or crystallized to high value,
    or the one in ten thousand (or less) that was improperly binned.
    * Same gotchas.
    * Same gotchas. Except Tants have a poor life that gets worse as
    temperature goes up. I would not recommend them for 50 year service;
    maybe 10 year service..
    * I know of the old wet can 'lytics that lasted on the average of 10-15
    years,with maybe 10 percent lasting to 20 years WITHOUT electrolyte
    replacement. And this is in "typical" home environment,some areas in the
    US hotter than others.
    The problem with the "dry" 'lytics is there is no liquid electrolyte
    that can be replaced.
    The Sprague TE series seems to be the exception, lasting over 20
    years with no apparent change (typical home environment).
    * Excellent; have seen no problems up to and including 200C.
    Around 210C or so, then something goes irrevocably sour.
    This info is not to be confused with usability,only as an indicator
    of possible reliability.
    * In the 70's or so, at (the original) Fairchild, they were making power
    transistors in the TO-3 package for hi-rel, and the Army told them to
    STOP plugging them into a test fixture as that decreased the reliability
    by at least an order of magnitude.
    The problem was, "merely" pluggint them in added stress to the
    leads,creating microcracks in the glass-to-kovar interface.
    So,extend that to anything that adds stress in lead=to=package interface.
    * *Temperature* cycling causes problems, most especially in vias,
    metal-glass-conductor (metal or doped silicon); due exclusively to the
    large difference in the coefficient of expansion.
    * There were attempts to glop silicone on top of a chip before
    encapsulation to reduce bondwire stresses..successful in that regard,but
    too much damn moisture got encapsulated with the glop.
    * Agree. Know noting about BGA issues.
    * X,Y,Z coefficients of expansion are all different and are grossly
    different that any parts you may encounter.
    Here is where the NASA stress-relief techniques come in handy.
    PCB vias should, in my opinion, be as large as one can get away with;
    none of this 14 mil-in-thick PCB. 20 mil is OK even at 200C.
    * I may have been the only vender that was RoHS compatible at least a
    year before the EU made an un-avoidable rule.
    One has no choice if one wishes to guarantee (essentially) PCBs up to
    204C.. silver bearing solder is the lowest temperature must.
    I am totally against the SAC crap, despite the reasons behind the use.
    Multicore makes Savbit, a tin-lead solder alloyed with a small amount
    of copper - to eliminate the pitting of soldering bits (irons to us
    USians) due to copper in the production bits alloying out and into the
    solder.
    There is NO SUCH "CONCERN" WRT reflow soldering!
    The added copper decreases the reliability of the solder connection.
    With regard to silver-bearing solder, the same can be said about SAC
    crap.
    * Maybe..with great care and atmospheric controls (NO moisture), baking
    of units beforehand, etc.
    * Review NASA specs WRT nicking of wire during stripping.
     
  15. I think they may the first to admit that they did not think the Voyagers
    would be operating for so long. It is one thing for the systems to last a
    long time, but a completely different thing if you are asked to make sure it
    will keep going.

    --
    ********************************************************************
    Paul E. Bennett IEng MIET.....<email://>
    Forth based HIDECS Consultancy.............<http://www.hidecs.co.uk>
    Mob: +44 (0)7811-639972
    Tel: +44 (0)1235-510979
    Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
    ********************************************************************
     
  16. Indeed. Some people are afraid of electrolytic capacitors, but the wear-outmechanisms are well known and the lifetime can be very long if you treat it as you should. The thermal cycle effects which is one of the major root causes for failures are low due to mechanical reliefs in the packages used

    Ceramic capacitors, that is used instead of electrolytic capacitors since they are thought to have better reliability, have horrible thermal cycling specs (at least for SMD types)

    Cheers

    Klaus
     
  17. I did design for ESA in an earlier job.

    We used the JPL Derating guidelines (Jet Propulsion Laboratory, which laterbecame a subdivision of NASA).

    The idea of course is to keep the subjected stimuli well below the ratings of the device. The stimuli is calculated from what is expected and any short time overload condition. Normally maximum 60% of the ratings for voltage,current and power.

    Reduced length document:

    http://engineer.jpl.nasa.gov/practices/1201.pdf


    When the basics is covered, the surroundings of the device is handled. In principle any device is scrutinized for any failure and a DFMEA analysis is done to make sure what kind of propagation a single error has. The errors is not just from components FIT, emvironment influences etc, but also from cosmic raditation. So a SEU (Single Event Upset) is also analyzed. For example, for ICs which has not passed the nessesary radiation limnits, the device is surround with components to protect it from the SEU and to reset it after the SEU

    Any device has a FIT number, not only the Space rated parts, which can be found for most devices digging deeper in the manufactor tests reports. The FIT is normally deduces from accelerated thermal cycling tests.

    As for the special RAD hard devices, that is used for Space designs, the dies are AFAIR special dies, used only for Space, with extensive testing on all important parameters

    So any device is considered to be failure prone, and to increase availability figures, redundant circuits are used, either fully redundant or partially redundant with voting systems

    The trend recently has been to try to use non-RAD HARD components for spaceflight, to see if it is possible to save costs with possibly lower reliability.

    Cheers

    Klaus
     
  18. For practical design, important items to consider apart from other mentioned in the thread is the difference in thermal expansion coefficients from components to the PCB. So for long reliability designs, placing ceramics on aFR4 substrate is not always optimal

    Leadfree solder may also not be optimal, although I think the discussion ofreliability of leadfree versus leaded designs have not ended

    Cheers

    Klaus
     
  19. <snip>

    You mean stay within a components rating? Novel idea.

    Cheers
     
  20. Sylvia Else

    Sylvia Else Guest

    The graph at the end indicates that reducing the stress ratio (as
    defined there), provides an increase in reliability, but not a dramatic
    one. One could suspect that what that graph is really showing is that
    the the higher the stress ratio, the more quickly a latent fault becomes
    manifest, rather than that the stress itself causes the fault.

    Sylvia.
     
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