Is "automotive" grade always better?

Question

I'm working on the parts list for a number of designs for low-voltage (24 VDC) industrial circuits that have no special safety requirements: so long as they don't catch fire no one could be hurt nor property damaged. But they will be used in environments where replacement is expensive, as they are sealed into a more expensive larger unit, and they are in a remote location far away so flying an engineer there to do the refit is very expensive. So replacing a £10 unit might cost several thousand if it fails in service. If the best parts were 10% or 20% more expensive, for our number of units, it's easily much cheaper than a single failure in the field. (Ignoring for the present purposes downtime and reputational costs.) Edit to add: these units are exposed to weather, and the overwhelming majority of failures in the field are moisture ingress, a small amount of DOA. We have ten year failure rate data, and have good approaches for housing etc.

To maximise reliability I was thinking about increasing margins in general: closer tolerance components, thicker tracks on the PCB etc, extra headroom in the power supply, extra temperature range parts, longer soak test, and so on.

I don't have experience of automotive (nor aerospace, nuclear, medical etc) industries, but was considering using the best available parts, within reason.

As far as I've been able to find out, all the AEC Q100 (101, 200) ratings are about reducing the number of failed devices, but they should perform exactly the same.

Assuming cost margins are acceptable, and performance is within spec, is there ever a reason to prefer an ordinary-grade part over an equivalent automotive-grade one?

Edited to clarify: I'm trying to understand if there are any negatives at all to automotive-grade parts other than price.

Edited again to clarify: Our starting point is reputable manufacturer via reputable distributor, such as Microchip/ST/Vishay etc and Mouser/Digikey/Arrow etc. We are not looking at parts via Ebay or Alibaba. We haven't looked at milspec and aerospace parts because a) they don't appear to be available through our channels, and b) are assumed to be way out of the price we're working to. Hence this question is focussed on automotive grade which is easily available and has a premium of 10%-100% for the parts we're looking at.

For a concrete example ATMEGA328PB-ABTVAO versus ATmega328PB-AN. Same package, reel size, temperature range (-40C to +105C), automotive part is about 8.5% more expensive (whole reels, manufacturer's web site prices). It is given as having a more conservative voltage (2.7 V vs 1.8 V) and maximum clock (16 MHz vs 20 MHz). My understanding is it's from the identical design, but with better testing and more conservative promises in order to minimise, ideally to zero, the number of parts which go outside spec?

The automotive part's datasheet has only the following to say:

7. Automotive Quality Grade The devices have been manufactured according to the most stringent requirements of the international standard ISO/TS 16949. This data sheet contains limit values extracted from the results of extensive characterization (temperature and voltage). The quality and reliability have been verified during regular product qualification as per AEC-Q100 grade 2 (–40°C to +105°C). (Datasheet p20)

Edited to add: some commenters have said automotive grade has better certified temperature range; note that is not the case for this particular part, where both the industrial -N unit and the automotive part have the same temperature range. Which is why I'm asking about what exactly "automotive" might imply, in general.

Answer 1

It means that the component underwent testing under specific Automotive standards and passed.

It doesn't mean that the non-Automotive component would not pass as well, it just wasn't tested.

If it is exactly the same component, you pay a bit extra for the automotive qualified component to compensate the manufacturer for paying for the testing, and you get a certificate that you can show to your customer. If your customer doesn't require the certificate, then buy the exact same component, not certified, and save a bit of money.

If it is not exactly the same component, then the automotive certified one is more reliable when used under the challenging automotive environment. But, if your product does not experience that same environment as the automotive one, then that certification doesn't necessarily tell you whether that component will survive longer in your product's environment or not.

EDIT:

are there any negatives, other than money?"

Possibly: an Automotive Qualified component that does not address issues that are not an issue in the automotive environment, such as low atmospheric pressure, deep sea pressure, ionizing radiation, or strong EMI, may actually be less reliable than a non Automotive Qualified component when used in environments other than automotive. For example, a wire-wound resistor (not Automotive Qualified ) may perform better in a nuclear application than a metal film resistor that is Automotive Qualified.

(Unlikely, but possible.)

Answer 2

In the comments you suggest your failures in the field are largely from moisture ingress, which is not going to be solved by buying "better" chips, so you need to look at preventing / mitigating against the effects of that first. Better sealing, careful venting, conformal coating, gentle heating (EG anti-frost / anti-dew) and simple things like clipping a pack of desiccant inside the enclosure all help keep moisture off your board.

It's worth noting here (ask me how I know) that sealing your enclosure too well can result in it gradually pumping itself full of condensation through capillary action over many thermal cycles (be it night-day or just operations of the equipment) which creates a surprising amount of suction and will pull tiny amounts of moisture in through seals, cable glands, even up inside the jackets of cables - small amounts that eventually add up to a puddle in the bottom of the enclosure that can't get out.

Generally automotive grade stuff is designed for higher temperature range which also implies potential for greater thermal cycling, which is a great way to crack solder joints and PCB traces etc. through expansion/contraction cycles. That's something you can (again) design to mitigate - not least by not running stuff too hot, so it's never starting from freezing cold and suddenly heating up massively, for example. Again, a small low-power heater circuit in the enclosure can knock the extremes off this as well as discouraging condensation / humidity.

There's also the question of vibration, which I don't see explicitly stated in your question or indeed mentioned in the automotive components datasheets... but I'm willing to bet manufacturers slapping automotive ratings on chips are at least aware of that aspect & will have tested against it.

Anyway - all this said, for an application such as yours, unless there's a huge price difference I would be buying the AEC-Q rated versions of components if they're available just as it's an easy shorthand for "should be pretty reliable", it tells you someone bothered to think about it & do some tests / qualifications on it.

Answer 3

The answer by Davide Andrea explain exactly what you should expect from an Automotive qualified component. I will just emphasise one particular part:

It means that the component underwent testing under specific Automotive standards and passed.

It doesn't mean that the non-Automotive component would not pass as well, it just wasn't tested.

---

Look at the tests that an AQ component has to pass to be valid and decide if these tests are close or similar to the test you would want to do for your product or application. Then decide if these AQ tests have some value for you or not. If yes (they reproduce tests you would have to do yourself), then by all mean buy the slightly more expensive component and save on your in house testing.

As a real life example: My company was making tools for deep drilling applications, we had to qualify our tools for quite severe environments, particularly for continuous operations at temperature over 150C (~300F), or even over 175C. Automotive standards could not guarantee that (best they do is 125C) so we had to try and test hundreds of components (over a decade and for multiple products obviously, not for a one off). Basically we had to test ourselve every component before it could be admitted in our database of acceptable component. Naturally the AQ components were often the first tested but we also tested industrial and commercial grade. Over the year that database grew and it become quite a piece of private IP for a company because this is knowledge absolutely unavailable anywhere (well a few other companies have something similar but they spent so much time/money building it that they don't share it willy nilly).

Now I am not telling you that you have to do all this testing yourself, but an interesting thing that came out of this component repository is that more than 70% of the parts we ended up using were the commercial grade. We had flash memory rated at 55C which we ran for thousands of hours at 170C without problem (this one had no AQ equivalent to consider anyway). None of our microprocessors were AQ either. Oh, and it wasn't just temperature, our shock and vibrations requirements were also stronger than Automotive standards (moisture wasn't a concern for us so can't comment about that).

So to answer your question: NO, Automotive grade is not always better. These components only guarantees you a certain set of specifications and resistances. If the specs you need are different, try to find a standard closer to your needs, and if no such standard exists, then start to think about your own testing.

By the way, our products also end up being tightly enclosed and sent away accross the globe, making servicing extremely difficult. Our way to stop too many rogue products going out the door was to test (for functionality) and then stress test, at various stages of the assembly and the final product. With experience, we found that most times the few components which were "flaky" were identified early and replaced before final assembly. This didn't happen so often, but the components actually failing in the field during use were even less so (not counting mechanical damages obviously, which was the largest cause of destructions).

Answer 4

Aside from the testing differences, you might see significant differences in availability.

Automotive grade components are designed to sell to automobile manufacturers (or their parts vendors), of which there aren't very many in the broad scope of things. A large auto group like General Motors would buy enough parts to warrant a production run just for them, and they often order parts directly from the manufacturer. Once they stop using the part, though, demand almost completely dries up and it's no longer economical to produce the specialized version of that part. This isn't a problem exclusive to "automotive-grade" components, it also applies to other types of specialty equipment grades (military, aerospace, marine, etc.). Specialty parts have to undergo special testing, which means lead times can be longer.

For the standard version of the part, demand isn't (generally) concentrated in one or two huge accounts. It gets bought by a diverse variety of customers of all sizes. It is significantly less likely that demand suddenly drops and the part is discontinued outside its planned and published lifecycle. Buying direct from the manufacturer is rarer, and you're much more likely to find the parts in stock at your preferred parts vendor.

I often substitute specialty-grade parts when I can't source the standard-grade parts for some reason. I would definitely hesitate to specify a specialty-grade part as my standard selection, though, unless I actually needed the additional temperature range (or whatever else is different in the specs). If down the road you have to swap that discontinued specialty part for a standard part that isn't rated to the same level, you risk having to do extensive re-testing and re-qualification on your equipment. It's generally not a problem the other way around since the replacement is rated to work in all situations where the original one worked.

Answer 5

Personally, I would not specify automotive rated parts in most cases if there were cheaper and as (or more) available parts from reliable suppliers that meet all the requirements. The expensive spot checking of large numbers of samples picked from manufacturing lots on a quarterly basis provides some additional assurance, but most unstressed parts are very, very reliable if the design is not deficient in some way.

If there is slack in the maximum BOM cost I would prefer to spend it in places where it will make a difference such as pumping up ratings on stressed parts rather than wasting it (and possibly causing availability issues). A power MOSFET that runs cooler and has more voltage rating and better SOA is going to add a lot more to reliability than any change to an ordinary resistor. Also it is possible for purchasing to substitute the automotive parts if the ordinary ones become unavailable.

That said, there are some features that were developed for automotive customers that are very nice with or without the rating. The relatively wide temperature range, and 'soft' connections that allow more PCB flexing without MLCC microcrack failures, for example.

Answer 6

This really comes down to a cost/benefit tradeoff - more expensive parts (unit) for better reliability. I'm going to use US dollars in the example that follows.

Lets say you have $10 unit (you said £10, so this is close) built with industrial grade parts that has a MTBF (mean time between failure) of 1 year, and costs $1,000 to replace in the field.

If you upgrade that unit with parts costing 2X as much, so now the unit costs $20, but you get a 2X improvement in the MTBF to 2 years, your total cost over two years has gone down from $2,020 (replacing 2 units) to $1,040 ( replace 1 unit in 2 years), clearly a cost saving.

What if that 2X reliability improvement required that you use parts that cost 10 times a much as your baseline design? Your total cost over two years is now $100 (for the unit) + $1,000 (for the replacement trip) for total of $1,100. This is still an improvement over your baseline design.

So the first thing you need to do is come up with the expected failure rate, or MTBF, for your $10, or whatever the actual cost is, design.

And obviously, things are different if the cost of your base unit $1,000, not $10 like I used. In that case, it may be cheaper to replace it every year rather than increase the unit cost by 2X.

Answer 7

In your example, the parts may well be identical. The very same controller can be reliable enough for automotive use if you keep the clock below 16 MHz and supply voltage above 2.7V, and at the same time be only consumer-grade at 20 MHz and 1.8V, respectively.

Many automotive-grade parts, however, are not the same as their consumer-grade equivalents. Typically, temperature range is wider (a wide temperature range is not that expensive to achieve in a microcontroller, but automotive-grade ELCOs and FETs will actually have a wider range). Anything that could be connected to the battery will have a wider over-voltage margin (12V automotive parts will typically remain operational up to at least 18-20V, and survive up to 25-30V). Again, this doesn't really affect an MCU which needs a regulated low-voltage supply anyway. Larger parts will typically have more expensive pin design, or have more unused pins, in order to cope with mechanical vibrations; but again, a tiny MCU is not heavy enough for its pin design to make a difference in MTBF.

There are also other minor differences, for instance, communication interfaces may have higher noise immunity, and quiescent currents may be substantially lower, so that they don't discharge the battery when not in use.

If high temperatures, vibrations and voltage surges are among your prime failure factors, using automotive parts may be a good idea. Otherwise, the benefit from using such parts will be limited. You might as well use consumer-grade parts and add a large margin on critical characteristics (relevant to your project) yourself.