How to determine useful life of electronics

[ElectricAl76]

Hi,
What are the techniques used in the industry to estimate the life expectancy (useful life) of electronic assemblies?
This is not related to the MTBF, it should answer how long can I guarantee a product.

Thanks

 

[IRstuff]

But, it is, since MTBF is usually shorter than useful life. Most requires are written one of 2 ways:

> Strictly 20 life
> Economic life, when the sum total of replaced parts exceeds 1/2 of new system cost

In either case, the life is maintained by replacing bad components. If there is no replacement, then the MTBF is the life.

Your specific requirements might dictate something else.

TTFN

FAQ731-376

 

[cranky108]

Either 1 year of sitting on a shelf, or 20 years in service.

This is probally dictated by the life of the capacitors, in the power supply.

 

[IRstuff]

No one guarantees 20 yr operation for consumer products. The longest warranties are for cars, somewhere between 5 and 7 years. And that's based on MTBF, and the economic breakeven point on the initial cost adder that covers the warranty.

TTFN

FAQ731-376

 

[ElectricAl76]

Thanks for the answers but according to the following article MTFB is not related to life expectancy.

Quote:
"In reality, there is no direct correlation between MTBF and the actual operating life of a product. In fact, it's possible to find a power supply with extremely high MTBF but very low operating life span, depending on the types of components used and actual operating conditions."

Article:

http://www.plantengineering.com/art...ake_power_supply_MTBF_for_life_expectancy.php

Does anyone know any other methods or is the MTBF the only way get some kind of answer?

BTW. It a low power application and the BOM does not have any electrolytic capacitors.

Thanks,

 

[ElectricAl76]

BTW: No part can be replaced or repaired in this application

 

[eng1ne]

If no part can be replaced in this assembly, then MTBF applies wholly and directly, taking into account operating conditions.

Once the first functional components fails, the assemblies useful life is over.

Also refer to the article for this quote:

"In reality, MTBF is the total functional life of a system component divided by the number of failures."

If Life = MTBF / 1, then Life = MTBF.

 

[IRstuff]

ElectricAl76

I think that your original statement missed the point of the article, to wit, MTBF is calculated, based on certain operational and environmental assumptions, so unless you know what's what, any single MTBF calculation may not have any bearing on expected life in a single, specific, situation.

So, if you correctly account for operation and environment, then MTBF is indeed the mean lifetime of the of the system in that service environment.

For the purposes of warranties, it's a gamble, so the beat that you can do, in the absence of user data, is to assume the worst-case operation and environment, determine the MTBF, and set your warranty cost and period accordingly.

TTFN

FAQ731-376

 

[ElectricAl76]

At the risk of sounding stubborn, here is a few more quotes:

What does MTBF have to do with lifetime? Nothing at all! It is not at all unusual for things to have MTBF's which significantly exceed their lifetime as defined by wearout -- in fact, you know many such things. A "thirty-something" American (well within his constant failure rate phase) has a failure (death) rate of about 1.1 deaths per 1000 person-years and, therefore, has an MTBF of 900 years (of course its really 900 person-years per death). Even the best ones, however, wear out long before that.
...
MTBF is, therefore an excellent characteristic for determining how many spare hard drives are needed to support 1000 PC's, but a poor characteristic for guiding you on when you should change your hard drive to avoid a crash.

"A major problem for many people with the term Mean Time Between Failures is that it is expressed as "time" when it is really used to indicate failure rate during the normal life period. To further confuse the issue, some people use the term MTBF to indicate Mean Time Before Failure, a case when it applies to wear-out modes and really does relate to service life. And, as I noted above, some people don't know what they are talking about and claim service life is equal to "Mean Time Between Failures"!"

http://www.faqs.org/faqs/arch-storage/part2/section-151.html

http://www.weibull.com/hotwire/issue22/hottopics22.htm

MTTF is what I am looking for.
Thanks for the replies anyway.

 

[IRstuff]

You really need to do some readnig no your own. MTTF is calculated the same way as MTBF.

TTFN

FAQ731-376

 

[VEBill]

In theory, adding "extra" components reduces reliability.

In reality, adding ESD protection circuits, EMI filtering, or even redundancy - all help real world reliability and increase system life time.