June 9, 2011
Some folks do burn-in of completed assemblies at 25C or 50C at longer
periods than 48 hours. Some folks do ESS testing rather than burn-in
testing. The type of testing depends a lot on how the individual
electronic parts in the assembly were tested. For example, if the parts
are military specification parts that were subjected to burn-in testing
by the part manufacturer, then you have some level of confidence that
the parts you receive will be "reliable"; that is, the part manufacturer
would have weeded out weak-knee type parts during the burn-in testing.
However, if you purchase the parts without burn-in testing by the
manufacturer, then some type of burn-in or ESS testing at the assembly
level may be warranted.
Regarding burn-in versus ESS testing. Although ESS testing can weed out
some % of defective parts, in my experience, if you do burn-in testing
at the assembly level followed by ESS testing, the % of additional
failures found by ESS testing is normally small since most of the latent
part failures would have been detected during the burn-in testing. We
could argue the benefit versus cost of ESS testing. Some folks mandate
it be done, others do not. It all depends on the risk factor for the
equipment. One advantage of ESS is that it is capable of determining if
the OEM manufacturing processes have changed over time and if these
changes are driving part failures. So once you have qualified the
design, it may be worth the expense to do ESS on a sample basis over
time.
Regarding burn-in time duration, if you look at various military
specifications, you will find that the burn-in time period is much
longer than 48 hours. However, this does not mean assemblies should be
burned-in for the same length of time. One thing that some folks do
during burn-in is to verify power supply output voltages are not
drifting out of tolerance over time. In some cases just testing for 48
hours may not be able to detect output voltage drift.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rivera, Raye
Sent: Wednesday, June 08, 2011 8:43 PM
To: [log in to unmask]
Subject: Re: [TN] How to determine Burn In duration?
Hi Robert,
Thanks for the reply. Those are some good ideas. I've never heard of the
approach of soaking at high temp, then doing a quick test before. That
sounds promising. We do some shake and bake testing on new products to
evaluate reliability much as you suggest.
The burn in process I am looking at is not so much a reliability test as
an attempt to force out any infant failures before the product leaves
the factory. The theory is that the right burn in duration will force
out infant failures but not significantly decrease the life of the unit.
Best regards,
Raye Rivera
QA Manager * Canoga Perkins * 818-678-3872 * [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Wednesday, June 08, 2011 2:21 PM
To: [log in to unmask]
Subject: Re: [TN] How to determine Burn In duration?
Hi,
This is more of a 2 cent version of help I pulled from my own
experience.
You want to test for the failure types you expect to dominate. I
generally think of two failures types, design and implementation.
Thermal cycling and shake on a small number of units will probably give
you more data on reliability than setting up 100 units and running them
for 48 hours at 50 C. You mention smaller number of units so I would
verify design margin and mechanical assembly to insure a solid design
and process.
You want to attempt to excite any failure modes, either mechanical or
electrical. I like to take a powered down unit, soak it at 90C, then
turn it on for a short functional test. Repeat this at higher temps
until the unit fails. The idea is to find where electrical parameters
shift with temp.
Soaking at high temp followed with a quick test allows elevated temp
testing of all components without frying key power components.
Many years ago I used this to check boards using 64K Bit DRAMS. (Yes it
was a while back.) But wow did it screen out bad components, you could
see major differences from lot to lot.
Also, test at low temps. Al caps really change value at low temps.
Do you have any existing failure data? What does it look like?
Bob K.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rivera, Raye
Sent: Wednesday, June 08, 2011 5:00 PM
To: [log in to unmask]
Subject: [TN] How to determine Burn In duration?
Hello Technetters,
Does anyone know of a good reference on how to reasonably set the
duration for burn in of products? I haven't been able to locate much
information on this topic.
Our products are primarily fiber optic telecom equipment. We burn them
in at 50 degrees C for 48 hours. This procedure was set up before my
time and I do not know how it was arrived at.
Lacking any better approach, I would probably put 10 or so units into a
long term burn in experiment and measure time to failure. Then, attempt
to fit to a Weibull distribution and see if I can get a theoretical
model for what percentage will fail after X hours of burn in. I'm not
sure if this is reasonable because the sample is small and the time to
failure may be quite long.
Does anyone know of a better approach? Thanks all!
Best regards,
Raye Rivera
QA Manager * Canoga Perkins
20600 Prairie Street * Chatsworth * CA 91311-6008
818-678-3872 * [log in to unmask]
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