HI folks - I agree with Guenter as the failure mechanism induced by thermal
cycling will not change if the testing is halted. However, Colin brought up
a good point: Did your customer specify that the testing was to be
continuous? There maybe some product use environment or product design
reason for having the design see 500 continuous cycles.

Dave Hillman
Rockwell Collins
[log in to unmask]


On Mon, Dec 14, 2015 at 4:45 AM, Grossmann, Günter <
[log in to unmask]> wrote:

> We do a lot of thermal cycling tests and quite often we have to remove the
> samples from the chamber for optical evaluation. The aim of the thermal
> cycles is to induce mechanical load due to the mismatch of the coefficients
> of thermal expansion. Because of the plasticity of the materials used in
> electronic applications low cycle fatigue will be activated as the dominant
> failure mechanism. In low cycle fatigue the sum of the cyclic plastic stain
> is the parameter which degrades the material and thus it is not necessary
> to run the test continuously in my opinion.
>
> Best regards
>
> Günter Grossmann
> Scientist
> Empa
> Swiss Federal Laboratories for Materials Science and Technology
> Überlandstrasse 129
> 8600 Dübendorf
> Switzerland
> Tel +41 58 765 4279
> Fax +41 58 765 6954
> [log in to unmask]
> www.empa.ch
>
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> > -----Ursprüngliche Nachricht-----
> > Von: TechNet [mailto:[log in to unmask]] Im Auftrag von colin mcvean
> > Gesendet: Sonntag, 13. Dezember 2015 10:55
> > An: [log in to unmask]
> > Betreff: Re: [TN] Query on Temperature Cycling testing
> >
> > Namaste Nagaraj,
> > In my opinion, the condition for the test is that it should be
> continuous and
> > any significant break in the test which allows for the parts under test
> to
> > 'normalize' will invalidate the test result. As its a customer
> qualification if I
> > was themI would have reservations about how reliable the product
> > performed given such a break. Personally I would scrap the samples and
> > repeat the test with fresh product. RegardsColin
> >
> >
> > Sent from Yahoo Mail for iPhone
> >
> >
> > On Sunday, December 13, 2015, 4:59 pm, Nagaraj U
> > <[log in to unmask]> wrote:
> >
> > Hi All,
> >
> > We are manufacturers of bare PCBs.
> >
> > We were conducting temperature cycling test as per Condition B of JESD22-
> > A104D (-55°C to +125°C). The test requirement was for 500 cycles. This
> testing
> > was a part of qualification of PCBs for one of our customer.
> >
> > We have loaded a set of 4 bare PCBs and 4 assembled PCBs (not powered on
> > - loaded in passive mode after assembly) in the thermal cycling chamber.
> >
> > Now, 350 cycles are completed, but the thermal cycling chamber has
> stopped
> > due to some issue with the thermal cycling equipment.
> >
> > Now my question......... can the testing be continued for another 150
> cycles
> > to complete 500 cycles OR should the whole exercise be started from
> > fabrication of fresh PCBs, Assembly and do the temperature cycling all
> over
> > again.
> >
> > OR, is there any standards which I could refer to handle this situation.
> >
> > Thanks in advance for your valuable inputs.
> >
> > Best Regards,
> > U.Nagaraj
> > MICROPACK LIMITED,
> > Bangalore, INDIA.
> > Kindly note: Our domain name has changed to micropack.in from micro-
> > pack.com, please update my email-id in your address book with the new
> > domain name - micropack.in
> >
> > [Logo]<http://www.micropack.in>
> >
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