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December 2015

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From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Mon, 14 Dec 2015 14:57:07 +0000
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I agree. There is no "condition for the test" to be continuous, and in fact there are instructions in other tests that if the test is stopped it may be continued to finish.
Electronic CCAs and PWBs and solder joints do not "normalize" when the test is stopped. If you understand what the test is doing, which is to simulate the solder joint's grain morphology over a period of time, you would also understand that the only way to "normalize" them would be to re-solder them.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Grossmann, Günter
Sent: Monday, December 14, 2015 4:45 AM
To: [log in to unmask]
Subject: [TN] AW: [TN] Query on Temperature Cycling testing

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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