Jack,
I fully understand the need of modelizing and finding the real base. I was among the first to seriously question the reliability results of the Pb free boards presented by NEMI here in Montreal, because they were using the SnPb reliability model. Different material must imply different cycling model.
What I am trying to ask is if the thermal cycling is the only way to assess reliability of joints, or something else, of a different approach or technology could be used to do so. Something that could show long term behaviour based on shorter tests. Just on the delirious side, maybe placing the test vehicle in a high pressure / vacuum chamber and cycling a couple of times would replace 100 regular cycles? Or who knows what... I was naming HAST, etc. because they are different, using mechanical stresses jointly with thermal cycling.
Thanks,
Ioan
> -----Original Message-----
> From: Jack Sherman [SMTP:[log in to unmask]]
> Sent: Monday, January 10, 2005 1:40 PM
> To: (Leadfree Electronics Assembly Forum); Tempea, Ioan
> Subject: Re: [LF] Lead-Free Acceleration Factor-use of Accelerated accelerations
>
> Ioan,
> HAST, HASSLE, HASTY, whatever they maay be called may be used, and you can address your query independently to Tony Chan, but they are meaningless and dangerous without establishment of activation energies....Twisting of paper clips is not an acceptiblle model for alloys.
>
> There be no necessity to have equal active and dwell times for the cycles. Real life doesn't have equal cycles, the evaluations are to establish usable reliability models, not to find out what makes a joint break. You can use an inadequate model, and you can smoke cigarettes and you can use a cell phone while you drive, but it doesn't establish roots and roots are what nourishes worthiness.
>
> It may well be that we are considering the wrong elements, by comparing SnPb to LF alloys.
> We should not be comparing what we have to what we have had, it is the reliability of what we want to use that we need, not how much better or poorer than last years model.
>
> It isn't an easy or inexpensive task, but it is an intensive and a pensive task.
> Hope this helps a bit.
>
> Cheers
> Jack
>
> "Tempea, Ioan" <[log in to unmask]> wrote:
>
> Hi everybody,
>
> if I get it right, there are chances that the dwell times be longer than the active times. In this case, the reliability tests based on cycling tend to be prohibitively long. So, besides costs from recycling fees and costlier materials, the companies will have to budget in longer time to market and eventually costlier tests.
>
> Aren't there any other alternatives? I remember back in school that for gears, the temp cycling was significantly reduced by applying stress on the tested train. In electronics there are all the HAST, HATS, etc. Can't they be used, or modified, so that the temp cycling be reduced?
>
> Best regards,
> Ioan
>
>
>
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