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January 2005

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From:
Jack Sherman <[log in to unmask]>
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Date:
Mon, 10 Jan 2005 12:30:07 -0800
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Ioan,  and LF test fitness colleagues,
We are on the same search, and perhaps your query will start a different thread:

 1. Is there a non thermal procedure that will predict integrity of a solder joint?
That's why I used the paper clip phrase. Grab the terminal and stress it mechanically the way
real life does it.

2. Is there a .05 to 0.1 Hz vibration that could be an evaluative three day duration test?
Some concrete fell at the Chicago Wrigley Field, some concrete fell at a Paris airport,  - - solder is sort of granular, and from a report last week, sort of several planar structures while it is in the molten state. Faults found at cross sections have been shown to be artifacts of the cross section. I have created faults by poor polishing and poor decorating procedures.

3.  Is it possible that the board layout itself predisposes some of the joints to be under more severe stress than others and the failed joints happenned to be in the wrong place?
  To determine root cause of some early field failures,  I sprinkled Lycopodium powder on a board and showed that a cooling fan mechanically vibrated the module and the powder showed amplitudes at several critical locations. Thats how we discovered that power supply filter coils, stand-up, thru hole, failed their solder joints, not because the solder joint was inadequate, but because the part itself waved much more than was expected.   One further one, ceramic chip capacitors broke their solder joints after only a few weeks of field use, not because the joint was poorly soldered, but because the length to width orientation was wrong for when the factory board shear knife caused the board to buckle momentarily.

So if I read thoughhts into your question,  lets look at other, different technologies, not crab about how expensive and time consuming and labor intensive the thermal methods are.

Thanks and regards
Jack
"Tempea, Ioan" <[log in to unmask]> wrote:
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" 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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To temporarily stop/(start) delivery of Leadree for vacation breaks send: SET Leadfree NOMAIL/(MAIL)
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