Hi Tom,
What happened to your e-mail address so you have to go through Mike?
In a message dated 5/23/05 11:43:56, [log in to unmask] writes:
> 1) Doing F/A post-"failure" is absolute. Cable-connector artifacts are 
> certainly fixable. Ring it out, fuss a bit, then re-set the Anatech, make some 
> notes and keep cycling/counting. In contrast, PWB artifacts are certainly a 
> serious diversion, and I agree must be considered separately from solder-joint 
> failures. Depending on whether you are looking at PWB features or solder-joint 
> features, you might be able to jumper around an identified anomaly and keep 
> going.
> A: Full agreement.
> 2) Manual-probe for opens (for solder-joints) is a very reassuringly 
> reliable confirmation of a properly set up Anatech's detection. The Anatech catches 
> them a few cycles sooner than the manual probe. During bench probing, make 
> sure you don't push down on the component, otherwise you'll get apparent 
> continuity again.
> A: There are muliple problems with manual probing: (1) they interupt the 
test, (2) they disturb the test and cause failures with this disturbing, (3) they 
are labor intensive, (4) many solder joint failures cannot be found that way, 
(5) solder joint failures are hardly ever opens—the fracture surfaces are like 
connector surfaces, and electrical opens occur only during mechanical shock, 
vibration, or temperature changes; and then only for micro-seconds, (5) manual 
probing will show failures many cycles (1000's) after they occur, if at all.
> 3) Resistance does not ease slowly upward.  It flickers a bit during ramps, 
> then skies to wide-open within a few cycles of the first flicker. Subtle 
> corrections for resistance/temperature effects and thresholds are typically not 
> that important.
> A: By the time you see a resistance increase it is way past the time of 
failure occurance. However, plated-through vias fail in this manner,
> 4) Fractures (visible and pry-apart-verified) always start happening long 
> before the joint starts showing resistance-increase or opens. You can see the 
> crumbled shear-plane working it's way thru the fillet waist, then developing 
> into cracks, which get worse and worse as cycling proceeds, then the joint 
> goes electrically wide-open.
> A: True, that is why you need a sensitive in-situ failure indication,
> 5) I certainly agree that failure definition is crucial. "Crack"-free life 
> is 1/4 to 1/2 electrical-open life, and that ratio depends on scores of 
> factors. Folks typically know that. Some of us use (or at least we think we use) a 
> definition of 1/2 fracture-plane area as the "life". That's tough to measure 
> (requires lots of tests and de-caps) and apply. Certainly predictor-models 
> and their users must cope with the crucial distinction between 
> life-at-first-shear-damage and life-at-first-full-open.
> A: "Life-at-first-shear-damage" is essentially the first cycle; "
life-at-first-full-open" is many thousands of cycles past when failure really occurred. 
The failure definition has to be unequivocally defined, full fracture, with the 
sensitive equipment that can detect it close to that point in time [no 
electrical equipment is capable to determine the exact time,
> 6) The "random" question is pervasive. Early-fail mavericks typically show 
> a workmanship reason, and their life could be discounted, in defining the 
> population metrics. We use any early-fail maverick (that shows statistically 
> out-of-family life, as anecdotal evidence in workmanship/QC guidance. Mavericks 
> aside, all the specimens in the population that's left (beta 6-9 typically, 
> in test), all look pretty much the same (certainly "same" is arguable, what 
> with void content and local geometry effects still undefined).
> A: When you get betas in the 6-9 range that means you are using a 
medium-severe to severe accelerated test ( beta values have a tendency to increase with 
the severity of the test as determined by the resulting mean cyclic lives), low 
acceleration tests yield betas below 5,
> 7) Early-fail mavericks are the bane of high-rel applications. What is 
> statistically representative and inevitable, and what is a fixable never-to-be 
> deployed maverick? We (not speaking as a company rep !!) always agonize over 
> whether we should we use a low maverick-inclusive beta in early fail 
> projections, or use a controlled-test beta-8 projection?  anyhow ....
> A: Quite frankly I see little evidence of early-fail mavericks.

Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com

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