Graham

Interesting, but is this not exactly what I have been saying since 1987?
(Not blowing my trumpet, but simply stating how long it takes for a new
idea to become more universally accepted).

Brian

Graham Naisbitt wrote:

> Hello folks Here is a rather belated observational input on the recent
> exchanges re SIR test results. I've been kinda pre-occupied with
> urgent stuff. Anyhow, Jarmo Kiiski asked about the statistical
> evaluation of data and I must point out that recent research data has
> proven that existing flux characterisation tests are....well, here is
> what has been put out by the British National Physical Research
> Laboratory: "The present standard method for evaluating board
> reliability and for flux qualification uses inappropriate test
> conditions, and hence provides unrealistic test data often with
> exceptionally high and misleading SIR values. This is the far reaching
> conclusion of a landmark European collaborative programme led by NPL
> which has now proposed a credible replacement test method"... (sic)
> that is "using finer pitches on the test coupons, lower voltages
> reflecting the actual device field strength and frequent monitoring to
> detect transient effects such as dendrite formation, as the key
> elements for a new test method. Another benefit is that test times can
> be reduced from 7 days to 3 days." I believe that what Jarmo, Cara and
> Amanda may be seeing/have seen, is "blips" in the occasional readings
> they have taken which may actually be dendrites forming and/or
> collapsing but largely missed because the measurements have been taken
> too infrequently - or did I miss something? Brian certainly hits the
> nail on the head by suggesting that the sample size is perhaps too
> small - he hit a few other things too, I guess! My view is that your
> measurements are insufficient to yield you the results you seek i.e.
> choosing the right process material. I certainly could not contribute
> to the debate on statistical interpretations. However, I would also
> suggest that unless you make a test of all process materials on a
> coupon that is more representative of your full production process you
> will continue to get unreliable results from both your material tests
> and the end product in the field. If its reliability matters, then you
> really should take note. Regards Graham Naisbitt
> [log in to unmask]
> www.concoat.co.uk
> Concoat Ltd
> Alasan House, Albany Park
> CAMBERLEY GU15 2PL UK
> Tel: +44(0)1276691100
> Fax: +44(0)1276691227

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