AT&T published an excellent reliability paper:
"A Comprehensive Surface Mount Reliability Model Covering Several
Generations of Packaging and Assembly Technology", by J. Clech et.al. IEEE
Trans on Comp. Hyb. and Manuf. Tech. Vol. 16, No. 8 Dec. 1993, p.949
It listed cycle to failure and damage assessment based on stress test,
storage, transport, operation, worst days and office enviornment work
conditions.
jk
>Return-Path: <[log in to unmask]>
>Date: Wed, 7 Jul 1999 15:49:54 EDT
>Reply-To: "TechNet E-Mail Forum." <[log in to unmask]>, [log in to unmask]
>Sender: TechNet <[log in to unmask]>
>From: Werner Engelmaier <[log in to unmask]>
>Subject: Re: [TN] [LF] "Drop-In" Replacement
>X-To: [log in to unmask], [log in to unmask]
>To: [log in to unmask]
>X-MIME-Autoconverted: from quoted-printable to 8bit by deimos.idirect.com
id PAA82089
>
>In a message dated 7/7/99 9:35:30, [log in to unmask] writes:
>>Hi, Werner,
>>What tests are sufficient to ensure "reasonable" reliability [of solder
>joints]?
>>Carol
>
>Hi Carol ,
>This sure is a loaded question, and can not be answered by a brief statement
>without being flip—so, you asked for it!
>Personally, and from experience, I rather assure solder joint reliability
>using an adequate modeling approach, taking into account both the
>physics-of-failure and the statistical failure distribution. The reason is
>that it is no more error-prone than testing and much less expensive and
>time-consuming. The time and cost factors of testing has led to test
>short-cut, with sometimes catastrophic consequences.
>Using a 'Design for Reliability (DfR)'-approach, of course, requires a
>reasonably good model. For near-eutectic Sn/Pb solders and their derivatives,
>we have the data on which a number of modeling approaches used in the
>industry are based. But for many of the newer soldering alloys, including all
>of the lead-free solders, we do not have sufficient data to determine a
>fatigue reliability model. Thus, until such time, any modeling requires
>assuming that the solder in question behaves similar to Sn/Pb and multiplying
>some safety (actually ignorance) factor (>=2xlife to acceptable failure
>probability).
>For the new solders, side-by side cyclic testing with eutectic (or 60/40)
>Sn/Pb solder from -20<->+100C (125C if substrate glass transition temperature
>is at least 150C) with 15 minute dwells at each temperature extreme (24
>cycles/day) with conventional chambers (or 5 minute dwells with chambers
>modified to provide temperature uniformity in the whole test volume; ~100
>cycles/day) with at least 32 equal continuity daisy-chains monitored with an
>Anatech Event Detector for both solders, is necessary. This will give an
>adequate data base to draw valid comparisons with near-eutectic Sn/Pb
>solders, and, to me more importantly, from which a fatigue reliability model
>can be derived.
>Tests that are sufficient to ensure "reasonable" reliability will be totally
>dependent on the product design together with its application. But to design
>such a test, you have to have an appropriate fatigue reliability model from
>which a valid acceleration factor for the test vis-a-vis the use conditions
>can be determined. Electronic application vary from easily met reliability
>reqirements for consumer products (~1,000 cycles (3 yrs) @ delta-T's ~10C &
>10% acceltable failure probability) to difficult to meet requirements for
>low-earth-orbit satellites (~90,000 cycles (10 yrs) @delta-T's ~35C & 0.001%)
>or automotive-under-hood equipment (~10,000 cycles (~3 yrs) @ delta-T's ~100C
>& 0.1%).
>
>Werner Engelmaier
>Engelmaier Associates, L.C.
>Electronic Packaging, Interconnection and Reliability Consulting
>7 Jasmine Run
>Ormond Beach, FL 32174 USA
>Phone: 904-437-8747, Fax: 904-437-8737
>E-mail: [log in to unmask], Website: www.engelmaier.com
>
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