In a message dated 06/09/99 12:32:32, [log in to unmask]
writes:
>Hi TechNet! I have a question involving the IPC-SM-785 failure definition.
>In paragraph 4.3.1 the definition of solder joint failure is stated as a
>short duration, high resistance spike (time = approximately 1usec and a
>resistance window of 300 ohms). However, in paragraph 7.8 failure criteria
>for solder joint fatigue tests, the failure detection limits are a polling
>time of 2 seconds or less, with a resistance window of 1000 ohms. This
>appears to be a contradiction within the guidelines. I understand that the
>use of a resistance window of 300 ohms will subject the test to a greater
>amount of noise and potential false negative responses but it has been my
>experience that these noise/false negative incidents can be handled with
>proper trouble shooting and test monitoring. I am looking for viewpoints-
>does a contradiction exist or is it an issue of tester confidence?
>Dave Hillman
Hi Dave,
Since I wrote those sections, I certainly can tell you how these sections
came about.
There is really no contradiction. Section 4.3.1 states that "solder joint
failure is defined as the complete fracture through the cross-section of the
solder joint with the solder joint parts having no adhesion to each other,
but that "the practical definition of failure is the interruption of
electrical continuity (>300 ohms) of periods greater than 1 micro-second",
because that is what you can measure.
In Section 7.8, solder joint failure for accelerated testing using
daisy-chains is indicated by a loop resistance of 1000 ohms or more. In this
definition the capability of the event detectors available at the time (1992)
plays a role, as well as the experience with false failure indications due to
electrical noise. While the event detectors now are capable of detecting
resistance spikes of less than 300 ohms, setting the apparatus to those
values has proven to be troublesome for some testers.
From my experience, I would say that neglecting the danger of false
indications, thers is not likely an appreciable difference in the reliability
results for threshold setting of 300 vs. 1000 ohms.
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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