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Test approach to isothermal fatigue measurements for lead-free solders.

Dusek, M; Hunt, C P (2006) Test approach to isothermal fatigue measurements for lead-free solders. NPL Report. DEPC-MPR 048

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Driven by European legislation, which comes into force in July 2006 and effectively bans the use of lead in solders, the electronics manufacturing industry is studying a range of potential lead-free solder replacements. A major concern is the reliability of the solder joints which has traditionally been predicted using modelling techniques and established materials data. Although the mechanical behaviour of lead-free solders is known to be different from that of their traditional counterparts, there is a dearth of credible materials data, and hence there is an urgent need to generate such data in order to evaluate the likely lead-free solder performance. There is also a realisation that any new materials data should be obtained from solder samples that have volumes similar to those of solder joints, and that the joints should be loaded in shear, mirroring the practical situation in the field. However, currently available test instruments do not readily meet these constraints. This paper describes a new approach developed at NPL to overcome these constraints, resulting in the design of the new instrument with a sample geometry that permits small solder volumes to be studied in pure shear. Example data are presented and illustrate how the fatigue resistance of solders can be characterised. Advantages of the new approach include (i) it can accommodate various solder alloys and surface coatings, (ii) the solder joint volumes mirror those in modern assemblies, (iii) the solder is under shear, (iv) the samples are relatively easy to manufacture, (v) the construction of the specimen allows direct microscopic examination during the test at room temperature. A 4-point measurement system for resistance monitoring has also been evaluated and found to correlate well with load drop during fatigue testing of solders.

Item Type: Report/Guide (NPL Report)
NPL Report No.: DEPC-MPR 048
Keywords: reliability, shear, joint size measurements
Subjects: Advanced Materials
Advanced Materials > Electronics Interconnection
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/3686

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