Dusek, M; Hunt, C P (2007) Low cycle isothermal fatigue properties of lead-free solders. NPL Report. DEPC-MPR 058

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Abstract

Driven by European legislation, that came into force in July 2006 banning the use of lead in solders in a number of consumer applications, the high reliability sector of the electronics manufacturing industry is urgently studying the 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 with established SnPb solder 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 report describes a new approach developed at NPL to overcome these constraints, resulting in the design of a new instrument IPTM (Interconnect Properties Test Machine), 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 decreases recorded during fatigue testing of solders. The results of this study reveal that lead-free solders at high temperatures have increased lifetimes. A route to predict a fundamental reliability variable of solder has been identified.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	DEPC-MPR 058
Subjects:	Advanced Materials Advanced Materials > Electronics Interconnection
Last Modified:	02 Feb 2018 13:15
URI:	http://eprintspublications.npl.co.uk/id/eprint/3786

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