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Developing a stress screening regime for isotropic electrically conductive adhesives.

Wickham, M; Zou, L; Hunt, C (2004) Developing a stress screening regime for isotropic electrically conductive adhesives. NPL Report. DEPC-MPR 005

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Recent renewed interest in isotropic conductive adhesives (ICAs) has been driven both by the impending restrictions on the use of lead in solders, and by the potentially increased recyclability of a range of products that use ICAs instead of solder for interconnection purposes. But wider use of these materials requires better understanding of the mechanisms of field failures, and an appropriate and agreed test method to assess both process quality and field reliability. In consequence, this work has been undertaken in order to review and investigate potential test regimes, and thereby to identify a representative accelerated ageing condition for assessing ICAs.
The study has involved examining joints on test boards produced from a matrix experiment using two ICA materials, a range of components, eight ageing regimes, and four assessment techniques (electrical conductivity, shear testing, drop testing and SIR). The results indicate that
(a) the performances of the two ICA materials were broadly similar – the resistances of the bulk materials were stable over all the testing regimes
(b) when used as component interconnect, the materials performed well, particularly when subjected to thermal cycling, exceeding the expectations of typical end-users
(c) the parameters of an appropriate stress screening regime are : unbiased joints, 85ºC, 85%RH for 1000 hours
(d) other potential screening regimes studied all exhibited significant drawbacks.
(e) it is recommended that for future work on ICAs the 85/85 damp heat test be used: it provides a means to differentiate between assembly parameters, particularly for leaded SM components.
The second phase of this project will study the effect of bias on the ICA joints during testing. Moisture is expected to play an important role in the likely failure modes experienced by biased joints, underlining the suitability of the recommended test regime

Item Type: Report/Guide (NPL Report)
NPL Report No.: DEPC-MPR 005
Subjects: Advanced Materials
Advanced Materials > Electronics Interconnection
Last Modified: 02 Feb 2018 13:16
URI: http://eprintspublications.npl.co.uk/id/eprint/3845

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