Wickham, M; Zou, L; Hunt, C (2005) Measuring the effect on isotropic electrically conductive adhesive reliability of substrate and component finishes. NPL Report. DEPC-MPR 031

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Abstract

As the transition away from lead-containing solders gathers momentum, isotropic conducting adhesives (ICAs) are being considered as possible replacements for conventional SnPb solder in certain applications. Consequently, the reliability of ICA joints is under scrutiny and in earlier work a suitable test regime was identified to generate relevant reliability data. In this work, those tests have been employed to investigate whether the finishes on the components and/or PCBs have any effect on the reliability of the ICA joints after exposure to damp heat conditions.
The effect of different finishes has been found to be very adhesive material dependent. Two adhesives were studied, one of which produced joints the reliabilities of which were relatively unaffected by changes in component or PCB surface finish. However, with the second material and components having the PdNi metal finish, the joints displayed a more stable resistance than those made using components having a high tin content plated finish. Performances could be further improved by cleaning the components prior to assembly, although this may not be feasible on a production environment.
The surface finish on the PCB was found to have a smaller effect than did the component finish. Again the results were dependent on the adhesive material, with the joints using the better performing material exhibiting little difference irrespective of the PCB surface finish. In the case of the second material, PCBs having the ENIG (electroless nickel/immersion gold) finish did produce joints which performed as well as those having the immersion tin or silver finishes. Cleaning ENIG subsequent joints for some component finish combinations.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	DEPC-MPR 031
Keywords:	ion chromatography, ICAs
Subjects:	Advanced Materials
Last Modified:	02 Feb 2018 13:16
URI:	http://eprintspublications.npl.co.uk/id/eprint/3278

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