An experimental methodology for the study of co‐planarity variation effects in anisotropic conductive adhesive assemblies

Abstract

Purpose

Non‐planarity of assemblies and co‐planarity variation effects on anisotropic conductive adhesive (ACA) assemblies have been a concern for ACA users since the materials are first devised. The primary objective of this paper is to introduce a new experimental method for studying co‐planarity variation effects on ACA assemblies.

Design/methodology/approach

The approach simulates non‐planarity through deliberate chip rotation during the ACA bonding process, thereby locking different levels of co‐planarity variation into ACA test assemblies. Scanning electron microscope (SEM) analysis and electrical joint resistance measurement using the four wire resistance (FWR) method are used to mechanically and electrically examine the connection quality of the ACA assemblies bonded with non‐planar joints, for which the chip and substrate patterns are specially designed to allow joint resistance measurement using the FWR method.

Findings

Typical experiments and their results are presented and analysed. The bond thickness differences between the SEM measurements and calculations indicate that the real rotations are smaller than those predicted by the calculations. The typical experimental results show that the joint resistance reduces as the deformation increases until reaching a relatively stable value after a certain deformation degree.

Research limitations/implications

The average joint resistances in the rotated samples are all bigger than those measured in the un‐rotated samples. This raises the question as to whether the joint resistances of ACA assemblies are more significantly affected by other affects of non‐planarity than just by its effect on bond thickness. However, before this can be confirmed, more research must be done to check if this behaviour happens for different bonding forces.

Originality/value

This paper reports a novel and simple experiment that can be used to examine the effects of co‐planarity variation on the electrical performance of ACA assemblies, by creating different bond thicknesses that are normally difficult to achieve by changing the bonding pressure, since ACA bond thicknesses are not linearly related to the bonding force. The merit of the technique is that there is no need to manufacture chip bumps and substrate pads with different geometries, or to control the bond pressure, to achieve bond thickness variation in ACA assemblies.

Citation

Dou, G., Whalley, D.C., Liu, C. and Chan, Y.C. (2010), "An experimental methodology for the study of co‐planarity variation effects in anisotropic conductive adhesive assemblies", Soldering & Surface Mount Technology, Vol. 22 No. 1, pp. 47-55. https://doi.org/10.1108/09540911011015148