Electrical conductive, characteristics of ACA bonding: a review of the literature, current challenges and future prospects.

Anisotropic Conductive Adhesives (ACAs) have been used in fine pitch electronics packaging for over a decade and provide a high density and low temperature bonding method in a range of niche applications. The principal objective of this paper is to provide significant insights into the basic conductive characteristics of ACAs based on a review of previously reported scientific research, and to identify the current challenges and future prospects for this technology. In order to provide a concise, structured overview of this topic, many detailed conductive models, mathematical solutions and research methodologies are presented based on the reviewed literature. These models can partially explain the conductive mechanisms of an ACA particle, but make a number of important sirnplifying assumptions. However, one model was developed and can be used to explain the conductive mechanism of an ACA particle more successfully. In conclusion, existing computational models, mathematical models and physical models have been used to estimate the resistance of an ACA particle and the particle contact area, and therefore constriction resistance, for a given degree of particle deformation, thereby almost achieving a model for the whole resistance of an ACA joint. The paper will close by identifying other research challenges remaining for this important electronics interconnection technology

Influence of etching solvent evaporation on the size of micro-via holes in PVP thin films

Via holes are a necessary component in traditional PCBs and IC interconnections. Such structures will also be required in organic electronics to achieve vertical communication between multiple layers. Inkjet printing has demonstrated its applicability in both hole creation and for other pattern generation requirements in various polymeric layers. However, the technique has not been systematically investigated. This paper is focused on a study of the effect of solvent evaporation rate on the size of inkjet-etched via holes for organic electronics, which is part of a more extensive investigation and evaluation of inkjet etching as a via hole fabrication technique. In this work, holes were etched in thin layers of poly(4-vinyl phenol) (PVP), which is a potential dielectric material for organic electronic structures. Ethanol, isobutanol and ethylene glycol were used as the etchants in order to study the effect of solvent boiling point and vapour pressure on the size evolution of via holes with the total number and the frequency of the solvent drops used to dissolve them. Isobutanol and ethylene glycol have higher boiling points than ethanol, leading to slower evaporation, which is believed to allow the dissolved polymer to flow backwards to the central area before complete solvent evaporation, resulting in hole refill. However it will be shown that applying temperatures higher than room temperature can accelerate solvent evaporation and eliminate the refill issue

Electrical method of monitoring percolation and abrasion of conducting spheres due to shear flow of a dense suspension in a narrow gap

This letter describes a method for studying the behavior of rigid particles in a dense suspension when they are forced into contact during flow within a narrow gap. The particles form transient percolating networks spanning the boundary walls, and will be crushed together. The method involves measuring the dc electrical resistance across the gap. The suspension e.g., solder paste consists of electrically conducting particles suspended in an insulating fluid. The electrical resistance drops when the particles are in contact with each other and the walls, and the insulating films on the surface of the conductors have been broken through. The results show a dramatic change in behavior as the ratio of gap to particle diameter is varied