Fabrication and characterisation of interconnects suitable for high frequency ultrasonic array transducers

Xiao, Ran (2013). Fabrication and characterisation of interconnects suitable for high frequency ultrasonic array transducers. University of Birmingham. M.Res.

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Abstract

Anisotropic conductive film (ACF) is a kind of conductive composite, which is used as the wire-free interconnection in the electric application and instruments to satisfy the requirements of the fine scale device, for example, the high frequency ultrasonic imaging for clinical applications. The electrical properties of the ACF and its behavior during the synthesis process are important for the properties improvement. In this thesis, it reports the syntheses of ACFs from silver coated conductive particles and Epoxy resin, a study of the conducting mechanism of the interconnect and the influence of the production route, content of conductive powders and microstructures of the prepared ACF. The ACFs are prepared directly from EPOFIX resin and silver coated copper powders. The minimum electric resistivity in the direction of applied pressure (vertical direction) of 50MPa ρ = 1.00(±0.5)Ωm was achieved, and the value in horizontal direction was 10\(^6\) times larger than in vertical direction, when the mass ratio of EPOFIX resin and silver coated conductive powders is 81:19, the bonding condition is 120℃/20min/1.5MPa. Its estimate service life is more than 5 years. There are four main factors affecting the properties of the ACF: bonding temperature, bonding time, bonding pressure and particle concentration. The bonding temperature is the most important parameter to accelerate the curing/bonding process of the ACF, but heating of the ACF to temperature above 180℃ will induce the bubbles in the ACF, because the air does not have enough time to escape from the ACF before it is fully cured: the higher bonding temperature, the shorter bonding time. The electric resistance in the direction of applied pressure of the ACF varied with applied pressure and there are three stages. The first stage is the resistance decrease stage when the pressure is at low; this stage corresponds with the contact improvement between the electrode and the conductive particles in the ACF. The second stage is the wide range resistance plateau stage when the pressure changes from 2.5MPa to 6MPa. This stage corresponds with the agglomerated particles crashed in ACF. The third stage is the plastic deformation of the conductive particles in ACF, which causes the electric resistance of the ACF to increase.

Type of Work:

Thesis (Masters by Research > M.Res.)

Award Type:

Masters by Research > M.Res.

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