Volume Fraction Of Conductive Particles Research Articles

Thermal percolation in mixtures of monodisperse spheres

The connectivity of individual species in a locally heterogeneous granular mixture strongly influences assembly-scale behavior. A behavioral transition is observed at the percolation threshold for a given constituent; that is, the mixing fraction at which the constituent has statistical connectivity between two opposing boundaries. This behavior is particularly evident in conductivity phenomena, e.g., the percolation of conductive particles (thermal, electric) or the relative degree of connectivity of the void space (hydraulic). Hard-core (first nearest-neighbor or lattice) percolation has been extensively studied experimentally, theoretically, and numerically. That hard-core percolation occurs in dense randomly packed bi-phasic mixtures of monodisperse spheres occurs at a mixing fraction of 0.15 v/v is well-accepted. Radiant conduction (e.g., heat), however, is influenced by hard-core “soft-shell” percolation, which is an nth-nearest neighbor problem and less well-studied. In the current work, we use discrete element method simulations coupled with a thermal network model that leverages a robust domain decomposition algorithm to simulate large assemblies of spheres to investigate soft-shell percolation numerically. Our results show that the thermal conductivity of a randomly packed assembly obeys a power law with respect to volume fraction of conductive particles while percolation threshold follows a power law with respect to coordination number. The ability of the pore fluid to transmit heat over a longer distance results in an increase of thermal conductivity and a decrease in thermal percolation threshold. Moreover, we observe that, contrary to previous findings, critical percolation density is not a dimensional invariant and depends on the microstructure of the assembly.

Tunable gold-chitosan nanocomposites by local field engineering

A method to control the permittivity and tunability in composite materials formed by conductive nanoparticles embedded in a flexible nonlinear dielectric matrix is proposed. The local field distributions in composite structures were determined and the field-induced permittivity was estimated for different volume fraction of conductive particles. The predicted tunability behavior agrees well with the observed trends obtained for gold nanoparticles embedded in chitosan matrix. The paper demonstrates the concept of engineered local fields in nanocomposites by using metallic nanoparticles as fillers in polymer matrix for tailoring the permittivity and tunability values.

Effects of Pad Array Dimensions and Misalignment Offsets on Optimal Fraction of Conductive Particles in Anisotropic Conductive Film Packages

The failure probability of anisotropic conductive film (ACF) packages is critically dependent on the volume fraction of conductive particles within the adhesive resin. In this study, the V-shaped curve method is used to determine the optimal volume fraction of conductive particles as a function of the bonding geometric parameters, the pad array dimension, and the misalignment offset between the upper and lower pads. In evaluating the corresponding failure probability of the ACF package, the probability of an opening failure is determined in accordance with a Poisson function model, while the probability of a bridging failure is derived using a box model. In computing the opening and bridging probabilities, the two models are modified to take account of the effects of package misalignments on the effective conductive area between opposing pads and the bridging path length between neighboring pairs of opposing pads, respectively. The opening and bridging probabilities are then combined using probability theory to establish the overall failure probability of the ACF package. In general, the results show that, for given bonding geometric parameters and misalignment offset, the optimal volume fraction of conductive particles remains approximately constant as the pad array dimension is increased. However, for given bonding geometric parameters and pad array dimension, the optimal volume fraction of conductive particles increases with an increasing misalignment error. Overall, the results show that, for any given values of the bonding geometric parameters, pad array dimension, and misalignment offset, the failure probability of the ACF package can be minimized by setting the volume fraction of conductive particles equal to the value corresponding to the tip of the V-shaped curve.

Strain effects on percolation conduction in conductive particle filled composites

The effect of uniaxial and multiaxial mechanical strain on the electrical conductivity of particle filled polymer composites is investigated in the framework of concentration-driven percolation. For composites consisting of low aspect ratio, rigid conductive particles in a compliant polymer matrix, a simple argument leads to the conclusion that the effective volume fraction of conductive particles (the ratio of total particle volume to the total volume of the deformed composite) plays a dominant role, with conductivity remaining isotropic despite the directional bias of the strain state. As such, conductivity is expected to exhibit classical power, law-dependence on concentration, which in this case takes the form of a strain-dependent effective volume fraction. Consideration of deformation effects on particle agglomerates suggest, however, that particle-to-particle network connections are likely to be affected most significantly along directions experiencing the most severe strains, introducing a directional bias in network connectivity at a higher length scale. To assess the importance of this possible directional bias, random resistor network models are used to study the conductivity of uniaxially strained composites. For conservative assumptions on the severity of the bias in bond probabilities, network conductivities exhibit approximately isotropic, concentration-driven behavior for moderate strains, supporting the predictive utility of the simple percolation conduction-effective volume fraction approach. Further corroboration is provided by experiments in the literature on silicone-graphite composites subjected to uniaxial compressive strain, where good agreement is obtained through moderate strains for the theoretically correct value of the conduction exponent in concentration-driven percolation.

Effects of thermal volume expansion on positive temperature coefficient effect for carbon black filled polymer composites

AbstractPolymeric positive temperature coefficient (PTC) materials have been prepared by incorporating carbon black (CB) into two different polymer matrices, crystalline high density polyethylene (HDPE) and amorphous polystyrene (PS). The effects of thermal volume expansion on the electrical properties of conductive polymer composites were studied. The volume fraction of conductive particles behaves like a switch from insulator to conductor in the polymeric PTC composite. Our mathematical model and experimental model have proved that the abrupt resistivity increase at PTC transition range and at the percolation curve close to the critical volume fraction for both polymeric PTC composites have the same conductive mechanism. The thermal expansion is one of the key factors responsible for the PTC effect and can be seen by comparing the PTC transition curves from model predictions and experiment. Furthermore, the model predicts PTC curves of CB/PS composite more successfully than it does for the CB/HDPE composite, and the reasons for this are also discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3078–3083, 2007

Characteristics of thick film resistors embedded in low temperature co-fired ceramic (LTCC) substrates

Commercial thick film resistors were embedded in low temperature co-fired ceramic (LTCC) substrates, and co-fired with substrates at temperatures between 800 and 900 °C. Adding glass frit and amorphous SiO 2 to calcium borosilicate glass ceramic substrates has not only lowered the shrinkage of the substrates, but also improved adhesion and maintained structure integrity of the resistor films. During sintering, the conductive phase particles in the resistor became agglomerated and sedimented, and glass diffused into the LTCC substrate layer. Increasing the dwelling time, the overall resistivity of the co-fired films decreased due to sedimentation of agglomerated conductive particles. The liquid eutectic phases penetrated into the substrates added with either SiO 2 or glass frit that the volume fraction of conductive particles was increased. The resistivity of the embedded resistors was determined by the volume fraction of conductive particles, which was influenced by the conductive particles sedimentation, microstructure of resistor films, and inter-diffusion between the resistors and substrates.

Formation of Thin Transparent Conductive Composite Films from Aqueous Colloidal Dispersions

This investigation examines the percolation and electrical resistivity behavior of films containing electrically conductive antimony-doped tin oxide particles in different polymer matrices. The polymers include gelatin, a soft polymer latex (glass transition temperature Tg room temperature). The films are formed through the evaporation of water from aqueous dispersions of conductive particles and film-forming polymers. The critical volume fraction of conductive particles for conductive network formation was found to be significantly lower when the film former was a polymer latex. This was attributed to differences in the interactions of particles in the colloidal state prior to the point where particles start to touch. In the critical transition region or slightly above the critical transition region, the hard latex provides an order of magnitude improved surface resistivity compared to that of the soft latex. This result was discussed in terms of the po...

Fine-pitch connection to rigid substrate using non-conductive epoxy adhesive

Journal of Electronics ManufacturingVol. 02, No. 01, pp. 7-12 (1992) PAPERSNo AccessFine-pitch connection to rigid substrate using non-conductive epoxy adhesiveHELGE KRISTIANSEN and ARE BJORNEKLETTHELGE KRISTIANSENCentre for Industrial Research, Forskningsveien 1, Mail Box 124 Blindern, 0314 Oslo 3, Norway Search for more papers by this author and ARE BJORNEKLETTCentre for Industrial Research, Forskningsveien 1, Mail Box 124 Blindern, 0314 Oslo 3, Norway Search for more papers by this author https://doi.org/10.1142/S0960313192000030Cited by:9 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail AbstractWe have carried out reliability testing of different interconnection technologies, mainly to connect driver electronics to liquid crystal displays. This work has involved connection between flexible circuits made of Kapton, and rigid glass substrates. One of the applications also involved connection between flexible circuits and FR-4 substrates. Tests have been performed both on test structures and on real displays. The two different interconnection technologies we have studied are anisotropic conductive films (ACF) and non-conductive epoxy adhesive (NCA). Anisotropic conductive film is at present extensively used in producing high-quality LCDs. The other technology is, as far as we know, not used in production at this moment. Anisotropic conductive films contain a small volume fraction of conductive particles to accomplish electrical conductivity between the two connected contact areas. With non-conductive adhesive we use the surface roughness on the individual contact areas to establish electrical contact. In comparison with conventional anisotropic conductive film (ACF), based upon thermoset adhesives, the use of non-conductive adhesive (NCA) has proved to be superior with respect to reliability. This result is verified by thermal cycling (−30°C to 90°C) and by humidity testing (85% RH/85°C), both on test structures and real displays.Keywords:Fine-pitch electrical connectionliquid crystal displaynon-conductive adhesiveanisotropic-conductive filmreliability FiguresReferencesRelatedDetailsCited By 9Conductive Adhesives for Flip-Chip ApplicationsDaoqiang Daniel Lu and C. P. Wong4 January 2013A Method to Connect Flexible Printed Circuits and Indium Tin Oxide Electrodes Using Non-Conductive Film and PlatingYohei Wakuda, Yoshiyuki Okura, Koichiro Kawate, Hideaki Yasui and Mitsuhiro Watanabe et al.1 Jan 2008 | Transactions of The Japan Institute of Electronics Packaging, Vol. 1, No. 1Koichiro KAWATE1 Jan 2007 | Journal of The Surface Finishing Society of Japan, Vol. 58, No. 12Processability and reliability of nonconductive adhesives (NCAs) in fine-pitch chip-on-flex applicationsW. K. Chiang, Y. C. Chan, Brian Ralph and Andrew Holland1 Mar 2006 | Journal of Electronic Materials, Vol. 35, No. 3Overview of conductive adhesive interconnection technologies for LCDsH. Kristiansen and J. Liu1 Jun 1998 | IEEE Transactions on Components, Packaging, and Manufacturing Technology: Part A, Vol. 21, No. 2Characterisation of electrical contacts made by non-conductive adhesiveH. Kristiansen, M. Gulliksen, H. Haugerud and R. FribergElectrical conductive characteristics of ACA bonding: a review of the literature, current challenges and future prospects Guangbin Dou, D.C. Whalley and Changqing LiuRecent advances in conductive adhesives for direct chip attach applicationsJ. LiuOverview of conductive adhesive interconnection technologies for LCD'sH. Kristiansen and J. Liu Recommended Vol. 02, No. 01 Metrics History Received 1 September 1991 Accepted 1 October 1991 KeywordsFine-pitch electrical connectionliquid crystal displaynon-conductive adhesiveanisotropic-conductive filmreliabilityPDF download