New, Z-direction anisotropically conductive composites

Abstract

This paper reports the development of a new class of anisotropically conductive materials based on magnetic alignment of conductive particles in nonconductive matrix materials such as elastomeric or adhesive polymers. These composites contain many vertically aligned but laterally isolated chains of ferromagnetic metal spheres, the ends of which protrude from the surfaces for better electrical contact. These novel composite structures exhibit Z-direction-only electrical conduction (>1012 to 1 anisotropy ratio), which, in combination with the compliant nature of the materials, can be exploited advantageously for a variety of electronic applications including fine-pitch, area-array, circuit interconnections, circuit-testing, heat sink interfacing, and sensor devices. The movement and alignment of magnetic particles in a viscous medium, and the stability of configurations in a magnetic field will be discussed. The properties of the composite materials as well as potential circuit and device applications will be discussed.

Influence of PCB Surface Finish and Thermal and Temperature/Humidity Aging on the Performance of a Novel Anisotropic Conductive Adhesive for Lead-free Surface Mount Assembly

“…The initial contact resistance was low for all PCB finishes (0.75-1.5 ohms) and it further reduced during 1000 hours of thermal aging, showing good thermal aging performance. 6. The contact resistance of the joints was found to increases with T&H aging.…”

“…One of the earliest publications that reported on the novel Z-direction conductive adhesive was from AT&T Bell Laboratories [6,7], based on the magnetic alignment of ferromagnetic metal spheres (silver coated nickel) that were dispersed in a non-conductive adhesive polymer. The authors [7] identified that with finer particles, the assemblies' revealed uniformity of resistance values when compared to large particles.…”

In Situ Tissue Engineering Using Magnetically Guided Three-Dimensional Cell Patterning

“…Ferromagnetic nano-or micro-particles (FMP) dispersed in liquid and subjected to a unidirectional magnetic field can be arranged into various 3D interparticle configurations. [12][13][14] FMP are especially suited for noninvasive tracking and directing labeled cells in vivo 15,16 and have been utilized for tissue engineering approaches, including seeding labeled cells into scaffolds 17 and for ''magnetic force-based cell manipulation'' for the arrangement of cell patterns in sheets for the construction of 3D multilayered tissues. 18,19 This approach has been used to create sheet layers of cells in patterns consisting of various cell types or for forming ring and tubular-like structures in urinary and vascular tissue engineering applications.…”

Surface polymerization of iron particles for magnetorheological elastomers

“…Conductive polymers for interconnection (CPI) are prepared from a thin sheet with aligned magnetic particles. CPI has potential applications in device interconnection and circuit testing 14. Sheets of transparent polymer with dispersed and vertically aligned ferromagnetic spheres have been used for touch‐sensitive screens and other visual communication devices 15.…”