Conductive adhesive layer

Kazuya H, Takeshi M, Manabu S, Takeshi K, Manabu T. Asahi glass. Electric double layer capacitor having an electrode bonded to a current collector via a carbon type conductive adhesive layer. US patent /6072692. 

In the past 20 years bendable and disposable medical electrodes evolved. Instead of a rigid metal plate serving as electrode, a metal mesh, foil or carbon impregnated rubber or vinyl, ensuring more flexibility in the electrode structure, are used. A conductive adhesive layer, usually in the form of a gel, is disposed on the conductive side of the material to provide a good electrical conductive contact between the conductive material and the patient s skin. Connection between the conductive material and an electrical stimulation device is provided by means of an electrical wire. Instead of wires, pressure buttons on top of the conductive material may alternatively be used. The outside face of the conductive material is covered with a nonconductive material to prevent electrical contact. 

Yoon el al. [112] reported an all-solid-state sensor for blood analysis. The sensor consists of a set of ion-selective membranes for the measurement of H+, K+, Na+, Ca2+, and Cl. The metal electrodes were patterned on a ceramic substrate and covered with a layer of solvent-processible polyurethane (PU) membrane. However, the pH measurement was reported to suffer severe unstable drift due to the permeation of water vapor and carbon dioxide through the membrane to the membrane-electrode interface. For conducting polymer-modified electrodes, the adhesion of conducting polymer to the membrane has been improved by introducing an adhesion layer. For example, polypyrrole (PPy) to membrane adhesion is improved by using an adhesion layer, such as Nafion [60] or a composite of PPy and Nafion [117],... 

The adhesion was measured using the ASTM standard tape test (100). The adhesion of the conductive copper layers proved to be excellent. 

Fabrication procedure of gold nanodisk electrodes (NEEs) is schematically shown in Fig. 3.14 (Menon and Martin 1995 Pereira et al. 2006). Step I A piece of the Au/Au-PC/Au membrane is first affixed to a piece of adhesive aluminum foil tape (Fig. 3.14a). Step II A rectangular strip of a copper foil, with a conductive adhesive, is then affixed to the upper Au-coated surface of the Au/Au-PC/Au membrane (Fig. 3.14b). This Cu foil tape acts as a current collector and working electrode lead for the NEE. Step III The upper Au surface layer from the portion of the Au/Au-PC/Au membrane not covered by the Cu foil tape is then removed by simply applying and then removing a strip of Scotch tape. Removal of the Au surface layer exposes the disk-shaped ends of the Au nanowires within the pores of the membrane (Fig. 3.14c). These nanodisks will become the active electrode elements. Step IV The NEE assembly is heat treated at 150°C for 15 min. This produces a water-tight seal between the Au nanowires and the pore walls. Finally, strips of strapping tape are applied to the lower and upper surfaces of the assembly to insulate the Al and Cu foil tapes (Fig. 3.14d). 

Adhesive layers with fillers for certain demands (e.g., electrically/heat conductive)... 

Conductive adhesives Adhesives with adhesive layers able to conduct electric current (silver particles) or heat (aluminum oxide, boron nitride) due to the addition of respective fillers. 

Filler Adhesive component in a solid, finely dispersed form that specifically modifies the processing properties of the adhesive and the properties of the adhesive layer (e.g., metal particles in electrically conductive adhesives, chalkstone, carbon black to increase viscosity). Fillers are not reactive partners in adhesive curing. 

Static DCB tests were also conducted using 12 and 36 ply adherends bonded with the same adhesive. Initially, precracks immediately grew into the composite adherends rather than within the adhesive layer. Results from these tests, which indicate the interlaminar energy release rate of the composite material, are shown in Fig. 9. The average energ> release rate of the composite material was approximately 550 J/m, 1250 J/m lower than the initiation energy release rate of the adhesive measured using the aluminum adherends. 

A new area of concern for electrical stability arises because of the increasing use of conductive adhesives as replacements for solder. Some conductive adhesives show unstable electrical-contact resistance when used on non-noble metal surfaces such as copper or tin-lead solder. Although stable on gold, palladium, platinum, and silver surfaces, the same adhesives were found to be unstable on tin, tin-lead, copper, and nickel surfaces.The unstable resistance and increase in resistance in temperature-humidity exposures have been attributed to the growth of an oxide layer separating the filler particles from the substrate at the interface, a mechanism similar to that for the loss of backside contact in die-attach materials. 

Most commercially available anisotropically conductive adhesives are formulated on the bridging concept, as illustrated in Fig. 1. A concentration of conductive particles far below the percolation threshold is dispersed in an adhesive. The composite is applied to the surface either by screen printing a paste or laminating a film. When a device is attached to a PWB, the placement force displaces the adhesive composite such that a layer the thickness of a single particle remains. Individual particles span the gap between device and PWB and form an electrical interconnection. For successful implementation of anisotropically conductive adhesives, the concentration of metal particles must be carefully controlled such that a sufficient number of particles is present to assure reliable electrical conductivity between the PWB and the device (Z direction) while electrical isolation is maintained between adjacent pads (X,Y directions). 

Materials for use as anisotropically conductive adhesives must satisfy requirements even more stringent than those defined previously for isotropically conductive adhesives. No specifications, however, have been defined specifically for these materials. When used for flip-chip applications, the adhesive not only serves as a physical and electrical interconnection between the device and the substrate, but also serves as the environmental protection and passivation layer. This fact, combined with high adhesive concentrations, makes the ionic contamination levels of these materials more critical than for isotropic conductive adhesives. In addition, the processing of these materials has a greater influence on joint reliability as the anisotropic electrical properties develop only after heat and pressure are applied to the joint. 

There are two reincarnations of this method, schematically illustrated in Fig. 2. The first method uses a silicon or glass wafer as a substrate material, while the second method uses a nickel Plate. A silicon or glass wafer is coated by evaporation or sputtering with a conductive seed layer ( 100 nm) such as Ni or Cu or Au. A thin layer ( 50 nm) of Ti or Cr is used to enhance adhesion of the conducting layer to the silicon substrate. The wafer is then coated with a layer of photoresist, which is subsequently exposed to UV light and developed so that the... 

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