Adhesives, electrically conductive carriers

Silver epoxies consist of silver flakes suspended in an adhesive carrier. The materials are designed so that the silver flakes touch each other when cured and provide an electrically conductive path. Generally, silver epoxies have lower conductivity than solder paste, but usually have the advantage of a reflow temperature lower than the temperature required for solder paste. 

Shaped articles, e.g. rods, fibers, and films, which are electrically conductive can be manufactured from composites containing a nonconductive flexible chain-carrier polymer and a conjugated polymer (e.g., POT, PDDT, poly-(thienylene vinylene)) [831,832]. Polyester blends containing PT can be used as synthetic fibers [833]. Electrically conductive resin adhesives, heat, stock, and moisture resistant with bifunctionality as adhesives and solders can consist of epoxy methacrylates and conducting polymers, e.g., PDDT, PODT [834,835]. 

The processes generally employed to fix electronic components on three-dimensional circuit carriers are reflow soldering and electrically conductive-adhesive gluing. The first step in reflow soldering is to print solder paste on to the pads of the circuit trace (Fig. 4.1). The electronic components are subsequently placed in these solder depots. The module, complete with its electronic components, is then heated in a reflow oven, the solder particles of the paste melt, and the molten solder flows over... 

Aiming at the CSP application market, Merix Corporation and Auburn University collaborated to develop anisotropic conductive adhesives called Area Bonding Conductive (ABC) adhesives. ABC adhesives are two-region thermoset adhesives with electrically conductive adhesive pads surrounded by a continuous oxide-filled dielectrical adhesive to form a total area bond. Both regions are solvent-free, B-staged, nontacky epoxies supplied on a Mylar carrier release film. In contrast to conventional ACAs, conductive areas of ABC adhesives are located only at bond pad locations. The assembly process for using ABC adhesives is shown in Fig. 9. The ABC adhesives... 

Aramid para-aramid, 2.8 Pa strength, 70 GPa modulus chopped staple or fibrid (pulp) 10-150 g/m2 Tensile strength up to 8 N/mm Density 80 kg/mm Improved impact resistance Smooth finish Good wear resistance Can be blended with conductive fiber Superior temperature resistance Aerospace adhesive carriers Automotive improved stone impact resistance Defence radar cross section Recreation skis, snow and surf boards, surf boards, canoes Industrial substrate for friction products wear resistance for high-speed rolls Electrical printed circuit boards... 

Thermally conductive adhesive tapes are double-sided, pressure-sensitive adhesive films filled with ceramic powder. The adhesive is typically supported either witii a carrier made from polyimide film or with aluminum foil to provide ease of handling and strength. If electrical isolation is required, polyimide is the carrier used. Acting in a fashion similar to elastomeric films, they require some initial mating pressure to conform to the surface irregularities. If the gap between the surfaces is too large, the adhesive tape is unable to fill it. Once a joint is formed with an adhesive tape, mechanical pressure is no longer required to maintain the mechanical or thermal performance of the joint [24]. 

---