Contact printing current application

Surface mount refers to a method of securing connectors to the conductors of a printed circuit board by soldering appropriately shaped contacts to the board surface. Higher contact densities can be achieved and the need to drill holes in the board is avoided. Contact spacings may vary from about 0.5 cm for large current-carrying applications to 0.18 cm or less when miniaturization and high density is a requirement. 

However, conductive elastomers have only ca <10-3 of the conductivity of solid metals. Also, the contact resistance of elastomers changes with time when they are compressed. Therefore, elastomers are not used where significant currents must be carried or when low or stable resistance is required. Typical applications, which require a high density of contacts and easy disassembly for servicing, include connection between liquid crystal display panels (see Liquid CRYSTALS) and between printed circuit boards in watches. Another type of elastomeric contact has a nonconducting silicone rubber core around which is wrapped metalized contacts that are separated from each other by insulating areas (25). A newer material has closely spaced strings of small spherical metal particles in contact, or fine solid wires, which are oriented in the elastomer so that electrical conduction occurs only in the Z direction (26). 

The formation of electrical contacts between metal structures and devices is an integral aspect of circuit construction at all scales of commercial importance. Currently photolithographic, screen printing and microsoldering techniques are the methods of choice to establish connections. However, these approaches require masks, templates or intimate physical contact with the components. Spatially Coupled Bipolar Electrochemistry (SCBE) is a novel technique which makes use of electric fields to create electrical connections between components, which not only avoids physical contact but is also applicable in principle to the formation of three dimensional circuitry. The SCBE technique has been developed to a point where the construction of functional robust circuits has been achieved. Preliminary data demonstrating the application of this approach to the formation of polypyrrole bridges between isolated gold structures is also presented. 

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