Method of producing integrated electrodes in plastic dies,...

Details Method of producing integrated electrodes in plastic dies,... Method of producing integrated electrodes in plastic dies,...

1999-06-17

2001-07-31

Mayekar, K. (Department: 1741)

Coating processes

Direct application of electrical, magnetic, wave, or...

Chemical deposition from liquid contiguous with substrate...

C427S123000, C427S404000

Reexamination Certificate

active

06268025

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing integrated electrodes in plastic dies containing cavities, to plastic dies with integrated electrodes and to applications of the same.
2. Description of the Related Art
DE 35 37 483 describes a method for the formation of a multitude of plate-shaped metallic microstructured bodies by molding a microstructured tool with a non-conductive molding compound. Thus a negative mold of the microstructured tool is filled up with metal by electrodeposition. Then the negative mold is removed. A removable conductive material is applied to the front surface of the tool. During molding this conductive material is transferred to the regions of the molding compound which are in contact with the front surface of the tool.
In a variation of this method, the non-conductive molding compound which fills up the spaces in the microstructured tool may be fixed by a layer of a conductive molding compound. The conductive molding compound contacts and covers the whole front surface of the tool.
DE 40 10 669 describes a method for producing negative molds of plate-shaped microstructured bodies. The base structure of the patterned negative mold forms a coherent area which is covered with a layer of conductive material. This negative mold may be filled with a metal by electroplating. A layer of a thermoplastic resin which is covered with a thin film of a conductive material is used for producing the negative mold. A mold insert is pressed into the heat softened layer of the thermoplastic resin via the thin conductive film. After cooling the thermoplastic resin, the negative mold is separated from the mold insert.
During the stamping process the coherent film of conductive material is split at the front surface of the mold insert corresponding to the pattern of the microstructure. The regions of the conductive film on the front surface of the mold insert stick to the front surface. During stamping the other regions of the film are pushed to the base of the structure of the mold insert by the thermoplastic resin flowing into the cavities of the mold insert.
Pieces of the film may remain as tinsel on the side walls of the structure. If necessary, the tinsel is removed from the negative mold by a laborious cleaning procedure before the negative mold is electroplated with metal. After demolding, the regions of the front surface of the mold insert form the base of the structure of the negative mold. This base is covered with a coherent conductive film which is contactable at its edge.
The tinsel on the side walls and on the front surface of the negative mold comes from the conductive film which is imperfectly split during the stamping process. Some tinsel touches on the conductive layer at the base of the negative mold structure. This results in partially conductive side walls of the structure and the directed deposition of metal in the negative mold is disturbed. Defects, cavities and thicker regions of the metal layer are thus created in the metallic microstructured body molded by electroplating.
The conductive film preferably consists of gold, copper, silver and alloys thereof or of carbon. A film like that on the coherent area of the base of the structure is suitable as an electrode for the electrodeposition of other metals, e.g., copper or nickel. This film is less suitable for the electroless deposition of these metals.
SUMMARY OF THE INVENTION
An object of the invention is to provide a method of producing integrated electrodes in patterned plastics dies more economically and to produce high-quality electrodes even in microstructured dies made of non-conductive resins.
This object is achieved, according to the present invention, by a method including the steps of producing a structured plastic die on a carrier plate which is transparent to electromagnetic radiation, filling the structure of the plastic die with a solution of a metal compound, irradiating the solution of the metal compound with electromagnetic radiation from the back side of the carrier plate via the carrier plate so that the electrodes are formed on the base of the structure, (bottoms of the cavities) and removing the solution of the metal compound from the structure of the patterned plastic die.
The patterned plastic die is produced by injection molding, reaction molding, thermoforming or some other method using a structured tool. After solidification of the resin within the tool the plastic die is separated from the tool. The resin structure complementary to the structure of the tool is located on a carrier plate having a certain thickness.
For producing the patterned plastic die on a carrier plate either a uniform resin is used or for the carrier plate a resin is used which is different from the resin used for the patterned layer. In the latter case, inter alia, the transparency of the resin for the carrier plate may be matched to the wavelength of the electromagnetic radiation applied. The carrier plate may be machined down from its back side to a thickness and a surface condition suitable for irradiation.
Suitable thermoplastic resins include, e.g., poly(methyl methacrylate), poly(oxymethylene), acrylonitril-butadiene-styrene and polyamide.
The term “solution of a metal compound” means a solution in the narrow sense, a suspension or a colloidal solution. The metal compound is a compound in the narrow sense, a metal complex or a metal itself. The dissolved metal compound may be an inorganic salt (e.g., silver nitrate, gold sulfite), an organic metal compound (e.g., palladium acetate, silver tosylate) or a metal complex (e.g., an amino complex like diamine silver complex or tetramine copper complex). The solution may contain several metals at the same time.
The solution of the metal compound filled into the cavities of the plastic die is irradiated from the back side through the carrier plate using laser light, ultraviolet light or X-rays. The radiation may enter the whole back side of the carrier plate with the same intensity or may enter the back side after passing a patterned mask which lies loosely on the back side of the carrier plate or which is fixed to the carrier plate as, e.g., a sputtered mask.
After irradiating, the solution of the metal compound is removed from the patterned plastic die (e.g., by rinsing).
During irradiation of the solution through the carrier plate the metal compound is transformed only in the immediate vicinity of the base of the structure, by which the metal is deposited on the base of the structure in a layer thus forming the electrodes. Owing to its lower transparency for the electromagnetic radiation applied, this layer prevents the dissolved metal compound from further transformation as well as the deposition of metal on the side walls of the structure even during continuous irradiation.
The wavelength of the electromagnetic radiation applied and the duration of the irradiation are matched to the resin employed for the carrier plate, to the thickness of the carrier plate and to the nature of the metal compound. If desired, the electrode may be reprecipitated, coated or etched and may be matched to certain requirements of the following process steps.
The base of the structure of the patterned plastic die may be coherent or not coherent. In the first case the integrated electrode is coherent and is therefore contactable at one point. In the second case the integrated electrodes are not coherent and are therefore contactable at several points.
A structure having a coherent electrode is suitable for electroless and electrophoretic deposition of a material as well as for electroplating, starting from the conductive electrode. A structure having non-coherent electrodes is suitable almost only for electroless deposition of a material, starting from the electrodes. Preferably, palladium solutions are used for the formation of electrodes necessary for the electroless deposition of metal. Nickel, copper, gold and other materials can be electrolessly deposited on a palladium electrode.
The electrodes on

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