MICRO-REPLICATION IN METAL

Abstract: With the intention of preventing damage to components as a result of heating of a chip and with the intention of limiting the affect of such heating, a chip carrying a waveguide connection or a fibre connection has been soldered firmly onto a metal surface or directly onto a metal lead frame, wherewith the thermal resistance will be much lower than in the case when the chip is soldered onto a ceramic or silicon carrier. The use of an embossing tool having an active embossing/stamping part (7) enables a microstructure that includes a V-groove (3) to be produced in the metal surface at low cost and with great precision for aligning a waveguide or a fibre with the chip. The embossing process may be carried out on the metal surface or directly on the metal lead frame. An embossing process can be automated relatively easily, since the material to be embossed can be worked in strip form. A construction method in which an optical chip is soldered to a metal carrier in which waveguide receiving or fibre receiving grooves have been embossed therein will improve heat dissipation and thus substantially increase the useful life of the finished component.

Description: MICRO-REPLICATION IN METAL FIELD OF INVENTION The present invention relates to a method of micro- replication in metal, a device for producing micro- replications in metal and to a metal micro-replicated element produced in accordance with the invention. Micro-replicating methods and devices are preferably intended for use in producing with great precision and at low costs reproduceable building optocomponents, contact devices or other precision elements adapted for aligning optical chips with waveguides or fibres . An optocomponent building element that has an aligning facility can be readily mounted on a circuit board while connected to a waveguide or to a fibre and to a laser or a photodiode . DESCRIPTION OF THE PRIOR ART A common method of aligning optical chips with waveguides or fibres in optocomponents is to etch a desired microstructure in silicon in the form of a V-groove into which a waveguide or fibre can be fitted. With techniques used at present, optical chips are often solder-mounted on a ceramic or silicon carrier. This method quickly presents problems with respect to the dissipation of heat generated in the mounted component . This problem is particularly pronounced in the case of mounted semiconductor lasers of small dimensions, with which the heat generating region is concentrated to narrow bands of circa 2 μm that extend transversely through the chip close to its surface. SUMMARY OF THE INVENTION With the intention of preventing damage to the chip as a result of its becoming hot, or with the intention of at least limiting the affects of such heating, a chip that carries a waveguide or fibre connection has been soldered either to a metal carrier or to a metal lead frame, wherewith the thermal resistance will be much lower than when the chip is solder- mounted on a ceramic or silicon carrier. The invention enables a microstructure to be produced with great precision with respect to the alignment of a waveguide or a fibre in a metal surface with the aid of an embossing/stamping tool at low cost. The embossing process may be carried out on a metal carrier or directly on a metal lead frame intended for plastic encapsulation. An embossing process can be automated relatively easily, since the material to be embossed can be worked in the form of short strips or in the form of long strips wound onto reels. An assembly in which optical chips are soldered onto metal carriers provided with embossed waveguide or fibre receiving grooves will result in improved heat dissipation and therewith greatly increase the useful life of the finished component with enhanced mean fault time (MFT) . BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a metal element provided with a microstructure in accordance with the invention. Figures 2A and B show respectively an inventive embossing tool from beneath and in section. Figures 3A and B are detailed illustrations of the active part of the inventive embossing tool, seen from one side and from above . DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Practical trials have shown that it is possible to emboss microstructures in copper with repeated high measurement precision and with only slight wear on the embossing tool used. Microstructures embossed in metal carriers enable optical components to be aligned and mounted directly on a copper lead frame or a lead frame made of some other alloy, for later inclusion as a building element in a plastic capsule, for instance. The embossing technique provides two obvious advantages over known techniques in which lasers are mounted on a carrier which is then mounted on a lead frame. Firstly, the costs entailed by purchasing and producing such carriers are eliminated. Secondly, advantages are also afforded with respect to dissipation of the heat that is generated in the active regions of the lasers. However, there is the added cost of the embossing process and of the tool required herefor. The precision tools to be used to emboss micro replications may be manufactured by grinding or otherwise working the tool material directly, or in the following manner, for instance: - Applying a photoresist to a silicon disc. - Fitting a photomask having a suitable groove pattern over the silicon disc. - Exposing the photoresist in those openings present in the photomask. - Washing away exposed resist or, alternatively, unexposed resist . - Etching the desired structure in the disc. - Washing away photoresist residues. This results in a plurality of mutually identical three- dimensional silicon structures in the case of two-dimensional photomasks. The aforesaid technique is known to the art, but is mentioned here to provide a better overall picture of the procedure used to produce an embossing tool with desired precision. This procedure can be continued in accordance with either one of the two alternative methods described below. Al ernative A 1. A patterned silicon disc is coated with a layer of material that possesses sufficient hardness. 2. The disc is plated with nickel or some other suitable material . The plating is planarised. 4. The silicon is etched so as to separated the plated and planarised moulding therefrom. The hardness of the plated surface can be enhanced by sputtering or further plating the surf ce with an appropriate metal . 5. The moulding is sawn in two, so as to separate the mutually identical structures. 6. A structure is placed in a holder in an embossing tool, said holder being adapted to the structure. 7. The various parts of the embossing tool are assembled to provide a finished embossing tool. Alternative B 1-4. According to Alternative A. 5. The non-planarised side is coated with a layer which makes later separation possible. 6. The disc is plated with nickel or some other metal. 7. The plating is planarised. 8. The two planarised mouldings are separated from one another. 9. The moulding is sawn in two so as to separate the mutually identical structures. 10. The moulding is placed in a holder and subjected to spark processing in an electro discharge machine (EDM) . 11. Spark processing is effected directly in the material in which microstructures shall be embossed in the metal/lead frame . 12. The various parts of the embossing tool are assembled to provide a finished embossing tool. Figure 1 illustrates an example of an embossed microstructure in a metal element 1 that has a recessed or sunken surface 2 which includes a V-groove 3 for aligning an optofibre or a waveguide. To facilitate mounting of a chip, the metal surface may also be provided with a chip mounting surface 4 that includes chip positioning markings in the form of grooves 5. The embossed metal surface enables a chip to be aligned with a waveguide or a fibre with a great degree of accuracy. As evident from Figures 2A and B, the embossing tool 6 may have the form of a stamp with which a protective holder 8 is arranged around the active part 7 of the tool. The active tool part will suitably have a configuration with which grooves, such as V-grooves, can be embossed in a metal surface. The protective holder will be sprung, e.g. with an Adiprene plate 9, so as to be able to expose the active tool part in the actual embossing process. Figures 3A and B show that the active part 7 may be configured with an embossing surface, which in this case is comprised of a flat surface 10 and a ridged area 11 such as to form a planar surface, or alternatively a recessed surface, and a V-groove when embossing a metal surface. In order to enable an optofibre to be fitted in the V-groove, the active tool part may have a width of 1.20 mm for instance, and the width of the ridge may be 0.16 mm and its length 3.20 mm, and the angle α may be 45°. With this micro replication in metal, a carrier in the form of lead frames and in strip form for instance, may be provided automatically in a manufacturing process with V- grooves and connected to a chip such as lasers or photodiodes . Waveguides or fibres can then be aligned automatically with the aid of the embossed grooves so as to obtain correct alignment of the waveguide or the fibre with the carrier mounted laser or photodiode. The inventive embossing technique enables micro replication to be achieved in the automatic manufacturing process to a high degree of reliability and with great precision at low costs. It will be understood that the invention is not restricted to the aforedescribed and illustrated exemplifying embodiment thereof, and that modifications can be made within the scope of the following Claims.

Claims: CLAIMS 1. A method of micro replicating in metal such as to provide in a metal surface a structure for aligning at least one waveguide or at least one fibre for instance, characterized by embossing at least one groove, such as a V-groove, in a metal surface with the aid of an embossing tool, wherein the groove is intended to receive a waveguide or a fibre for alignment of said waveguide or fibre with a laser or photodiode mounted on the metal surface, for instance. 2. Means for carrying out micro replication in metal to provide a structure for, e.g., the alignment of at least one waveguide or fibre, characterized in that said means is an embossing tool (6) whose active part (7) has a configuration (11) which will provide at least one groove, such as a V- groove, in the metal surface when embossing said surface, wherein the groove is intended to receive a waveguide or fibre for the alignment of said waveguide or fibre with, e.g., a laser or a photodiode mounted on the metal surface. 3. Means according to Claim 2, characterized in that the active part (7) is comprised of a plated and planarised metal element separated from a silicon disc in which the structure has been etched, wherein the metal structure has a configuration (11) which in the embossing process will form at least one waveguide or fibre receiving groove, such as a V-groove, in the metal surface. 4. Means according to Claim 2, characterized in that the active part (7) has been ground to a configuration (11) which in the embossing process will form at least one waveguide or fibre receiving groove, such as a V-groove, in the metal surface . 5. A micro-replicated metal element having in one surface thereof a structure for, e.g., aligning at least one waveguide or at least one fibre, characterized in that the structure included in the metal surface (1) comprises at least one groove (3), e.g. a V-groove, in which a waveguide or a fibre can be fitted for alignment of said waveguide or said fibre with, e.g., a laser or a photodiode mounted on said metal surface.

Inventors: BLOM CLAES, LARSSON OLLE, BLOM, CLAES, LARSSON, OLLE
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)
Application year: 1997
Main classification: B21D22
IPC codes: B21D22, G02B6