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MANUFACTURING COMPONENTS USING ELECTROFORMING TECHNOLOGY (UV-LIGA)

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1. Introduction

Emerging in 1998, this additive component manufacturing technology combines lithography (through UV light exposure) and electroforming. The acronym UV-LIGA directly refers to this. Traditional manufacturing methods are generally associated with the use of a specific type of machine (machining center, stamping press or Electrical discharge machining (EDM) machine). In watchmaking, it is mainly nickel alloys (particularly nickel phosphorus) that are used with this technology. UV-LIGA technology is more of a manufacturing process broken down into different steps:

2. Component design

UV-LIGA technology makes it possible to obtain component profiles that are impossible to achieve with other manufacturing methods. For example, an Escapement wheel can be perforated according to a defined structure in order to reduce its weight as much as possible without weakening its rigidity. It is therefore important to have a good understanding of this technology in order to take advantage of it right from the design stage of the component.

3. Creation of the photomask

The profile of the component to be produced is printed at a 1:1 scale on a glass plate. The component to be produced is reproduced as many times as possible on the surface of the photomask. The Light (UV) can thus only pass outside the outline of the components to be produced.

4. Manufacturing the wafer

The wafer is, in a way, the mold that will be used to manufacture the component through additive growth. It is a Silicon Disc whose surface is gold-plated to improve its electrical conductivity. A layer of photosensitive resin, thicker than the component to be manufactured, is then applied to the previously gold-plated surface of the wafer.

5. Structuring the mold

This step involves superimposing the photomask on the wafer and irradiating its surface with UV rays. Of course, thanks to the filter provided by the photomask, only the surfaces of the components to be produced will be protected from UV rays. The resist exposed to UV rays will harden through polymerization and cannot be dissolved during the next step.

6. Dissolution of the non-irradiated resist

After being exposed to UV rays, the wafer is immersed in a bath that dissolves, with extreme precision, the surfaces of the wafer that were not exposed to UV rays, meaning the precise surface of the components to be produced. Through this operation, as many molds of the component to be produced are obtained as the wafer surface can accommodate. At this stage, the mold of the component to be produced is complete, as is the lithography part of the process.

7. Manufacturing the component through material growth

The mould is immersed in an electrolytic bath. An electric current flows between an anode immersed in the bath and the case back of the mould (gilded), which forms the cathode. The metal particles suspended in the bath are deposited in successive layers on the base of the mould and then over the entire height of the component, perfectly following the boundaries of its outline as defined by the resin.

8. Surface grinding

The upper surface of the mould-component assembly is then ground to bring all the components to their final thickness and to ensure the flatness and parallelism of the various surfaces of the component.

9. Dissolving the mould

Once ground, the assembly is immersed in a bath that dissolves the hardened resin of the mould and its substrate. The finished components are released from the mould and ready to be assembled.

UV-LIGA technology offers numerous advantages over traditional component manufacturing methods. The design and technicality of components have immediately benefited from it. Thanks to the level of precision offered by this method and the absence of mechanical stress during component manufacturing, the limits in terms of technicality and design are masterfully pushed back.

Although the process requires several steps, implementation is fast and its cost is controlled. Components made using this process are always perfectly identical and compliant with the original design. Precision is expressed in microns and, in the total absence of tooling, extremely tight tolerances can be achieved.

Thanks to this precision and the absence of cutting tools, surface finishes generally require no further treatment. This is a major advantage, particularly when it comes to gears, since friction is minimized thanks to the quality of the surfaces obtained with this technology. Finally, the nickel-phosphorus typically used is Non-magnetic. A quality particularly valued in the manufacturing of Escapement components.

The numerous advantages of this process quickly made it an essential and widely used technology. It has truly freed the creativity of designers and improved the performance of watches. With the rise of Silicon, UV-LIGA technology is one of the major developments of this century.