Method for manufacturing a horological component and component produced according to said method

Abstract

A method for manufacturing metal horological components, includes the steps of forming a multilevel mould made of a photosensitive resin, with a UV-LIGA method, and galvanically depositing a layer of at least one metal starting from a conductive layer in order to form a block that substantially reaches the upper surface of the photosensitive resin.

Claims

1. A method for manufacturing at least one horological component, comprising: a) providing a substrate and applying a first resin layer of photosensitive resin on the substrate; b) performing a hot stamping, using a stamp, of the first resin layer, by pressing the stamp up to a predefined distance from the substrate so as to keep a layer of resin, in order to shape the first resin layer, the stamp being made of transparent material; c) irradiating the shaped first resin layer through the stamp while the stamp is pressed against the substrate and in contact with the first resin layer in order to define at least a first level of the component; d) applying a second layer of photosensitive resin covering a resultant structure from step c), then irradiating the second resin layer through a mask defining a second level of the component and dissolving non-irradiated regions of the second photosensitive resin layer in order to form a mould comprising a first level and a second level; e) depositing an electrically conductive layer on surfaces of the first resin layer and the second resin layer; f) depositing a metal layer by electroforming in the mould, starting from the electrically conductive layer, in order to form the component; g) machining the metal layer by a mechanical method, so as to adjust a height of the component, and releasing the component.

2. The method according to claim 1, wherein step b) is carried out under vacuum.

3. The method according to claim 1, wherein during step b), the first resin layer is heated to between 70? C. and 150? C.

4. The method according to claim 1, wherein the stamp has an imprint in relief in order to define said at least first level of the component.

5. The method according to claim 1, wherein during step e), the electrically conductive layer is implemented by global deposition on all exposed surfaces of the first resin layer and the second resin layer.

6. The method according to claim 1, wherein during step e), the electrically conductive layer is deposited by a physical vapour deposition, or printing with an ink or conductive resin.

7. The method according to claim 1, wherein said electrically conductive layer is Au, Ti, Pt, Ag, Cr or Pd.

8. The method according to claim 1, wherein the substrate is made of silicon.

9. The method according to claim 1, wherein the electrically conductive layer has a thickness of between 50 nm and 500 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the present invention will emerge more clearly from the detailed description which follows of an exemplary embodiment of a method according to the invention, this example being given purely by way of illustration and not being limiting, in combination with the attached drawing in which:

(2) FIGS. 1 to 8 to illustrate the method steps according to an embodiment of the invention in view of the producing of a horological component.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

(3) The substrate) used in step a) of the method according to the invention is, for example, formed by a silicon substrate. During the first step a) of the method illustrated in FIG. 1, a layer of photosensitive resin is deposited on the substrate. The photosensitive resin 3 used in this method is preferably an octofunctional epoxy-based negative resin available under the reference SU-8 designed to polymerise under the action of UV radiation.

(4) According to a particular embodiment of the invention, the resin is in the form of a dry film; the resin is therefore applied by lamination on the substrate 1.

(5) Alternatively, the photosensitive resin could be a positive photoresist, which is designed to decompose under the action of UV radiation. It will be understood that the present invention is not limited to any particular type of photosensitive resin. A person skilled in the art would know to choose a photosensitive resin suitable for their needs from all the known resins which are suitable for UV photolithography.

(6) The first resin layer 3 is deposited on the substrate 1 by any appropriate means, by centrifugal coating, spinning or even spraying to the desired thickness. Typically, the resin thickness is between 10 ?m and 1000 ?m, and preferably between 50 ?m and 300 ?m. Depending on the desired thickness and the deposition technique used, the resin layer 3 will be deposited in one or two steps.

(7) The first resin layer 3 is then typically heated to between 90 and 120? C. for a duration depending on the deposited thickness in order to remove the solvent (pre-bake step). This heating dries and hardens the resin.

(8) Subsequent step b) illustrated in FIG. 2 consists of performing a hot stamping of the first resin layer 3 in order to shape and define a first level of the horological component. The resin is first heated to a temperature between 70? C. and 150? C. at which it becomes viscous in order to enable its shaping by crushing it using a stamp 2 which presses it. This step is performed under vacuum in order to avoid the formation of air bubbles during the pressing of the resin layer 3. According to the invention, the stamp 2 is pressed to a predefined distance from the substrate 1 in such a way as to keep a layer of resin on the substrate 1.

(9) Advantageously, the stamp 2 has an imprint in relief which can have variations in height and thus enabling at least a first level of the component to be defined, said at least first level thus has a complex three-dimensional geometry which is not possible to obtain by a conventional LIGA method.

(10) It can also be considered to form two or more layers by means of the stamp in order to produce the complete geometry of the component to be obtained.

(11) Subsequent step c) illustrated in FIG. 3 consists of irradiating the first resin layer 3 with UV radiation in order to define the first level of the component to be formed and thus to form a single photopolymerised region 3a.

(12) According to an advantageous embodiment, the stamp 2 is made of a transparent material such as borosilicate glass. Such a stamp 2 made of transparent material makes it possible to irradiate the first resin layer 3 directly through the stamp 2 when the latter is pressed against the substrate 1, in contact with the resin layer, the irradiation of the resin layer being able to be performed hot or at ambient temperature.

(13) An annealing step (post-bake step) of the first resin layer 3 may be necessary in order to complete the photopolymerisation induced by the UV radiation. This annealing step is preferably carried out between 90? C. and 95? C. The photopolymerised region 3a becomes insensitive to a large majority of solvents. By contrast, the photopolymerised regions can be subsequently dissolved by a solvent.

(14) Subsequent step d) illustrated in FIG. 4 consists of depositing a second layer 6 of photosensitive resin covering the structure resulting from preceding step c). The same resin is used during this step, and the thickness can be greater than that deposited during step a). In general, the thickness varies as a function of the geometry of the component that it is desired to obtain.

(15) The next step consists of irradiating the second resin layer 6 through a mask defining a second level of the component, and dissolving the non-irradiated regions of the second photosensitive resin layer 6. At the end of this step (FIG. 4), a mould is obtained comprising a first and a second level formed by the photopolymerised regions 3a and 6a.

(16) The dissolving of the non-photopolymerised regions is performed using a suitable solvent, such as PGMEA (propylene glycol methyl ether acetate). A mould made of photopolymerised photosensitive resin 3a, 6a defining a first level and a second level of the component is thus obtained at the end of step d).

(17) Step e) illustrated in FIG. 5 consists of depositing, for example by physical vapour deposition (PVD), a conductive layer 4, in other words a layer capable of starting a metal deposition by galvanic means. Typically the conductive layer 2 is Au, Ti, Pt, Ag, Cr or Pd, or a stack of at least two of these materials, and has a thickness between 50 nm and 500 nm. For example, the conductive layer 4 can be formed of a chromium or titanium sublayer covered with a layer of gold or copper. According to the invention, the electrically conductive layer 4 is implemented by global deposition on all the exposed surfaces, sides included.

(18) A person skilled in the art could likewise consider implementing a 3D printing in order to deposit the conductive layer 4.

(19) Subsequent step f) illustrated in FIG. 6 consists of depositing, in the formed mould, by electroforming or galvanic deposition, a layer 7 of a metal starting from the electrically conductive layer 2 until the desired thickness is obtained. In the case where a small thickness is required, the growth is relatively short, which allows hollow components to be obtained.

(20) Metal in this context shall of course also include metal alloys. Typically, the metal will be chosen from the set comprising nickel, copper, gold or silver and, as alloys, gold-copper, nickel-cobalt, nickel-iron, nickel-phosphorus or nickel-tungsten. In general, the multilayer metal structure is made entirely of the same alloy or metal. However, it is also possible to change metal or alloy during the galvanic deposition step, so as to obtain a metal structure having at least two layers of different nature.

(21) The electroforming conditions, in particular the composition of the baths, the geometry of the system, the voltages and the current densities, are chosen for each metal or alloy to be electrodeposited according to well-known techniques in the art of electroforming.

(22) Step g) illustrated in FIG. 7 consists of machining the metal layer 7 by a mechanical method so as to adjust the height of the component and to separate the different parts if necessary (since galvanic growth starts everywhere, all the parts located on the same support are connected to one another).

(23) The last step illustrated in FIG. 8 consists of releasing the component by removing, by means of a succession of wet or dry etching steps, the substrate, the conductive layers or the resin layers, operations familiar to a person skilled in the art. For example the conductive layer 4 and the substrate 1 are removed by means of wet etching, which allows the component to be released from the substrate 1 without damaging it. In particular, the substrate made of silicon can be etched using a potassium hydroxide solution (KOH).

(24) At the end of this first sequence, a component caught in the resin layers is obtained. A second sequence consists of removing the first layer 3 and the second layer 6 of resin by O.sub.2 plasma etching, interspersed with wet etching of the intermediate metal layers.

(25) At the end of this step, the components obtained can be cleaned, and possibly taken on a machine-tool in order to carry out machining or aesthetic finishing. At this stage, the parts can be directly used or even subjected to various decorative and/or functional treatments, typically physical or chemical depositions.

(26) The method of the invention has particularly advantageous application for the manufacture of components for timepieces, such as springs, pallets, wheels, appliques, etc. Through this method, it is possible to produce components in very diverse shapes and having more complex geometries than those obtained via conventional photolithography operations. Such a method also makes it possible to obtain shell like components which are relatively light and robust, and which have good reliability in terms of geometries.