CH716966A2 - A method of manufacturing a watch component and a component obtained according to this method. - Google Patents

Abstract

The present invention relates to a method of manufacturing a metal watch component characterized in that it comprises the steps of forming, by a preferential method of the LIGA-UV type combined with hot stamping, a multilevel photosensitive resin mold on a substrate (1) and galvanically depositing a layer (7) of at least one metal from at least two conductive layers to form a block substantially reaching the upper surface of the photosensitive resin.

Description

Field of the invention

The present invention relates to a method of manufacturing a complex multi-level metal structure using LIGA technology. The invention also relates to such a metallic structure, in particular to horological components, obtained by this method.

Background of the invention

Processes corresponding to the definition above are already known. In particular, the article by A. B. Frazier et al. titled „Metallic Microstuctures Fabricated Using Photosensitive Polyimide Electroplating molds“ and published in the journal of Microelectromechanical systems (Vol. 2, N deg. 2, June 1993) describes a process for the fabrication of multilevel metallic structures by galvanic growth in polyimide molds produced by photolithography of layers of photosensitive resin. This process comprises the following steps: create on a substrate a sacrificial metal layer and an initiation layer for a subsequent galvanic growth step, spreading a layer of photosensitive polyimide, irradiate the polyimide layer with UV radiation through a mask corresponding to the contour of a level of the structure to be obtained, develop the polyimide layer by dissolving the non-irradiated parts so as to obtain a polyimide mold, fill the mold with nickel up to the height thereof by galvanic growth, and obtain a substantially flat upper surface, deposit a thin layer of chromium on the entire upper surface by vacuum vaporization, deposit on the chromium layer a new layer of photosensitive resin, irradiate the resin layer through a new mask corresponding to the contour of the next level of the structure to be obtained, develop the polyimide layer so as to obtain a new mold, fill the new mold with nickel up to its height by galvanic growth. separate the multi-level structure and the polyimide mold from the sacrificial layer and the substrate, separate the multi-level structure from the polyimide mold.

It will be understood that the method which has just been described can, in principle, be implemented iteratively to obtain metal structures having more than two levels.

[0004] The patent document WO2010 / 020515A1 describes the manufacture of a part at several levels by producing a complete photoresist mold corresponding to the final part to be obtained before the step of galvanic deposition of the metal of the part in the mold. Only multi-level rooms whose level projections are included in each other are possible by this method.

[0005] Also known from patent document EP2405301A1 is a photoresist mold comprising at least two levels, the levels formed in the substrate comprising only vertical and smooth sides.

These methods only allow the manufacture of parts whose basic geometries are cylindrical, and do not allow the manufacture of parts comprising complex geometries such as bevels or chamfers.

Summary of the invention

[0007] The present invention aims to remedy the aforementioned drawbacks as well as others by providing a method making it possible to manufacture multilevel metal watch components, by combining a hot stamping step with LIGA technology. , in which a conductive layer is combined with a resin layer for each level to allow reliable galvanic growth in the case of multilevel components.

[0008] Another object of the present invention is to allow the manufacture of watch parts exhibiting complex geometries which are usually infeasible via LIGA technology.

[0009] To this end, the invention relates to a method for manufacturing a watch component comprising the following steps: a) providing the substrate, depositing a first electrically conductive layer thereon, and applying a first layer of photosensitive resin; b) performing a hot stamping via a pad of the first resin layer, by pressing the pad to the substrate, to shape it and define a first level of the watch component; c) irradiating the first shaped resin layer through a mask defining a first level of the component and dissolving the non-irradiated areas of the photosensitive resin layer to show in places the first electrically conductive layer; e) apply a second layer of photosensitive resin covering the structure resulting from step c), then irradiate the second layer of resin through a mask defining a second level of the component and dissolve the non-irradiated areas of the second layer of photosensitive resin to form a mold comprising a first and a second level; f) depositing a metal layer by electroforming in the mold from the first conductive layer to form the component, the layer substantially reaching the top surface of the second layer of photosensitive resin; g) successively removing the substrate, the first conductive layer and the resin to release the component.

This method therefore allows the production of multilevel parts.

According to other advantageous variants of the invention: step b) is carried out under vacuum. during step b), the first resin layer is heated between 70 ° C and 150 ° C; the stamp has an imprint in relief, at least part of the imprint being arranged to be pressed directly against the surface of the substrate during step b); said stamp imprint defines said at least a first level of the component; the method comprises an optional step d), following step c), which consists in locally depositing a second electrically conductive layer on the irradiated zones of the first resin layer; the second electrically conductive layer is deposited through a stencil mask; the second electrically conductive layer is implemented by global deposition on all exposed surfaces (including sides) then completely removed except on the upper surface of the first resin layer, where it has been protected by means of a spar deposited by buffering ; the second electrically conductive layer is deposited by printing a conductive ink or resin; said first layer and said second electrically conductive layer are of the Au, Ti, Pt, Ag, Cr, Pd type or a stack of at least two of these materials; the substrate is made of silicon; the first conductive layer has a thickness of between 50nm and 500nm; the second conductive layer has a thickness of between 50nm and 500nm.

Finally, the invention relates to a watch component, obtained according to a method according to the invention, such as an anchor or an escape wheel for example.

It is therefore understood that the method of the invention finds a particularly advantageous application for the manufacture of components for timepieces.

Brief description of the drawings

Other characteristics and advantages of the present invention will emerge more clearly from the following detailed description of an embodiment of a method according to the invention, this example being given only for purely illustrative and non-limiting, in conjunction with the attached drawing in which: FIGS. 1 to 8 illustrate the process steps of an embodiment of the invention with a view to producing a timepiece component.

Detailed description of a preferred embodiment

The substrate 1 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 process is deposited, for example, by a physical vapor deposition (PVD), a first conductive layer 2, that is to say a layer capable of starting a metallic deposition by galvanic means. . Typically, the first conductive layer 2 is of the Au, Ti, Pt, Ag, Cr or Pd type (FIG. 1), or a stack of at least two of these materials, and has a thickness of between 50nm and 500nm. For example, the first conductive layer 2 can be formed from an underlayer of chromium or titanium covered with a layer of gold or copper.

The photosensitive resin 3 used in this process is preferably a negative type resin based on octofunctional epoxy such as SU-8 resin designed to polymerize under the action of UV radiation.

According to a particular embodiment of the invention, the resin is in the form of a dry film, the resin is then applied by lamination to the substrate 1.

[0018] 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 a few particular types of photosensitive resin. Those skilled in the art will know how to choose a photosensitive resin suitable for their needs from among all the known resins which are suitable for UV photolithography.

The first resin layer 3 is deposited on the substrate 1 by any suitable means, by centrifugal coating, by spinning, or by spraying to the desired thickness. Typically the resin thickness is between 10 μm and 1000 μm, and preferably between 30 μm and 300 μm. Depending on the desired thickness and the deposition technique used, the first resin layer 3 will be deposited in one or more times.

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

The next step b) illustrated in Figure 2 consists in performing a hot stamping of the first resin layer 3 to shape it and define a first level of the watch component. The resin is first of all heated to a temperature between 70 ° C and 150 ° C where it becomes viscous to allow it to be shaped by crushing it by means of a pad 8 pressing it. This step can be carried out under vacuum to avoid the formation of air bubbles during the pressing of the resin layer 3. According to the invention, the pad 8 is pressed until complete crushing, up to the substrate 1 so that Only a residual film of resin remains on top of the conductive layer where the pad portions have been pressed against the substrate.

Advantageously, the pad 2 has a relief imprint which may have variations in height and thus making it possible to define at least a first level of the component, said at least first level thus exhibiting a complex three-dimensional geometry that it is not possible to obtain by a conventional LIGA process.

It can also be considered to form two or more levels by means of the buffer to achieve the complete geometry of the component to be obtained.

The next step c) illustrated in Figure 3 consists in irradiating the first resin layer 3 by means of UV radiation through a mask 4 defining the first level of the component to be formed and thus the photopolymerized areas 3a and non-light-cured areas 3b.

This step makes it possible to guarantee that the residual film of resin remaining after the pressing of the pad disappears to reveal the conductive layer, and makes it possible to structure the resin as usually carried out in LIGA.

An annealing step (post-bake step) of the first resin layer 3 may be necessary to complete the photopolymerization induced by UV irradiation. This annealing step is preferably carried out between 90 ° C and 95 ° C. The photopolymerized zones 3a become insensitive to a large majority of solvents. On the other hand, the non-photopolymerized zones can subsequently be dissolved by a solvent.

Then, the non-photopolymerized areas 3b of the first layer 3 of photosensitive resin are dissolved to reveal in places the first conductive layer 2 of the substrate 1 as in Figure 4. This operation is carried out by dissolving the non-photopolymerized areas 3b using a suitable solvent, such as PGMEA (propylene glycol methyl ethyl acetate). A photopolymerized photosensitive resin mold 3a, formed by the combination of a stamping and photolithography operation, defining the first level of the component is thus obtained.

According to an optional step d) illustrated in Figure 5, depositing a second conductive layer 5 on the photopolymerized areas 3a during the previous step. This second conductive layer 5 can have the same characteristics as the first conductive layer 2, namely that it is of the Au, Ti, Pt, Ag, Cr, Pd type or a stack of at least two of these materials, and has a thickness between 50nm and 500nm.

According to a first variant of the invention, a stencil mask is used which is positioned via an optical alignment. Such equipment makes it possible to guarantee good alignment of the mask with the geometry of the photopolymerized zones 3a on the substrate and thus guarantee a deposition only on the upper surface of the photopolymerized zones 3a while avoiding deposition on the sides of the photopolymerized resin 3a because the mask is kept as close as possible to substrate 1.

According to a second variant of the invention, the second electrically conductive layer is implemented by global deposition on all the exposed surfaces (including sides) then completely removed except on the upper surface of the first resin layer, where it was protected by means of a savings deposited by buffering.

A person skilled in the art could also consider the implementation of a 3D printing to deposit the second conductive layer 5.

Such solutions allow selective and more precise deposition of the second electrically conductive layer 5, and therefore to have no deposition on the sides of the photopolymerized resin 3a.

The next step e) illustrated in Figure 6 consists in depositing a second layer 6 of photosensitive resin covering the structure resulting from the previous step. The same resin is used during this step, and the thickness is greater than that deposited during step a). Generally the thickness varies depending on the geometry of the component that is to be obtained.

The next step is to irradiate the second layer 6 of resin through a mask 4 "defining a second level of the component and dissolve the non-irradiated areas 6b of the second layer 6 of photosensitive resin. At the end of this step (figure 6), a mold is obtained comprising a first and a second level revealing in places the first electrically conductive layer 2 and the second electrically conductive layer 5.

The next step f) illustrated in Figure 7 consists in depositing in the mold, by electroforming or galvanic deposition, a layer 7 of a metal from the first layer 2 and optional second layer 5 electrically conductive until form a block preferably reaching a height less than the height of the mold, this allowing better mechanical strength during subsequent machining. By metal in this context are of course understood metal alloys. Typically, the metal will be chosen from the group comprising nickel, copper, gold or silver, and, as an alloy, gold-copper, nickel-cobalt, nickel iron, nickel-phosphorus, or again nickel-tungsten. In general, the multilayer metal structure is made entirely from the same alloy or metal. However, it is also possible to change the metal or alloy during the galvanic deposition step so as to obtain a metal structure comprising at least two layers of different types.

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

The metal layer 7 can be machined by a mechanical process so as to obtain a thickness predefined by the thickness of the component to be produced. Depending on the face on which this operation must be performed, the recovery can be done in wafer.

Step g) consists in releasing the component by eliminating by a succession of etching steps, wet or dry, the substrate, the conductive layers or the resin layers, operations familiar to those skilled in the art. For example, the first conductive layer 2 and the substrate 1 are removed by means of wet etching, which makes it possible to release the component from the substrate 1 without damaging it. Notably, the silicon substrate can be etched with a solution based on potassium hydroxide (KOH).

At the end of this first sequence, a component is obtained taken from the first and second resin layers, the second conductive layer 5 also still being present in places.

A second sequence consists in removing the first layer 3 and the second layer 6 of resin by means of O2 plasma etchings, spaced with wet etchings of the intermediate metal layers.

At the end of this step, the components obtained can be cleaned, and optionally taken up on a machine tool to carry out machining or an aesthetic termination. At this stage, the parts can be used directly or else subjected to various decorative and / or functional treatments, typically physical or chemical deposits.

The method of the invention finds a particularly advantageous application for the manufacture of components for timepieces, such as springs, anchors, wheels, appliques, etc. Thanks to this process, it is possible to produce components of more diverse shape and having complex geometries than those obtained by conventional photolithography operations. Such a method also makes it possible to obtain robust components which have good reliability in terms of geometries.

Claims (15)

1. A method of manufacturing at least one watch component comprising the following steps: a) providing a substrate (1), depositing thereon a first electrically conductive layer (2), and applying a first layer of photosensitive resin (3); b) performing a hot stamping via a pad of the first resin layer (3), by pressing the pad (8) to the substrate, to shape the first resin layer and define a first level of the watch component; c) irradiating the first resin layer (3) shaped through a mask (4) defining at least a first level of the component and dissolving the non-irradiated areas (3b) of the photosensitive resin layer (3) to reveal in places the first electrically conductive layer (2); d) apply a second layer of photosensitive resin (6) covering the structure resulting from step c), then irradiate the second layer of resin (6) through a mask (4 ") defining a second level of the component and dissolve the non-irradiated areas (6b) of the second layer of photosensitive resin (6) to form a mold comprising a first and a second level; e) depositing a metal layer (7) by electroforming in the mold from the first layer (2) to form the component, the layer (7) substantially reaching the upper surface of the second photosensitive resin layer (6); f) successively removing the substrate, the first conductive layer and the resin to release the component. 2. A method of manufacturing at least one watch component comprising the following steps: a ') providing a substrate (1), depositing thereon a first electrically conductive layer (2), and applying a first layer of photosensitive resin (3); b ') irradiating the first resin layer (3) through a mask (4) defining at least a first level of the component and dissolving the non-irradiated areas (3b) of the photosensitive resin layer (3) to reveal in places the first electrically conductive layer (2); c ') applying a second layer of photosensitive resin (6) covering the structure resulting from step c), d ') performing a hot stamping via a buffer of the second resin layer (3) to shape the second resin layer and define a second level of the watch component; e ') irradiating the second resin layer (6) shaped through a mask (4 ") defining a second level of the component and dissolving the non-irradiated areas (6b) of the second photosensitive resin layer (6) to form a mold comprising a first and a second level; f ') depositing a metal layer (7) by electroforming in the mold from the first layer (2) to form the component, the layer (7) substantially reaching the upper surface of the second layer of photosensitive resin (6); g ') successively removing the substrate, the first conductive layer and the resin to release the component. 3. Method according to claim 1 or 2, characterized in that step b) or step d ') is carried out under vacuum. 4. Method according to claim 1 or 2, characterized in that during step b) or step d '), the first resin layer is heated between 70 ° C and 150 ° C. 5. Method according to one of claims 1 to 4, characterized in that the pad has an imprint in relief, at least part of the imprint being arranged to be pressed directly against the surface of the substrate during step b ). 6. Method according to claim 5, characterized in that said stamp imprint defines said at least a first level of the component. 7. Method according to claim 1 or 2, characterized in that it comprises an optional step d), following step c) or step b '), which consists in locally depositing a second electrically layer. conductive (5) on the irradiated areas (3a) of the first resin layer (3). 8. Method according to claim 7, characterized in that the second electrically conductive layer (5) is deposited through a template mask (4 '). 9. The method of claim 7, characterized in that during step d), the second electrically conductive layer (5) is implemented by global deposition on all the exposed surfaces (including sides) and then completely removed except on the upper surface of the first resin layer, where it has been protected by means of a buffer deposited by buffering. 10. The method of claim 7, characterized in that during step d), the second electrically conductive layer (5) is deposited by printing an ink or a conductive resin. 11. Method according to one of the preceding claims, characterized in that said first layer (2) and said second electrically conductive layer (5) are of the Au, Ti, Pt, Ag, Cr, Pd type. 12. Method according to one of the preceding claims, characterized in that the substrate (1) is made of silicon. 13. Method according to one of the preceding claims, characterized in that the first conductive layer (2) has a thickness between 50nm and 500nm. 14. Method according to one of the preceding claims, characterized in that the second conductive layer (5) has a thickness between 50nm and 500nm. 15. Timepiece component obtained according to a process according to one of claims 1 to 14.