EP2579104B1 - Method for manufacturing a composite timepiece - Google Patents

Description

Technical area

The present invention relates to the field of mechanical watchmaking. It relates, more particularly, to a method of producing a composite timepiece comprising at least a first metal layer and a second silicon-based layer.

State of the art

In watchmaking, interest in silicon and silicon-based parts is growing. Indeed, the use of lithographic masking techniques and deep etching DRIE (Deep Reactive Ion Etching) allows the manufacture of complex parts, made with great precision. Series production is industrially advantageous. In addition, the tribological properties of silicon are also used for parts intended to be rubbed in order to limit or eliminate the use of lubricants. Furthermore, LIGA technology (Röntgenlithographie, Galvanoformung, Abformung) is increasingly being used to produce complex metal parts.

In some applications, it is sought to produce silicon-metal composite parts. This may be useful for giving sufficient weight to a rocker made of silicon, or to overcome the mechanical weaknesses of a silicon-based part, related to the lack of plastic domain of this type of material, in particular to ensure fixing a silicon-based part to another element. Currently, techniques such as galvanic growth or vapor phase metallization are used. However, the achievable thicknesses are limited and the reproducibility of these techniques is not suitable for industrial production of very precise parts. Furthermore, the deep etching techniques DRIE on the one hand and LIGA on the other hand, are both complex to implement and have a relatively large number of steps, so that combining these two techniques is relatively complicated.

Examples of silicon-metal composite parts are disclosed in the documents EP 2 154 582 and EP 2 104 005 : the document EP 2 154 582 discloses an assembly formed of a metal pinion and a silicon gear comprising an impression of the pinion toothing in the surface of the toothed wheel, while the document EP 2 104 005 discloses a composite silicon-metal balance.

The object of the present invention is to provide a method for producing a silicon-metal composite part in an industrializable manner.

Disclosure of the invention

More specifically, the invention relates to a method for producing a composite part, as defined in the claims.

Brief description of the drawings

• les figures 1a,1b et 1c illustrent schématiquement les étapes principales de la réalisation d'au moins une partie de la couche métallique,
• les figures 2a, 2b et 2c illustrent schématiquement les étapes principales de la réalisation de la couche à base de silicium,
• les figures 3a, 3b, 3c et 3d illustrent schématiquement les étapes principales de l'assemblage de la partie de la couche métallique et de la couche à base de silicium, et
• les figures 4a, 4b, 4c, 5 et 6 proposent des exemples d'application de l'invention.

Other details of the invention will emerge more clearly on reading the description which follows, made with reference to the appended drawing in which:

• the Figures 1a, 1b and 1c schematically illustrate the main steps of producing at least part of the metal layer,
• the Figures 2a, 2b and 2c schematically illustrate the main steps of the realization of the silicon-based layer,
• the figures 3a , 3b , 3c and 3d schematically illustrate the main steps of assembling the portion of the metal layer and the silicon-based layer, and
• the Figures 4a, 4b, 4c , 5 and 6 provide examples of application of the invention.

Mode (s) of realization of the invention

According to a first aspect, the present invention relates to a method of producing a composite timepiece comprising a first metal layer and a second silicon-based layer.

With reference to Figures 1a, 1b and 1c on the one hand, a first part defining at least a portion of the first metal layer is produced. As will be understood later, during the stages of the figure 1 depending on the variants chosen for the other steps of the method, it is possible either to produce only a portion of the metal layer of the composite part or the entire metal layer of the composite part.

• Fer, Titane, Chrome, Nickel, Cuivre, Zinc, Aluminium, Argent, ou en acier, laiton ou bronze, par exemple. Ce substrat étant sacrificiel, on essaiera de limiter son coût. La surface du substrat peut être traitée ou non, les traitements possibles étant des traitements thermiques, des oxydations ou des nitrurations. On peut également envisager d'utiliser un substrat 1 de type SOI (de l'anglais Silicon On Insulator), dans certains cas où il y aurait une utilité à conserver tout ou partie de ce substrat.

The following steps are performed. We first have a first substrate 1 based on silicon, glass or metal according to the following list:

• Iron, Titanium, Chrome, Nickel, Copper, Zinc, Aluminum, Silver, or steel, brass or bronze, for example. This substrate being sacrificial, we will try to limit its cost. The surface of the substrate can be treated or not, the possible treatments being heat treatments, oxidations or nitrurations. One can also consider using a substrate 1 of the type SOI (English Silicon On Insulator), in some cases where there would be a utility to keep all or part of this substrate.

One or more conductive layers 2 (pure metal or alloy) are then deposited by evaporation or spraying. The metals or alloys used can be typically titanium, chromium, tantalum, gold, copper, nickel, platinum, silver, a gold-tin alloy ...

Then, on the conductive layer 2, a metal growth 4 by LIGA technology, this metal growth 4 defining all or part of the first metal layer.

To do this, a layer of 5 to 1000 μm of photoresist 3 is formed on the conductive layer 2 by photolithography in order to obtain cavities in the resin, the cavities making the conductive layer 2 apparent. Photolithographic techniques, including the steps of masking, insolation and dissolution being well known to those skilled in the art, they will not be described in more detail.

On the exposed conductive layer 2 at the bottom of the cavities, a galvanic metal growth is then carried out in the cavities to obtain the metal growth 4.

The free surface of the metal growth 4 is then laid flat, typically by surface abrasion, such as polishing, lapping or grinding. In an incidental way and without affecting the other stages of the process, the resin is polished simultaneously. This step is important for the rest of the process. Indeed, a surface resulting from a galvanic growth is, a priori, not perfectly flat and is therefore not a good basis for a connection with another room. The surface abrasion allows a grinding of the surface of the metallic growth 4.

Finally, the photoresist 3 is removed dry, plasma type, or wet, by reaction in a suitable chemical solution. These steps are also well known to those skilled in the art and are therefore not described further. It will be noted that the surface abrasion step can also be carried out after the removal of the photoresist 3.

The metal growth 4 thus defines one or more metal parts disposed on and secured to the first substrate 1, this or these metal parts forming what will be all or part of the metal layer of the composite part.

It will be noted that, as shown in figure 1c the steps of the LIGA process for structuring photoresist 3 and galvanic growth can be repeated so as to obtain a metal growth 4 at several levels. If necessary, an intermediate metal layer of attachment is deposited on the surface of a previous level, before depositing and structuring the resin. Each level is thus built on the previous one.

Furthermore, a second part defining the second silicon-based layer is produced by performing the following steps, illustrated with reference to the Figures 2a to 2c . First of all, a second substrate 10 based on silicon is provided. It may be a silicon wafer or an SOI type substrate. The surface of the second substrate can be treated or not. The treatments that can be applied to a silicon surface are, for example, heat treatments, oxidations or nitriding.

Next, photolithographic masking 12 is carried out on at least one face of this second substrate 10. This photolithographic masking 12 is produced by depositing a layer of photosensitive resin of 1 to 100 μm on the relevant face of the second substrate. A mask is then deposited on said layer of photoresist and the resin is insulated through the mask by exposure to UV rays. Finally, the insolated resin is removed chemically, in order to obtain cavities in the resin layer and thus define the photolithographic masking 12. These masking, insolation and dissolution steps are well known to those skilled in the art they will not be described in more detail. If necessary, an intermediate mask of silicon oxide may be used.

Then, a DRIE etching is carried out at the surfaces left free by the photolithographic masking, symbolized by the reference 14 on the figures 2 .

Then, photolithographic masking by plasma or wet dry type is removed by reaction in a suitable chemical solution.

Etching thus makes it possible to obtain a silicon-based part etched in the second substrate 10, this silicon-based part forming what will be the silicon-based layer of the composite part.

Note that the etching can be performed on both sides of the second substrate. Moreover, by performing several photolithographic masking, it is also possible to perform multilevel etchings.

Next, assemble the composite part by performing the following steps. The first and second parts are respectively positioned so as to bring into contact, on the one hand, the metal part (s) integral with the first substrate (1) and intended to form the metal layer of the composite part and, on the other hand, the the silicon-based parts integral with the second substrate 10 and intended to form the silicon-based layer of the composite part ( figure 3a ). If necessary, indexing elements may be provided on each of the parts, so that they are perfectly positioned one with reference to the other, depending on the composite part that is desired.

The first and second parts are then welded together, applying a pressure and / or temperature to weld the first part to the second part. In the example described here, the bonds created are Si-Metal bonds resulting from the formation of an intermetallic alloy. Typically, this step can be carried out by applying a temperature of between 100 and 600 ° C. and a pressure of between 0.5 and 10 bars.

In order to promote the assembly of the first and second parts and to improve the accuracy of their relative positioning, which must be optimal, it is also possible, after the removal of the photolithographic mask 12 on the second substrate 10, to deposit a metallic layer of interface 16 on the silicon-based parts intended to come into contact with the first metal part. Preferably, the metal interface layer 16 is made of the same metal as the galvanic growth 4. figure 3b illustrates this situation. The assembly operation is then between two metal layers, by means of a thermo-compression welding, applying a temperature between 100 and 600 ° C and a pressure between 0.5 and 10 bar. The metal interface layer 16 deposited on the second substrate will then form, with the metal growth 4 of the first part, the assembly of said first metal layer of the composite part.

Finally, the composite part is released by selectively removing the first substrate 1 ( figure 3c ). The metal growth 4 deposited on it remains welded to the second piece. This elimination is also carried out by dry etching plasma type, or wet by reaction in a suitable chemical solution or by mechanical means. The figure 3d represents the same step in the case where a metal interface layer 16 has been used. It will be noted that the distinctive hatches used in the figure are only there to clarify the diagrams but have no physical significance. Indeed, after thermo-compression welding, there is no discontinuity between the interface metal layer 16 and the galvanic growth 4.

The method which has just been described makes it possible to produce in an industrially manner, that is to say accurate and reproducible, composite parts, comprising a metal layer and a silicon-based layer, both of which may present complex three-dimensional shapes. This method can advantageously be used to produce parts watchmaking, in particular parts where the silicon is advantageous, but should preferably be combined with metal parts to compensate for its fragility or its low density.

An example of application relates to a timepiece 20 intended to be mounted on an axis ( Figures 4a, 4b and 4c ). Typically, it may be a wheel or a pinion. It is known that fixing such a mobile silicon on an axis is problematic, since the silicon does not withstand the stresses applied during a traditional hunting. Thus, the second layer 22 made of silicon has a hole sized to allow the free passage of the axis. It therefore does not undergo mechanical stress during assembly on the axis. The first metal layer 24 comprises, it, a hole sized to cooperate rigidly with the axis.

The figure 4b shows a variant of the timepiece 20, in which the hub of the silicon-based part comprises a multilevel etching, defining, on the one hand, a housing for the metal layer 24 and, on the other hand, a structure elastic at the hub allowing centering on the axis. During assembly, the elastic structure can be deformed and allows to center the composite part on the axis. Fixing is performed on the metal layer 24.

The figure 4c proposes a further variant of the timepiece 20, in which the second layer 22 made of silicon comprises, on either side of its hub, a metal layer 24. As for the first variant, the hole of the hub of the second layer 22 is dimensioned so that the latter does not undergo stress. Furthermore, each of the metal layers 24 has a hole sized to cooperate rigidly with the axis. The axis is thus guided on each side of the silicon-based part. The holes of the first and second layers are arranged coaxially.

It is thus the metal layer 24 or the metal layers 24 which undergo / undergo the constraints related to the fixing which can be carried out by driving, riveting, shrinking, brazing, welding or other processes. known assembly. The method allows great accuracy and remarkable efficiency in the arrangement of the metal layer at the hub of the silicon-based layer. A similar construction may more generally be used for different cases in which a silicon-based part is to be assembled to another part. It is possible to mention the assembly of a silicon bridge on a platinum, the driving of a stone in a silicon bridge, the fixing of a metal dart on a silicon anchor, the assembly of a ferrule or of a stud on a silicon-based hairspring, the assembly of a return spring or a pawl on a silicon wheel.

A second application of the method according to the invention consists in producing metal inertial masses 34 on a rocker 32 made of silicon. The invention can be applied to any other component requiring the addition of point masses or unbalance.

A third application 40 of the method according to the invention consists in producing metal decorations on a silicon-based part 42. The production of the first metal layer 44 by LIGA technology makes it possible to obtain particularly complex shapes that can provide decorations. .

The method according to the invention thus offers the possibility of producing a composite part, having, for both its metal part and its silicon-based part, complex shapes, but nevertheless extremely precise. Thanks to the fact that the pieces are made independently of each other, the realization of each of them can be done without altering the other and without being embarrassed by it.

This description has been given by way of non-limiting illustration of the invention. Those skilled in the art will be able to adapt it on the basis of their general knowledge, without departing from the scope as defined by the claims.

Claims (11)

1. A method for producing a composite timepiece comprising a first metal layer and a second silicon-based layer, including the following steps:

   A. producing the first part defining at least part of the first metal layer by performing the following steps:

   a. obtaining a first silicon-, glass- or metal-based substrate (1),

   b. performing, on the first substrate, metallic growth (4) using the LIGA technology, said growth defining said at least one part of the first layer,

   B. producing a second part defining the second silicon-based layer by performing the following steps:

   a. obtaining a second silicon-based substrate (10),

   b. performing, on at least one face of the second substrate, photolithographic masking (12), and

   c. performing DRIE etching at the surfaces left free by the photolithographic masking, then

   d. removing the photolithographic masking,

   C. assembling the composite part by performing the following steps:

   a. positioning the first and second parts, respectively, so as to put said at least one part of the first metal layer and the second silicon-based layer in contact,

   b. welding the first and second parts together while applying a pressure and/or a temperature allowing welding by thermocompression or the formation of an inter-metallic alloy and the creation of a bond between the first and second parts,

   c. freeing the composite part by eliminating the first substrate.
2. The method according to claim 1, characterized in that step B further includes the following operation, carried out after removing the masking:

   e. depositing a metal interface layer (16) on the parts designed to form, with the part of the first metal layer, the assembly of said first layer.
3. The method according to claim 2, characterized in that the deposition of the metal interface layer (16) is done by depositing one or more layers by evaporation or sputtering.
4. The method according to claim 3, characterized in that the metal interface layer (16) is made with a base of titanium, chrome, tantalum, gold, copper, nickel, platinum, silver, or a gold-tin alloy.
5. The method according to claim 1, characterized in that step B further includes an operation for producing an intermediate mask made from silicon oxide.
6. The method according to one of claims 1 to 5, characterized in that step A.b. is done by:

   - A.b.1 structuring a layer of 5 to 1000 µm of photosensitive resin (3) before the lithography in order to obtain cavities in said resin,

   - A.b.2 performing galvanic metal growth in said cavities, and

   - A.b.3 removing the resin,

   step A.b. further including a step for flattening the obtained surface, done either before or after step A.b.3.
7. The method according to claim 6, characterized in that the flattening of the obtained surface is done by polishing, grinding or milling.
8. The method according to one of claims 6 and 7, characterized in steps A.b.1 to A.b.2 are repeated so as to obtain a metal layer with several levels.
9. The method according to claim 8, characterized in that, between two cycles of steps A.b.1 to A.b.2, an intermediate metal catching layer is deposited.
10. The method according to one of the preceding claims, characterized in that step B.c. for DRIE etching is carried on several different levels.
11. The method according to one of the preceding claims, characterized in steps B.b., B.c. and B.d. are carried out on two opposite faces of said second part.

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