Timepiece component

Abstract

Watch component based on a brittle material characterized in that it comprises at least a surface part of brittle material covered by a coating (10) comprising at least two CE layers of elastic material (11) separated by a CR layer of material more resistant (12) than the elastic material (11).

Description

[0001] The present invention relates to a watch component made from a fragile material, in particular silicon. It also relates to a watch movement and a timepiece, in particular a wristwatch, comprising at least one such watch component.

[0002] Document WO2014 / 006229A1 discloses a silicon watch hairspring. This hairspring comprises a multi-layer coating with a succession of alternating layers of TiO 2 and Al 2 O 3 , respectively.

[0003] Silicon is a material with multiple advantages for the manufacture of watch components. On the one hand, it allows the simultaneous manufacture of a large number of small parts, with micrometric precision. On the other hand, it has a low density and a diamagnetic character. This material does, however, have a disadvantage: it has little or no plastic deformation domain, which makes it a relatively fragile material. Mechanical stress or shock can lead to breakage of the component. This fragility of silicon watch components is accentuated by their cutting from a silicon substrate, generally carried out using a deep etching technique, for example by deep reactive ion etching (DRIE).A specific feature of this type of engraving is to form openings with slightly wrinkled sides that present surface flatness defects in the form of ripples (in English "scalloping"). This results in a certain roughness of the engraved sides that weakens the mechanical resistance of the component. In addition, flatness defects can generate crack initiations, particularly in the event of mechanical stress, and lead to breakage of the component. In the event of breakage of a silicon watch component within a watch movement, the result is not only that the watch movement no longer functions, but also that there is a significant amount of silicon debris scattered within the watch movement, originating from the broken watch component.

[0004] An object of the present invention is to provide a watch component which does not include the drawbacks of the state of the art.

[0005] More specifically, a first object of the invention is to propose a watch component which does not produce a multitude of scattered debris in the event of breakage.

[0006] For this purpose, the invention is based on a watch component as defined by the claims.

[0007] These objects, characteristics and advantages of the present invention will be explained in detail in the following description of particular embodiments made without limitation in relation to the attached figures among which: There figure 1 schematically represents a watch component in section according to a first embodiment of the invention. The figure 2 schematically represents a watch component in section according to a second embodiment of the invention. The figure 3 represents an enlargement of a photograph of a test piece at the time of its rupture, made of fragile material covered with a coating according to the embodiment of the invention. The figure 4 represents an enlargement of a photograph of a test piece at the moment of its rupture, made of brittle material, similar to that of the figure 3 but without coating according to the embodiment of the invention. The figure 5 represents the resistance obtained on different batches of watch components, highlighting the positive results obtained by implementing an embodiment of the invention.

[0008] As presented above, the invention is particularly concerned with watch components based on fragile materials, i.e. materials likely to break by generating several debris which dissociate from the watch component and scatter in a watch movement. We therefore understand by fragile material a non-ductile material which breaks without prior and residual plastic deformation. These materials are preferably micro-machinable, i.e. obtained from micro-fabrication techniques involving photolithography. The invention is particularly suitable for silicon, in any form, for example including doped or porous silicon, but could alternatively also be adapted for other materials such as for example diamond, quartz, glass, silicon carbide, ceramic based on alumina or zirconia, fragile amorphous metals or sapphire.Such a watch component may be entirely or almost entirely formed from said fragile or brittle material, ignoring its thin coating which will be described later. Alternatively, a watch component could be based on such a material, that is to say comprise by weight at least 51% of such a material, or even at least 80% of such a material. It may therefore be a hybrid material which has a fragile or brittle effect. We will use the term “fragile material” improperly to designate the entire heart of the watch component, including the parts of said heart which may not be directly in the fragile material at the base of the watch component.

[0009] The concept of the invention consists in covering at least a portion of the surface of the watch component, preferably the surface of the area of ​​the watch component subjected to the greatest tensile stress, using a multi-layer coating comprising at least two layers of elastic material separated by a layer of material more resistant than the elastic material. Such a coating forms a protective layer for the watch component to prevent the scattering of debris in the event of breakage of the component by holding the different pieces together. In the case of a coating extending over substantially the entire periphery of the watch component or over the areas that will be subjected to deformation stress, it is considered that such a coating forms an encapsulation of the watch component.

[0010] There figure 1 schematically illustrates a watch component 1 according to a first embodiment of the invention. This watch component 1 comprises a main volume or core 2 made of silicon, originating for example from a step of cutting a silicon wafer. It further comprises a coating 10 which extends over its entire outer surface, over its entire periphery, more particularly over the periphery of its core 2. According to an advantageous manufacturing method which will be described subsequently, this outer surface is formed by cutting a wafer, and mainly has three surfaces. A first surface 3 is substantially planar and corresponds to the upper face of the cut wafer, a second opposite surface 4, substantially planar and parallel to the first surface 3, corresponds to the lower face of the cut wafer. Finally, a third surface 5 forms a flank, which continuously connects the two aforementioned surfaces 3, 4.

[0011] The coating 10 is a multi-layer coating, which comprises a first CE layer, in contact with the silicon core 2 of the watch component 1, in an elastic material 11. It comprises a third outer CE layer in the same elastic material 11. These two layers are separated by a second CR layer in a more resistant material 12. In this first embodiment, the CE layers are made of parylene and the CR layer is made of aluminum oxide deposited by ALD.

[0012] There figure 2 illustrates a second embodiment, which differs from the first in that the intermediate CR layer of the coating of more resistant material 12, made of silicon oxide, has a variable thickness at the flank 5. This intermediate layer also has a constant thickness at the first and second surfaces 3, 4, this thickness being greater at the first surface 3 than at the second surface 4. The two CE layers of elastic material 11 complete this intermediate layer to form an overall coating of constant thickness. In this second embodiment, the CE layers are made of parylene and the CR layer is made of silicon oxide deposited by PVD.

[0013] On the figures 1 et 2 , the thickness of the coating 10 is not to scale, it is greatly increased in order to better visualize this coating, which is in reality very thin. Its thickness E is likely to vary within a certain range. Generally speaking, the coating 10 comprises at least one layer CE of elastic material 11 with a thickness greater than or equal to 0.05 µm, or even greater than or equal to 0.3 µm. The coating 10 also advantageously comprises at least one layer CE of elastic material 11 with a thickness less than or equal to 5 µm, or even less than or equal to 3 µm. Finally, the sum of the thicknesses of the different layers CE of elastic material of the coating 10 is advantageously greater than or equal to 0.1 µm, or even 0.6 µm, and / or less than or equal to 20 µm, or even less than or equal to 12 µm. Note that the different CE layers of elastic material 11 may or may not have the same thickness. This thickness may or may not be variable.

[0014] On the other hand, a CR layer of more resistant material 12 of the coating 10 has a thickness greater than or equal to 15 nm, or even greater than or equal to 30 nm. The coating 10 also advantageously comprises a layer of more resistant material 12 with a thickness less than or equal to 150 nm or even less than or equal to 100 nm, or even less than or equal to 70 nm. Finally, the sum of the thicknesses of the different CR layers of more resistant material 12 is greater than or equal to 15 nm, or even greater than or equal to 30 nm, and / or is less than or equal to 450 nm, or even less than or equal to 300 nm, or even less than or equal to 210 nm.

[0015] In addition, the materials of the coating 10 may be different from those used in the embodiments described. In all cases, the elastic material 11 has a modulus of elasticity less than or equal to 10 GPa, or even less than or equal to 5 GPa, or even less than or equal to 3 GPa. As a variant or addition, the elastic material 11 has an elongation at break greater than or equal to 10%, or even greater than or equal to 20%, or even greater than or equal to 30%. This elastic material 11 may therefore be parylene, or alternatively a PTFE, an acrylic resin, silicone or a polymer from the urethane family. Different layers of elastic material 11 of the same coating 10 may be in the same elastic material or in a different elastic material.

[0016] On the other hand, the more resistant material 12 is said to be “more resistant” in comparison with the resistance of the so-called “elastic” material. It has a modulus of elasticity greater than or equal to 30 GPa, or even greater than or equal to 45 GPa, or even greater than or equal to 60 GPa. Alternatively, it has a modulus of elasticity intermediate between that of the fragile material of the core of the watch component and that of the elastic material of the elastic layer. It advantageously has a modulus of elasticity greater than or equal to that of an adjacent layer of elastic material 11 increased by 50%. This more resistant material 12 may be a metal or an alloy or graphite or an oxide, more particularly silicon oxide or silicon nitride. Different layers of more resistant material 12 of the same coating 10 may be in the same material or in a different material.

[0017] Naturally, the invention is not limited to the embodiments described. Thus, the coating 10 may comprise any other number of layers than the three layers shown. It may for example comprise at least two, or even at least three, or four, layers of elastic material 11 and at least one, or even at least two, or three, layers of more resistant material 12. In order to limit the influence thereof on the dimensions and behavior of the component, it advantageously comprises at most four layers of elastic material 11 and at most three layers of more resistant material 12, but could comprise more. It advantageously comprises an alternation of layers of elastic material 11 and layers of more resistant material 12. It further advantageously comprises a first inner layer of elastic material 11 and a last outer layer of elastic material 11.The adjectives "inside" and "outside" are used in reference to any direction from the core 2 of the watch component 1 to the outside of the watch component 1.

[0018] The invention is particularly interesting for a watch component 1 chosen from a toothed wheel, an escape wheel, a hand, a plate pin, an anchor, a lever, a lever, a flat spring, such as a balance spring, a flexible blade system or another component with a spring function.

[0019] THE figures 3 et 4 illustrate the particular effect of a layer of elastic material 11 on a silicon watch component 1. The figure 3 illustrates the rupture of a silicon test piece covered by a coating according to the second embodiment as illustrated by the figure 2 . There figure 4 illustrates in comparison the rupture of the same test piece in oxidized silicon without coating. As this appears on the figure 4 , a multitude of debris 22 are scattered. On the contrary, the same test piece covered with a layer according to the second embodiment makes it possible to prevent this scattering of debris, as illustrated in the figure 3 . A first advantage of using several layers of parylene is to make its effect more reliable: if one layer is damaged, there remains a priori an effect guaranteed by another layer. On the other hand, at least one layer of parylene is not in direct contact with the exterior, and is protected from possible external aggressions by at least one more rigid layer of the coating.

[0020] Comparative bending tests were carried out on silicon specimens obtained by DRIE cutting from a silicon wafer, according to methods known to those skilled in the art. As a note, due to the fragile nature of the material, the same treatments on the same specimen lead to different results from one watch component to another identical one a priori subjected to the same constraints. For this reason, it is necessary to carry out tests on batches of identical specimens, then to make a statistical analysis to determine whether or not an effect exists.

[0021] The results obtained for six different batches of test specimens are illustrated in the figure 5 The flexural breaking strength, represented on the ordinate, of each component (specimen) of each batch was measured. This figure illustrates in particular for each batch the average, minimum and maximum breaking strength.

[0022] The first two batches OXY1 and OXY3 consist of 30 oxidized silicon specimens, comprising a silicon oxide layer on the surface with respective thicknesses of 1 µm and 3 µm. The average value of the flexural strength of these two batches is around 2000 MPa. Furthermore, in the event of rupture, all these specimens generate multiple scattered debris.

[0023] The following two batches correspond to specimens similar to batch OXY3 but covered with a pure, single-layer, uniform parylene coating, with respective thicknesses of 0.5 µm and 5 µm. Surprisingly, the addition of such a coating made of elastic, low-strength material significantly increases the tensile strength of the specimens. Indeed, the average strength is around 5000 MPa.

[0024] The fifth batch consists of silicon specimens coated with a metallic coating, comprising a 15 nm thick titanium bonding layer and an 80 nm gold layer. This resistant coating achieves a slight increase in average resistance compared to the first two batches, but significantly less than the two batches using a parylene coating. Furthermore, such a coating does not retain debris when the specimens break.

[0025] Finally, the last batch corresponds to the second embodiment of the invention, comprising a coating consisting of alternating four layers of parylene of approximately 1 µm, and three intermediate layers of silicon oxide with a thickness of 0.01 µm, for a total coating thickness varying between 3.7 and 4.7 µm. It appears that the average resistance of this batch exceeds 6000 MPa with minimum values ​​above 4000 MPa: the invention therefore makes it possible to optimize the resistance of a watch component. The invention therefore also relates to a watch component having an average resistance greater than or equal to 6000 MPa, and / or having a minimum resistance greater than or equal to 3000 MPa, or even greater than or equal to 4000 MPa. Furthermore, the invention makes it possible to limit the scattering of debris.

[0026] Finally, it therefore appears that a coating combining a flexible material (an elastic material as defined previously) with a more resistant material (also as defined previously) makes it possible to take advantage of the synergy between the two materials, not only to address the technical problem of non-dispersion of debris in the event of rupture, an effective protective effect thanks to the elastic material, but also at the same time makes it possible to optimize the resistance of the watch component, in particular thanks to the addition of a more resistant material to the elastic material in the thickness of the coating 10. This very advantageous behavior was unpredictable and therefore proves to be surprising.

[0027] The invention also relates to a watch movement and a timepiece as such, comprising one or more watch components as described previously.

[0028] The method for manufacturing a watch component according to the invention comprises a first phase of manufacturing a blank of a watch component, in a known manner. For example, this first phase may comprise an initial step consisting of providing a substrate made of fragile micro-machinable material. This substrate is for example a silicon wafer. In a subsequent step, the wafer is covered with a protective coating, in particular at least one of its two so-called upper and lower faces, for example with a photosensitive resin. The method continues with a step of forming a pattern in the protective coating. The pattern is produced by creating openings through the layer of photosensitive resin. The protective coating providing openings constitutes a protective mask.A step of etching the silicon wafer through the protective mask, in particular by deep reactive ion etching (DRIE) then makes it possible to dig openings in the silicon in line with the opening(s) of the mask, in order to obtain a blank of a silicon watch component. Alternatively, such a blank of a watch component can be formed by any other process than that mentioned above, for example by a laser cutting technique. The blank obtained forms the core 2 of the watch component 1. It has a shape very close to the final watch component.

[0029] The invention relates to a second manufacturing phase, consisting of depositing a coating as described previously on all or part of the surface of said blank.

[0030] The coating deposition step is carried out by alternating the deposition of layers of elastic material and more resistant material respectively.

[0031] This deposition step can be done uniformly, by evaporation, CVD or ALD. Alternatively, it can be done by a directional technique, such as physical vapor deposition, also called PVD (for “Physical Vapor Deposition”) or plasma-enhanced chemical vapor deposition, also called PECVD (for “Plama-Enhanced Chemical Vapor Deposition”). In such a case, the coating flow is oriented on the first surface 3, perpendicular to this surface. Such a directional method makes it possible to achieve the second embodiment of the figure 2 .

[0032] The manufacturing method may comprise an intermediate step, before the step of depositing the coating, consisting of a step of smoothing and / or thermal oxidation of the surface of the blank of the watch component. Thus, the core 2 of the watch component may be covered with an oxidation layer, for example a silicon oxide, before the deposition of the coating according to the invention.

Claims

1. A horology component based on a fragile material, comprising at least one surface part of fragile material covered with a coating (10) comprising at least two layers CE of elastic material (11) separated by a layer CR of a material (12) stronger than the elastic material (11), said elastic material (11) of said two layers CE having an elastic modulus less than or equal to 10 GPa, or even less than or equal to 5 GPa, or even less than or equal to 3 GPa and / or said elastic material (11) of said two layers CE having an elongation at break greater than or equal to 10%, or even greater than or equal to 20%, or even greater than or equal to 30%, and said stronger material (12) having an elastic modulus greater than or equal to 30 GPa, or even greater than or equal to 45 GPa, or even greater than or equal to 60 GPa, and / or having an elastic modulus greater than or equal to that of an adjacent layer made of elastic material (11) increased by 50%, and / or having an elastic modulus somewhere between that of an adjacent layer made of elastic material and that of said fragile material.

2. The horology component as claimed in the preceding claim, characterized in that said elastic material (11) of said two layers CE is the same or is a different material.

3. The horology component as claimed in one of the preceding claims, characterized in that the coating comprises at least one layer CE made of an elastic material (11) which is parylene or a PTFE, an acrylic resin, silicone or a polymer from the urethane family.

4. The horology component as claimed in one of the preceding claims, characterized in that the coating comprises at least one layer CE of an elastic material (11) of a thickness greater than or equal to 0.05 µm, or even greater than or equal to 0.3 µm, and / or less than or equal to 5 µm, or even less than or equal to 3 µm, and / or In that the sum of the thicknesses of the various layers CE of elastic material (11) of the coating is greater than or equal to 0.1 µm, or even greater than or equal to 0.6 µm, and / or less than or equal to 20 µm, or even less than or equal to 12 µm.

5. The horology component as claimed in one of the preceding claims, characterized in that said stronger material is a metal or an alloy or an oxide or a nitride, more particularly silicon oxide or silicon nitride.

6. The horology component as claimed in one of the preceding claims, characterized in that said layer CR of stronger material (12) has a thickness es greater than or equal to 15 nm, or even greater than or equal to 30 nm, and / or less than or equal to 150 nm, or even less than or equal to 100 nm, or even less than or equal to 70 nm, and / or In that the total thickness of the layer or layers CR of stronger material (12) of the coating (10) is greater than or equal to 15 nm, or even greater than or equal to 30 nm, and / or is less than or equal to 450 nm, or even less than or equal to 300 nm, or even less than or equal to 210 nm.

7. The horology component as claimed in one of the preceding claims, characterized in that the coating (10) has all or some of the following characteristics: - it extends over the entire surface of the periphery of the fragile material, notably over the entire exterior surface of the horology component ; and / or - each layer of elastic material (11) has a constant or variable thickness ; and / or - the layer or layers of stronger material (12) has or have a thickness that is constant or variable, notably variable over the flanks (5) ; and / or - it comprises an alternation of layers CE of elastic material (11) and of layers CR of stronger material (12) ; and / or - it comprises at least two, or three, or four, layers of elastic material (11) and at least one, or two, or three, layers of stronger material (12) ; and / or - it comprises a first, inner, layer of elastic material (11) and a last, outer, layer of elastic material (11).

8. The horology component as claimed in one of the preceding claims, characterized in that the fragile material is silicon, silicon covered with oxide, quartz, glass, silicon carbide, an alumina-based or zirconia-based ceramic, or diamond, sapphire, or fragile amorphous metals.

9. The horology component as claimed in one of the preceding claims, characterized in that said component is one of the elements from the group including a toothed wheel, an escapement wheel, a hand, an impulse pin, a pallet, a lever, a pallet stone, a flat spring, such as a spiral spring, a flexible-blade system or another component having a spring function.

10. The horology component as claimed in one of the preceding claims, characterized in that said component has a mean strength greater than or equal to 6000 MPa, and / or wherein the horology component has a minimum strength greater than or equal to 3000 MPa.

11. A horology movement, characterized in that said movement comprises a horology component as claimed in one of the preceding claims.

12. A timepiece, characterized in that said timepiece comprises a horology component as claimed in one of claims 1 to 10 or a horology movement as claimed in the preceding claim.

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