CH715668A2 - Watch component in micro-machinable material and method of manufacturing such a component. - Google Patents

Abstract

The invention relates to a timepiece component (2a, 2b) made of micro-machinable material, characterized in that it comprises at least one surface part of smoothed micro-machinable material comprising an oxide layer of thickness greater than 1 micrometer for increase its mechanical resistance. The invention also relates to a method of manufacturing such a timepiece component, in which a part forming a blank of the timepiece component is produced from a micro-machinable material, comprising a step of smoothing at least part of the surface of the part, and a step of mechanical reinforcement of the part by the formation on said at least part of the surface of the part of an oxide layer of thickness greater than 1 micrometer.

Description

[0001] The invention relates to a method of manufacturing a watch component from a micromachinable material, for example silicon. It also relates to a horological component, and to a horological movement and a timepiece comprising such a horological component.

[0002] Silicon is a material having 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. However, this material has a drawback: it has little or no plastic deformation domain, which makes it a material with fragile behavior. A mechanical stress or a shock can thus lead to a rupture of the component without prior deformation. The handling of watch components made of silicon, in particular during their manufacture and assembly, is therefore particularly delicate.

[0003] The fragility of watch components made of silicon is accentuated by their cutting in a silicon substrate, generally carried out by a deep etching technique, for example by deep ionic reactive etching DRIE (from the English "Deep Reactive Ion Etching") . One specific feature of this type of etching is that it forms openings having slightly wrinkled sides which have surface defects in the form of scalloping or in the form of pitting. This results in a certain roughness of the etched sides which weakens the mechanical strength of the component. In addition, these defects present on the surface of the sidewalls can generate the initiation of cracking, in particular in the event of mechanical stress, and lead to the component breaking under stresses lower than the usual resistance of the material.

[0004] To improve the mechanical properties of watch components made of silicon, several approaches have already been proposed.

A first approach, described in document EP1904901, consists in forming a layer of silicon oxide by thermal oxidation of silicon at a temperature between 900 ° C and 1200 ° C. The oxide layer formed results from a conversion of the silicon on the surface of the component into silicon oxide. This document specifies that this layer is at least 5 nm and remains strictly less than 1 micron in practice.

[0006] Document EP2277822 describes a variant of this first approach, in which the oxide layer formed is then dissolved. The formation of the silicon oxide layer and then its dissolution make it possible to remove the surface layer of silicon comprising some of the defects and / or the initiation of cracks and to round off the roughness. This solution finally consists in carrying out a smoothing of the silicon surface called by oxidation - deoxidation.

[0007] These two solutions, which apply the first approach for oxidation, have the drawback of consuming silicon and of modifying the initial dimensions of the silicon blank of the watch component.

[0008] A second approach described in the document "Silicon Profile Transformation and Sidewall Roughness Reduction Using Hydrogen Annealing" by Lee et al. (IEEE, 2005), is based on a solution for smoothing the sides of silicon components in a field remote from watchmaking by means of a hydrogen treatment. The migration of silicon is favored by hydrogen and temperature, and makes it possible to smooth out the surface defects of the flanks without consuming silicon, and therefore without affecting the initial dimensions of the component. The effectiveness of such an approach is however controversial and it was mainly developed with the aim of forming rounded / spherical three-dimensional structures in silicon.

[0009] This solution has been applied to the watchmaking field in order to round off the sharp edges of parts cut from various materials, as described in document CH702431.

[0010] The present invention proposes an improved solution for reinforcing a watch component from a micromachinable material, for example silicon.

To this end, the invention is based on a method of manufacturing a watch component, in which a part is produced forming a blank of the watch component from a micro-machinable material, characterized in that it comprises a step of smoothing at least part of the surface of the part, and in that it comprises a step of forming on said at least part of the surface of the part an oxide layer of thickness greater than 1 micrometer, or even greater than or equal to 2 micrometers, or even greater than or equal to 2.5 micrometers, or even greater than or equal to 3 micrometers, or even greater than or equal to 3.2 micrometers, to reinforce the watch component.

The invention also relates to a watch component as such obtained by such a method.

[0013] The invention is precisely defined by the claims.

The invention will be better understood with the aid of the following description of particular embodiments of a method of manufacturing a watch component made without limitation in relation to the accompanying figures, among which: <tb> <SEP> FIG. 1 represents the resistance obtained on different batches of watch components for several coating thicknesses with an oxide layer. <tb> <SEP> FIG. 2 represents the resistance obtained on different batches of watch components, showing the positive results obtained by the implementation of an embodiment of the invention. <tb> <SEP> FIG. 3 represents a device for regulating a watch movement in top view, comprising watch components according to one embodiment of the invention. <tb> <SEP> FIG. 4 represents the regulator device of a watch movement in section. <tb> <SEP> FIG. 5 represents a blocker mobile of the regulator device according to one embodiment of the invention.

The concept of the invention consists in reinforcing a watch component made from a micromachinable material using a thick oxide layer, that is to say having in particular a thickness clearly greater than the thicknesses chosen by the solutions of the state of the art, in combination with a smoothing of the component. The existing solutions for reinforcing a silicon component using an oxide layer apply in practice an oxide thickness strictly less than 1 μm. Obtaining such an oxide thickness is time-consuming, typically requiring overnight treatment, and results in a modification of the dimensions of the component.

[0016] Comparative tests consisting in varying the thickness of the oxide layer, in particular beyond the limit of 1 μm, were carried out on three-point bending specimens. As a note, due to the fragile nature of the material, the same reinforcement treatments lead to different results from one watch component to another identical one, subject a priori to the same constraints. For this reason, it is necessary to carry out tests on batches of identical components, then to make a statistical analysis to see or not an effect. FIG. 1 represents the results obtained for four batches with an oxide thickness respectively equal to 0.3 μm, 1 μm, 2.6 μm, and 3 μm. The tensile strength of each component of each batch was measured. It appears that the mean tensile strength increases very slightly with increasing thickness until reaching the thickness of 2.6 µm, then stabilizes around 2000 MPa, without improvement for the greater thickness of 3 µm. The small improvement in the breaking strength with regard to the large increase in the treatment time required to increase the thickness of the oxide layer ultimately makes this approach very unattractive. In other words, the effect of the large thicknesses is not significantly effective with regard to the time devoted to the production of these large thicknesses and the large thickness of material impacted.

For these reasons, it was never imagined to implement an oxide thickness greater than 1 μm. This first prejudice has been overcome by the invention, in which the choice of thicknesses which are significantly increased and combined with a preliminary smoothing step, which will be specified later, made it possible to lead to unexpected reinforcements of the watch components. Smoothing has never been combined with the formation of an oxide layer as part of the mechanical reinforcement of a component, considering these two solutions as equivalent alternatives. This second prejudice has also been overcome by the invention, which will demonstrate a great improvement brought about by the combination of smoothing with an oxide layer.

The method of 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 phase can comprise an initial step consisting in providing a substrate made of micromachinable material. This substrate is for example a wafer (or “wafer” according to the English terminology) of silicon. In a following 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 by a photosensitive resin. The process continues with a step of forming a pattern in the protective coating. The pattern is made by creating openings through the layer of photosensitive resin. The protective coating leaving openings constitutes a protective mask. A step of etching the silicon wafer through the protective mask, in particular by deep reactive ion etching DRIE ("Deep Reactive Ion Etching" according to English terminology) then makes it possible to dig openings in the silicon to the right of the or opening (s) of the mask, in order to obtain a blank for a silicon watch component.

The invention relates to a second phase of reinforcement of such a timepiece component blank, which can moreover as a variant be formed during the first phase by any method other than that mentioned above, for example by a laser cutting technique.

[0020] A first embodiment of the invention consists in implementing a step of smoothing the timepiece component blank, before forming a thick oxide layer. Such a thick oxide layer is formed over all or part of the surface of the timepiece component blank, preferably over its entire surface, or even at least 50%, or even 75%, of its surface. This thick oxide layer can be produced by a method as described in document EP1904101, or by any other equivalent method. The smoothing step of this first embodiment comprises an oxidation and deoxidation step, for example as described in document EP2456714. An oxidation - deoxidation phase may for example comprise thermal oxidation at 1100 ° C. for 2 hours 40 minutes, according to the process described in document EP1904101, followed by dissolution in hydrofluoric acid of the oxide thus formed.

A second advantageous embodiment of the invention adds a hydrogen smoothing sub-step to a prior step of smoothing by oxidation deoxidation as mentioned above, before forming the thick oxide layer of similar manner to the first embodiment. The hydrogen smoothing step corresponds to a treatment with hydrogen as described in document CH702431. It comprises an annealing treatment of the watch component blank, or at least of its treated surface, in a reducing atmosphere under temperature and pressure conditions suitable to cause the migration of silicon atoms from the sharp edges, so as to round them off. According to one embodiment, this hydrogen smoothing step is carried out at a temperature of between 600 ° C and 1300 ° C and at a pressure strictly greater than 100 Torr. As a side note, hydrogen smoothing moves the silicon atoms, as mentioned above: by observing the edges, we see that the hydrogen smoothing produces a kind of bulge around the edge, which has the effect of indirect effect of rounding them off.

Finally, it appears that other embodiments can be implemented, comprising any intermediate step of surface smoothing, in particular from smoothing by oxidation-deoxidation and / or by a smoothing step with hydrogen and / or by a smoothing step by heat treatment, before forming a thick oxide layer.

In all these embodiments, the thick oxide layer has a thickness preferably greater than 1 μm, or even greater than or equal to 1.5 μm or to 2 μm or to 2.5 μm or to 3 μm or at 3.2 µm. The oxide layer is advantageously less than or equal to 5 μm. This oxide layer advantageously has a constant thickness. As a variant, it can have a variable thickness. In this case, the previous values apply to the average thickness, or to the median thickness value. In addition, in the embodiments described, the thick oxide layer has been obtained by a process as described in document EP1904101, but it can alternatively be obtained by any other process.

In order to demonstrate the advantage of the method for manufacturing a reinforced watch component according to the embodiments of the invention described above, comparative tests were carried out on three-point bending test specimens. As a note, due to the fragile nature of the material, the same reinforcement treatments lead to different results from one watch component to another identical one, subject a priori to the same constraints. For this reason, it is necessary to carry out tests on batches of identical components, then to make a statistical analysis to see or not an effect.

[0025] FIG. 2 represents the breaking strength of each part of each batch, which makes it possible to see the amplitude of the results for each batch. For each of these batches, it is particularly interesting to observe the minimum breaking strength, as well as the average breaking strength.

A first batch (batch 1) of parts is a reference batch, which does not implement the invention. This lot includes silicon parts cut by the DRIE method with initial equipment, without any post-treatment. The average breaking strength is low and the risk of premature failure of a component is high, due to the minimum measured breaking stress of less than 500 MPa.

The second batch (batch 2) is a batch which includes silicon parts similar to batch 1, produced with cutting by the DRIE method with a second equipment, but comprising a strengthening treatment by the growth of a layer oxide three microns thick, without smoothing. This second batch is an intermediate experiment leading to the invention, which implements the advantage of a thick oxide layer. It appears that the average breaking strength of this second batch is higher, of the order of 2000 MPa, and that the minimum breaking stress is above 1500 MPa.

The third batch (batch 3) comprises silicon parts similar to batch 1, produced with cutting by the DRIE method with a first equipment, but comprising a strengthening treatment by an intermediate step of smoothing by oxidation-deoxidation ( growth of 1 micron of oxide - HF dissolution) before the growth of an oxide layer 2.87 microns thick. This third batch corresponds to the first embodiment of the invention mentioned above. The average breaking strength is greatly increased (4000 MPa) compared to batch 2.

The fourth batch (batch 4) comprises silicon parts similar to batch 1, produced with cutting by the DRIE method with a first equipment, but comprising a reinforcement treatment by an intermediate step of smoothing by oxidation-deoxidation ( growth of 1 micron of oxide - HF dissolution) then a hydrogen smoothing step, before the growth of an oxide layer 2.87 microns thick. This fourth batch implements the second advantageous embodiment of the invention described above. The performances are clearly improved here compared to the other batches, both in terms of the average breaking stress, which is around 5000 MPa, and for the minimum breaking stress on the batch, which exceeds 3000 MPa. Different types of defects are eradicated by the combination of different smoothings and the final oxide layer, very thick, helps to seal and smooth the last defects present.

[0030] FIG. 2 therefore clearly illustrates the surprising advantageous effects obtained by the implementation of a method according to the invention.

In a variant not shown, it should be noted that satisfactory results can be obtained by implementing only a hydrogen smoothing step followed by the growth of a thick oxide layer.

[0032] As a note, the invention can be combined with other known treatments, which also participate in improving the performance of such a watch component. Thus, a treatment for the mechanical reinforcement of the part by an isotropic type etching fluid can be implemented, for example by a method as described by document EP2937311.

On the other hand, the oxide layer according to the invention can optionally be covered by any other coating, of small thickness, to further improve the resistance or to provide another property to the watch component, such as a different tribology. Thus, the thick oxide layer of the invention is a surface layer in that it is positioned close to the surface of the component, but is not necessarily the outermost layer of the component.

As a note, in the examples described above, the watch component therefore comprises a silicon base, covered with a thick oxide layer, which is silicon dioxide. As a variant, one could use any other method for depositing an oxide layer, possibly different from the silicon oxide described here. As a further variant, a layer of silicon nitride or carbide could be deposited. As a further variant, a layer of titanium carbide or nitride could be deposited. Finally, any thick layer could be used, as long as it makes it possible to seal the residual surface defects of the part. According to another variant, several superposed layers, possibly of different materials, among the aforementioned layers, could be used.

The method of the invention therefore allows the manufacture of watch components made from a micromachinable material and having enhanced mechanical properties. In the examples described above, the micromachinable material is silicon. As a variant, one could use a substrate made of quartz, diamond or any other micromachinable material suitable for the manufacture of a watch component. In this case, the smoothing and strengthening treatments must be adapted to each of these materials.

On the other hand, the method of the invention is suitable for the manufacture of any watch component, in particular a watch component comprising flexible parts to allow its assembly. By way of illustrative and non-limiting examples, the watch components can be toothed wheels, escape wheels, any escapement component, needles, plate pegs, lifts as well as levers or other springs. watchmakers, such as a clockwork mainspring or an oscillator spiral spring.

[0037] For example, the method can be adapted for producing the components of a regulator device. Such a regulator device is illustrated in Figures 3 to 5. In particular, it comprises in particular an escape wheel 3 pivoted about an axis A3 and a blocker 2 comprising a first blocker mobile 2a pivoted about a third axis. A2a and a second blocker mobile 2b pivoted about a fourth axis A2b, all three arranged in the same plane P and made of silicon.

[0038] Such components, due to their particularly small dimensions and the inherently fragile nature of the material used, prove to be difficult to assemble. The risk of breakage when these components are driven off their axis is high. Thus, in a privileged manner, the components 2a, 2b, and 3 each include a central opening delimited by elastic arms, the ends of which are intended to cooperate with their respective axis. The dimensioning of the elastic arms is defined so as to provide an adequate holding torque for the components 2a, 2b, 3 on each of their respective axes A2a, A2b, A3. Preferably, the outline of the central opening is non-circular, like the openings of elastic ferrules as described in document WO2011 / 116486 or document WO2013 / 045706.

Due to the small dimensions of the arms, it is necessary to maximize the mechanical strength of the material and the method of the invention makes it possible to reduce the risk of breakage linked to the minimum breaking stress on the batch.

[0040] The invention also relates to a watch component manufactured according to the manufacturing process which has just been described, as well as a timepiece incorporating this watch component.

The watch component based on a micromachinable material will therefore be characterized in that at least part of its surface will have undergone a smoothing and comprises an oxide layer of thickness greater than or equal to 1, or even 2, or even 3 micrometers to increase its mechanical strength, or even other thickness values listed above.

[0042] Also advantageously, the watch component is characterized in that it has an average breaking strength greater than or equal to 3000 MPa, or even 4000 MPa.

Advantageously also, the invention applies well to so-called rigid watch components, that is to say whose operation does not call or very little to a property of elasticity, on the contrary for example springs, in particular outside a clockwork mainspring or a rocker spring. These rigid components can have elastic parts useful for their assembly as described above, but not used subsequently in their horological function. In other words, such horological components do not restore any energy which would come from an elastic deformation during their operation. For such components, the breaking strength is particularly high and stressed, since they cannot for example elastically dampen any forces undergone since they are not designed to exploit elasticity.

Claims (12)

1. Watch component based on a micromachinable material characterized in that it comprises at least a surface portion of smoothed micromachinable material comprising an oxide layer greater than 1 micrometer thick to increase its mechanical strength . 2. Watch component according to the preceding claim, characterized in that the oxide layer has a thickness greater than or equal to 2 micrometers, or even greater than or equal to 2.5 micrometers, or even greater than or equal to 3 micrometers, or even greater than or equal to at 3.2 micrometers. 3. Watch component according to one of the preceding claims, characterized in that the micromachinable material is silicon and the oxide layer is silicon oxide. 4. Watch component according to one of the preceding claims, characterized in that it is a silicon watch component of an escapement device. 5. Watch component according to one of claims 1 to 4, characterized in that it is a rigid watch component without restitution of energy by elasticity and / or in that it is one of the elements of the group comprising a cogwheel, escape wheel, needle, chainring pin, lift. 6. Watch component according to one of the preceding claims, characterized in that the watch component has an average resistance greater than or equal to 3000 MPa, or even greater than or equal to 4000 MPa. 7. Watch movement, characterized in that it comprises a watch component according to one of the preceding claims. 8. Timepiece, characterized in that it comprises a watch component according to one of claims 1 to 6 or a timepiece movement according to the preceding claim. 9. A method of manufacturing a watch component, in which a part is produced forming a blank of the watch component from a micromachinable material, characterized in that it comprises a step of smoothing at least one part. of the surface of the part, and in that it comprises a step of mechanically strengthening the part by forming on said at least part of the surface of the part an oxide layer with a thickness greater than 1 micrometer, or even greater than or equal to 2 micrometers, or even greater than or equal to 2.5 micrometers, or even greater than or equal to 3 micrometers, or even greater than or equal to 3.2 micrometers. 10. A method of manufacturing a watch component according to the preceding claim, characterized in that the step of producing the part forming a blank comprises micromachining of the part, in particular by deep reactive ionic etching or DRIE („Deep Reactive Ion Etching “) and / or by a laser cutting technique. 11. A method of manufacturing a watch component according to one of claims 9 or 10, characterized in that the step of smoothing said at least part of the surface of the part comprises a step of smoothing with hydrogen and / or a step of smoothing by oxidation-deoxidation and / or a step of smoothing by heat treatment. 12. A method of manufacturing a watch component according to one of claims 9 to 11, characterized in that it comprises a step of mechanically strengthening the part treatment with an isotropic type etching fluid.