Complex micromechanical part

A method of fabricating a micromechanical part in a single-piece made of a synthetic carbon-allotrope includes forming a substrate which includes the negative cavity for the micromechanical part to be fabricated, coating the negative cavity of the substrate with a layer of the synthetic carbon allotrope in a thickness of between 0.2 μm and 20 μm, the thickness being less than the depth of the negative cavity, removing from the substrate a larger thickness than the thickness of the deposited layer, so as to leave a limited thickness of the layer of material in the negative cavity, and removing the substrate so as to release the single-piece micromechanical part formed in the negative cavity comprising an external surface of comparable roughness to that of the substrate.

This is a National Phase Application in the United States of International Patent Application PCT/EP2012/050127 filed Jan. 5, 2012, which claims priority on European Patent Application No. 11153243.8 of Feb. 3, 2011. The entire disclosures of the above patent applications are hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to a complex micromechanical part made from any material, such as, for example, a carbon-based material, and a method of fabricating a part of this kind.

BACKGROUND OF THE INVENTION

Fabrication of a micromechanical part purely from synthetic diamond or DLC (diamond like carbon) is very expensive and is not tribologically advantageous due to the unfavourable roughness generated by the thick layer deposition process or by an etching method in the bulk. Consequently, it is currently preferred to coat the micromechanical part using a thin layer of synthetic diamond or DLC, although this does not allow all shapes to be obtained.

SUMMARY OF THE INVENTION

It is an object of this invention to overcome all or part of the aforecited drawbacks by proposing a micromechanical part having a complex geometry which uses a minimum quantity of material with greatly improved roughness and a very favourable scrap rate and production cost.

The invention therefore relates to a method for fabricating a single-piece material micromechanical part, characterized in that it includes the following steps:a) Forming a substrate comprising the negative cavity for said micromechanical part to be fabricated.b) Coating said negative cavity of the substrate with a layer of material.c) Removing from the substrate a greater thickness than that of the deposited layer, so as to leave a limited thickness of said layer in said negative cavity.d) Removing the substrate to release the micromechanical part formed in said negative cavity.

It is thus clear that the method allows the fabrication of a single-piece micromechanical part, i.e. with no discontinuity of material, which has a “skin” of material, i.e. a small amount of material, the external surface of which reproduces the very favourable roughness of the substrate which very substantially reduces the cost of the material required on the outer layer and improves overall roughness, especially on the external surface, to perfect its tribological performance.

In accordance with other advantageous features of the invention:The negative cavity includes a wall forming a toothing;The material is crystallised or amorphous carbon-based;Between step b) and step c), the method includes step e): filling the cavity coated in the first material with a second material so as to obtain, after steps c) and d), a micromechanical part in a first material which is reinforced and/or decorated with a second material;Between step c) and step d), the method includes step f): filling the cavity coated in the first material with a second material so as to obtain, after step d), a micromechanical part in a first material which is reinforced and/or decorated with a second material;In step f), the second material is formed to protrude from said cavity so as to form an additional functional element of the micromechanical part;The second material includes a metal or metal alloy;The micromechanical part forms an exterior part, balance spring, balance, pallet lever, bridge, wheel set or escape wheel of a timepiece.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As explained above, the invention relates first of all to a single-piece micromechanical part for example made of a carbon-based material. “Carbon based” means a synthetic carbon allotrope in crystalline form, such as diamond or one or several layers of graphene, or in amorphous form, such as diamond like carbon (DLC).

Of course, advantageously according to the invention, other types of materials, which can be deposited in layers and which have tribological advantages, may be used as an alternative to a synthetic carbon allotrope. This alternative material may be, for example, a silicon based compound, i.e. for example silicon nitride, silicon oxide or silicon carbide.

This micromechanical part was devised for applications within the field of horology. However, other domains may very well be envisaged, such as, in particular, aeronautics, jewelry or the automobile industry.

Within the field of horology, this micromechanical part may, for example, form part of the exterior of the watch, the balance spring, balance, pallet levers, bridges or even the wheel sets, such as the escape wheels, completely or partially from a base of synthetic carbon allotrope or an alternative material as explained hereinbefore.

A first embodiment of the method of fabricating this micromechanical part is presented inFIGS. 1 to 5. In step a, the method consists in forming a negative cavity3in a substrate1, for the future micromechanical part11,21,31,41. A large variety of substrates1is possible. Preferably, the material of substrate1is selected for its very low roughness, i.e. the natural feature of having a smooth surface.

By way of example,FIGS. 1 and 2show step a formed from a silicon substrate1for which it is possible to obtain very good roughness, i.e. an arithmetic mean deviation Ra of substantially less than10nm. Thus, in a first phase illustrated inFIG. 1, substrate1is coated with a mask2having holes4which leave a top portion of substrate1exposed. In a second phase, etching is performed in holes4. This may be wet or dry etching. Finally, in a third phase illustrated inFIG. 2, the mask2is removed leaving only the negative cavity3made in substrate1.

A second step b consists in coating at least negative cavity3with a layer5of thickness e1of the material desired for the future micromechanical part. In the example illustrated inFIG. 3, substrate1is entirely coated with a layer5, i.e. at least in cavity3etched in step a. Like the deposited material, the type of deposition can be very varied. In a non-limiting manner, step b may include chemical vapour phase deposition, physical vapour phase deposition or electrodeposition.

In a third step c, the method consists in removing one portion of substrate1coated with layer5, in order to leave a limited thickness of said layer5in said negative cavity3. Preferably according to the invention, a larger thickness e2is removed from substrate1than thickness e1of layer5, as illustrated inFIG. 4. It is thus clear that the layer5present in cavity3of substrate1is henceforth independent, i.e. not joined to the rest of layer5deposited in step b.

In a fourth and last step d of the first embodiment, the method consists in removing substrate1so as to release the micromechanical part formed in cavity3. Consequently, in the above example in which substrate1is made of silicon, step d may consist in a selective etch of the silicon. This may, for example, be obtained by a chemical etch using a bath comprising tetramethylammonium hydroxide (TMAH and TMAOH).

At the end of step d, as illustrated inFIG. 5, there is obtained a micromechanical part formed exclusively by layer5whose geometry matches cavity3present in substrate1. Advantageously, the external surface, i.e. the surface which was directly in contact with substrate1, has very good roughness, i.e. comparable to that of substrate1, and is preferably used as the mechanical contact surface. Finally, for a height e3of the micromechanical part comprised between 10 μm and 500 μm, a thickness e1of only 0.2 μm to 20 μm of layer5is deposited. The savings in material and production costs due to the shortened time in step b are thus immediately clear.

Consequently, it is clear that a micromechanical part is obtainable whose elementary section is formed by at least two secant and non-aligned segments, so that one of said at least two segments forms the height e3of the micromechanical part. Said height e3is greater than the thickness e1of each segment. Naturally, depending on the complexity of cavity3, the elementary section may be a simpler, substantially U-shaped section, i.e. comprising three segments.

Thus, depending on the complexity of cavity3, the micromechanical part is formed by the projection of at least one elementary section having two or three segments on a rectilinear or non-rectilinear directrix (including revolution). Moreover, it is not any more difficult to form very complex or variable sections such as, for example, forming a toothing on a wall of cavity3which will form a corresponding toothing for one of the segments of the section.

By way of non-limiting example, micromechanical parts11,21,31,41which can be produced according to the first embodiment, are shown inFIGS. 6 to 10. Thus,FIG. 6shows a micromechanical part11whose substantially U-shaped elementary section is projected on a rectilinear directrix.FIG. 7shows a micromechanical part21having a similar elementary section to that of micromechanical part11but which is projected on a sinusoidal, i.e. non-rectilinear directrix. It is also clear that it is possible to produce a micromechanical part formed half from part11and the other half from part21, both transversely and longitudinally in a single-piece, without complicating the method.

FIGS. 8 and 9show an example elementary section capable of having two segments which is projected in revolution to obtain a micromechanical part31in the form of a cap. This type of micromechanical part could, for example, be secured to an element to improve its tribological relationship with another member. By way of example, micromechanical part31may be secured to the end of a pivot32of an arbour33so that pivot32cooperates with a bearing via micromechanical part31.

Finally,FIG. 10shows a last example of a more complex micromechanical part41, which does not make the method more difficult to implement. Micromechanical part41includes a substantially discoid plate43from the periphery of which a toothing45projects orthogonally and whose centre comprises a pipe47forming a hole48for cooperation, for example, with a pivot pin.FIG. 10thus shows that that the thickness of toothing45and of plate43is formed by the thickness e1of layer5deposited in step b of the method.

A second alternative embodiment to the first embodiment explained above is shown inFIGS. 11 to 13. Steps a to d remain identical to the first embodiment. However, as illustrated inFIG. 11, between step b and step c, step e is performed consisting in filling the hollows6in cavity3coated in first material5, with a second material7. Thus, after steps c and d which are similar to the first embodiment and illustrated respectively inFIGS. 12 and 13, there is obtained a micromechanical part made in a first material5reinforced and/or decorated with a second material7.

Preferably, the filling of hollows6is achieved by galvanic deposition or hot deformation. The second material is preferably a metal or metal alloy which may or may not be amorphous. However, in an alternative, there is nothing to prevent the type of deposition and/or nature of the deposited material from being changed.

Consequently, in the fourth step c, not only is the thickness of said layer5limited in said negative cavity3but the deposition7of the second material is flattened and preferably made flush with said limited part of layer5. Finally, in a fifth and final step d of the second embodiment, the method consists in removing substrate1so as to release the micromechanical part formed in cavity3, with the same variants and advantages as in the first embodiment.

At the end of step d, as illustrated inFIG. 13, there is obtained a micromechanical part formed by layer5, whose geometry matches cavity3present in substrate1and which is reinforced and/or decorated with deposition7. Advantageously, the external surface formed by layer5, i.e. the surface which was directly in contact with substrate1, has very good roughness, i.e. comparable to that of substrate1and is preferably used as the contact surface.

According to another advantage of the invention, it is henceforth possible to coat parts with thin layers, which was impossible to achieve previously because of the particular conditions required for thin layer deposition, such as, for example, the pressure, temperature or compounds used. By way of non-limiting example it is thus possible, advantageously according to the invention, to form a mainly metallic part from a deposition7, which is diamond coated from layer5, whereas currently, to the Applicant's knowledge, it is difficult to diamond coat a metallic part.

Finally, for a height e3of the micromechanical part of between 10 μm and 500 μm, a thickness e1of layer5of between only 0.2 μm and 20 μm is deposited, the rest being made up by deposition7. The savings in material costs and production costs due to the shortened time of step b of depositing layer5are immediately clear, with the rest of the part being formed by less expensive deposition7.

Consequently, it is clear that it is possible to obtain a micromechanical part with the same elementary sections as in the first embodiment. By way of non-limiting example,FIG. 14shows a micromechanical part51which can be produced according to the second embodiment. Micromechanical part51includes a substantially discoid plate53, comparable to plate43ofFIG. 10, from whose periphery a toothing55projects orthogonally and whose centre includes a pipe57forming a hole58for cooperation, for example, with a pivot pin.FIG. 14thus shows that that the thickness of toothing55and of pipe57are formed by the thickness e1of layer5deposited in step b of the method, the rest being made up by portion52formed by deposition7in step e.

FIGS. 15 to 16show a third alternative embodiment to the first embodiment explained above. Steps a to d remain identical to the first embodiment. However, as illustrated inFIG. 15, a fourth step f is performed between step c and step d, which consists in filling the hollows6in cavity3, coated in first material5, with a second material17. Thus, after step d, which is similar to the first embodiment and illustrated inFIG. 16, there is obtained a micromechanical part, made in first material5, reinforced and/or decorated with a second material7.

Compared to step e of the second embodiment, step f is intended to fill hollows6of cavity3, and, advantageously, can also form a protruding level of thickness e3so as to form an additional functional element of the micromechanical part as illustrated inFIG. 15.

Step f preferably includes a phase of structuring a mould18on substrate1after step c, followed by a phase of filling the recess jointly formed by hollows6of cavity3and the pierced holes in mould18. Finally, step f includes a phase of removing mould18from the surface of substrate1.

The phase of structuring mould18may, for example, be formed by photolithography using a negative or positive photosensitive resin. Further, the filling phase may, for example, be performed using electrodeposition. The second material is preferably a metal or metal alloy which may or may not be amorphous. However, there is nothing to prevent the type of deposition and/or nature of the deposited material from being changed.

Step f may also include a last step of lapping and/or polishing the top portion of deposition17. Consequently, in a fifth and final step d of the third embodiment, the method consists in removing substrate1, so as to release the micromechanical part formed in cavity3, with the same advantages as in the first embodiment.

At the end of step d, as illustrated inFIG. 16, there is obtained a micromechanical part formed by layer5, whose geometry matches cavity3present in substrate1and which is reinforced and/or decorated with deposition17. Advantageously, the external bottom surface formed by layer5, i.e. the surface which was directly in contact with substrate1, has very good roughness, i.e. comparable to that of substrate1and is preferably used as the contact surface.

According to another advantage of the invention, it is henceforth possible to coat parts with thin layers, which was impossible to achieve previously because of the particular conditions required for thin layer deposition, such as, for example, the pressure, temperature or compounds used. By way of non-limiting example it is thus possible, advantageously according to the invention, to form a mainly metallic part from a deposition17, which is partially diamond coated from layer5, whereas currently, to the Applicant's knowledge, it is difficult to diamond coat a metallic part.

Moreover, in the third embodiment, the micromechanical part also includes a second top level entirely formed by deposition17, i.e. with no layer5, so as to form an additional functional element of the micromechanical part. This functional element may, in a non-limiting manner, be a toothing12, hole14and/or a shoulder16, intended, for example, to cooperate with another member.

As in the first two embodiments, the savings in material costs and production costs due to the shortened layer5deposition step are immediately clear, with the remainder of the part being formed by a less expensive deposition17, yet offering a potentially very complex geometry.

Consequently, it is clear that it is possible to obtain a micromechanical part with the same elementary sections as in the first two embodiments. By way of non-limiting example,FIG. 17shows a micromechanical part61, which can be produced according to the third embodiment. Micromechanical part61includes a substantially discoid plate63, comparable to plate43ofFIG. 10, from whose periphery a toothing65projects orthogonally and whose centre includes a pipe67forming a hole68, the rest being filled by deposition17in step f. On a second level, exclusively formed by deposition17, micromechanical part61has a wheel62whose periphery includes a toothing64and whose centre includes a hole of preferably smaller section than hole68, intended, for example, to cooperate with a pivot pin.

Of course, this invention is not limited to the illustrated example but is capable of various variants and alterations that will appear to those skilled in the art. In particular, several micromechanical parts, which may or may not be of identical design, may be fabricated at the same time on the same substrate. Further, in the example ofFIG. 4or ofFIG. 12, it is seen that the removal of substrate1also forms a part of substantially U-shaped section formed by layer5on the periphery and the bottom portion of substrate1.

Consequently, it is not only possible to form several cavities3, which may or may not be identical, on substrate1, but also to form the cavities on several faces of substrate1, i.e. steps a and c, and possibly e or f may be applied to several faces of substrate1. In the case of the second and third embodiments, it is therefore possible to envisage obtaining a single-piece part formed by layer5on the periphery and/or bottom portion of substrate1and a reinforced and/or decorated part formed by layer5and deposition7,17on the top portion of substrate1.

Further, the embodiments can be combined with each other. Thus, by way of non-limiting example, part51may be produced via the third modified embodiment. Indeed, steps a to c could be implemented followed by a step f with a similar deposition17to deposition7of the second embodiment, i.e. not protruding from cavity3. Evidently, the modified step f of the third embodiment would be similar to step e of the second embodiment but performed after step c and not after step b.

Finally, although the Figures show substantially perpendicular segments, it is clear that the angle that they form in relation to each other may also be acute or obtuse.