HK1138075B - Timepiece component and method for making same - Google Patents

Description

Clock component and method for manufacturing same

Technical Field

The present invention relates to a timepiece component and a method of manufacturing the same.

More particularly, the present invention relates to a clock component formed using micro-fabrication techniques.

Background

Some timepiece components are now made of silicon, such as balance springs and balances. The benefits of silicon are attributed to its lightness, its elasticity, its non-magnetic properties, and its ability to be processed using microfabrication techniques, particularly using Deep Reactive Ion Etching (DRIE) techniques.

However, silicon does have some drawbacks: it is fragile, in other words it does not have any plasticity, which makes it difficult to connect a silicon wheel to an axle, for example. Moreover, its extreme lightness does not allow components such as the balance or the balance to be made entirely of silicon and formed in small dimensions, said components having to have sufficient inertia or unbalance.

Other materials than silicon, which can be processed by itself by microfabrication techniques and whose use is envisioned for making clock parts, have the same disadvantages. These materials are, in particular, diamond, quartz, glass and silicon carbide.

Disclosure of Invention

The invention is intended to allow the microfabrication of clock parts for applications that have hitherto been impossible to envision due to the said disadvantages of the materials used.

To this end, a timepiece component is provided which comprises a structure which can be formed by micro-fabrication techniques, characterized in that it also comprises at least one element, formed in or at the periphery of the structure, and formed of a material different from the structure.

The elements may alter the mechanical properties of the component so that the component may be used in a given application while maintaining the advantages of the materials used to form the structure. This element can be used, for example, to increase the inertia/mass ratio of the balance or the unbalance/mass ratio of the balance, or to absorb some of the stresses locally generated by the wheel axle drive. It will be noted that the elements are formed in or at the periphery of the structure, rather than added thereto. Thus, the entire clock component may be fabricated by micro-fabrication techniques, for example, techniques that allow for micron-scale accuracy. Thus, the element does not impair the manufacturing accuracy of the component.

Particular embodiments of the clock unit according to the invention are defined in the appended claims 2 to 12.

The invention also provides a method of manufacturing a timepiece component, including a step of forming a structure by micro-fabrication techniques, characterized in that it further includes a step of forming at least one element in or at the periphery of the structure, the material of said element being different from the material of the structure, so that the final timepiece component includes said structure and said element.

Particular embodiments of the method are defined in the appended claims 14 to 28.

Drawings

Other features and advantages of the present invention will become apparent upon reading the following detailed description of several embodiments of the invention, with reference to the accompanying drawings, in which

Fig. 1 and 2 are a top plan view and an axle cross-sectional view, respectively, of a balance according to the invention;

fig. 3 is a perspective view of a top according to the invention;

fig. 4 and 5 are a top plan view and an axle cross-sectional view, respectively, of a balance according to the invention;

FIG. 6 is a perspective view of a top according to another embodiment;

FIG. 7 schematically illustrates a method of manufacturing a clock component such as that shown in FIGS. 1-3;

FIG. 8 schematically illustrates a method of manufacturing a clock component such as that shown in FIGS. 4 and 5;

fig. 9 schematically shows a method of manufacturing a balance and pinion; and

fig. 10 schematically shows a method for producing the pendulum mass shown in fig. 6.

Detailed Description

With reference to fig. 1, a balance 1 for a timepiece movement (movement) according to the invention comprises a main silicon structure 2 and a metal element 3. The silicon structure 2 comprises an annular central part 4, arms 5 extending radially from the central part 4, and closed profiles 6 at the ends of these arms 5, the profiles 6 defining a through cavity 7, for example in the shape of a bean. The cavities 7 are filled with metal elements 3, respectively, and form separate edge sections with these elements 3.

The metal member 3 is formed of a material having a higher density than silicon. Thus, they make the periphery of balance 1 heavier and increase the inertia of the balance to achieve the desired inertia. The internal parts of balance 1 formed by central part 4 and arm 5 are very light, since they are formed of silicon and they are largely hollow. Since the internal components of the balance have less influence on inertia than the peripheral components, a large inertia/mass ratio can be achieved. Thus, balance 1 has the same inertia as a traditional metal balance, and the total mass is smaller. In particular, it is advantageous in that it reduces the friction on the pivot of the axle of the balance in the bearing.

In an alternative embodiment, the edges may be continuous, i.e. the edge segments 3, 6 may contact each other.

The metal element 3 is typically formed of gold; however, they may be formed of another metal, especially another metal having a high density, such as platinum.

The silicon structure 2 and the metal elements 3 are formed by micro-fabrication or micro-formation techniques. Thus, balance 1 can be manufactured with a high degree of precision. Thus, its inertia is precise, which will facilitate pairing (pairing) with the balance spring to obtain the desired frequency of the balance spring adjustment device for the timepiece movement. An example of the manufacturing process of balance 1 will be described below.

As shown in fig. 2, the metal element 3 is in the same plane as the silicon structure 2 and has the same constant height as the latter. In this way, metal element 3 can occupy a large volume without increasing the height of balance 1. Alternatively, however, the metal elements 3 may extend beyond the cavity 7, for example in order to enhance the retention of these elements 3 in the silicon structure 2.

As shown in fig. 1 and 2, balance 1 can be mounted on its axle by arranging a ring 8 formed of a soft metal material such as gold in central part 4 of silicon structure 2 and by driving the axle of the balance, designated by reference numeral 9, into this ring 8. The ring 8 is sized to deform when the hub 9 is driven in and thus to absorb some of the stress exerted by the hub 9 to prevent silicon breakage. In fig. 2, reference numerals 10 and 11 denote a large roller and a small roller of an escape mechanism.

With reference to fig. 3, the mass 12 of the automatic winding mechanism for a timepiece according to the invention comprises a main silicon structure 13 and a metal element 14. The silicon structure 13 comprises a thin main part 15 and a thicker peripheral part 17, said thin main part 15 comprising a hole 16 for mounting the gyroscope (oscillatingmass)12 on a wheel or ball bearing. The mass 12 can be mounted on its axle or its ball bearings in the same way as the balance 1, i.e. using an intermediate piece made of soft material.

The metal element 14 fills each through-hole cavity 18 in the thick peripheral part 17. The metal member 14 is formed of a material having a higher density than silicon, such as gold or platinum. Thus, they make the periphery of the mass 12 heavier and increase its unbalance to obtain the required unbalance. Thus, the internal part 15 of the mass 12 is very light, since it is made of silicon and is thin. The inner part 15 can be hollowed out to be made lighter. Since the inner components of the pendulum mass have less influence on the imbalance than the peripheral components, a large imbalance/mass ratio can be achieved. Thus, with the same unbalance as a conventional metal pendulum, the total mass of the pendulum 10 is smaller. This is advantageous, inter alia, because it reduces friction. An example of the manufacturing process of the gyro 12 will be described below.

Referring to fig. 4 and 5, a gear 20 for a timepiece mechanism according to the invention comprises a main silicon structure 21 and an annular metal element 22, the element 22 being formed in a central through-hole cavity in the structure 21. The axle may pass through a central bore 23 in element 22. The diameter of the central bore 23 is chosen to be smaller than the diameter of the axle so that the gear 20 is mounted on the axle by driving. Since the material forming the element 22, for example gold or nickel, is highly deformable, as opposed to silicon, some of the stress applied by the axle will be absorbed by the element 22, which will prevent the silicon from breaking. Thus, an element such as element 22 constitutes a means of locally absorbing the driving stresses without impairing the precision of the manufacture of the part, since, as will be seen hereinafter, element 22 may be formed by micro-manufacturing or micro-molding techniques.

It will be seen that the metal elements shown in fig. 4, 5, such as element 22, can also be formed in the central cavity of the silicon structure of balance 1 or of balance mass 12, and can replace annular element 8.

Also, in the example shown, the height of the elements 22 is the same as the silicon structure 21. In an alternative embodiment, the element 22 may be higher than the structure 21, so as to define, for example, a pinion, which is coaxial with the gear 20 and is fixedly connected thereto. An exemplary method for making this alternative embodiment is described below.

Fig. 6 shows a pendulum mass 25 according to an alternative embodiment of the invention. This mass 25 differs from the mass 12 shown in fig. 3 in that the metal element 14 is replaced by a metal element 26 formed on a peripheral surface 27 of the main silicon structure, designated by the reference numeral 28. The element 26 has the shape of a circular arc and extends over the entire length and height of the surface 27. In order to strengthen the connection between the element 26 and the silicon structure 28, anchoring protrusions embedded in the element 26 may be provided on the peripheral surface 27. A typical method of manufacturing the gyroscope 25 will be described below. In a similar manner to element 26, an annular metal element may be formed continuously or discontinuously on the peripheral surface of the silicon structure to make, for example, a balance.

Fig. 7 schematically illustrates an exemplary method of manufacturing the components shown in fig. 1, 2 and 3. In a first step (fig. 7a), a silicon structure 30, having one or more parts of a cavity 31, is formed by Deep Reactive Ion Etching (DRIE). For simplicity, the structure 30 is shown as having only a single height. In the case of balance 1, a single DRIE step is necessary. In the case of the gyroscope 12, two DRIE steps are carried out to produce the thin part 15 and the thick part 17. In the second step (fig. 7b), a first layer of photosensitive resin 32, a metal layer 33, and a second layer of photosensitive resin 34 are successively formed on a support plate 35 formed of, for example, silicon or heat-resistant glass. In a third step (fig. 7c), the support plate 35 and its layers 32, 33, 34 and the silicon structure 30 are adhesively joined together, using the photosensitive resin layer 34 as an adhesive. In a fourth step (fig. 7d), the exposed part of the photosensitive resin 34, i.e. the part facing the cavity 31, is removed by means of a photolithographic method using the silicon structure 30 as a mask. In a fifth step (fig. 7e), metal is formed in the cavity 31 by electroforming (current growing) from the exposed part of the metal layer 33, and by using the silicon wall of the cavity 31 as a mold. The plate 35 and the layers 32, 33, 34 are then removed (fig. 7f), leaving the silicon structure 30 with the metal elements 37 formed in the initial cavity 31, and a levelling operation, for example by lapping, is performed so that the elements 37 are the same height as the structure 30.

During the fourth and fifth steps, some areas 36 may be masked in a manner known per se, so that they are not subjected to electroforming. These regions 36 are, for example, empty regions (emptyspace) between silicon components that are left out during DRIE processing, thereby forming barriers (bars) that keep the structure 30 connected to other structures that are simultaneously formed in a single plate. These obstacles break at the end of the manufacturing process to separate the parts.

The support plate 35 and the silicon structure 30 may be joined together in a different manner than described above (third step; fig. 7c), for example by hot-pressing the metal layer 33 to the structure 30 (in this case, the photosensitive resin layer 34 is omitted) or by replacing the photosensitive resin layer 34 by dry liquid silica.

Further details regarding the above-described process can be found in the article entitled "Fabric of ultra high magnetic structural insulation" published by Debbie G.Jones and Albert P.Pisano on the Proceedings of IMECE04 of 2004 ASME International Mechanical engineering Congress and Exposion, Annam, Calif., where a similar process for making ferromagnetic structures in silicon is described.

Figure 8 schematically illustrates how a central annular metal element such as element 22 shown in figures 4 and 5 can be formed. Figure 8 shows more precisely how the central element can be formed simultaneously with the peripheral elements. The first to fourth steps are similar to the steps of fig. 7a to 7d, respectively. A fifth step, shown in fig. 8a, comprises filling the cavity 31 of the silicon structure 30 with a photosensitive resin, such as SU-8 resin. A sixth step (fig. 8b) consists in removing the SU-8 resin by means of a photolithographic method, except at the central part of the central cavity 38 corresponding to the hole in the central metal element. A seventh step (fig. 8c) comprises forming a metal in the cavities 31, 38. In the central cavity 38, the metal is formed only around the remainder 39 of the SU-8 resin. Subsequently, the support plate 35 and its layers 32, 33 and 34 are removed (fig. 8d) and the remaining part 39 of the SU-8 resin is removed (fig. 8 e). Thus, one or more peripheral metal elements 40 are obtained, for example for increasing the inertia of the component, and a central annular element 41, for example to allow driving the axle.

Fig. 9 schematically illustrates a typical method of manufacturing a component comprising an annular central metal element such as element 22 shown in fig. 4 and 5, but having a higher height to define a pinion. The first to fourth steps are similar to the steps of fig. 7a to 7d, respectively. The fifth step shown in fig. 9a involves forming a photoactive SU-8 resin 50 in the central cavity of the silicon structure 30 and beyond the cavity to the upper surface of the silicon structure 30. A sixth step (fig. 9b) consists in photo-structuring the photosensitive resin 50 to define a cavity 51 with the silicon structure 30, which has the form of an annular central element and its pinion. A seventh step (fig. 9c) comprises electroforming metal in the cavities 51. Subsequently, the support plate 35 and its layers 32, 33 and 34, as well as the photosensitive resin 50, are removed (fig. 9d and 9e), leaving the silicon structure 30 and the annular metal element 22b formed in the structure 30 and extending beyond the structure 30 to define the pinion gear 22 b. A central bore 22c passes through the combination 22a, 22b into which the axle can be driven. In alternative embodiments, the ring element 22a may define other elements than a pinion, such as a cam or a heart-piece.

Fig. 10 schematically shows how the metal element 26 of the pendulum 25 shown in fig. 6 can be formed. In a first step (fig. 10a), the silicon structure 28 is formed by two DRIE steps, a back plate 35 with successive layers of photoresist 32, metal 33 and photoresist 34 is attached to the structure 28, the portion of the photoresist 34 outside the structure 28 is removed to expose the metal layer 33, and then a portion of the photosensitive SU-8 resin 42 is formed outside the structure 28 to form a cavity 43 using the silicon structure 28, in a similar manner to the portion 39 of fig. 8. In a subsequent step (fig. 10b), metal is electroformed in the cavities 43. In a subsequent step (fig. 10c), the support plate 35 and its layers 32, 33, 34 and the resin 42 are removed.

In all of the methods described above, the silicon structure is substantially covered by a silicon dioxide layer prior to the electroforming step. This layer is produced by the natural oxidation of silicon. The thickness of the silicon structure can be increased by placing it in an oxidation furnace prior to electroforming. Silica in fact enhances some of the mechanical properties of silicon, such as the coefficient of friction or mechanical strength. Other coatings may also be deposited on the silicon structure if desired. It will thus be appreciated that the metal elements do not necessarily have to be in direct contact with the silicon, but may be in contact with the silicon dioxide wall or with a specific coating.

In addition to a high level of precision, it will be appreciated that the method of manufacturing a component according to the invention described above allows a large number of components to be formed simultaneously from a single plate.

Although the invention has been described above in relation to silicon structures, it may be applied to other materials that can be processed by micro-fabrication techniques, in particular by DRIE techniques, such as diamond, quartz, glass or silicon carbide.

Claims (27)

1. A timepiece component comprising a structure (2; 13; 21; 28) formed by a microfabrication technique and at least one element (3; 14; 22; 26) formed of a material different from that of the structure, characterised in that the element is metallic and is electroformed in or at the periphery of the structure.

2. The clock component of claim 1, wherein the structure is made of silicon.

3. The clock component of claim 1, wherein the structure is made of diamond, quartz, glass, or silicon carbide.

4. A timepiece component according to any one of claims 1 to 3, wherein the element (3; 14; 22) fills a cavity in the structure (2; 13; 21).

5. Timepiece component according to any one of claims 1 to 3, characterised in that said elements (3; 14; 22; 26) lie in the same plane and are of the same height as the structure (2; 13; 21; 28).

6. A timepiece component according to any one of claims 1 to 3, wherein said elements (22a, 22b) project beyond the plane of the structure (30).

7. Timepiece component according to any one of claims 1 to 3, including a balance (1), and said element (3) is located at the periphery of the structure (2) and is intended to increase the inertia/mass ratio of the balance.

8. Timepiece component according to any one of claims 1 to 3, characterised in that it comprises a mass (12; 25) for an automatic winding mechanism, whereas said elements (14; 26) are located at the periphery of the structure (13; 28) and are intended to increase the unbalance/mass ratio of the mass.

9. Timepiece component according to any one of claims 1 to 3, characterised in that it is intended to be driven onto a support member and in that said element (22) comprises a central hole (23) intended to receive the support member.

10. Timepiece component according to claim 9, wherein said element (22a) protrudes beyond the plane of the structure (30) and defines a pinion (22b), a cam or a chronograph heart, outside the plane of the structure (30).

11. Timepiece component according to claim 9, characterised in that it comprises a balance (1) or a balance mass.

12. Clock unit according to claim 9, characterized in that it comprises a wheel (20).

13. A method of manufacturing a timepiece component comprising a structure (2; 13; 21; 28) and at least one element (3; 14; 22; 26) formed of a material different from that of the structure, characterized in that the element is metallic and in that the method comprises a step of forming the structure (2; 13; 21; 28) by micro-fabrication techniques and a further step of electroforming the element (3; 14; 22; 26) in or at the periphery of the structure, so that the final timepiece component comprises the structure and the element.

14. The method of claim 13, wherein the step of forming the structure is accomplished by using a deep reactive ion etching technique.

15. A method according to claim 13 or 14, characterized in that the structure is made of silicon.

16. A method according to claim 13 or 14, characterized in that the structure is made of diamond, quartz, glass or silicon carbide.

17. A method according to claim 13 or 14, characterized in that the step of electroforming the element comprises depositing the material of the element in a cavity (31; 38; 43; 51) defined at least partly by the structure (30), wherein the cavity is used as a mould.

18. Method according to claim 17, characterized in that the cavity (31) is completely defined by the structure (30).

19. The method of claim 17, wherein the cavity (38; 43; 51) is defined in part by the structure (30) and in part by the photosensitive resin (39; 42; 50).

20. A method as claimed in claim 19, wherein the step of electroforming the element (26) comprises depositing the material of the element in a cavity (43) defined by the structure (28) and a photosensitive resin (42) formed outside the structure (28), so as to form the element (26) on the peripheral surface (27) of the structure (28) after removal of the photosensitive resin (42).

21. Use of a method according to claim 13 or 14 for making a balance (1), said element (3) being placed at the periphery of the structure (2) and being intended to increase the inertia/mass ratio of the balance.

22. Use of the method according to claim 13 or 14 for manufacturing a mass (12; 25) for an automatic winding mechanism, said elements (14; 26) being placed at the periphery of the structure (13; 28) and being intended to increase the unbalance/mass ratio of the mass.

23. A method as claimed in claim 19, characterized in that the step of electroforming the element (22) comprises depositing the material of the element in a cavity (38) of a structure (30) whose central portion comprises a photosensitive resin (39), so that, after removal of the photosensitive resin (39), the element (22) comprising the central hole (23) is formed in the cavity.

24. A method as claimed in claim 23, wherein the cavity (51) extends out of the plane of the structure (30) and is shaped so that, after the step of electroforming the element (22a), it defines a pinion (22b), a cam or a timepiece heart.

25. Use of the method according to claim 23 for manufacturing a timepiece component (20) for being driven onto a support member, using a central aperture (23) of the element (22) for receiving the support member.

26. Use according to claim 25, wherein the clockwork component is a balance or a pendulum.

27. Use according to claim 25, wherein the clock member is a wheel.