How to manufacture a hairspring

Abstract

To provide a method for manufacturing a batch of a plurality of horologic balance springs having an average rigidity within a predetermined range.SOLUTION: The method includes: a) a step 20 of forming, on a wafer, a plurality of horologic balance springs different from those required to obtain a batch of horologic balance springs; b) a step 21 of forming, on the wafer, a plurality of systems exhibiting a reference rigidity for determining the rigidity of a plurality of timepiece balance springs; c) a step 22 of determining the rigidity of the plurality of systems formed; d) a step 26 of calculating a dimensional correction to be applied to the plurality of timepiece balance springs formed, based on the determined rigidity of the plurality of systems; and e) a step of modifying the dimensions of the formed timepiece balance springs on the basis of the dimensional corrections calculated to obtain a batch of timepiece balance springs whose average rigidity is within a predetermined range.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to the field of watch part manufacturing. More specifically, the present invention relates to a method for manufacturing a batch of multiple watch whiskers having an average rigidity within a predetermined range. [Background Art]

[0002] Prior art documents describe methods for manufacturing multiple watch whiskers on a wafer using etching techniques such as laser etching, plasma etching, deep reactive-ion etching (DRIE), or wet etching.

[0003] However, when using such methods, it is typical for geometric variations to occur between whiskers formed in the same pattern on the same wafer.

[0004] To overcome these drawbacks, solutions have been proposed in prior art documents, particularly Patent Documents 1 and 2, that describe methods for manufacturing whiskers.

[0005] In Patent Document 1, the manufacturing method includes the following steps: a) forming a whisker having dimensions larger than those required to obtain a whisker of a predetermined rigidity; b) determining the rigidity of the whisker formed in step a) by measuring the vibration frequency of the whisker coupled with a template having a predetermined inertia; c) calculating the thickness of the material to be removed to obtain a whisker of a predetermined rigidity; and d) removing the calculated thickness of the material from the whisker formed in step a). Steps b), c), and d) can be repeated to further improve dimensional quality.

[0006] Patent Document 2 describes a manufacturing method comprising the following steps: a) forming a hairspring smaller than the dimensions required to obtain a hairspring of predetermined stiffness; b) determining the stiffness of the hairspring formed in step a) by measuring the oscillation frequency of the hairspring coupled to a balance wheel having predetermined inertia; c) calculating the required thickness of material to be added to obtain a hairspring of predetermined stiffness; and d) modifying the hairspring formed in step a) to compensate for the required thickness of material, wherein steps b), c), and d) are repeatable to further improve dimensional quality.

[0007] Such methods can be improved, in particular, to limit wafer contamination that may occur during the measurement steps being implemented.

[0008] In this situation, it is understood that there is a need to find solutions that will lead to such improvements. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] European Patent No. 3181938 [Patent Document 2] European Patent No. 3181939 [Overview of the project]

[0010] One object of the present invention is to propose a method for manufacturing a batch of multiple watch hairsprings that satisfy the above-described requirements.

[0011] Another objective is to improve the manufacturing precision of a batch of hairsprings where the average stiffness is within a given range.

[0012] The present invention relates to a method for manufacturing a batch of watch hairsprings having an average rigidity within a predetermined range, and this method is: a) The step of forming multiple hairsprings on a wafer, each having dimensions different from the dimensions required to obtain a batch of multiple hairsprings whose average rigidity is within the predetermined range, b) The step of forming a plurality of systems on the wafer that represent reference stiffness for determining the stiffness of the plurality of watch hairsprings whose average is within the predetermined range, c) A step of determining the rigidity of the plurality of systems that have been formed, d) A step of calculating a dimensional correction to be applied to the plurality of watch hairsprings formed based on the determined rigidity of the plurality of systems, e) A step of correcting the dimensions of the formed watch hairsprings based on a dimensional correction calculated to obtain a batch of the watch hairsprings in which the average stiffness is within the predetermined range. Includes.

[0013] In other embodiments, The step of forming a batch of multiple watch hairsprings and the system is carried out by etching, particularly deep reactive ion etching. In the forming step, each system is manufactured on a wafer for one hairspring in a batch of multiple hairsprings. The step of forming the plurality of systems involves manufacturing, on a wafer, a plurality of vibrating elements constituting each system such that the system surrounds the hairspring associated with the wafer. The step of forming the plurality of systems involves manufacturing a single vibrating element constituting each system on a wafer in the vicinity of the hairspring to which the system is associated on the wafer. The determination step includes a substep of estimating the resonant frequency of at least one system associated with a hairspring in a batch of multiple hairsprings. The determination step includes a substep of defining the stiffness of each system using an electronic device that runs an algorithm that calculates the stiffness based on the estimated resonant frequency. The stiffness defined for each system is the stiffness of one of its multiple vibration elements, the average stiffness of all of its multiple vibration elements, or the average stiffness of one sample of its multiple vibration elements. The calculation step includes a substep of determining, from the determined stiffness, the thickness of the material to be added to or removed from the dimension of at least one hairspring in a batch of multiple hairsprings. The vibrating element is said to have a tuning fork shape. [Brief explanation of the drawing]

[0014] Other features and advantages of the present invention will be better understood by reading the following description given in relation to non-limiting specific embodiments of the present invention. That description is given for illustrative purposes with reference to the following accompanying drawings.

[0015] [Figure 1] This is a diagram of a wafer containing a batch of multiple watch hairsprings. The multiple watch hairsprings are all formed simultaneously on the wafer, particularly by etching, according to embodiments of the present invention. [Figure 2] This is an enlarged view of the vibration element of the system showing the reference stiffness. The system is contained in the wafer shown in Figure 1 according to an embodiment of the present invention. [Figure 3] This is a cross-sectional diagram of a hairspring blade manufactured using the method according to an embodiment of the present invention. The cross-section has dimensions necessary to obtain a batch of multiple watch hairsprings having an average rigidity within a predetermined range. [Figure 4] This is a cross-sectional diagram of a hairspring blade formed on a wafer using the method according to an embodiment of the present invention. The dimensions of this cross-section are larger than the dimensions of the cross-section of the manufactured hairspring blade shown in Figure 3. [Figure 5] This is a cross-sectional diagram of a hairspring blade formed on a wafer using the method according to an embodiment of the present invention. The dimensions of this cross-section are smaller than the dimensions of the cross-section of the manufactured hairspring blade shown in Figure 3. [Figure 6] It is a logic diagram regarding a method for manufacturing a batch of a plurality of clock whiskers according to an embodiment of the present invention. The average rigidity of the plurality of clock whiskers is within a predetermined range.

Embodiments for Carrying Out the Invention

[0016] FIG. 6 schematically shows a method for manufacturing a batch or a set of a plurality of whiskers 2a whose average rigidity is within a predetermined range. The purpose of such a method is to ensure a very high dimensional accuracy of the plurality of manufactured whiskers 2a, and at the same time, accurate rigidity is guaranteed for these whiskers 2a.

[0017] In FIG. 1, a batch of a plurality of clock whiskers 2b, 2c is formed on a wafer 1. In the batch, each whisker 2b, 2c includes a collet intended to be rigidly connected to a pivoting mandrel. The clock whiskers 2b, 2c further include an elastically flexible strand. This strand is connected at one end to the collet, wound spirally to form a plurality of continuous turns, and the last turn is extended by an attachment segment. The attachment segment is intended to be attached to a stationary temp cock, for example, by a stud.

[0018] Such a method includes a step 20 of forming a plurality of whiskers 2b, 2c having dimensions E, E3, H2, H3 different from the dimensions E1, H1 required to obtain a batch of a plurality of whiskers 2a whose average rigidity is within a predetermined range on the wafer 1. <0000,099>

[0019] During step 20, a plurality of hairsprings 2b and 2c are formed on the wafer 1. These hairsprings 2b and 2c are preferably formed simultaneously on the wafer 1. These hairsprings 2a and 2c can be formed on the wafer 1 by, for example, deep reactive ion etching, laser etching, chemical etching, or etching using a focused ion beam. It should be noted that these hairsprings 2b and 2c preferably have similar geometric shapes.

[0020] These hairsprings 2b, 2c formed on the wafer 1 have blades having cross-sections 4b, 4c with dimensions E2, H2, E3, H3. If the shape of such blades is polygonal, the cross-sections 4a, 4b, 4c are characterized by heights H1, H2, H3 and thicknesses E1, E2, E3. These dimensions are different from the dimensions E1, H1 required to obtain a batch of multiple hairsprings 2a with an average stiffness within a predetermined range. In other words, the blades of each hairspring 2b, 2c may have cross-sections 4b, 4c, and the dimensions E2, H2, E3, H3 of these cross-sections may be greater than or less than the required dimensions E1, H1 of the cross-section 4a of the manufactured hairspring 2a blades that allow for an average stiffness within a predetermined range.

[0021] In the context of the said method, wafer 1 is preferably made from doped or undoped silicon. The silicon may be single-crystal, polycrystalline, or amorphous. Furthermore, the silicon may have the crystal orientations {1,1,1}, {-1,1,1}, {-1,-1,1}, {-1,-1,1} which maximize the Young's modulus of silicon. Alternatively, wafer 1 may be made from quartz, glass, ceramic, metal, or alloy.

[0022] It should be noted that during the forming step 20, the multiple clock hairsprings 2b and 2c that are formed are The dimensions E2 and H2 may be larger than the dimensions E1 and H1 required to obtain a batch of multiple watch hairsprings 2a whose average stiffness is within a predetermined range, i.e., the blade height H2 and / or blade thickness E2 may be larger than the blade height H1 and / or blade thickness E1 of the watch hairspring 2a whose average stiffness is within a predetermined range. The dimensions E3, H3 may be smaller than the dimensions E1, H1 required to obtain a batch of multiple watch hairsprings 2a having an average stiffness within a predetermined range, i.e., the blade height H3 and / or blade thickness E3 may be smaller than the blade height H1 and / or blade thickness E1 of the multiple watch hairsprings 2a having an average stiffness within a predetermined range.

[0023] The method further includes step 21 of forming a system on wafer 1 that indicates a reference stiffness 3 for determining the stiffness of a plurality of hairsprings 2a whose average is within a predetermined range. Step 21 is performed on the same wafer 1 containing the plurality of formed hairsprings 2b, 2c, preferably simultaneously with step 20 of forming the hairsprings 2b, 2c. During step 21, a system 3 for each hairspring 2b, 2c of a batch of the plurality of formed hairsprings is formed on wafer 1. The system 3 consists of at least one vibrating element 10 located in immediate vicinity of the corresponding hairspring 2b, 2c. Similar to step 20 of forming the hairsprings 2b, 2c, the vibrating element 10 of each system 3 is preferably formed by etching. It should be noted that there are as many systems 3 as there are hairsprings 2b, 2c on wafer 1, and the height of the vibrating element 10 is similar to the height of wafer 1, and therefore similar to the height of the hairsprings 2b, 2c. Alternatively, in order to obtain a good representation of the rigidity in this wafer 1, the wafer 1 may contain a minimum sample of the system 3.

[0024] As already mentioned, the system 3 preferably includes a plurality of vibrating elements 10. Such elements 10 include at least one blade and may extend essentially linearly. The element 10 includes a mounting end 5a and at least one free end 5b, 5c. The element 10 has a different geometric shape and dimensions from the hairspring of the wafer 1. Of course, the height mentioned above is an exception.

[0025] Each vibrating element 10 is enclosed within an opening 9 made in the wafer 1. The opening 9 defines a space in which the vibrating elements 10 can freely perform controlled mechanical vibration motion.

[0026] More specifically, the vibrating element 10 includes a mounting end 5a and two free ends 5b, 5c. The vibrating element 10 includes a rod / stem 6 to which the mounting end 5a is provided. The rod 6 extends linearly into the opening 9 and has two arms 7, 8 on its extension that form two flexible blades or two flexible branches folded along the rod 6. More specifically, such arms 7, 8 are positioned close to the rod 6 in the opening 9 and are substantially parallel in this configuration. These two arms 7, 8 are connected to form a "U" shape, each containing a free end of the vibrating element 10. It should be noted that each of these arms 7, 8 may have a thickness similar to or substantially similar to the thickness of the hairspring.

[0027] In the vibration element 10, the rod 6 has higher rigidity than the two arms 7 and 8 that constitute the vibration element 10. Furthermore, the length of these arms 7 and 8 is between 1 mm and 2 mm, preferably 1.5 mm. The thickness of these arms 7 and 8 is between 10 and 60 μm, preferably 30 μm.

[0028] Furthermore, this vibrating element 10 has the general shape of a tuning fork or is a tuning fork.

[0029] As described above, each vibration element 10 is selected to allow for optimal isolation of the influence of the embedded portion on the resonant frequency. More specifically, during harmonic excitation, the embedded portion has a non-negligible influence on the resonant frequency. In the case of vibration element 10, there is a significant isolation between the resonant frequency of the embedded portion and that of arms 7 and 8. The correlation between the resonant frequency and stiffness becomes independent of the etching quality of the embedded portion.

[0030] This does not apply to a vibrating element composed of a blade whose main linear cross-section is variable, and whose distal end terminates at a locally enlarged portion of the cross-section forming a mass body. In such a configuration, variations in blade thickness lead to changes in the embedded portion, and consequently, changes in resonance. The correlation here requires considering the influence of the embedded portion, which introduces a complexity not present in the method according to the present invention for implementing a vibrating element 10 such as a tuning fork. Furthermore, since the blade has closed corners, complex operations must be implemented to form the blade on the wafer by deep reactive ion etching. In such a situation, it is understandable that large variations occur at each of these corners, changing the resonant frequency. For example, a variation of the radius of the neck casting of the embedded portion on the order of 2 μm results in a difference of the order of 20 nm in the prediction of the etching thickness of the linear blade. Furthermore, for this blade, and other types of blades other than the tuning fork, manufacturing tolerances of the embedded portion hinder obtaining a good frequency-stiffness correlation.

[0031] During step 21, each vibrating element 10 of system 3 associated with the hairsprings 2b and 2c is positioned on the wafer 1 at the periphery of the hairsprings 2b and 2c, particularly in the immediate vicinity of them. That is, the multiple vibrating elements 10 of system 3 are formed on the wafer 1 such that they surround the hairsprings 2b and 2c to which they are associated.

[0032] It should be noted that the arrangement of these vibration elements 10 in each system 3 on the wafer 1 is preferably such that the arms 7 and 8 are arranged to maximize or minimize Young's modulus, especially if the wafer 1 is silicon-based. More specifically, since silicon is anisotropic, this arrangement prevents Young's modulus from fluctuating as a function of angle when determining stiffness. Furthermore, to improve the accuracy of the correlation between stiffness and measurement frequency, the maximum Young's modulus is preferable.

[0033] It should be noted that during step 21, the system 3 is configured such that the average stiffness of the watch hairsprings 2b and 2c manufactured on the wafer 1 is within a predetermined range.

[0034] Furthermore, the vibration element 10 is configured so that its stiffness can be easily determined using an electronic device that determines the stiffness of these systems 3. The electronic device implemented by this method is in a non-limiting and non-exclusive manner. • Processing units such as computers, • A module that drives / induces the mechanical vibration motion of the vibration element 10 around its stable equilibrium position. • Includes a module for measuring the resonant frequency of the vibrating element 10 in mechanical vibration motion.

[0035] The processing unit of the electronic device includes at least one processor and a memory element. The processing unit can execute instructions to implement a computer program intended to drive / control a drive module and a measurement module, and can also perform computation / processing operations while at least one algorithm stored in the memory element is implemented. This algorithm may include machine learning algorithms and / or mathematical formulas. This algorithm can implement a predictive or simulation model, which allows for the determination of the stiffness of system 3 from the measurement of its resonant frequency.

[0036] It should be noted that such a vibrating element 10 can be likened to a tuning fork in the sense that it vibrates at a stable frequency despite changes in predetermined parameters, particularly those related to the embedded portion and the manufacturing process. This stable frequency varies depending on one determined parameter, in this case, stiffness.

[0037] One of the parameters of the vibration element 10 significantly alters the resonant frequency, causing the influence of the other parameters to become negligibly small.

[0038] The method then includes a step 22 in which the rigidity of the system 3 associated with the hairsprings 2b and 2c formed on the wafer 1 is determined. This step 22 includes a substep 23 in which the resonant frequency of at least one of the systems 3 associated with the hairsprings 2b and 2c is estimated. During the substep 23, at least one vibrating element 10 of at least one of the systems 3 is driven in mechanical vibration motion around its stable equilibrium position. During this motion, the resonant frequency of the vibrating element 10 is determined in the measurement phase 24.

[0039] In this embodiment of the present invention, the resonant frequencies of all of the multiple vibration elements 10 of the system 3 are measured, and the average of these frequencies is then calculated to correspond to the resonant frequency of the system 3. In this context, the determined average frequency is considered to represent the frequency of each vibration element 10 of the system 3.

[0040] Alternatively, the measured resonant frequency of system 3 may be the resonant frequency of a single vibration element among its plurality of vibration elements 10, or the resonant frequency of a sample of those plurality of vibration elements 10.

[0041] Once the resonant frequency is estimated, step 22 includes a substep 25 that defines the stiffness of each system 3, during which the electronic device runs an algorithm that calculates the stiffness from the estimated resonant frequency of system 3.

[0042] The method then includes a step 26 in which a dimensional correction is applied to each hairspring 2b, 2c of a batch of multiple hairsprings, based on the stiffness determined for the relevant system 3. During step 26, the quantification of the dimensional correction applied to the hairsprings 2b, 2c is determined.

[0043] For this purpose, step 26 includes a substep 27 which determines, based on the determined stiffness, the thickness e of the material to be added to or removed from at least one dimension of the hairsprings 2b, 2c in a batch of hairsprings formed during step 20, and obtains a batch of hairsprings 2a in which the average stiffness is within a predetermined range.

[0044] The dimensional correction substantially corresponds to the thickness e of the material removed from or added to the hairsprings 2b and 2c in order to change at least one of the dimensions E2, H2, E3, and H3 of the hairsprings 2b and 2c. At least one of the dimensions E2, H2, E3, and H3 is, • Only blade heights H2, H3, or • Only blade thicknesses E2 and E3 are available, or This refers to both the heights H2 and H3, and the thicknesses E2 and E3.

[0045] The dimensional correction may be made over one or more different lengths of the blades of the hairsprings 2b and 2c, or over the entire length of the blades.

[0046] By determining dimensional corrections, such substep 27 is used to help create the geometric shapes of the hairsprings 2b, 2c that give rigidity within a predetermined range.

[0047] The method then includes step 28 of modifying the dimensions E2, E3, H2, H3 of multiple watch hairsprings 2b, 2c based on a dimensional correction calculated to obtain a batch of multiple watch hairsprings 2a in which the average stiffness is within a predetermined range.

[0048] In this context, if the dimensions E2, H2 of a plurality of hairsprings 2b are greater than the dimensions E1, H1 required to obtain a batch of a plurality of watch hairsprings 2a having an average stiffness within a predetermined range, step 28 includes a material removal substep 29 depending on the calculated thickness e of the material to be removed. Such removal may be carried out during a process well known in the prior art, which involves oxidizing and then deoxidizing these plurality of hairsprings 2b. The purpose of such substep 29 is to reduce the dimensions of the cross-section 4b of the hairspring 2b over a given length of the blade or over its entire length.

[0049] If the dimensions E3, H3 of a plurality of hairsprings 2c are smaller than the dimensions E1, H1 required to obtain a batch of a plurality of hairsprings 2a having an average stiffness within a given range, step 28 includes a material addition substep 30 depending on the calculated thickness e of the material to be added. Such material addition may be carried out during a process known in the prior art, such as thermal oxidation, galvanic growth, physical deposition, chemical deposition, atomic layer deposition, or other additive processes. The purpose of such substep 30 is to increase the dimensions E3, H3 of the cross section 4c of the hairspring 2c over a given length of the blade or over its entire length.

[0050] Therefore, this type of method makes it possible to correct dimensional errors in hairsprings manufactured by such methods that implement photolithography and / or DRIE techniques with high precision provided by the system exhibiting a reference stiffness 3. [Explanation of Symbols]

[0051] 1. A wafer containing at least one hairspring. 2a. Manufactured hairspring 2b. A hairspring formed on a wafer to have a cross-section larger than the cross-sectional dimensions of the manufactured hairspring. 2c. A hairspring formed on a wafer to have a cross-section smaller than the cross-sectional dimensions of the manufactured hairspring. 3. System indicating standard stiffness 4a. Cross-section of a manufactured hairspring 4b. Cross-section of a formed hairspring with dimensions larger than the dimensions of the manufactured hairspring cross-section. 4c. Cross-section of a formed hairspring, smaller in dimensions than the cross-section of a manufactured hairspring. 5a. Mounting end of the vibrating element 5b. The first free end of the vibrating element 5c. The second free end of the vibrating element 6. Rods / trunks of the vibrating element 7. First flexible arm of the vibration element 8. Second flexible arm of the vibration element 9. Opening where vibration elements are placed 10. Vibration elements

Claims

1. A method for manufacturing a batch of multiple watch hairsprings (2a) having an average rigidity within a predetermined range, a) A step (20) of forming a plurality of hairsprings (2b, 2c) on a wafer (1) having dimensions different from the dimensions required to obtain one batch of the plurality of hairsprings (2a), b) Step (21) of forming a plurality of systems (3) on the wafer (1) that indicate a reference stiffness for determining the stiffness of the plurality of watch hairsprings (2a), wherein the average of the stiffness is within the predetermined range, c) A step (22) of determining the rigidity of the plurality of systems (3) that have been formed, d) A step (26) to calculate a dimensional correction to be applied to the plurality of watch hairsprings (2b, 2c) formed based on the determined rigidity of the plurality of systems (3), e) A step of correcting the dimensions of the plurality of watch hairsprings formed based on a dimensional correction calculated to obtain a batch of the plurality of watch hairsprings in which the average stiffness is within the predetermined range. Includes, In the forming step (21), each system (3) is manufactured on the wafer (1) for one hairspring of the plurality of hairsprings (2b, 2c) in the batch, A method comprising the step (21) of forming the plurality of systems (3), wherein, on the wafer (1), a plurality of vibrating elements (10) constituting each system (3) are manufactured such that the system (3) surrounds the one hairspring (2b, 2c) associated with the wafer (1).

2. The method according to claim 1, wherein the step (20) of forming the batch of the plurality of hairsprings (2b, 2c) and the step (21) of forming the plurality of systems (3) are performed by etching.

3. The method according to claim 1, wherein the step (21) of forming the plurality of systems (3) is to manufacture the plurality of vibrating elements (10) constituting each system (3) in the wafer (1) in the vicinity of the one hairspring (2b, 2c) to which the system (3) is related in the wafer (1).

4. The method according to claim 1, wherein the determining step (22) includes a substep (23) of estimating the resonant frequency of at least one system (3) associated with one hairspring of the batch of the plurality of hairsprings (2b, 2c).

5. The method according to claim 1, wherein the determining step (22) includes a substep (23) of estimating the resonant frequency of at least one system (3) associated with one hairspring of the plurality of hairsprings (2b, 2c) in one batch, and the determining step (22) includes a substep (25) of defining the stiffness of each system (3) using an electronic device that performs an algorithm for calculating the stiffness based on the estimated resonant frequency.

6. The method according to claim 1, wherein the determining step (22) includes a substep (23) of estimating at least one resonant frequency of each system (3) relating to one hairspring of one batch of the plurality of hairsprings (2b, 2c), and the determining step (22) includes a substep (25) of defining the stiffness of each system (3) using an electronic device that performs an algorithm for calculating the stiffness based on the estimated resonant frequency, wherein the stiffness defined for each system (3) is the stiffness of one of its plurality of vibrating elements (10), the average stiffness of all of its plurality of vibrating elements (10), or the average stiffness of one sample of its plurality of vibrating elements (10).

7. The method according to any one of claims 1 to 6, wherein the calculating step (26) includes a substep (27) of determining the thickness (e) of material to be added to or removed from the dimension of at least one of the hairsprings (2b, 2c) in a batch of the plurality of hairsprings (2b, 2c) from the determined stiffness.

8. The method according to claim 1, wherein the vibrating element (10) has a tuning fork shape.

9. The method according to claim 2, wherein the etching includes deep reactive ion etching.

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