HK1200799B - Method of fabricating a single-piece micromechanical component including at least two distinct functional levels - Google Patents

Description

Method for producing a micromechanical component comprising at least two different functional heights

Technical Field

The invention relates to a method for producing a micromechanical component of one piece comprising at least two different functional levels.

Background

It is known to form metal components having a plurality of different functional heights using a continuous LIGA type process, i.e. by including a resin mould having a structure and a stack of layers of metal electroformed within the cavity of the mould.

However, it is difficult to perform these successive steps for forming a plurality of functional levels, since the functional levels must be properly referenced to each other. Furthermore, it is clear that this difficulty involves higher costs than two electroformed depositions on a single level.

Disclosure of Invention

The object of the present invention is to overcome all or part of the aforementioned drawbacks by proposing an alternative method of manufacturing a micromechanical component in one piece comprising at least two different functional heights, which is less expensive to implement.

The invention therefore relates to a method for producing a micromechanical component of one piece comprising at least two different functional levels, characterized in that it comprises the following steps:

a) forming a silicon substrate, a top surface of the silicon substrate being electrically conductive;

b) constructing a mold with a photosensitive resin to form a cavity, a base of the cavity being formed by the conductive top surface;

c) filling the cavity of the mold by electroforming (galvanoplasty) to form a metal part;

d) selectively machining a portion of the metal part to form an integral micromechanical component having at least two different functional heights;

e) releasing the micro-mechanical member from the silicon substrate and the photosensitive resin.

It is clear that, advantageously according to the invention, the unitary micromechanical components, each having at least two different functional levels, are formed by metal parts formed by a LIGA process in a specific mold and then machined directly on the substrate, in order to exploit the advantage of the precise positioning of each metal part on the substrate.

As a result, the external dimensions and possibly the internal dimensions remain highly accurate due to the LIGA process, and the rest of the integrated micromechanical component enjoys a lower machining accuracy than the LIGA process, thereby saving manufacturing costs. A one-piece micromechanical component comprising at least two different functional heights is thus obtained, which is easier to manufacture and at the same time maintains a very high precision of the outer part and possibly of the inner part.

According to other advantageous features of the invention:

-making the top surface conductive by doping the silicon substrate and/or by depositing a conductive layer on the silicon substrate;

-the thickness of the silicon substrate is between 0.3mm and 1 mm;

-step b) comprises the following phases: f) depositing a photosensitive resin layer on the conductive top surface of the silicon substrate; g) selectively irradiating a portion of the photosensitive resin; h) developing (develop) the photosensitive resin to construct the mold;

-the metal part is formed of a nickel-phosphorus base, such as NiP or NiP 12;

-said method comprises, between said step c) and said step d), the steps of: i) flattening the mold and the metal part by grinding (lapping);

-said method comprises in said step e) the following phases: j) removing the photosensitive resin; k) removing the silicon substrate;

-said method further comprises, between said phase j) and said phase k), the following phases: l) depositing a coating on the micromechanical component-substrate assembly;

-said phase i) is achieved by physical or chemical vapour deposition or electroforming;

-forming a plurality of micromechanical components on the same substrate.

Furthermore, the invention relates to a timepiece characterized in that it comprises an integral micromechanical component according to any one of the preceding variants, comprising at least two different functional levels.

Drawings

Further features and advantages will be apparent from the following description, given by way of non-limiting example with reference to the accompanying drawings, in which:

figures 1 to 5 are diagrams of successive steps of a method according to a first embodiment of the invention;

figures 6 and 7 are diagrams of the final steps of the method according to the second embodiment of the invention;

figures 8 to 10 are views of a metal part electroformed and then machined using a method according to a first variant of the invention;

figures 11 to 13 are views of a metal part electroformed using a method according to a second variant of the invention and then machined and then assembled;

figures 14 to 16 are views of a metal part electroformed using a method according to a third variant of the invention and then machined and then assembled;

fig. 17 is a block diagram of a method according to the invention.

Detailed Description

The object of the present invention is to provide a method for producing a micromechanical component of one piece comprising at least two different functional levels, which is less expensive to implement. It is a further object of the invention to manufacture all or part of a micromechanical component according to such a method. The micromechanical component is preferably intended to be mounted in a timepiece. Of course, it is also possible to envisage applying the invention in other fields, for example, in particular in the aeronautical or automotive industry.

As shown in fig. 17, the invention relates to a method 1 for producing a monolithic micromechanical component 31, 41, 61, 91 comprising at least two functional levels.

According to the method 1, as shown in fig. 1, a first step 3 is used to form a silicon substrate 2, the top surface 4 of which is electrically conductive. Preferably, the top surface 4 is made conductive by doping the silicon substrate 2 and/or by depositing a conductive layer on the silicon substrate 2.

In any event, it is important that the subsequent electroformed deposit adhere as strongly as possible to the substrate 2. In fact, a very secure fixation of the metal parts 21, 51, 81 to the top surface 4 and incidentally to the substrate 2 is critical for step 9.

Preferably, according to the invention, the thickness of the silicon substrate 2 is between 0.3mm and 1 mm. In addition, if a conductive layer is used, the conductive layer will preferably be gold-based, i.e. made of pure gold or an alloy thereof. Finally, the conductive layer may be deposited, for example, by physical or chemical vapor deposition or any other deposition method.

The method 1 is followed by a second step 5, as shown in fig. 2, the second step 5 being for constructing a mold from a photosensitive resin 6 to form a cavity 8, the base of which is formed by the conductive top surface 4 of the substrate 2.

It is clear that fig. 2 is a simplified diagram and that very complex shapes can be constructed. Therefore, a plurality of cavities 8 not necessarily having the same shape can be configured within the resin 6 in step 5, so that a plurality of micromechanical components 31, 41, 61, 91 can be formed on the same substrate 2.

Step 5 preferably comprises three stages. Step 5 comprises a first stage of depositing a layer 6 of photosensitive resin on the conductive top surface 4 of the substrate 2. This stage can be achieved by spin coating or ultrasonic spraying. The second stage is used to selectively illuminate a portion of the photosensitive resin. It is therefore clear that depending on the properties of the photosensitive resin, i.e. depending on whether the resin is positive or negative, the illumination will be concentrated on the desired future cavity 8 or on parts other than the desired future cavity 8.

Finally, step 5 ends with a third stage for developing the selectively irradiated photosensitive resin 6 to build up the mold, i.e. to harden the remaining photosensitive resin 6 located between the cavities 8. This third stage is generally obtained by chemical etching for forming the cavity 8 and subsequent thermal treatment for hardening any resin still present.

Method 1 is followed by a third step 7 as shown in fig. 3, the third step 7 being for filling the cavity 8 of the mould by electroforming to form the metal part 21, 51, 81. As explained above, the metal parts 21, 51, 81 have the same model in projection. It is therefore clear that the LIGA process does not have any additional implementation difficulties, e.g. forming other functional models at higher heights.

Advantageously according to the invention, thanks to the very precise photolithography of step 5, method 1 makes it possible to manufacture metal parts 21, 51, 81 with high precision of the external dimensions and possibly of the internal dimensions, said dimensions being able to comply with the extremely high tolerances required for micromechanical components in the field of horology. By "internal dimension" it is meant that the openings/or holes in the metal parts 21, 51, 81 may be formed in step 7 directly from any part of the structured resin 6 embedded in the cavity 8.

In order to implement the method for manufacturing the micromechanical component 31, 41, 61, 91 for watch making, it is preferable to use a material that is tribologically advantageous for contact with ruby, steel or brass parts. Furthermore, the sensitivity to magnetic fields needs to be low. Finally, to facilitate step 9, materials that are not too hard are preferred. Thus, in view of the above constraints, it has been found that an alloy formed of nickel and phosphorus (NiP), and in particular an alloy of this type having a proportion of phosphorus substantially equal to 12% (NiP 12), is particularly suitable for filling the cavity 8 in step 7.

Method 1 is followed by step 9, as shown in fig. 4, step 9 being intended to selectively machine a portion of metal component 21, 51, 81 to form micromechanical component 31, 41, 61, 91 having at least two different functional heights. As described above, the thickness of the metal parts 21, 51, 81 having the same profile in projection is then varied to form at least two functional models at a plurality of heights. The required micromechanical components 31, 41, 51, 91 are thus obtained without the need to form a plurality of stacked functional heights by means of a continuous LIGA process.

The importance of each metal part 21, 51, 81 being firmly attached to the top surface 4 of the substrate 2 is therefore evident. In fact, during the machining in step 9, each metal part 21, 51, 81 will be subjected to large stresses. Thus, if the adhesion is insufficient, the method 1 loses the advantage of accurately positioning each metal part 21, 51, 81 on the substrate 2, or may even shear the metal parts 21, 51, 81 to such an extent that they are separated from the substrate 2.

In contrast, in the case of a firm attachment, due to the precise positioning of each metal part 21, 51, 81 on the substrate 2, each metal part 21, 51, 81 still on the substrate 2 can be machined in step 9 with an automated machine which can be programmed with precise dimensions. It is to be noted that although step 9 is used to machine each metal part 21, 51, 81, it is also possible to machine a portion of the structured resin 6 by means of stresses caused by the tools used or the volume to be removed, as indicated by the empty spaces visible in fig. 4.

Finally, the method 1 ends with step 11, shown in fig. 5, step 11 being intended to release the micromechanical components 31, 41, 61, 91 from the substrate 2 and the photosensitive resin 6, as shown in fig. 5. Thus, in a first stage 12, step 11 is used to remove the photosensitive resin 6, and then in a second stage 14 the substrate 2 is removed. Stage 12 may be implemented, for example, by plasma etching, while stage 14 is preferably implemented by chemical etching. In a preferred manner, when a conductive layer is used to form the conductive top surface 4, this layer will also be removed in stage 14 and possibly restored by selective chemical etching.

Of course, the invention is not limited to the examples shown, but can have various modifications and alterations apparent to those skilled in the art. In particular, the method 1 may comprise an optional step 10, interposed between step 7 and step 9, which step 10 is used to flatten the metal parts 21, 51, 81 and the mold formed by the photosensitive resin 6 by grinding. This optional step may be required to ensure the dimensions of the micromechanical component 31, 41, 61, 91, i.e. to ensure that the mould is completely filled.

It is also conceivable to apply a predetermined layer to a plurality of metal parts 21, 51, 81 by their presence on the same substrate 2. In this way, method 1 may comprise an optional stage 16, as shown in fig. 6, between stage 12 and stage 14, which optional stage 16 is used to deposit coating 13 on the micromechanical component 31, 41, 61, 91-substrate 2 assembly. This optional phase 16 may be achieved, for example, by physical or chemical vapor deposition, electroforming, or any other type of deposition.

At the end of phase 14, micromechanical component 31, 41, 61, 91 is thus obtained, partially covered with layer 13, as shown in fig. 7. Preferably, the layer 13 is used to improve the tribological properties of the micromechanical component 31, 41, 61, 91, for example formed of an allotrope of carbon, for example graphite or diamond-like carbon. However, the layer may also have other functions, for example, changing the color or hardness of the micromechanical component 31, 41, 61, 91.

An exemplary timepiece application is shown in the three variants shown in fig. 8 to 16. A first variant, illustrated in fig. 8 to 10, shows the metal part 21 obtained in step 7 of the method 1. The components are generally represented as a star with double gear rings 22, 24 including a central bore 26. At the end of step 11 of method 1, it is thus possible to obtain micromechanical components in the form of escape wheel 31 shown in fig. 9 or in the form of escape wheel 41 shown in fig. 10, both of which are monolithic and comprise at least two different functional levels that may or may not be coated with layer 13.

Thus, in the case of fig. 9, the eight arms 33 of the metal part 21 have been machined so that the end of each arm forms a tooth 22 at a lower height. The remaining part of the metal part 21 remains unchanged, in particular the hole 26 and the eight arms 35, each end of said arms 35 forming a second tooth 24 at a lower level and at a higher level.

Alternatively, in the case of fig. 10, the eight arms 43 of the metal part 21 have been machined so that the end of each arm forms a tooth 22 at a lower height. Likewise, the area surrounding the hole 26 has been machined so that the hole 26 is only present in the lower level. Finally, eight arms 45 and a portion of the higher height have been machined so that only the ends of the arms 45 remain, while the second teeth 24 remain at the lower and higher heights.

The second variant shown in fig. 11 to 13 shows the metal part 51 obtained in step 7 of the method 1. The member 51 is substantially in the form of an H-shaped member having two parallel portions 53, 55 connected to each other by a transverse portion 57. As shown in fig. 11, the transverse portion 57 comprises a central portion 56 which is more flared in cross-section than the rest of said transverse portion.

At the end of step 11 of method 1, it is thus possible to obtain a micromechanical component in the form of fork 61 shown in fig. 12, which is monolithic and comprises at least two different functional levels that may or may not be coated with layer 13. Thus, the metal part 51 is machined to two depths, i.e. to three functional heights, on two parallel portions 53, 55 and to a single depth on the non-flared part of the transverse portion 57.

In the example of fig. 12, the fork 61 therefore comprises only the entire parallel portion 53, 55 at the lower level, to form two horns 62, 64. The intermediate height only partially includes the parallel portions 53, 55 and the non-flared portions of the transverse portion 57 to form shoulders 63 and 65. Finally, only the central portion 56 of the lateral portion 57 of the metal part 51 is preserved to form a column only in the top level.

As seen in fig. 13, fork 61 may then be installed by pressing centerpost component 56 into hole 76 of lever 73 to form pallet fork 71. The stem 73 with the integrated prongs 78 may be obtained by the LIGA process. In addition to fork 61, lever 73 can be provided with a pallet shaft 79 and pallet stones 75, 77 on arms 72, 74 of the lever. Obviously, according to the invention, it is also advantageously possible to obtain all or part of pallet 71 using method 1 according to the invention. For example, pallet-stones 75 and 77, rod 73, dart 78 and hole 76 can be integral and obtained with method 1 of the invention.

A third variant, shown in fig. 14 to 16, shows a metal part 81 obtained in step 7 of method 1. The member 81 is substantially in the form of a U-shaped member having two parallel portions 83, 85 connected to each other by a base 87. As shown in fig. 14, the base portion is thicker than the parallel portions to form a substantially cross-shaped opening 86.

At the end of step 11 of method 1, it is thus possible to obtain a micromechanical component in the form of fork 91 shown in fig. 15, which is monolithic and comprises at least two different functional levels that may or may not be coated with layer 13. Thus, the metal part 81 is machined to a single depth on the two parallel portions 83, 85 and to two depths on the base 87, i.e. to form three functional heights.

In the example of fig. 15, the fork 91 therefore comprises only the entire parallel portion 83, 85 at a lower height, to form two horns 92, 94. The intermediate height only partially includes the base 87, forming a column 93 that is constricted by a shoulder 95 to form the top height. Finally, the constriction serves to free the opening 86 at the higher level and to form four posts 96, 97, 98, 99.

As seen in fig. 15, the fork 91 can then be mounted by pressing the posts 96, 97, 98, 99 into the holes 106 of the rod 103, so as to form the pallet 101. The stem 103 with the integrated prongs 108 may be obtained by the LIGA process. In addition to fork 91, lever 103 can also be provided with an escapement fork shaft and pallet stones on arms 102, 104 of the lever, as in the second variant. Obviously, according to the invention, it is also advantageously possible to obtain all or part of pallet 101 using method 1 according to the invention. For example, pallet-stone, rod 103, dart 108 and hole 106 can be integral and obtained with method 1 of the invention.

As a result, it is advantageous according to the invention that the outer dimensions 22, 24, 53, 55, 56, 83, 85 and possibly the inner dimensions 26, 86 remain highly accurate due to the LIGA process, and the rest of the integrated micromechanical component 31, 41, 61, 91 enjoys machining accuracy to save manufacturing costs. A one-piece micromechanical component 31, 41, 61, 91 comprising at least two different functional heights is thus obtained, which is easier to manufacture and at the same time maintains a high precision of the outer part 22, 24, 53, 55, 56, 83, 85 and possibly of the inner part 26, 86.

The invention is of course not limited to the examples shown, but can have many variations and modifications apparent to a person skilled in the art. In particular, in the field of horology, the micromechanical member 31, 41, 61, 91 is in no way limited to all or part of a wheel set or pallet. Other timepiece components, in particular a bridge, a plate or a balance, are envisaged.

Furthermore, as mentioned above, it is also possible to envisage applying the invention to other fields than watchmaking, for example the aeronautical or automotive industry.

Claims (11)

1. Method (1) for manufacturing a micromechanical component (31, 41, 61, 91) of unitary type comprising at least two different functional heights, characterized in that it comprises the following steps:

a) forming a silicon substrate (2), a top surface (4) of which is electrically conductive;

b) constructing a mould with a photosensitive resin (6) to form a cavity (8) the base of which is formed by the conductive top surface (4);

c) filling the cavity (8) of the mould by electroforming to form a metal part (21, 51, 81);

d) -selectively machining a portion of said metal part (21, 51, 81) to form a unitary micromechanical component (31, 41, 61, 91) having at least two different functional heights;

e) -releasing the micromechanical component (31, 41, 61, 91) from the silicon substrate (2) and the photosensitive resin (6).

2. The method (1) according to claim 1, wherein the top surface (4) is made electrically conductive by doping the silicon substrate (2) and/or by depositing an electrically conductive layer on the silicon substrate (2).

3. The method (1) according to claim 1, wherein the thickness of the silicon substrate (2) is between 0.3mm and 1 mm.

4. Method (1) according to claim 1, characterized in that said step b) comprises the following phases:

f) depositing a layer of photosensitive resin (6) on the conductive top surface (4) of the silicon substrate (2);

g) selectively irradiating a portion of the photosensitive resin (6);

h) developing the photosensitive resin (6) to construct the mold.

5. A method (1) according to claim 1, wherein the metal part (21, 51, 81) is formed of a nickel phosphorous base (NiP, NiP 12).

6. Method (1) according to claim 1, characterized in that it comprises, between said steps c) and d), the following steps:

i) -flattening said mould and said metal part (21, 51, 81) by grinding.

7. Method (1) according to claim 1, characterized in that said method (1) comprises, in said step e), the following phases:

j) removing the photosensitive resin;

k) removing the silicon substrate;

and the method (1) further comprises, between the phase j) and the phase k), the following phases:

l) depositing a coating (13) on the micromechanical component (31, 41, 61, 91) -substrate (2) assembly.

8. Method (1) according to claim 7, characterized in that said phase i) is achieved by physical or chemical vapour deposition.

9. Method (1) according to claim 7, characterized in that said stage i) is achieved by electroforming.

10. Method (1) according to claim 1, characterized in that a plurality of micromechanical components (31, 41, 61, 91) are formed on the same silicon substrate (2).

11. Timepiece, characterized in that it comprises a one-piece micromechanical component (31, 41, 61, 73, 91, 103) according to any one of claims 1 to 10, comprising at least two different functional heights.