MOULD FOR ELECTROPLATING AND ITS MANUFACTURING PROCESS

Abstract

A process for manufacturing a mould including: a) providing a first substrate made of photosensitive glass of thickness of at least equal to the height of the mould, b) illuminating the first substrate with UV rays through a mask the windows of which correspond to the depression of the mould in order to create illuminated zones, c) carrying out a heat treatment on the first substrate obtained in step b) in order to crystallize the illuminated zones, d) providing a second substrate having at least one conductive layer on its surface, e) joining the first substrate obtained in step c) with the second substrate so that the conductive layer is located between the first substrate and the second substrate, f) removing the illuminated and crystallized zones of the first substrate so as to uncover the conductive layer, forming a cavity with sidewalls and a bottom occupied by the conductive layer of the mould.

Description

This application claims priority from European patent application No. 17195237.7 filed on Oct. 6, 2017, the entire disclosure of which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a mould intended to manufacture a micromechanical part by electroplating and to its manufacturing process.

BACKGROUND OF THE INVENTION

Electroplating has been used and known for a long time. LIGA processes (LIGA being the well-known abbreviation of the German expression “Röntgenlithographie, Galvanoformung & Abformung”) were developed in the 80s and have proved to be very advantageous for manufacturing high-precision metal microstructures.

The principle of the LIGA technique consists in depositing a layer of photoresist on a conductive substrate or a substrate coated with a conductive layer; in carrying out, through a mask corresponding to the outline of the desired microstructure, an x-ray irradiation by means of a synchrotron; in developing, i.e. in removing via physical or chemical means, the sections of the photoresist layer that were not exposed, in order to define a mould having the outline of the microstructure; in galvanically depositing a metal, typically nickel, in the photoresist mould; then in removing the mould in order to release the microstructure.

The quality of the microstructures can hardly be criticized, but the need to employ an expensive piece of equipment (synchrotron) makes this technique incompatible with mass production of microstructures that must have a low unit cost.

For this reason analogous processes based on the LIGA process but using photoresists that are sensitive to UV have been developed. Such a process is for example described in the publication by A. B. Frazier et al, entitled “Metallic Microstructures Fabricated Using Photosensitive Polyimide Electroplating Molds”, Journal of Microelectromechanical systems, Vol. 2, N deg. 2, June 1993, for the manufacture of metal structures by electroplating metal in resist moulds made of polyimide-based photoresist. This process comprises the following steps:

• • providing a substrate including a conductive surface for seeding a subsequent electroplating step,
  • applying to said conductive seeding surface a (polyimide) photoresist layer,
  • irradiating the photoresist layer with UV through a mask corresponding to the outline of the desired microstructure,
  • developing the portions of the photoresist layer that were not irradiated by dissolving them so as to obtain a photoresist mould,
  • galvanically depositing nickel in the open portion of the mould up to the height of the latter,
  • separating the obtained metal structure from the substrate, and
  • removing the photoresist mould.

This process is widely used in the field of watch and clock making to manufacture precision components. However, it proves to be the case that, of the numerous timepiece components produced, many have a “spring” function, the spring working in the plane of the component or of the movement. The combination of the parameters “thickness of the component—sought-after spring constant” may thus lead to very narrow spring-wire geometries (of a few tens of microns, or even less) for thicknesses of a several hundred microns.

Similarly, sometimes component design requires narrow slits to be defined between two portions of the component, a mobile portion and a fixed portion for example.

In these two cases, the conventional UV-LIGA technique reaches its limits, both in terms of the aspect ratio (height/width ratio) of the gap to be filled with metal during the growth operation, and in terms of the aspect ratio of the resist separating two nearby geometries.

Furthermore, guaranteeing that the photoresist preserves its geometry (verticalness, size, etc.) in the galvanic bath is difficult, this handicapping the robust manufacture of these specific timepiece components.

There is therefore a need for a process allowing such drawbacks to be overcome.

SUMMARY OF THE INVENTION

The aim of the present invention is to remedy the drawbacks associated with the conventional UV-LIGA process by providing an alternative mould allowing the risks of deformation of the resist forming the mould used in said conventional UV-LIGA process to be overcome.

Another aim of the invention is to provide a mould allowing micromechanical parts having high-aspect-ratio geometries to be produced by electroforming.

To this end, the invention relates to a process for manufacturing a mould comprising the following steps:

• • a) providing a first substrate made of photosensitive glass of thickness of at least equal to the height of the mould
  • b) illuminating said first substrate with UV rays through a mask the windows of which correspond to the depression of the mould in order to create illuminated zones
  • c) carrying out a heat treatment on the first substrate obtained in step b) in order to crystallize the illuminated zones
  • d) providing a second substrate having at least one conductive layer on its surface
  • e) joining the first substrate obtained in step c) with the second substrate so that the conductive layer is located between the first substrate and the second substrate
  • f) removing the illuminated and crystallized zones of the first substrate so as to uncover the conductive layer, in order to form at least one cavity the sidewalls of which and the bottom occupied by the conductive layer of which form said mould.

Such a method allows a mould made of glass, which is more rigid and insensitive to the effects of the galvanic growth bath used to form a micromechanical part using said mould, to be produced.

The invention also relates to a process for manufacturing by electroplating a metal micromechanical part, comprising the following steps:

• • g) manufacturing a mould of said micromechanical part using the process for manufacturing a mould as defined above
  • h) filling the mould with a metal by galvanic growth from the conductive layer in order to form said micromechanical part
  • i) releasing the micromechanical part obtained in step h) from its mould.

The invention also relates to a multi-mould plate intended to manufacture at least one micromechanical part by electroplating, including a first substrate made of photosensitive glass of thickness at least equal to the height of the micromechanical part, a second substrate securely fastened to the first substrate, at least one conductive layer provided between the first substrate and second substrate, the first substrate including at least one mould for the micromechanical part, which mould is formed by a cavity formed in said first substrate and the bottom of which is occupied by the conductive layer, allowing a metal to be deposited by galvanic growth in said cavity in order to form said micromechanical part.

BRIEF DESCRIPTION OF THE DRAWINGS

Other particularities and advantages of the invention will become more clearly apparent from the description that is given thereof below, by way of completely nonlimiting indication, with reference to the appended drawings, in which:

FIGS. 1 to 5 are representations of the successive steps of a process for manufacturing a micromechanical part according to a first embodiment of the invention; and

FIGS. 6 to 11 are representations of successive steps of a process for manufacturing a micromechanical part according to a second embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to FIGS. 1 to 5, the present invention relates to a process for manufacturing a micromechanical part 1, 1′ by electroplating. The process preferably includes a process for manufacturing a mould 3, 3′, followed by an electroplating step and a step of releasing the part 1, 1′ from said mould 3, 3′, respectively.

The process for manufacturing a mould 3, 3′ according to the invention includes successive steps intended to manufacture a mould 3, 3′:

A first step a) of the process for manufacturing the mould 3, 3′ consists in providing a first substrate 5 made of photosensitive glass of thickness at least equal to the height of the mould.

Such a photosensitive glass is for example available from Schott A. G. under the trade name Foturan®, or from Hoya Corp. under the reference PEG3® or from LifeBioScience Inc. under the trade name Apex™.

Advantageously according to the invention, the use of photosensitive glass makes it possible to generate in the glass a wide variety of geometries than etching silicon- or ceramic-based materials.

The second step b) of the process for manufacturing the mould 3, 3′ consists in illuminating the first substrate 5 with UV rays, at a wavelength corresponding to the photosensitive glass, through a mask that is opaque at said wavelength and the windows of which correspond to the depressions of the moulds to be produced, in order to create illuminated zones 7, 7′. Thus, depending on the amount, orientation and distribution of the illumination, only those zones 7, 7′ of the first substrate 5 which are exposed to the UV radiation are structured to form the depressions of the moulds to be produced. The illumination source may for example be a UV lamp the spectral distribution peak of which is located between 200 and 400 nm.

The third step c) of the process of manufacturing the mould 3, 3′ consists in carrying out a heat treatment on the first substrate 5 obtained in step b) in order to crystallize the illuminated zones 7, 7′, as shown in FIG. 1. This heat treatment is carried out at high temperature, preferably between 500° C. and 600° C. This heat treatment allows the illuminated zones 7, 7′ to be made more selective with a view to removal thereof in step f), as will be seen below.

The fourth step d) of the process for manufacturing the mould 3, 3′ consists in providing a second substrate 8, said substrate comprising at least one conductive layer 10 on its surface. Advantageously, the conductive layer is formed by depositing, on the second substrate 8, a layer 10 of a metal chosen from the group comprising chromium, titanium, and gold, gold being preferred. The conductive layer 10 preferably has a thickness comprised between 0.1 μm and 0.5 μm.

The metal layer 10 has the double advantage of, on the one hand, being conductive in order to allow the electroplating step h) to be implemented and, on the other hand, of allowing the second substrate to be joined to the first substrate by soldering in step e), as will be described below.

The second substrate 8 is preferably made from a material that is resistant to acid attack. Advantageously, the second substrate 8 is silicon-based.

The fifth step e) of the process for manufacturing the mould 3, 3′ consists in joining the first substrate 5 comprising the illuminated and crystallized zones 7, 7′, i.e. the substrate such as obtained in step e), to the second substrate 8 in such a way that the conductive layer 10 is located between the first substrate 5 and the second substrate 8, as shown in FIG. 2.

In this first variant of the invention, the two substrates 5 and 8 are joined by soldering by way of the conductive metal layer 10.

The sixth step f) of the process for manufacturing the mould 3, 3′ consists in removing the zones 7, 7′ illuminated in step b) and crystallized in step c) of the first substrate 5, so as to uncover the conductive layer 10 in order to form at least one cavity 12, 12′ the vertical sidewalls of which and the bottom occupied by the conductive layer 10 of which form said mould 3, 3′, as shown in FIG. 3.

Advantageously, step f) of removing the illuminated and crystallized zones 7, 7′ of the first substrate 5 is carried out by chemical etching, and preferably by dissolving with hydrofluoric acid. For example, this chemical etch may be carried out in an ultrasonic bath of about 10% hydrofluoric acid at room temperature.

A mould 3, 3′ the sidewalls of which are made of photosensitive glass is thus produced.

It will be noted that, contrary to conventional practice, the process according to the invention does not comprise a final higher-temperature (600-700° C.) crystallizing step for completely crystallizing the remaining photosensitive glass.

The present invention also relates to a process for manufacturing by electroplating a metal micromechanical part 1, 1′. Said process comprises a step g) that consists in manufacturing a mould 3, 3′ for said micromechanical part 1, 1′ using the process for manufacturing a mould 3, 3′ described above. The following step h) consists in filling the mould 3, 3′ with a metal by galvanic growth from the conductive layer 10 in order to form said micromechanical part 1, 1′, as shown in FIG. 4.

The metal is advantageously chosen from the group comprising nickel, copper, gold or silver, and the alloys thereof, such as gold-copper, nickel-cobalt, nickel-iron, and nickel-phosphorus.

Preferably, the height of the mould is slightly larger than the height of the part to be manufactured and is equal to the thickness of the first substrate 5. The height of the micromechanical part is comprised between 50 μm and 500 μm. The use of a substrate made of photosensitive glass allows, depending on the thickness, parts to be obtained the minimum width of certain geometries of which may be comprised between 10 μm and 30 μm, and hence such particular geometries of micromechanical parts obtained using the process of the invention may have a high aspect ratio comprised between 1 and 20. Such a micromechanical part 1, 1′ could, for example, be a return spring, a jumper-spring, a single-piece flexible guiding system, a compliant geometry for decreasing play, etc.

The electroforming conditions, in particular the composition of the baths, the geometry of the system, the voltages and the current densities, are chosen for each metal or alloy to be electroplated using techniques that are well known in the art of electroforming (see for example Di Bari G. A. “electroforming” Electroplating Engineering Handbook 4th Edition, edited by L. J. Durney, published by Van Nostrand Reinhold Company Inc., N.Y., USA 1984).

It is possible, in a subsequent step h′), to rectify the metal deposit electroformed with the first substrate 5. This step may be carried out by grinding and polishing in order to directly obtain microstructures having a planar upper surface in particular having a surface finish compatible with the requirements of the watch- and clock-making industry vis-à-vis the production of upmarket movements.

The following step i), which is illustrated in FIG. 5, consists in releasing the micromechanical part 1, 1′ obtained in step h) or h′) from its mould 3, 3′. To this end, chemical etching processes (for example HF processes for photosensitive glass, KOH processes for silicon) may be employed.

The micromechanical part 1, 1′ thus released may be used directly or where appropriate after suitable machining.

FIGS. 6 to 11 show a second variant of implementation of the process for manufacturing a mould according to the invention. This process is practically identical to the first variant described above, with the exception of a steps e) and f). The first substrate 5 comprising the illuminated and crystallized zones 7, 7′, as shown in FIG. 6, is obtained in steps a) to c) such as described above. In this second variant, the first substrate 5 and the second substrate 8 are joined in step e) by temporarily soldering the first substrate 5 to the second substrate 8 by means of a resist layer 16 provided between said first substrate 5 and the conductive layer 10, as shown in FIG. 7. To do this, the same type of resist as that used in semiconductor fabrication processes may be used for the temporary soldering steps. The resist layer 16 in question has a thickness comprised between 2 μm and 10 μm.

Furthermore, in this second variant, the step f) comprises removing the illuminated and crystallized zones 7, 7′ of the first substrate 5 so as to uncover the resist layer 16 as shown in FIG. 8. Next, step f) comprises a substep f′) of removing the uncovered resist layer 16 from the bottom of the cavity 12, 12′ after the illuminated and crystallized zones 7, 7′ of the first substrate 5 have been removed, so as to uncover the conductive layer 10, as shown in FIG. 9.

The micromechanical part 1, 1′ is then produced as in the electroplating manufacturing process described above, as shown in FIGS. 10 and 11. The step i) of releasing the part 1, 1′ from its mould 3, 3′ is carried out using chemical etching processes (for example HF processes for photosensitive glass, and KOH processes for silicon).

The processes according to the present invention allow micromechanical parts having narrow and rigid geometries to be produced with a high precision in batch mode.

Specifically, in a particularly advantageous manner, several moulds 3, 3′ are produced in the same first substrate 5, 5′. These moulds are not necessarily identical to one another. A multi-mould plate 14 is then obtained as illustrated in FIG. 3.

This multi-mould plate 14 is intended to be used to manufacture at least one micromechanical part 1, 1′ by electroplating. According to the invention, it includes a first substrate 1, 1′ made of photosensitive glass of thickness at least equal to the height of the micromechanical part 1, 1′, a second substrate 8 securely fastened to the first substrate 5, at least one conductive layer 10 provided between the first and second substrates 5, 8, and optionally a resist layer 16 provided between the first substrate 5 and the conductive layer 10. The first substrate 5 includes at least one mould 3, 3′ for the micromechanical part 1, 1′, which mould is formed by a cavity 12, 12′ formed in said first substrate 5 and the bottom of which is occupied by the conductive layer 10, allowing a metal to be deposited in said cavity 12, 12′ by galvanic growth with a view to forming said micromechanical part 1, 1′. The first and second substrates 5 and 8, the conductive layer 10 and the resist layer 16 are such as defined above.

In addition, the moulds obtained according to the invention are made of photosensitive glass, which is more rigid then the resists conventionally used to form such moulds, and which is insensitive to the effects of galvanic growth baths. The process for manufacturing micromechanical parts according to the invention is therefore particularly robust, in particular for the manufacture of high-aspect-ratio parts.

The processes according to the invention also allow the galvanic growth in step h) to be easily initiated by virtue of the use of a conductive layer 10 of good quality at the bottom of the mould 3, 3′.

Furthermore, the process for manufacturing micromechanical parts according to the invention is simple to implement because it does not require a complex and localized deposition of metal (stencil mask) to form the layer used to initiate the galvanic growth.

Lastly, the process for manufacturing micromechanical parts according to the invention allows geometries etched by Bosch® DRIE to be avoided. Hence scalloping does not occur, avoiding the need for an additional smoothing step.

Claims

1. A process for manufacturing a mould comprising the following steps:

a) providing a first substrate made of photosensitive glass of thickness of at least equal to the height of the mould

b) illuminating said first substrate with UV rays through a mask having windows which correspond to the depression of the mould in order to create illuminated zones

c) carrying out a heat treatment on the first substrate obtained in step b) in order to crystallize the illuminated zones

d) providing a second substrate having at least one conductive layer on its surface

e) joining the first substrate obtained in step c) to the second substrate so that the conductive layer is located between the first substrate and the second substrate

f) removing the illuminated and crystallized zones of the first substrate so as to uncover the conductive layer, in order to form at least one cavity the sidewalls of which and the bottom occupied by the conductive layer of which form said mould.

2. The process according to claim 1, wherein the second substrate is based on silicon.

3. The process according to claim 1, wherein the conductive layer is formed by depositing, on the second substrate, a layer of a metal chosen from the group consisting of chromium, titanium and gold.

4. The process according to claim 1, wherein the step e) of joining the first substrate and second substrate is carried out by soldering the conductive layer of the second substrate to the first substrate.

5. The process according to claim 1, wherein the step e) of joining the first substrate and second substrate is carried out by soldering the first substrate to the second substrate by means of a resist layer provided between the first substrate and the conductive layer.

6. The process according to claim 5, wherein step f) comprises a substep f′) of removing the resist layer uncovered in the cavity after removal of the illuminated and crystallized zones of the first substrate, so as to uncover the conductive layer.

7. The process according to claim 1, wherein the step f) of removing the illuminated and crystallized zones of the first substrate is carried out by chemical etching.

8. The process according to claim 1, wherein a plurality of moulds are produced in the same first substrate.

9. A process for manufacturing by electroplating a metal micromechanical part, wherein it comprises the following steps:

g) manufacturing a mould of said micromechanical part using the process for manufacturing a mould according to claim 1

h) filling the mould with a metal by galvanic growth from the conductive layer in order to form said micromechanical part

i) releasing the micromechanical part obtained in step h) from its mould.

10. A multi-mould plate intended to manufacture at least one micromechanical part by electroplating, wherein it includes a first substrate made of photosensitive glass of thickness at least equal to the height of the micromechanical part, a second substrate securely fastened to the first substrate, at least one conductive layer provided between the first substrate and second substrate, the first substrate including at least one mould for the micromechanical part, which mould is formed by a cavity formed in said first substrate and the bottom of which is occupied by the conductive layer, allowing a metal to be deposited by galvanic growth in said cavity in order to form said micromechanical part.

11. The multi-mould plate according to claim 10, wherein the second substrate is based on silicon.

12. The multi-mould plate according to claim 10, wherein the conductive layer is a layer of a metal chosen from the group consisting of chromium, titanium and gold.

13. The multi-mould plate according to claim 10, wherein it comprises a resist layer provided between the first substrate and the conductive layer.