CH714227A2 - Mold for electroplating and its manufacturing process. - Google Patents

Abstract

The invention relates to a method for manufacturing a mold (3, 3 ') comprising the following steps: a) providing a first substrate (5) made of photosensitive glass with a thickness at least equal to the height of the mold (3, 3') b) illuminating said first substrate (5) by UV radiation through a mask whose windows correspond to the cavity of the mold (3, 3 ') to create illuminated areas (7, 7') c) thermally treating the first substrate (5) obtained in step b) to crystallize the illuminated areas (7, 7 ') d) providing a second substrate (8) having at least one conductive layer (10); ) at the surface e) assembling the first substrate (5) obtained in step c) to the second substrate (8) so that the conductive layer (10) lies between the first (5) and second (8) substrates f ) removing the illuminated and crystallized areas (7, 7 ') of the first substrate (5) so as to expose the conductive layer (10) to form at least one cavity (12, 12 ') whose side walls and the bottom occupied by the conductive layer (10) constitute said mold (3, 3'). The invention relates to the field of micromechanical parts in particular for watch movements.

Description

Description

FIELD OF THE INVENTION [0001] The invention relates to a mold for manufacturing a micromechanical part by electroplating and its manufacturing process.

BACKGROUND OF THE INVENTION [0002] Electroplating has been used for a long time. The processes of the LIGA type (well-known abbreviation from the German "RöntgenLithographie, Galvanoformung & Abformung") developed in the 1980s have proved to be of interest for the manufacture of high precision metal microstructures.

In principle, the LIGA technique involves depositing on a conductive substrate or coated with a conductive layer, a layer of a photosensitive resin, to be carried out through a mask corresponding to the contour of the desired microstructure irradiation X by means of a Synchrotron; to develop, that is to say to remove by physical or chemical means the portions of the non-irradiated photoresist layer to define a mold having the contour of the microstructure, to galvanically deposit a metal, typically nickel, in the photosensitive resin mold and then remove the mold to release the microstructure.

The quality of the microstructures obtained is not critical, but the need to implement expensive equipment (Synchrotron) makes this technique little compatible with a mass production of microstructures to have a low unit cost.

This is why on the basis of this LIGA process have been developed analogous processes but using UV photosensitive resins. Such a method is for example described in 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 electrodeposition of metal in polyimide-based photosensitive resin molds. This process comprises the following steps: - providing a substrate comprising a conducting conductive surface for a subsequent electroplating step, - applying a layer of photoresist (polyimide) to said conductive conducting surface, - irradiating with UV the photosensitive resin layer through a mask corresponding to the contour of the desired microstructure, - developing by dissolving the non-irradiated portions of the photosensitive resin layer so as to obtain a photosensitive resin mold, - galvanically depositing nickel in the part open the mold up to the height thereof, - separate the metal structure obtained from the substrate, and - eliminate the photosensitive resin mold.

This method is widely used in the field of watchmaking for the manufacture of its precision components. However, it turns out that many of the watch components made include a function "spring" spring operating in the plane of the component or movement. The combination of the parameters "thickness of the component-spring stiffness sought" can thus lead to very narrow leaflet geometries (of a few tens of microns or less) for thicknesses of several hundred microns.

Similarly, it happens that the design of the components requires to be able to define narrow slots between two parts of the component, a mobile, the other fixed, for example.

In both cases, the conventional LIGA-UV method has limits, both in terms of aspect ratio (height / width ratio) of the gap to be filled with metal during growth, and the aspect ratio. of resin separating two close geometries.

In addition, to ensure that the photosensitive resin retains its geometries (verticality, size, ...) in the galvanic bath remains delicate, which handicaps the robust manufacture of these specific watch components.

There is therefore a need for a method to overcome such drawbacks. SUMMARY OF THE INVENTION [0011] The object of the present invention is to overcome the disadvantages associated with the conventional LIGA-UV process, by proposing an alternative mold making it possible to overcome the risks of deformation of the resin forming the mold used in said conventional LIGA-UV process.

Another object of the invention is to provide a mold for producing micromechanical parts having high aspect ratio geometries by electroforming.

For this purpose, the invention relates to a method of manufacturing a mold comprising the following steps: a) to provide a first photosensitive glass substrate of thickness at least equal to the height of the mold b ) illuminating said first substrate by UV rays through a mask whose windows correspond to the cavity of the mold to create illuminated areas; c) performing a heat treatment of the first substrate obtained in step b) to crystallize the illuminated areas; d) providing a second substrate having at least one surface conductive layer; e) assembling the first substrate obtained in step c) to the second substrate so that the conductive layer is between the first and second substrates; illuminated and crystallized areas of the first substrate so as to expose the conductive layer to form at least one cavity whose side walls and the bottom occupied by the conductive layer; said mold.

Such a method allows for a glass mold, more rigid and insensitive to the effects of the galvanic growth bath used to form a micromechanical part from said mold.

The invention also relates to a method of manufacturing by electroplating a micromechanical component, comprising the following steps: g) manufacturing a mold of said micromechanical component according to the method of manufacturing a mold defined hereinbelow; sus-h) filling the mold with a metallic material by galvanic growth from the conductive layer to form said micromechanical part i) release the micromechanical part obtained in step h) of its mold.

The invention also relates to a molding plate intended to manufacture at least one micromechanical piece by electroplating, comprising a first photosensitive glass substrate of thickness at least equal to the height of the micromechanical part, a second substrate secured to the first substrate, at least one conductive layer provided between the first and second substrates, the first substrate comprising at least one mold of the micromechanical part consisting of a cavity formed in said first substrate and whose bottom is occupied by the conductive layer , for depositing by galvanic growth a metal material in said cavity to form said micromechanical part.

BRIEF DESCRIPTION OF THE DRAWINGS [0017] Other particularities and advantages will become clear from the description which is given hereinafter, by way of indication and in no way limitative, with reference to the appended drawings, in which: FIGS. 1 to 5 are representations of the successive steps of a method of manufacturing a micromechanical part according to a first embodiment of the invention; and figs. 6 to 11 are representations of the successive steps of a method of manufacturing a micromechanical part according to a second embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0018] Referring to FIGS. 1 to 5, the present invention relates to a method of manufacturing a micromechanical part 1,1 'by electroplating. The method preferably comprises a method of manufacturing a mold 3, 3 ', followed by an electroplating step and a step of releasing the workpiece 1,1' from said mold 3, 3 ', respectively.

The method of manufacturing a mold 3, 3 'according to the invention comprises successive steps for manufacturing a mold 3, 3': [0020] A first step a) of the mold manufacturing process 3, 3 consists in providing a first substrate 5 of photosensitive glass with a thickness at least equal to the height of the mold.

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

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

The second step b) of the manufacturing process of the mold 3, 3 'consists of illuminating the first substrate 5 by UV rays, at a wavelength corresponding to the photosensitive glass, through a mask opaque to said length of light. wave and whose windows respectively correspond to the footprints molds to achieve to create illuminated areas 7, 7 '. Thus, depending on the quantity, the orientation and the distribution of the illumination, only the zones 7, 7 'of the first substrate 5 exposed to UV rays are structured to form the imprints of the molds to be produced. The illumination source may for example be a UV lamp whose spectral distribution peak is between 200 and 400 nm.

The third step c) of the manufacturing process of the mold 3, 3 'is to perform a heat treatment of the first substrate 5 obtained in step b) to crystallize the illuminated areas 7, 7', as shown in FIG. . This heat treatment is carried out at a high temperature, preferably between 500 ° C. and 600 ° C. This heat treatment makes the illuminated areas 7.7 'more selective for their elimination according to step f) as will be seen below.

The fourth step d) of the manufacturing process of the mold 3, 3 'is to provide a second substrate 8, said substrate having at least one conductive layer 10 at the surface. Advantageously, the conductive layer is formed by a deposit on the second substrate 8 of a layer 10 of a metallic material selected from the group comprising chromium, titanium, and gold, gold being preferred. The conductive layer 10 preferably has a thickness of between 0.1 μm and 0.5 μm.

The metal layer 10 has the dual advantage of being conductive to allow the implementation of the electroplating step h) and secondly to allow the assembly by welding of the second substrate to first substrate according to step e) as will be described hereinafter.

The second substrate 8 is made of a material preferably resistant to acid attacks. Advantageously, the second substrate 8 is based on silicon.

The fifth step e) of the manufacturing process of the mold 3, 3 'consists in assembling the first substrate 5 comprising the illuminated and crystallized zones 7.7', as obtained in step c), to the second substrate 8 so that the conductive layer 10 is between the first substrate 5 and the second substrate 8, as shown in FIG. 2.

In this first variant of the invention, the assembly of the two substrates 5 and 8 is made by welding through the metal conductive layer 10.

The sixth step f) of the manufacturing process of the mold 3, 3 'is to eliminate the zones 7, 7' illuminated in step b) and crystallized in step c) of the first substrate 5, so as to make appearing the conductive layer 10 to form at least one cavity 12, 12 'whose vertical side walls and the bottom occupied by the conductive layer 10 constitute said mold 3, 3', as shown in FIG. 3.

Advantageously, step f) of removing the illuminated and crystallized zones 7, T of the first substrate 5 is carried out by etching, preferably by dissolution with hydrofluoric acid. For example, this etching can be carried out in a bath of about 10% hydrofluoric acid at room temperature and under ultrasound. A mold 3, 3 'whose side walls are made of photosensitive glass is thus formed.

It should be noted that, contrary to the usual practice, the method according to the invention does not include a final crystallization step at higher temperature (600-700 ° C) to fully crystallize the remaining photosensitive glass.

The present invention also relates to a method of manufacturing by electroplating a metal micromechanical part 1,1 '. Said method comprises a step g) which consists in manufacturing a mold 3, 3 ', of said micromechanical part 1,1' according to the method of manufacturing a mold 3, 3 'described above. The following step h) consists of filling the mold 3, 3 'with a metallic material by galvanic growth from the conductive layer 10 to form said micromechanical part 1,1', as represented in FIG. 4.

The metallic material is advantageously chosen from the group comprising nickel, copper, gold or silver, and their alloys, such as alloy gold-copper, nickel-cobalt, nickel-iron, and nickel-phosphorus.

Preferably, the height of the mold is slightly greater 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 between 50 pm and 500 pm. The use of a photosensitive glass substrate makes it possible, depending on the thickness, to produce parts whose minimum width of certain geometries can be between 10 μm and 30 μm, such that these particular geometries of micromechanical parts obtained according to the The method of the invention may have a high aspect ratio of between 1 and 20. Such a micromechanical part 1,1 'could, for example, be a return spring, a jumper, a one-piece flexible guide system, a compiling game computational geometry, etc.

The electroforming conditions, in particular the composition of the baths, the geometry of the system, the voltages and current densities, are chosen for each metal or alloy to be electro-deposited according to the techniques well known in the art of the art. electroforming (see for example Di Bari GA "electroforming" Electroplating Engineering Handbook 4th Edition written by LJ Durney, published by Van Nostrand Reinhold Company Inc., NY USA 1984).

It is possible, in a subsequent step h '), to proceed to the leveling of the electro-formed metal deposition with the first substrate 5. This step can be done by abrasion and polishing in order to directly obtain microstructures having a planar upper surface having in particular a surface state compatible with the requirements of the watch industry for the production of high-end movement.

The next step i) illustrated in FIG. 5 is to release the micromechanical part 1,1 'obtained in step h) or h') of its mold 3, 3 '. For this purpose, chemical etching processes can be used (for example HF for photosensitive glass, KOH for silicon).

The micromechanical part 1,1 'and released can be used directly or where appropriate after appropriate machining.

Figs. 6 to 11 represent a second variant of implementation of the method of manufacturing a mold according to the invention. This method is practically identical to the first variant described above, with the exception of steps e) and f). The first substrate 5 comprising the illuminated and crystallized areas 7, 7 ', as shown in FIG. 6, is obtained according to steps a) to c) as described above. In this second variant, the assembly of the first substrate 5 with the second substrate 8 according to step e) is performed by temporarily welding the first substrate 5 with the second substrate 8 by means of a resin layer 16 provided between said first substrate substrate 5 and the conductive layer 10, as shown in FIG. 7. To do this, one can use for example the same type of resin as that used in semiconductor manufacturing processes for temporary welding steps. The objective resin layer 16 has a thickness of between 2 μm and 10 μm.

In addition, in this second variant, step f) comprises the elimination of the illuminated and crystallized zones 7, 7 'of the first substrate 5 so as to reveal the resin layer 16 as shown in FIG. 8. Then step f) comprises a sub-step f) of removing the resin layer 16 that has appeared in the bottom of the cavity 12, 12 'after the elimination of the illuminated and crystallized zones 7, 7' of the first substrate 5, so as to reveal the conductive layer 10, as shown in FIG. 9.

The micromechanical part 1, 1 'is then performed as in the electroplating manufacturing process described above, as shown in Figs. 10 and 11. Stage i) of release of the part 1, 1 'from its mold 3, 3' is carried out by chemical etching processes (for example HF for the photosensitive glass, KOH for the silicon).

The methods according to the present invention make it possible to produce micromechanical parts having narrow and rigid geometries with high precision, in "batch" mode.

Indeed, in a particularly advantageous manner, several molds 3, 3 'are made on the same first substrate 5, 5'. These molds are not necessarily identical to each other. This produces a molding plate 14 as illustrated in FIG. 3.

This plate molding 14 is intended to manufacture at least one micromechanical part 1,1 'by electroplating. According to the invention, it comprises a first substrate 1, 1 'of photosensitive glass with a thickness at least equal to the height of the micromechanical part 1, 1', a second substrate 8 integral with the first substrate 5, at least one layer conductor 10 provided between the first and second substrates 5, 8, and optionally a resin layer 16 provided between the first substrate 5 and the conductive layer 10. The first substrate 5 comprises at least one mold 3, 3 'of the micromechanical part 1 , 1 'constituted by a cavity 12, 12' formed in said first substrate 5 and whose bottom is occupied by the conductive layer 10, for depositing by galvanic growth a metal material in said cavity 12, 12 'to form said piece of micromechanical 1,1 '. The first and second substrates 5 and 8, the conductive layer 10 and the resin layer 16 are as defined above.

In addition, the molds obtained according to the invention are photosensitive glass, which is more rigid than a resin traditionally used to form molds, and insensitive to the effects of galvanic growth baths. The method of manufacturing the micromechanical parts according to the invention is therefore particularly robust, especially for the manufacture of high aspect ratio parts.

The methods according to the invention also make it easy to start the galvanic growth according to step h) through the use of a conductive layer 10 of good quality mold bottom 3, 3 '.

In addition, the method of manufacturing the micromechanical parts according to the invention is simple to implement because it does not require localized and complex metal deposition (mask-pinning) to form the starting layer of the galvanic growth.

Finally, the method of manufacturing micromechanical parts according to the invention avoids geometries etched by Bosch® DRIE. There is therefore no scalloping that would require an additional step of smoothing.

Claims (13)

claims 1. A method of manufacturing a mold (3, 3 ') comprising the following steps: a) providing a first substrate (5) of photosensitive glass with a thickness at least equal to the height of the mold (3, 3) b) illuminating said first substrate (5) by UV radiation through a mask whose windows correspond to the cavity of the mold (3, 3 ') to create illuminated areas (7, 7') c) perform a treatment thermal of the first substrate (5) obtained in step b) to crystallize the illuminated areas (7, 7) d) to provide a second substrate (8) having at least one conductive layer (10) surface e) assemble the first substrate (5) obtained in step c) to the second substrate (8) so that the conductive layer (10) is between the first (5) and the second (8) substrates; f) eliminating the zones (7); , 7 ') illuminated and crystallized from the first substrate (5) so as to expose the conductive layer (10) to form at least one cavity (12, 12') with the side walls and the bottom occupied by the conductive layer (10) constitute said mold (3, 3 '). 2. Method according to claim 1, characterized in that the second substrate (8) is based on silicon. 3. Method according to one of the preceding claims, characterized in that the conductive layer (10) is formed by depositing on the second substrate (8) a layer of a metal material selected from the group comprising chromium, titanium and gold. 4. Method according to one of the preceding claims, characterized in that the step e) of assembling the first (5) and second (8) substrates is made by welding the conductive layer (10) of the second substrate (8). ) to the first substrate (5). 5. Method according to one of claims 1 to 3, characterized in that the step e) of assembling the first (5) and second (8) substrates is performed by welding the first substrate (5) with the second substrate (8) by means of a resin layer (16) provided between the first substrate (5) and the conductive layer (10). 6. Method according to claim 5, characterized in that step f) comprises a sub-step f) of removing the resin layer (16) appeared in the cavity (12, 12 ') after the elimination of the zones illuminated and crystallized (7, 7 ') of the first substrate (5), so as to reveal the conductive layer (10). 7. Method according to one of the preceding claims, characterized in that the f) elimination step of the illuminated and crystallized zones (7, 7 ') of the first substrate (5) is carried out by etching, preferably by dissolution with hydrofluoric acid. 8. Method according to one of the preceding claims, characterized in that a plurality of molds (3, 3 ') are formed on the same first substrate (5). 9. A method of manufacturing by electroplating a micromechanical metal part (1, 1 '), characterized in that it comprises the following steps: g) manufacturing a mold (3, 3') of said micromechanical part (1 , 1 ') according to the manufacturing method of a mold (3, 3') according to one of claims 1 to 8 h) fill the mold (3, 3 ') with a metallic material by galvanic growth from the conductive layer (10) for forming said micromechanical component (1, 1 ') i) releasing the micromechanical component (1, 1') obtained in step h) from its mold (3, 3 '). Molding plate (14) intended to manufacture at least one micromechanical part (1, 1 ') by electroplating, characterized in that it comprises a first substrate (5) made of photosensitive glass having a thickness at least equal to height of the micromechanical part (1, 1 '), a second substrate (8) integral with the first substrate (5), at least one conductive layer (10) provided between the first (5) and second (8) substrates, the first substrate (5) comprising at least one mold (3, 3 ') of the micromechanical part (1, 1') constituted by a cavity (12, 12 ') formed in said first substrate (5) and whose bottom is occupied by the conductive layer (10), for depositing by galvanic growth a metal material in said cavity (12, 12 ') to form said micromechanical part (3, 3'). 11. Molding plate (14) according to claim 10, characterized in that the second substrate (8) is based on silicon. 12. Molding plate (14) according to one of claims 10 and 11, characterized in that the conductive layer (10) is a layer of a metal material selected from the group consisting of chromium, titanium and gold . 13. Molding plate (14) according to one of claims 10 to 12, characterized in that it comprises a resin layer (16) provided between the first substrate (5) and the conductive layer (10).