This application claims priority from European Patent Application No. 09155123.4 filed Mar. 13, 2009, the entire disclosure of which is incorporated herein by reference.
The invention relates to a mould for fabricating a micromechanical part using galvanoplasty and the method of fabricating said mould.
Galvanoplasty has been used and known for a long time. LIGA type methods (a well know abbreviation for the German term “rontgenLIthographie, Galvanoformung & Abformung”) are more recent. They consist in forming a mould by photolithography using a photosensitive resin, and then, by galvanoplasty, growing a metal deposition, such as nickel, therein. The precision of LIGA techniques is much better than that of a conventional mould, obtained, for example, by machining. This precision thus allows the fabrication of micromechanical parts, particularly for timepiece movements, which could not have been envisaged before.
However, these methods are not suitable for micromechanical parts with a high slenderness ratio, such as a coaxial escape wheel made of nickel-phosphorus containing, for example 12% phosphorus. Electrolytic depositions of this type of part delaminate during plating, because of internal stresses in the plated nickel-phosphorus, which cause it to split away at the interface with the substrate.
It is an object of the present invention to overcome all or part of the aforementioned drawbacks, by proposing an alternative mould that offers at least the same fabrication precision and allows fabrication of parts with several levels and/or a high slenderness ratio.
The invention therefore concerns a method of fabricating a mould that includes the following steps:
According to other advantageous features of the invention:
The invention also relates to a method of fabricating a micromechanical part by galvanoplasty, characterized in that it includes the following steps:
Finally, the invention advantageously relates to a mould for the fabricating of a micromechanical part by galvanoplasty, characterized in that it includes a substrate, a part made of silicon-based material mounted on said substrate and comprising at least one cavity that reveals an electrically conductive surface of said substrate, allowing an electrolytic deposition to be grown in said at least one cavity.
According to other advantageous features of the invention:
Other features and advantages will appear more clearly from the following description, given by way of non-limiting illustration, with reference to the annexed drawings, in which:
As
Mould fabrication method 3 includes a series of steps for fabricating a mould 39, 39′ that includes at least one part 21 made of silicon-based material. In a first step 9 of method 3, a wafer 21 made of silicon-based material is coated on the top and bottom thereof with electrically conductive layers, respectively referenced 20 and 22 as illustrated in
In a second step 11, a substrate 23, which may also be silicon-based, is coated on the top thereof with a layer 24 of adhesive material, as illustrated in
According to an alternative of the invention, the adhesive layer 24 and bottom conductive layer 22 are inverted, as explained below.
In a fourth step 15, one part 26 of the conductive layer 20 on the top of wafer 21 is removed to reveal part of wafer 21 as illustrated in
Etching step 17 preferably includes an anisotropic dry attack of the deep reactive ion etching type (DRIE).
According to a first variant of step 17, the material of the conductive layer 20 on the top of wafer 21 is chosen to act as a protective mask. Thus, when the assembly of mask 20-wafer 21 is subjected to the anisotropic etch, only the unprotected parts 26 of the wafer are etched. At the end of step 17, at least one cavity 25 is thus obtained in wafer 21, the bottom of which partially reveals bottom conductive layer 22 as illustrated in
According to a second variant of step 17, firstly, a protective mask is coated on wafer 21, preferably in the same shape as removed parts 26 for example, via a photolithographic method using a photosensitive resin. Secondly, when the mask-wafer assembly is subjected to the anisotropic etch, only the unprotected parts of the wafer are etched. Finally, in a third phase, the protective mask is removed. At the end of step 17, at least one cavity 25 is thus obtained in wafer 21, the bottom of which partially reveals the bottom conductive layer 22 as illustrated in
In the case of the aforecited alternative illustrated in triple lines in
After step 17, the invention provides two embodiments. In a first embodiment, illustrated in a single line in
According to this first embodiment, it is clear that the micromechanical part obtained has a single level whose shape is identical throughout the entire thickness thereof.
According to a second embodiment of the invention, illustrated in double lines in
Part 27 is preferably formed on conductive layer 20 in a recess 28 of larger section than the removed parts 26, for example, via a photolithographic method using a photosensitive resin.
Moreover, as illustrated in
In the second embodiment, mould 39 fabrication method 3 ends after step 19, and the micromechanical part fabrication method 1 continues with galvanoplasty step 5 and step 7 of releasing the part from said mould.
Galvanoplasty step 5 is achieved by connecting the deposition electrode to conductive layer 22 on the bottom of wafer 21, firstly, to grow an electrolytic deposition in cavity 25 of said mould, and then, exclusively in a second phase, in recess 28, as illustrated in
Indeed, advantageously according to the invention, when the electrolytic deposition is flush with the top part of cavity 25, it electrically connects conductive layer 20, which enables the deposition to continue to grow over the whole of recess 28. Advantageously, the invention allows fabrication of a part with a high slenderness ratio, i.e. wherein the section of cavity 25 is much smaller than that of recess 28, avoiding delamination problems even with a nickel-phosphorus material containing, for example, 12% phosphorus.
Owing to the use of silicon under conductive layer 20, delamination phenomena at the interfaces decrease, which avoids splitting, caused by internal stresses in the electrodeposited material.
According to the second embodiment, fabrication method 1 ends with step 7, in which the part 41 formed in cavity 25 and then in recess 28 is released from mould 39. Release step 7 could, for example be achieved by delaminating layer 24 or by etching substrate 23 and wafer 21. According to this second embodiment, it is clear, as illustrated in
This micromechanical part 41 could, for example, be a coaxial escape wheel, or escape wheel 43-pinion 45 assembly with geometrical precision of the order of a micrometer, but also ideal referencing, i.e. perfect positioning between said levels.
According to second variant of method 1 illustrated by a double dotted lines in
Preferably, according to this second variant, substrate 23 is formed from a silicon-based material and is etched to form a hollow 35 in mould 39′.
As can be seen, preferably between
As illustrated in double dotted lines in
Preferably, firstly, as illustrated in
Thirdly, protective mask 30 is removed. At least one hollow 35 is thus obtained in substrate 23, the bottom of which partially reveals adhesive layer 24, as illustrated in
Of course, in a similar way to that explained above, a conductive layer can also be deposited on substrate 23 instead of photostructured resin mask 30, the material of which is chosen so that it can act as protective mask.
Likewise, in the case of the aforecited alternative in which adhesive layer 24 and bottom conductive layer 22 are inverted, it is no longer necessary to continue said hollow 35 into adhesive layer 24 to reveal conductive layer 22 or, possibly, deposition 33.
After step 17 of the second variant of method 1, the invention can also provide the two aforecited embodiments, i.e. continuing with galvanoplasty step 5 and release step 7, or continuing with a step 19 to form at least one additional level on substrate 23. To simplify the Figures,
Preferably, whichever embodiment is chosen, as illustrated in
After the new steps 17 or 19, galvanoplasty step 5 is performed by connecting the deposition electrode to conductive layer 22 to grow an electrolytic deposition in hollow 35, but also to continue the growth of deposition 33 in cavity 25, and then, exclusively in a second phase, in recess 28, as illustrated in
According to this second variant, it is clear, as illustrated in
This micromechanical part 41′ could, for example, be a coaxial escape wheel 43′, 45′ with its pinion 47′, or a wheel set with three levels of teeth 43′, 45′, 47′ with geometrical precision of the order of a micrometer, but also ideal referencing, i.e. perfect positioning between said levels.
Of course, the present invention is not limited to the example illustrated, but is open to various alterations and variants, which will be clear to those skilled in the art. In particular, part 27 could include a pre-etched silicon-based material, and then be secured to conductive layer 20.
Moreover, several moulds 39, 39′ are fabricated from the same substrate 23 to achieve series fabrication of micromechanical parts 41, 41′, which are not necessarily identical to each other.
Likewise, a rod 29 can be formed in cavity 25 to form a shaft hole 42 for the future part 41, even within the scope of the first, single level embodiment. One could also envisage changing silicon-based materials for crystallised alumina or crystallised silica or silicon carbide.
Finally, layer 20 formed in step 9, and then partially pierced in step 15, can also be obtained via a single, selective, deposition step 15. This step 15 could then consist, firstly, in depositing a sacrificial layer in the same shape as section 26, prior to deposition of conductive layer 20. Secondly, a conductive layer 20 is deposited on top of the assembly. Finally, in a third phase, the sacrificial layer is removed and, incidentally, the conductive layer part deposited thereon, which provides the same layer 20 as that visible in
Number | Date | Country | Kind |
---|---|---|---|
09155123 | Mar 2009 | EP | regional |
Number | Name | Date | Kind |
---|---|---|---|
5234571 | Noeker | Aug 1993 | A |
5529681 | Reinecke et al. | Jun 1996 | A |
5944974 | Fahrenberg et al. | Aug 1999 | A |
6214245 | Hawkins et al. | Apr 2001 | B1 |
7448277 | Gogoi et al. | Nov 2008 | B2 |
7887995 | Niwa et al. | Feb 2011 | B2 |
7960090 | Terasaki et al. | Jun 2011 | B2 |
8021534 | Niwa et al. | Sep 2011 | B2 |
8148049 | Murayama et al. | Apr 2012 | B2 |
20040191704 | Nishi et al. | Sep 2004 | A1 |
20060160027 | Niwa et al. | Jul 2006 | A1 |
20100236934 | Cusin et al. | Sep 2010 | A1 |
Number | Date | Country |
---|---|---|
40 01 399 | Jul 1991 | DE |
0 547 371 | Jun 1993 | EP |
1 462 859 | Sep 2004 | EP |
1 681 375 | Jul 2006 | EP |
2 060 534 | May 2009 | EP |
2005-256110 | Sep 2005 | JP |
Entry |
---|
European Search Report issued in corresponding application No. EP09155123, completed Sep. 11, 2009. |
Office Action mailed Sep. 24, 2012 in co-pending related U.S. Appl. No. 12/723,191. |
Office Action received May 9, 2013 in corresponding Chinese patent application 201010134011.0. |
Number | Date | Country | |
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20100230290 A1 | Sep 2010 | US |