Abstract:
The invention relates to a method of manufacturing ( 1 ) a mechanical part ( 51 ) including the following steps:
       a) providing ( 3 ) a substrate ( 53 ) made of micro-machinable material;   b) etching ( 5 ), with help of photolithography, a pattern ( 50 ) that includes said part through said entire substrate;       
 
     According to the invention, the method further includes the following steps:
       c) assembling ( 13 ) a clip ( 91 ) on said part so that said part ( 51 ) is ready to be mounted without the portion made of micro-machinable material having to be touched;   d) releasing ( 11 ) the part ( 51 ) from the substrate ( 53 ) so as to mount said part in a device such as a timepiece movement.       
 
     The invention concerns the field of timepiece manufacture.

Description:
[0001]    This application claims priority from European Patent Application No. 08160143.7 filed Jul. 10, 2008, the entire disclosure of which is incorporated herein by reference. 
       FIELD OF THE INVENTION  
       [0002]    The invention relates to a method of manufacturing a mechanical part made from a micro-machinable material and, more specifically, a part of this type that will be used for manufacturing a timepiece. 
       BACKGROUND OF THE INVENTION  
       [0003]    Manufacturing a timepiece part in a crystalline, silicon-based material is known. Indeed, the use of a micro-machinable like crystalline silicon has advantages in terms of manufacturing precision, owing to advances in current methods particularly within the electronics field. Thus, while it may be possible to manufacture balance springs, it is not yet possible to apply micro-machinable materials to all timepiece parts because of their insufficient tribological properties. Moreover, current manufacturing methods remain complex to implement and require direct handling of the manufactured parts, at the risk of damage to such parts. 
       SUMMARY OF THE INVENTION  
       [0004]    It is an object of the present invention to overcome all or part of the aforecited drawbacks by proposing a method that allows, simple, reliable pre-assembly of the part preventing any handling of the functional portions thereof so that the part is ready to be mounted in a device, such as a timepiece, without having to be touched. Moreover, the method allows high quality manufacture of a micromechanical part that can be applied to most mechanical timepiece parts. 
         [0005]    The invention therefore relates to a method of manufacturing a mechanical part including the following steps:
       a) providing a substrate made of micro-machinable material;   b) etching, with help of photolithography, a pattern that includes said part through said entire substrate;
 
characterized in that it further includes the following steps:
   c) assembling a clip on said part so that the latter is ready to be mounted without the portion made of micro-machinable material having to be touched;   d) releasing the part from the substrate so as to mount it in a device such as a timepiece movement.       
 
         [0010]    According to other advantageous features of the invention:
       step c) includes these steps: e) mounting said substrate on a support fitted with forks, so that the forks cooperate with said part and f) assembling the clip on the part mounted against the support;   step e) includes these steps: g) guiding the substrate relative to said support using alignment means so as to orient said substrate reliably and h) sliding the substrate and the part respectively against at least one pin and the forks secured to the support so as to abut against a shoulder of said at least one pin and said forks respectively, in order to prepare for assembly of the clip;   the alignment means are located higher than said at least one pin and said forks so as to guarantee the consecutiveness of steps g) then h);   the support includes several alignment means so as to improve the guiding of step g);   the method further includes, between steps b) and c), these steps: i) mounting said etched substrate on a base so as to leave the top and bottom surfaces thereof accessible, and j) depositing a coating of better tribological quality than said micro-machinable material on the external surface of said part;   step h) includes these steps: k) guiding the substrate relative to said base using alignment means so as to orient said substrate reliably and  1 ) sliding the substrate against at least one pin secured to the support so that the substrate abuts against a shoulder of said at least one pin made at a distance from said support so as to keep the substrate high relative to said support;   the alignment means are located higher than said at least one pin so as to guarantee the consecutiveness of steps k) then l);   the support includes several alignment means so as to improve the guiding in step k);   during step b), at least one bridge of material is etched in the pattern so as to keep the part secured to the substrate;   said at least one bridge of material includes a narrow section at the end of said part connected to the pattern for creating a zone of weakness that can facilitate step e);   step d) is made by relative movement between the part and the substrate so as to break said at least one bridge of material;   several parts are manufactured from the same substrate;   said micro-machinable material is selected from the group including crystalline silicon, crystalline silica and crystalline alumina.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0024]    Other features and advantages will appear more clearly from the following description, given by way of non-limiting indication, with reference to the annexed drawings, in which: 
           [0025]      FIG. 1  is a diagram of a substrate after a photolithography and etch step; 
           [0026]      FIG. 2  is an enlargement of one part of  FIG. 1 ; 
           [0027]      FIG. 3  is a diagram of a step of assembly onto a base according to the invention; 
           [0028]      FIG. 4  is a diagram of a coating deposition step; 
           [0029]      FIG. 5  is a diagram of a step of assembly onto a support according to the invention; 
           [0030]      FIG. 6  is a diagram of a clip assembly step according to the invention; 
           [0031]      FIG. 7  is a flow chart of the method of the invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0032]    The example illustrated in  FIG. 7  shows the flow chart of a method that is generally designated  1 . Method  1  mainly includes 6 steps  3 ,  5 ,  7 ,  9 ,  11  and  13  for manufacturing a mechanical part  51 , whose core is made from a base of micro-machinable material. Indeed, a micro-machinable material, because of its precision of less than a micrometer, is particularly useful for manufacturing a part, for example, of a timepiece and advantageously replaces the metal material that is usually used. 
         [0033]    In the following explanation, the micro-machinable material may be crystalline silicon based like, for example, mono-crystalline silicon, crystalline silica, like quartz, or crystalline alumina, like corundum (also called synthetic sapphire). Evidently, other micro-machinable materials could be envisaged. 
         [0034]    Step  3  consists in taking a substrate  53 , made of micro-machinable material like, for example, a mono-crystalline silicon wafer used for manufacturing electronic components. Preferably, a thinning phase is provided in step  3  so as to adapt the final thickness of part  51 . This phase may be achieved by a mechanical or chemical back lapping technique. 
         [0035]    Step  5  consists in making a pattern  50 , which includes the mechanical part  51  to be manufactured, through the entire substrate  53 , by photolithography, then etching. Advantageously, as can be seen in  FIGS. 1 and 2 , the larger size of substrate  53  relative to that of part  51  allows several patterns  50  to be etched and thus several parts  51  to be manufactured from the same substrate  53 . 
         [0036]    In the example illustrated in  FIGS. 1 and 2 , each mechanical part  51  is an escape wheel for a timepiece. Of course, method  1  allows other timepiece parts to be manufactured, but also, as explained below, several different parts on the same substrate  53 . 
         [0037]    Step  7  consists in mounting the etched substrate  53 , on a base  55 , so as to leave its top and bottom surfaces accessible. This step facilitates implementation of step  9 , which consists in depositing a coating of better tribological quality than said micro-machinable material on the external surface of part  51 . Indeed, placing substrate  53  higher than base  55  facilitates deposition of the coating in that it allows the top, thickness and bottom of each part  51  to be accessed. 
         [0038]    Step  9  allows deposition of a coating that advantageously replaces any insufficient tribological qualities of the micro-machinable material. 
         [0039]    This coating may, for example, be carbon allotrope based. One could also envisage depositing a crystalline carbon coating like synthetic diamond by chemical phase deposition (CVD). Amorphous carbon such as diamond-like-carbon (DLC) could also be deposited by phase vapour deposition (PVD). Of course, one or several other materials could be used as a replacement or addition to carbon. Other deposition methods could also be envisaged. 
         [0040]    Step  13  consists in assembling a clip  91  on the part  51  using a support  81  so that the pre-assembled part  51  is ready to be mounted without the part made of micro-machinable material having to be touched. 
         [0041]    Step  11  consists in releasing each part  51  from substrate  53 . Thus, in the example illustrated in the Figures, according to method  1 , several dozen mechanical parts  51  can be obtained on the same substrate  53 . In the example illustrated in  FIGS. 1 to 6 , one could thus obtain, for example, escape wheels whose core is made of mono-crystalline silicon and, in accordance with the embodiments explained below, which include an external surface made of synthetic diamond and/or a pre-assembled clip  91 . 
         [0042]    From the main steps  3 ,  5 ,  7 ,  9 ,  11  and  13  each of the embodiments will now be explained. In a first embodiment, method  1  includes the consecutive steps  3 ,  5 ,  13  and  11  illustrated by a single line in  FIG. 7 . The first step  3  consists in taking a substrate  53  made of micro-machinable material. 
         [0043]    Then the second step  5  consists in making patterns  50 , each including a mechanical part  51  to be manufactured, through the entire substrate  53  by photolithography then etching. According to the first embodiment illustrated in the flow chart of  FIG. 7 , the second step  5  includes three phases  15 ,  17  and  19 . 
         [0044]    In a first phase  15 , a protective mask is structured on substrate  53 . Preferably, the protective mask is made using a photosensitive resin. The protective mask is thus formed using selective radiation for structuring said mask in a shape corresponding to each pattern  50  to be made. Because of this step  15 , it will be possible to etch any flat shape selectively on substrate  53  in a very precise manner. 
         [0045]    In a second phase  17 , an anisotropic etch of the substrate  53 —protective mask assembly is performed. A deep reactive ionic etch (DRIE) is preferably used. The anisotropic etch can etch substrate  53  in an approximately rectilinear manner in the zones that are not protected by said protective mask. The etch during second phase  17  is preferably carried out over the entire thickness of substrate  53  and, possibly, along a crystallographic axis of the micro-machinable material that is favourable to such etch. 
         [0046]    Moreover, according to the invention, each pattern  50 , as illustrated in  FIGS. 1 and 2 , preferably has two bridges of material  57 . These bridges enable part  51  to be held in place relative to substrate  53  until step  11 . As visible in  FIG. 2 , bridges of material  57  include a narrow section at the end connected to the pattern of part  51  for creating a zone of weakness that can facilitate release step  11 . 
         [0047]    Finally, according to the first embodiment, the second phase  17  is also used for etching holes  59 , forming a part of the alignment means, in substrate  53 . In the example illustrated in  FIG. 1 , it can be seen that three holes  59  have been formed, distributed at approximately 120 degrees from each other and in proximity to the ends of substrate  53 . 
         [0048]    In a third and last phase  19  of second step  5 , the protective mask is removed from the surface of substrate  53 . A substrate  53  is then obtained that includes several patterns  50  including a part  51  secured to substrate  53  by two bridges of material  57  as illustrated in  FIGS. 1 and 2 . Of course, in step  5 , one could envisage making a single bridge of material  57  or more than two. 
         [0049]    According to the first embodiment, the third step  13  consists in assembling a clip  91  to part  51  using a support  81  so that the pre-assembled part  51  is ready to be mounted without the part made of micro-machinable material having to be touched. Step  13  includes phases  25  and  27 . 
         [0050]    The first phase  25  consists in mounting substrate  53  onto a support  81 , fitted with forks  87 , so that the teeth  82  of one fork  87  cooperate with each part  51  and thus facilitate the assembly of clip  91 . As visible in  FIG. 5 , first of all by moving substrate  53  closer to support  81  along direction D, substrate  53  is guided along directions E using alignment means so that substrate  53  is oriented reliably relative to support  81 . 
         [0051]    The alignment means are preferably formed by a chamfered column  80 , mounted in the extension of a pin  85  secured approximately perpendicular to support  81 , which cooperates with one of the recesses  59  made in substrate  53  in step  5 . Method  1  preferably includes three alignment means  80 ,  59  so as to improve guiding in first phase  25 . 
         [0052]    Secondly and lastly, by continuing to bring substrate  53  closer to support  81  along translation D, substrate  53 , then each part  51  slides respectively against each pin  85  and each fork  87 , both of which are secured to support  81 . The second time period ends when substrate  53  and each part  51  abut approximately against the shoulder  88  of each pin  85  and the shoulder of each fork  87  formed in the bottom of space  84  delimited by teeth  82 . 
         [0053]    As visible in  FIG. 5  at the end of phase  25 , substrate  53  and each part  51  (still secured to substrate  53 ) are placed in a stable manner and the only degree of freedom they have is translation D upwards. In the example illustrated on the pattern at the top right of  FIG. 2 , three teeth  82  of a fork  87  can be seen, whose shape corresponds to the free space between two arms of escape wheel  51 . Of course, forks  87  will be adapted depending upon the part  51  being manufactured. Support  81  is preferably formed from a material that does not damage part  51  like, for example, a plastic polymer. 
         [0054]    Alignment means  80 ,  59  are preferably located higher vertically then pins  85  and forks  87  in order to guarantee the consecutiveness of the first stage then the second stage. 
         [0055]    In the second phase  27  of third step  13 , a clip  91  is assembled onto each part  51 . In the example illustrated in  FIG. 6 , a first assembled part  51  and a second part  51  further to the right, whose clip  91  has not yet been assembled can be seen. Of course, this  FIG. 6  is used for better comprehension. Indeed, assembly of clips  91  should not be limited to assembly one-by-one using tweezers  89 , but could of course be achieved at the same time for each part  51  using an automated machine. 
         [0056]    As can be seen in the part  51  to the right which is not assembled, first of all, clip  91  is moved along translation F towards the pierced centre  69  of the part  51  contained in space  84  delimited by teeth  82 . Preferably, the maximum translation of clip  91  relative to centre  69  is delimited by the height of hole  86  made in the extension of space  84 , which allows clip  91  to be reliably mounted relative to part  51 . 
         [0057]    Secondly, once all of clips  91  have been placed on all of parts  51 , clip  91  and part  51  are definitively secured to each other, for example, by being heated in a furnace so that the adhesive, present on each clip  91 , polymerises, which has the effect of securing each clip  91  in its associated centre  69 . 
         [0058]    At the end of step  13 , one thus obtains a substrate  53 , wherein the part  51  of each pattern  50  is pre-assembled. Advantageously, according to the invention, the dozens of parts  51  can thus still be handled together and can be supplied with or without support  81  directly to the production line of a device, such as for example a timepiece movement. 
         [0059]    The fourth and last step  11  consists in exerting a relative movement between part  51  and substrate  53  so as to break bridges of material  57 . Advantageously, according to the invention, this movement can be achieved by pulling directly on clip  91 , which allows each part  51  to be finally mounted without any direct handling of the micro-machinable material. Step  11  can thus be achieved manually using tweezers or an automated machine. 
         [0060]    In the example illustrated in  FIGS. 1 and 2 , part  51  is an escape wheel and clip  91  is its pivoting pin. However, the invention is in no way limited to this and, by way of example, part  51  could be another type of gear train, a crown or even a balance spring-collet assembly, just as clip  91  could be a different functional part from a pivoting pin. 
         [0061]    The second embodiment is provided for the case where the micro-machinable material has sufficient tribological features for the intended application of part  51 . In the second embodiment, method  1  has the consecutive steps  3 ,  5 ,  7 ,  9 ,  13  and  11  as illustrated by a double line in  FIG. 7 . The first steps  3 ,  5  remain unchanged relative to the first embodiment. As shown in  FIG. 7 , instead of passing from step  5  to step  13  as in the first embodiment, the second embodiment passes first via steps  7  and  9  prior to passing to step  13 , which advantageously means that a coating can be deposited on each of parts  51  of substrate  53 . 
         [0062]    According to the second embodiment, the third step  7  consists in mounting the etched substrate  53  on a base  55  so as to leave the top and bottom surfaces of substrate  53  accessible in order to prepare for deposition step  9 . Step  7  includes phases  21  and  23 . 
         [0063]      FIG. 3  illustrates an example base  55  according to the second embodiment. Base  55  is a plate, the material of which can withstand the temperatures of step  9 , such as, for example, a ceramic. In order to keep substrate  53  high relative to base  55 , the base has pins  61  for cooperating with holes  59  made in substrate  53  during step  5 . For the same reasons as base  55 , pins  61  are preferably made of tungsten or tantalum. 
         [0064]    Preferably, each generally cylindrical pin  61  has a low part  63  connected to a high part  65  of smaller section by means of a shoulder  67 . The low part  63  is mounted approximately perpendicularly in base  55  in a fixed manner. In the extension of the high part  65  there is a chamfered column  60  that belongs to alignment means cited below. 
         [0065]    In the first phase  21 , as seen in  FIG. 3 , by moving substrate  53  closer to base  55  along direction A, substrate  53  is guided along directions B using alignment means so that substrate  53  is reliably oriented relative to base  55 . 
         [0066]    The alignment means are preferably formed by the chamfered column  60  cooperating with one of recesses  59 . Method  1  preferably includes three alignment means  60 ,  59  to improve guiding in first phase  21 . 
         [0067]    In a second phase  23 , continuing to move closer along translation A, substrate  53  slides against each high part  65  of pins  61  until substrate  53  is approximately abutting against shoulder  67  of each pin  61 . As seen in  FIG. 3  at the end of step  7 , substrate  53  is placed stably and its only degree of freedom is in translation A upwards. 
         [0068]    In the example illustrated in  FIG. 2 , on patterns  50  at the bottom right, and at the top left, a variant can be seen of alignment means column  60 -hole  59 . This variant is provided where the space at the ends of substrate  53  means that holes  59  cannot be made. According to the variant, two columns  93 ,  97  are provided that each cooperate with an empty part of a pattern  50 . The two patterns  50  are preferably as far as possible from each other and each is in proximity to the ends of substrate  53 . In the example illustrated in  FIG. 2 , it can be seen that each column  93  and  97  of approximately trigonal shape cooperates with a different pattern  50  along a central symmetry in order to improve guiding in step  21 . The symmetry is preferably achieved relative to the centre of substrate  53  and uses patterns  50  to the top left and bottom right of the example illustrated in  FIG. 1 . 
         [0069]    Alignment means  60 ,  59 ,  93 ,  97  are preferably located higher vertically than pins  61  so as to guarantee the consecutiveness of phases  21  then  23 . 
         [0070]    According to the second embodiment, the fourth step  9  consists in depositing a coating on the outer surface of each part  51 . As explained above, the coating may, for example, be a carbon allotrope for improving the tribology of each part  51 , particularly by reducing its friction coefficient. As illustrated in  FIG. 4  by arrow C, in step  9  a coating is deposited below, across the thickness of and above substrate  53  via step  7  for placing substrate  53  high up and because substrate  53  was etched right through in step  5 . 
         [0071]    At the end of step  9 , substrate  53  is removed from base  55 , then the second embodiment implements step  13  in the same way as the first embodiment. At the end of step  13 , a substrate  53  is thus obtained wherein the part  51  of micro-machinable material of each pattern  50  is coated with a deposition and pre-assembled with a clip  91 . Advantageously according to the invention, dozens of parts  51  can thus still be handled together and can be supplied with or without support  81  directly to the assembly line of a device, such as for example, a timepiece movement. 
         [0072]    The sixth and last step  11  consists in exerting a relative movement between part  51  and substrate  53  so as to break bridges of material  57 . Advantageously according to the invention, this movement can be achieved by pulling directly on clip  91 , which enables each part  51  to be finally assembled without any direct handling of the micro-machinable material and/or the deposited coating. Step  11  can thus be achieved manually using tweezers or using an automated machine. As for the first embodiment, the invention according to the second embodiment is not limited to an escape wheel as illustrated in  FIGS. 1 and 2 . 
         [0073]    Of course, the present invention is not limited to the illustrated example but is capable of various variants and alterations which will appear to those skilled in the art. In particular, a third embodiment of method  1  could be envisaged that includes the consecutive steps  3 ,  5 ,  7 ,  9  and  11  as illustrated by a triple line in  FIG. 7 , which would produce a part  51  including a deposited coating but wherein step  11  would be made more difficult because of the lack of gripping means such as clip  91 , which is present in the first and second embodiments. Step  11  could then consist in applying stress to bridges of material  57  so that they break in order to retrieve said part. 
         [0074]    The three variants show that the invention can offer simplified organisation between each step because parts  51  are only removed from substrate  53  in the last step  11 . The advantage of this is that dozens of parts  51  can be moved between each step by handling substrate  53  alone.