CH699476B1 - A method of manufacturing a silicon timepiece component. - Google Patents

Abstract

The invention relates to a method for manufacturing a silicon watch component comprising the steps of: forming the component by etching silicon, rounding the edges (a) to the component, to increase its mechanical strength.

Description

The present invention relates to the manufacture of watch components in silicon.

Due to its many advantages, in particular its low density, elasticity and non-magnetism, silicon is increasingly used to manufacture watch components, including watch movement components such as wheels, springs, and the like. spirals or exhausts. Its use for this purpose has been described in particular in patent applications EP 0 732 635, EP 1 422 436, EP 1 473 604, EP 1 850 193, EP 1 826 635 and WO 2007/000 271.

Silicon nevertheless has the disadvantage of being fragile. A silicon component can easily break, crack or crack under impact or when handled. The handling of such components during the assembly of a movement is therefore delicate. Breaks in silicon components may also occur during operation when the watch is shocked.

To increase the mechanical strength of a silicon component, it is proposed in the patent application WO 2007/000 271 to coat it with a silicon dioxide layer at least five times thicker than the thickness of the silicon component. thickness of native silicon dioxide. If this solution makes it possible to make the silicon component less fragile, the risks of breaking it remain high.

The present invention aims to provide another way to increase the mechanical strength of a silicon watch component, which can be combined with that of coating the silicon dioxide component.

For this purpose, there is provided a method for manufacturing a silicon watch component, comprising the steps of: form the component by silicon etching, round the edges of the component.

[0007] Because the silicon watch components are obtained by micro-fabrication techniques, their edges are generally very sharp, that is to say have a small radius of curvature. The pressures exerted on the latter during contact or impact can therefore be very high and exceed the elastic limit of silicon. The edges are therefore zones of weakness in which chipping occurs or breaks or cracks that can propagate in crystalline planes. By rounding the edges, the radius of curvature is increased locally and the contact pressures on the surface of the component are thus reduced. A substantial increase in the mechanical strength of the component can then be obtained.

It is certainly known in the art of horology to work the edges of some parts using abrasive tools such as files. This is called "champing". But the parts in question are metallic, and the goal is to eliminate burrs. Moreover, in chamfering, the edges are not rounded off but are replaced by chamfers or bevels, usually cut at 45 °.

[0009] Preferably, the edge-rounding step comprises applying a bulk polishing treatment to the component.

[0010] Said ridges typically comprise at least one edge defined by surfaces of the component forming a substantially straight angle between them.

The step of forming the component by silicon etching is preferably performed according to the method of deep reactive ion etching DRIE.

The method may further comprise, before or after the edge-rounding step, a surface treatment step of forming a layer on the surface of the component to further increase its mechanical strength. This layer is preferably made of silicon dioxide and preferably has a thickness of at least 0.5 micron.

The step of forming the component by silicon etching may be performed in a silicon layer already having at least one polished surface.

Other features and advantages of the present invention will appear on reading the following detailed description with reference to the accompanying drawings, in which: <tb> - fig. 1 <sep> schematically shows a method of manufacturing one or more silicon watch components according to a preferred embodiment of the invention; <tb> - fig. 2 <sep> is a partial perspective view of an exhaust anchor made by DRIE, showing more particularly a pallet of this anchor; <tb> - fig. 3 <sep> is a partial perspective view of the same anchor after rounding the edges.

FIG. 1 shows the different steps of the preferred embodiment of the method according to the invention.

In a first step (FIG 1a), a silicon on insulator (SOI: Silicon On Insulator) plate consisting of a stack of a support layer 1 made of silicon (Si), of a second layer 2 of silicon dioxide (SiO2) and a third layer 3 of silicon (Si). Layer 2 serves as an adhesive bonding layers 1 and 3. In SOI plates of this type found on the market, the surface 1a of the support layer 1 in contact with the layer of silicon dioxide 2 is polished, as well as the surface 3a of the third layer 3 in contact with the silicon dioxide layer 2 and the surface 3b of the third layer 3 opposite the surface 3a.

In a second step (FIG 1b), an etching mask (not shown) is formed on the surface 3b and the third layer 3 is etched through this mask according to the DRIE method so as to form the desired component or a set of desired components in layer 3.

In a third step (Figure 1c), the etching mask is removed. The silicon dioxide layer 2 is also removed to separate the third layer 3 from the support layer 1 and separate the various components 4 formed in the third layer 3.

A fourth step may be provided (FIG 1d) of coating the components 4 with a layer of silicon dioxide 5 over their entire outer surface to increase their mechanical strength. This step is carried out by a surface treatment such as a thermal oxidation treatment, a chemical vapor deposition (CVD) or a physical vapor deposition (PVD), in order to obtain a layer of silicon dioxide. greater thickness than the so-called "native" silicon dioxide layer forming naturally in the presence of air. The thickness of the silicon dioxide layer 5 is preferably at least 0.5 micrometers.

At the end of these three or four steps, the components 4 obtained have an upper surface 6, a lower surface 7 and sidewalls 8 each forming a substantially straight angle with each of the upper and lower surfaces 6, 7. DRIE method makes it possible to obtain a good perpendicularity between the flanks 8 and the surfaces 6, 7, more precisely of an angle between the flanks 8 and the surfaces 6, 7 diverging by at most 2 ° from the right angle. Because the surfaces 3a and 3b were polished, the surfaces 6, 7 are also polished. The edges 9 between the flanks 8 and the surfaces 6, 7 are sharp. Fig. 2 shows an example of a component, in this case an escape anchor, as obtained at the end of the third or fourth step, with its sharp edges 9.

According to the invention, to increase their mechanical strength, is subjected to the components 4, after the third step, between the third and fourth steps or after the fourth step, an additional treatment of rounding their edges (Fig. 1e). Working the edges using abrasive tools, as is done in chamfering metal parts, is not feasible here because of the fragility of silicon. To round the edges, the present invention proposes to apply a bulk polishing treatment to the components. Bulk polishing means a treatment in which the components are placed inside a container (tank, chamber, bowl, etc.) in which abrasive elements are located and in which a movement is maintained to produce friction between components and abrasive elements. The abrasive elements are generally in the form of particles carried by carrying bodies of larger size and the assembly comprising the components to be treated and the carrier bodies with the abrasive particles may be bathed in a liquid. The maintained movement may be a vibratory movement or back and forth applied to the container.

Such polishing in bulk polishes the entire outer surface of each component. The present inventors have found that, surprisingly, such polishing of the entire outer surface, to round the ridges 9, could be performed without degrading the already polished surfaces 6, 7. A condition to be respected nevertheless is to separate sufficiently the components of each other and the container wall and surround each of the components with sufficient carrier bodies and abrasive particles to prevent shocks.

The bulk polishing of the components typically lasts between 8 hours and 16 hours depending on the type of components (wheels, gears, anchors and escape wheels, rockers, other pivoted parts, coil springs, barrel springs, springs jumper, bearings, etc.) that one wishes to treat. The longer the treatment time, the greater the radius of curvature of the edges. However, care should be taken that the processing remains short enough so that the component ratings are not substantially altered. Fig. 3 shows by way of illustration the anchor of FIG. 2 after the polishing step in bulk.

[0024] A coating may be formed on the surface of the components, for example a crystallized carbon diamond coating (DLC), to improve their tribological properties. Such a coating may be deposited on the silicon itself, if the fourth step is not implemented, or on the silicon dioxide layer 5 in the opposite case.

The silicon dioxide layer 5 may be replaced by a layer of another material also having the effect of increasing the mechanical strength of the components, for example a layer of nitride or silicon carbide or carbide or titanium nitride, as also proposed in WO 2007/000271.

Claims (8)

A method of manufacturing a silicon watch component, comprising the steps of: - forming the component by silicon etching, - round the edges of the component. 2. Method according to claim 1, characterized in that the step of rounding the edges comprises the application of a polishing treatment in bulk to the component. 3. Method according to claim 1 or 2, characterized in that said ridges comprise at least one edge defined by surfaces of the component forming a substantially straight angle between them. 4. Method according to any one of claims 1 to 3, characterized in that the step of forming the component by etching silicon is performed according to the method of deep reactive ion etching. 5. Method according to any one of claims 1 to 4, characterized in that it further comprises, before or after the step of rounding edges, a surface treatment step of forming a layer on the surface component to improve its mechanical strength. 6. The method of claim 5, characterized in that the surface treatment step comprises forming a layer of silicon dioxide on the surface of the component. 7. Method according to claim 6, characterized in that the surface treatment step consists in forming a layer of silicon dioxide having a thickness of at least 0.5 microns on the surface of the component. 8. Method according to any one of claims 1 to 7, characterized in that the step of forming the component by etching silicon is performed in a silicon layer already having at least one polished surface.