EP1837722B1 - Micro-mechanical component in an insulating material and method of manufacture thereof - Google Patents

Description

Technical area

The present invention relates to a micro-mechanical part made of an insulating material, and more particularly to a fixed or mobile part of a watch movement whose proximity to other parts does not disturb the operation of a moving part, directly, or indirectly by the attraction of particles.

Technological background

Insulating materials, such as silicon and its compounds, quartz, diamond, glass, ceramics or others are increasingly used to make micro-mechanical parts, whether fixed parts , such as plates or bridges, or moving parts for example part of the drive train, or the control system such as the balance spring, balance or exhaust.

It has been observed, in particular on a spiral completely isolated from other parts for example by pitting and gluing by means of a non-conductive glue, that the use of silicon had a disadvantage. Indeed, after a certain period of operation, a number of turns located between the curve on the outside and the curve inside the spiral tends to stick to the cock, which necessarily adversely affects the isochronism of the regulating system. The same phenomenon could be observed with other parts made of silicon or another insulating material, which would also ultimately have a detrimental effect on isochronism.

The document EP 1 422 436 discloses the manufacture of a spiral spring from the cutting of a monocrystalline silicon plate. The coil spring has a silicon oxide coating to minimize thermal drift.

The document US 2002/171150 discloses the manufacture of a mobile silicon structure whose faces are coated with metal silicide in order to limit the influence induced by electrostatic charges.

The document US 2002/0060954 discloses an electronic movement whose generator is braked magnetically by a quartz time reference.

The document EP 1 482 282 discloses an electronic movement with a display means detecting means for automatically correcting undue movements of the display means.

Summary of the invention

The present invention therefore aims to provide a solution to the problem mentioned above by providing a fixed or mobile micro-mechanical part made of an insulating material whose surface treatment avoids the risk of bonding.

For this purpose the invention relates to a micro-mechanical part made of an insulating material, such as silicon, and its compounds, diamond, glass, ceramic or other, all or part of its surface is coated with a thin deposit of an electrically conductive material such as a layer of a metallic material or a conductive non-metallic material. The conductive deposit preferably has a thickness of less than 50 nm. This very thin deposit invisible to the naked eye, but detectable by the current means of analysis eliminates the risk of attraction and bonding by a neighboring room, this attraction may be due to may be due to friction or tension that can create electrostatic charges in the room.

This deposit may be performed on a piece of insulating material monoblock or composite, that is to say, at least the outer surface is of insulating material.

Among the materials making it possible to achieve the above-mentioned purpose, the stainless and amagnetic metals such as gold, platinum, rhodium and palladium are preferably chosen.

Among the non-metallic conductive materials one will preferably choose one of the group comprising graphite, carbon, doped silicon, and conductive polymers.
These metals can be deposited by known methods making it possible to control the thickness by adjusting the operating conditions, for example by sputtering, PVD, doping, ion implantation or by an electrolytic process. The same techniques can be used to deposit conductive non-metallic materials.

In a preferred embodiment, said micro-mechanical part is a part of the kinematic chain of a watch movement, such as a hairspring, an anchor, an escape wheel or a toothed wheel, or any which other fixed part may for example be the bearing of the axis of a mobile. In the following detailed description, the invention will be more particularly illustrated by a hairspring which is the most sensitive part of a watch movement.

The invention also relates to a timepiece incorporating such a micro-mechanical part.

Brief description of the drawings

• la figure 1 représente en vue de dessus partiellement arrachée un balancier-spiral pourvu d'un spiral traité selon l'invention, et
• la figure 2 est une représentation en coupe selon la ligne II-II de la figure 1, avec représentation de la partie arrachée.

Other features and advantages of the present invention will appear more clearly in the following description of an example embodiment, given by way of nonlimiting illustration, with reference to the appended drawings in which:

• the figure 1 represents in plan view partially cut away a sprung balance provided with a spiral treated according to the invention, and
• the figure 2 is a sectional representation along line II-II of the figure 1 , with representation of the part torn off.

Detailed description of the invention

The invention will be more particularly illustrated by a sprung balance adjusting device shown in FIG. figure 1 , in which the spiral 1 is made, for example, of silicon, by adapting the micro-machining processes used in the manufacture of integrated circuits or accelerometers from a silicon wafer or other amorphous or crystalline insulating material. For example, wet chemical etching, plasma dry machining or reactive ion etching (RIE) can be carried out using masks appropriate to the desired contour for the hairspring.

Given the small dimensions, the same silicon wafer makes it possible to manufacture a batch of spirals whose characteristics are determined by the thickness of the wafer and the shape of the masks, said characteristics being calculated for operation of the spiral in a plane.

Referring now to the figure 2 , whose sectional representation is limited to the hairspring 1 and the cock 9, there is shown in the left side the behavior of the turns 11 after a certain time of operation when the hairspring 1 has not undergone any treatment. As can be seen, the turns 11 deviate from their normal position shown in dotted lines by being attracted by the cock 9 and can even stick to it, which obviously disturbs the normal walking, that is to say to say a march having only movements of extension / contraction in a plane.

In the right part is shown spiral 1 after treatment, the dotted line representing the position that would occupy the turns 11 in the absence of treatment. As we see the spiral stays perfectly in a plane. Surprisingly, it has been found that by carrying out a treatment consisting of a very small deposition of an electrically conductive material such as a metallic material on all or part of the surface of the turns, the harmful effect is annihilated. previously described, without modifying the intrinsic mechanical properties of the spiral. "Very low deposition" means a deposit having a thickness of less than 50 nm, preferably between 10 and 20 nm. When the deposit is less than 50 nm, the intrinsic mechanical properties of the part are not modified and the deposit is invisible to the naked eye, but nevertheless detectable by the current analysis techniques. The material used is preferably a stainless and non-magnetic metal such as gold, platinum, rhodium, palladium, when it is a metallic conductive material. This deposition can be carried out by means of various known methods, such as sputtering, PVD deposition, ion implantation or electroplating.

By way of example, a gold deposit of 15 nm has been carried out by "sputtering", that is to say by performing a cathodic sputtering under vacuum, with a gold target, by applying a current of 60 mA for 15 seconds.

When a non-metallic conductive material is deposited, it will preferably be chosen from the group comprising graphite, carbon, doped silicon, and conducting polymers and deposition techniques and thicknesses as mentioned above will be used.

A silicon spiral has just been described, but other non-conductive amorphous or crystalline materials may also be used, as indicated above, and be treated with a surface metallization avoiding the risk of attraction or sticking.

It is also possible to use a composite material to produce for example a hairspring having a silicon core and a thick coating of silicon dioxide on which the deposition of conductive material of small thickness will be performed.

A "composite material" may also include a metal core embedded in an insulating material.

Claims (8)

1. Balance-spring made of at least one insulating material and to be integrated in a timepiece movement, said insulating material including a silicon core on which a silicon dioxide coating is formed with a thickness greater than 50 nm, characterized in that all or part of the surface of the balance-spring is coated with a deposition of conductive material.
   that it.
2. Balance-spring according to the preceding claim, characterized in that the conductive material is a metallic material.
3. Balance-spring according to the preceding claim, characterized in that the metal is selected from among gold, platinum, rhodium and palladium.
4. Balance-spring according to claim 1, characterized in that the conductive material is a non-metallic conductive material.
5. Balance-spring according to the preceding claim, characterized in that the non-metallic conductive material is selected from among graphite, carbon, doped silicon and conductive polymers.
6. Balance-spring according to any of the preceding claims, characterized in that the deposition of conductive material has a thickness of less than 50 nm.
7. Balance-spring according to any of the preceding claims, characterized in that the deposition of conductive material has a thickness comprised between 10 and 20 nm.
8. Timepiece including a micro-mechanical part according to any of the preceding claims.

Images