Swiss Patent News: Spiral watch springs for mechanical watches


On 8 February 2019, the Swiss Federal Patent Court (SFPC) granted a request for preliminary injunctive relief to Centre Suisse d'Electronique et de Microtechnique SA (claimant) against Cendre+Métaux Microtech SA and Cendres+Métaux SA (defendants 1 and 2) based on alleged patent infringement. The claimant's patent is the Swiss part of the European Patent EP 1422436 ("spiral watch spring and its method of production"). Spiral watch springs are used in the balance wheel (in German: Unruh), the part that operates as a power regulator for mechanical watches. The claimant's patent is in force and licensed to high profile watchmakers in Switzerland such as Rolex SA and Patek Phillippe SA.


Left: Drawing from EP 1422436 patent claims. Middle: common spiral watch springs. Right: balance wheel of a spiral 

Factual background of the case

On September 2018, the claimant filed a request for preliminary injunctive relief before the SFPC with the request to enjoin defendants 1 and 2 from manufacturing, storing, offering, selling or introducing spiral watch springs in the market designed to equip the balance wheel of a mechanical watch with spiral watch springs that are cut out of a spiral-formed stick derived from a monocrystalline-oriented silicon plate, have a stick with a silicon core and have an encircling outer layer of amorphous silicon oxide. On October 23, the defendants filed an answer to the request, and briefs were exchanged on 23 November 2018 and 4 December 2018. The relevant patent had already been subject to a prior nullity-claim before the SFPC in 2012 in which the regular judge and specialised subject-matter judges concluded that the patent was valid (i.e. new, non-obvious and not unlawfully extended by the formulation of its claims). The core value of the patented manufacturing process lies in the increased resistance of the material to thermic changes and magnetic field influence. The process also secures replicability in manufacturing without substantial fluctuation.

Patent and spiral springs in dispute

The defendant did not contest that its own spiral springs bear features identical to many patent claims in EP 1422436, but it stressed out that its own products beared two distinctive differences, namely that (i) its spiral springs are not cut out of a silicon stick (but of a silicon plate) and (ii) the used silicon plate does not provide for a monocrystalline 001-orientation (while the crystal orientation used under the claimant's devices provide for a 110-orientation). Furthermore, the defendant contested that the defendant 2 participated in any of the alleged patent infringement actions. To elaborate roughly on the crystalline orientation of silicon, bear in mind the following: Silicon is a classic half metal and has features of both metals and non-metals. It can be "crystalised" by the supersaturation process (in German: Übersättigung), which is usually achieved by melting, evaporating or cooling down a dilution. Silicon crystallises in a "diamond lattice" under which every atom connects to four neighbouring atoms in a tetrahedral form with a degree of 109.5 between each atom's connective partner.



Left: Crystallography of silicon. Right: silicon crystal diamond lattice microstructure (both available on

Based on this, twelve different direction vectors are discernible within a silicon diamond lattice (110, 101, 011, 1'10, 1'01, 01'1, 11'0, 101', 011', 1'1'0. 1'01' and 01'1'1). Below is a visual example of how a 001 silicon crystal orientation and a 110 silicon crystal orientation look on a molecular structure level. Depending on where the silicon is "cut out" from the crystalline structure, the material will bear a different structure.

Picture: available under

Patent infringement assessment

When assessing the alleged patent infringement, the SFPC pre-defined the technical expert assessing the case as an "expert in microfabrication-mechanic with particular knowledge of mechanical watch making".

Patent novelty

As a first step, the SFPC assessed the defendants' defense that the claimed patent lacked novelty based on three pre-existing patents (European and two US patents). When examining the first pre-existing patent (EP 635), the court held the patent did not reveal that a spiral spring must be cut out of a monocrystalline 001-oriented silicon stick. The silicon material was only one of eight suggested materials in the pre-existing patent and the monocrystalline 001-orientation was only one of three possibilities. The relevant expert in the field would not have a cause to choose such materials and apply the same manufacturing details to achieve an increased temperature resistance. Furthermore, the claims pertaining to external surfaces did not provide for a temperature coefficient and did not consist of silicon oxide. Based on the "task-solution-approach" of the European Patent Office and used by the SFPC, the invention reflected in the claimant's patent was not considered manifest under the pre-existing patents. The court concluded the same for two US-American patents brought in the case by the defendants (US 5'783'973 and US 2002/0104475 A1[application]). While both patents address the use of micromechanical elements made out of silicon to achieve increased temperature resistance. They address a different technical field and different applications than mechanical watches (e.g. a tuning fork gyroscope or a block of 110 crystalline-oriented silicon). The court concluded that the claimant's patent was sufficiently inventive to be regarded as valid for the preliminary injunction proceedings.

Patent infringement

In its second step, the SFPC compared the defendants' spiral springs with the patent claims listed in EP 1422436, assessing whether the features fulfil the same criteria or achieve the same effect as the technical doctrine in the claimants' patent. Under the "equivalency doctrine", a patent infringement exists even if there are distinct differences and alterations that achieve a substantially equivalent effect. The three-tiered equivalency test usually builds upon the following three questions: Firstly, does an altered feature of a patent claim together with the rest of the patent claims fulfill the same function as the non-altered patent claim? Secondly, is the equivalent effect obvious for a technical expert? And thirdly, from the objective view of an expert reader, was or was not the patent claim willingly constricted to abandon an equivalent function from the claim's scope? This derives from the interpretation protocol to Art. 69 EPÜ and Art. 66 para. a. of the Swiss Federal Patent Act. While almost all features of the defendants' products were considered identical to the patent claims listed in EP 1422436, two differences or alterations remained debated: the defendants' spiral springs were not cut out of a silicon stick, but out of a silicon plate and the used silicon plate for manufacturing did not provide for a monocrystalline 001-orientation, but a 110-orientation.

The court held that a spiral spring cut out of a 110-crystalline oriented silicon wafer objectively achieves the same function as the patented procedure of a spiral spring cut out of a monocrystalline 001-oriented silicon stick. Even the fact that the defendants' material was not cut out, but put through plasma-etching procedures was considered irrelevant since "cutting out" in the sense of the patent claims means "carving out" in the broadest sense of the term. The patent prosecution documents of EP 1422436 did not indicate why the cutting out of a 110-crystalline-oriented silicon wafer was not mentioned. Therefore, a chosen "omission" by the claimant could not be easily inferred. This seems persuasive as the thermic and anti-magnetic stability achieved under the patent's doctrine does not rely on the crystal orientation of the silicon used, but merely on the material and the manufacturing process itself. An expert would therefore not infer that features he considers equivalent were omitted on purpose under the claimant's patent claims.

Based on the above, the SFPC concluded that all of the defendant's patent claims have been used in the defendants' products and altered features would fulfil the claims in an equivalent manner. A patent infringement was therefore considered credible and a preliminary injunction granted. Nevertheless, the SFPC held that it was not credible that defendant 2 engaged in manufacturing or distributing the allegedly infringing items. The request for preliminary injunction against defendant 2 was rejected.

Note that the parties are still free to dispute this matter in the course of ordinary court proceedings (but not preliminary injunction proceeding) before the SFPC.

Lessons learned

As this case shows, patent litigation is highly unpredictable and strongly depends on technical expertise. In particular, the equivalency test is not to be underestimated, which is why even substantial alterations or differences in a market product to a registered patent claim can amount to a patent infringement if the disputed feature fulfills a substantially equivalent function. Furthermore, similar pre-existing patents do not always represent a lack of novelty. Under the "task-solution-approach" it is important to investigate whether an invention was manifestly presented to a subject-matter expert in the pre-existing patent specifications or whether this was only one of many options, which the expert could choose from and craft a new invention. Only in the former can one infer that a registered patent lacks novelty and should be considered null and void.

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