Concept of equivalent features
Express exclusion of features during prosecution
Unforeseeable feature and equivalents
Equivalence under Mexican law

The scarcity of patent litigation in Mexico as compared to other jurisdictions has resulted in a lack of case law in several key areas. One such area is the situation where a product does not have all features of the claims of a granted patent, but is so close that it appears that a feature has been changed to circumvent patent coverage through the incorporation of an equivalent feature. This is known as the 'doctrine of equivalents'.

Concept of 'equivalent features'

The term 'claim' refers to a technical description of certain features that are considered essential to a patented invention and define it as unique. These features make the invention special and are thus protected by the patent. Consequently, only products or processes that have all of the essential features recited in at least one of the claims of a patent are considered to be infringing.

However, the interpretation of a claim depends on how it is written and, in turn, on the skill and experience of the drafter and the knowledge available to him or her at the time. Thus, a badly written claim will be harder to enforce, giving infringers an opportunity to circumvent patent rights by making modifications that still fall under the teachings of the patent at issue. Therefore, the doctrine of equivalents states that a patent is considered to be infringed if some of the claimed features were substituted for other features that are equivalent to the claimed features or perform the same functions.

Parts XI, XII, XIII and XIV of Article 213 of the Industrial Property Law state that infringement occurs when a patented product or process is exploited through means reserved to the patent holder. However, the law provides no rules for determining what constitutes a 'patented product' or a 'patented process'; it merely indicates that the rights conferred by a patent are determined by the granted claims (under Article 21), and that such claims are to be interpreted according to the description and drawings. This lack of clarity in the interpretation of patent infringement - mostly affecting patent holders, which must prove strict violation of the patent claims - should allow for the doctrine of equivalents to be applied in Mexico without the need for legislative amendments.

Conceptually, the doctrine of equivalents is necessary to protect patent holders from copies of their patented inventions that are expressly designed to avoid the language of the granted claims, but nonetheless use the fundamental principles described in the patent.

Express exclusion of features during prosecution

The doctrine of equivalents can be abused by patent holders that broaden the scope of the originally granted claims to features that the holder did not originally consider for protection. Under this approach, the public will never be able to read the claims and determine the scope of the exclusivity being granted, which may lead to abuse and a lack of clarity in the patent system. Accordingly, prosecution estoppel is a necessary tool for defence against infringement under the doctrine of equivalents. The patent rights must cover - under the doctrine of equivalents or otherwise - any form in which an invention could be copied, unless the patent holder has previously expressed its clear intention to exclude such a form.

Unforeseeable feature and equivalents

Criteria adopted and broadly studied in the United States, derived from cases such as Johnson & Johnston Ascos Inc v RE Serv Co (2002) and further clarified in Festo Corp v Shlketsu Kinzoku Kogyo Kabushiki Co (2003), have seen the doctrine of equivalents evolve as follows:

  • If the equivalent feature is the result of technology that was developed after the filing date of the patent, it would have been impossible for the patent holder to include such a feature in the patent.
  • Once the new technology has been developed, those skilled in the art can combine the knowledge of the patent with the new technology, thus obtaining a result which those skilled in the art would expect based on the later developed knowledge, by virtue of which such a feature may be considered equivalent and should be deemed an infringement. If the feature that is allegedly equivalent was part of the prior art, the analysis must show whether those skilled in the art could have inferred or foreseen that the feature in question could be substituted by another feature.

As infringement is an act that occurs after a patent application has been filed and granted, modification for the sake of equivalence always occurs after the event. Therefore, if the possibility of modifying the feature was evident before the event to those skilled in the art, a product with features that were foreseeable but not claimed would not be covered by the patent because the patent holder (being a person skilled in the art) had the opportunity to exclude such foreseeable features or variations from protection.

In Mexico, anyone can file and prosecute a patent and inventors commonly file patents without using a patent agent. Furthermore, no accreditations are available for patent prosecutors in Mexico; as a result, the quality of prosecution and drafting of certain patents is questionable. The above criteria work most effectively in a jurisdiction that has an advanced patent system, led by certified professionals in patent prosecution.

Equivalence under Mexican law

Literal approach to infringement
Several articles of the Industrial Property Law are relevant to interpreting the claims of a patent in the event of infringement. Article 12 defines the term 'claim' as the essential features of an invention that define the scope of the patent (under Article 21).

Similarly, Article 25 expressly sets out the rights that are reserved to the patent holder, including the possibility of preventing others from using patented products and processes and from manufacturing, selling, offering for sale or importing patented products or processes. The law uses the vague expression 'patented product' or 'patented process', which refers not to the claimed invention, but rather to the protection given by the patent.

The interpretation of patents in Mexico is also affected by Article 12 of the Agreement Establishing the Rules for Filing Applications before the Mexican Institute of Industrial Property. This article expressly governs the practice of drafting claims in two parts. It states that, where applicable, the claims of a Mexican patent must contain a description of the features of the prior art that are essential for the practice of the invention, followed by the words 'characterised in that' or a similar phrase, after which the novel and inventive features for which protection is sought must be listed.

This framework makes clear that Mexican law requires a literal approach to determining infringement. In other words, in order to determine whether a product infringes a patent under Articles 21 and 213 of the Industrial Property Law, an infringing product must contain every feature of at least one patent claim. Technically, it must be proven that all of the claim's essential features are present in the infringing product in order for it to be considered an infringement. The essential nature of the features must be emphasised - the number of features in the claim is the minimum number of features that must be present in a product or process in order for it to be considered to be the 'patented product' or the 'patented process', depending on the specific phrasing of the claim itself with regard to the terms 'comprising', 'consisting of' or similar.

Consequently, if the allegedly infringing product lacks at least one of the essential features of a claim, a literal approach dictates that it cannot be deemed to infringe the patented invention.

Infringement by substitution of an essential feature for another
One of the main criteria for the application of the doctrine of equivalents is that at least one of the features in a claim be absent from the infringing product. This means that the literal approach to infringement must have led to a negative result.

Strictly speaking, given that the law does not establish a specific criterion for determining whether a process or product is patented, and given the failure of the literal infringement approach, the first conclusion could be that there is no infringement. However, Article 21 of the law clearly states that claims can be interpreted in light of the description and drawings; therefore, the law provides that the interpretation of claims can go beyond the way in which they are written.

Accordingly, where infringement cannot be established under the literal approach because at least one of the essential features is absent from the allegedly infringing product, the nature of such feature must still be analysed in order to determine the possibility of infringement through an equivalent feature in the context of the description and drawings of the patent.

Under the institute's filing rules, when a patent is drafted in two parts it is important to consider that only the features after the characterising phrase are novel and inventive. This involves consideration of the balance to be achieved by the public in understanding what is known, what is new and what can be substituted by an equivalent.

Accordingly, if an allegedly infringing product differs from the patent claims in a feature that is part of the prior art section of the claim, not part of the characterising section, it could be considered that the inventor sees these features not as novel and inventive, but rather as necessary for the invention's use. Therefore, the lack of such a feature in the infringing product must clearly be considered equivalent if all features in the characterising section are present in the same product. This is consistent with the doctrine of equivalents since, in this case, novel and inventive features of the invention are clearly evident in the infringing product, even though the prior art features have been substituted or even eliminated.

The characterising section supposedly includes the features that are intended to be protected and that are therefore novel and inventive. In principle, the absence of these features could lead to a fundamental difference from the infringing product. Therefore, under the traditional approach to equivalence, such a feature must be analysed according to its function and in the context of the description in order to determine whether it has been substituted by an equivalent feature.

Although the filing rules provide an initial guide to the interpretation of claims, the analysis of equivalents in Mexico cannot be reduced to this type of claim because some patents do not include such drafting, and the fact that a certain feature is not in a product does not exclude the possibility that it has been substituted by another equivalent feature.

Therefore, the same analysis of whether a person skilled in the art could substitute such a feature for an equivalent feature in light of the description and drawings must be carried out for all features in the claim, just as in the case of the features in claims drafted in two parts with a characterising section.

This criterion is clearly inconsistent with some US decisions in terms of foreseeable features, but two differences justify this criterion under Mexican law and practice.

First, the Mexican patent system has no register of certified professionals who are qualified to undertake patent prosecution before the institute. Accordingly, many patents are filed directly by inventors or by legal professionals who are not necessarily skilled in patent prosecution. The holders of such patents would be unable to use the doctrine of equivalents and would have no recourse against copies of their inventions with obvious and insignificant variations or changes.

Second, if the claim included a feature which the patent holder had expressly excluded from protection during prosecution, it would have been either excluded from the claim or put in the prior art section of a two-part drafting. Both issues must be corrected through a nullity action before the same patent office, which is a separate proceeding - unlike in the United States, where validity and infringement are analysed by the same court concurrently.

Therefore, it appears that in Mexico, an approach similar to that taken in Graver Tank & Manufacturing Company v Linde Air Products Company (1950) and Warner Jenkinson v Hilton Davis Chem (1997) would be more suitable.

For further information on this topic please contact Juan Carlos Amaro or Héctor Elias Chagoya at Becerril, Coca & Becerril SC by telephone (+52 55 5263 8730), fax (+52 55 5263 8731) or email ([email protected] or [email protected]).

An earlier version of this update first appeared in IP Value 2012 - An international guide for the boardroom, published by IAM magazine, part of the IP Media Group. For further information please visit