Ambiguous Patent Claims

Patents have a reputation of being difficult to read and understand and a key part of most patent litigation proceedings is ‘construing’ or providing meaning to the claims of the patent. A recent decision of the Federal Court considered a series of claims which it determined were not possible to be understood – the claims were ambiguous. As a result, the claims were declared invalid.

Declaring claims invalid for being ambiguous is rarely done in Canada. Various decisions have held over the years that claims are invalid for being ambiguous only if it is not possible to give the claim meaning. As Justice Hughes said in Pfizer Canada Inc. v. Canada (Minister of Health), 2005 FC 1725 at 53, “ambiguity is truly a last resort, rarely, if ever, to be used.”

Claim construction involves looking at the words of the claim and giving meaning to those words through the eyes of the ‘skilled person’, a hypothetical person interested in the technology at issue. As stated by the Supreme Court (Whirlpool at para 45):

The key to purposive construction is therefore the identification by the court, with the assistance of the skilled reader, of the particular words or phrases in the claims that describe what the inventor considered to be the “essential” elements of his invention.

In practice, this process can be difficult and is typically very contentious in litigation. Many patent disputes are determined by the claim construction. Once the meaning of the claims has been determined, then often infringement and validity are resolved as well.

In the recent decision of Tekna Plasma Systems Inc. v. AP&C Advanced Powders & Coatings Inc., 2024 FC 871, Justice McHaffie concluded that, “with the exception of a few claims in the ’236 Patent, it is impossible for the skilled reader to know or determine whether or not a powder particle has a depletion layer within the meaning of the patents’ claims. Neither the claims nor the disclosure of the patents provide the reader with the ability to understand and assess whether a particle has a depletion layer, and thus whether a given process or system reads on the claims or not.”

In Tekna, the skilled person, with experience in the production metal powders and the analysis of such powders, was faced with determining the meaning of two layers on a reactive metal powder in accordance with the claims, with a first layer “being a depletion layer deeper and thicker” than the second layer. The court determined that this term would not have a known meaning to the skilled person and the skilled person would not have any way to distinguish between a particle that has a ‘depletion layer’ of the claim 1 and a particle that does not.

This finding was determinative of ambiguity. Without the skilled person being able to determine in advance whether something would infringe the claim or not, the claim is invalid.

The Federal Court of Appeal had earlier described some principles for assessing whether a claim was ambiguous: a) the claim may be invalid if the language used is avoidably ambiguous or obscure; b) but not invalid it the phrase can be interpreted using grammatical rules and common sense; c) if it impossible to determine its scope it is ambiguous than it is ambiguous; but d) not invalid if it is simply not concision and lucidity.

It has been rare that a claim is invalid for being ambiguous. In 2017 in Bombardier Recreational Products Inc. v. Arctic Cat Inc., 2017 FC 207 aff’d 2018 FCA 207, claims on a design of a snowmobile were found invalid for ambiguity where it was unclear what new position was required by the claims: “The problem in this case is that the rider’s forward position, which is manifested by some measurements according to the inventors, never teaches how the configuration will be obtained or, for that matter, whether the measurements are a valid prediction of a new configuration.”

In a trial that I was involved in, we successfully persuaded the court in Pollard Banknote Limited v. BABN Technologies Corp., 2016 FC 883, that a dependent claim invalid because it contradicted the main claim: “In my view, claim 2 cannot be given any reasonable interpretation because the additional limitation of claim 2 is incompatible with the elements of claim 1 which are incorporated into claim 2 by its dependency.” More recently, several dependent claims where found ambiguous due to inconsistencies with parent claims in NCS Multistage Inc. v. Kobold Corporation, 2023 FC 1486 at 1138.

The decision in Tekna shows the importance of clear drafting of patent applications and the use language that is either known to the industry or defined in the description of the patent to avoid findings of ambiguous, and therefore invalid, claims.