In Williamson v. Citrix Online, LLC (Fed. Cir. 2015), the Federal Circuit issued an en banc opinion that changes the rules for functional claiming. Patentees will want to pay close attention to this opinion to mitigate the risk of having their patents construed in an unintended manner, or, worse, having their patents invalidated.

As background, functional claiming is a practice by which a patentee attempts to claim something by what it does rather than by what it is. An example of this type of functional claim is “a recording element,” which could be claimed more structurally as “electromagnetic media.” Under ordinary claim construction rules, functional claiming can be a powerful tool to obtain broad patent scope that covers multiple ways of performing a function or achieving a desired result.

A means-plus-function claim is a type of functional claim that is governed by different rules. Means-plus-function claiming is authorized by 35 U.S.C. § 112 (f) (pre-AIA para. 6), which allows a patentee to express a claim in terms of a means or step for performing a function without reciting structure. Patentees indicate they wish to rely on this framework by reciting “means for” or the like within their claims. Continuing with the example above, such a claim would recite “means for recording.” Importantly, such claims are construed to cover the structure described in the specification for performing the function, and equivalents thereof. If structure sufficient to perform the function is not provided in the specification, the claim is invalid as indefinite. Typically, unless they consciously made the decision to use the “means for” phrasing, patentees want to avoid their functional claims being interpreted under this framework to obtain the benefits of broad functional claiming without being tied to the specific structure disclosed in the specification. Prior to Williamson, there was a strong presumption that unless a patentee used the word “means,” the claim was not subject to the statutory means-plus-function framework and would therefore be construed under ordinary methodology.

In Williamson, the Federal Circuit changed that by overruling its previous line of cases establishing the strong presumption against invoking the means-plus-function framework for claims that do not recite the phrase “means for.” Now the standard for determining whether or not the statutory means-plus-function framework applies is whether the words of the claim are understood by persons of ordinary skill in the art to have a sufficiently definite meaning as the name for structure. When the claim does not use the term “means,” the statutory means-plus-function framework will still apply if a challenger can demonstrate the term fails to “recite sufficiently definite structure” or claims a “function without reciting sufficient structure for performing that function.” This change will cause more patents to be interpreted under the statutory means-plus-function framework and potentially invalidated under that framework.

The phrase at issue in Williamson was “distributed learning control module.” Using the rule articulated above, the Federal Circuit determined the statutory means-plus-function framework applied. Under that framework, it turned to the specification to determine the structure corresponding to the claimed function. Unfortunately for the patentee in this case, the Federal Circuit determined the specification did not disclose adequate corresponding structure and invalidated the claim as indefinite.

This issue will likely be most important for software cases where functional claiming is prevalent and specifications can sometimes be thin on structure. However, the rule could also implicate even simple mechanical cases as words like “mechanism” and “device” could invoke the means-plus-function statute in some circumstances. Avoiding these words, or at least including some claims with alternate phrasing, will help mitigate being stuck with an unintended means-plus-function claim construction. And, in all cases, patentees must include a description of structure corresponding to the functions recited in the claims to avoid the worst-case scenario of patent invalidity based on a lack of written description.