Federal Circuit Rules A “Fastening Stem” Need Not Fasten Separate Pieces
On April 4, 2022, the Court of Appeals for the Federal Circuit (CAFC) issued a precedential opinion vacating claim constructions ordered by the United States District Court for the District of Massachusetts in No. 1:17-cv-12375-IT, Judge Indira Talwani. Littelfuse, Inc. v. Mersen USA EP Corp., __ F.3d __ (Fed. Cir. April 4, 2022). In its order, the CAFC concluded that the district court’s constructions incorrectly limited claim scope to a preferred embodiment and rendered certain dependent claims superfluous.
Plaintiff brought a patent infringement action alleging defendant infringed plaintiff’s ’281 patent. The ’281 patent is directed to a fuse end cap apparatus for providing an electrical connection between a fuse and an electrical conductor. The specification of the ’281 patent describes a generic fuse end cap embodiment and three specific embodiments: a “machined end cap,” a “stamped end cap,” and an “assembled end cap.” The machined end cap and the stamped end cap are manufactured from a “single piece of … material,” while the assembled end cap is formed “from two separate pieces of … material.”
Independent claim 1 of the ’281 patent recites “[a] fuse end cap comprising: a mounting cuff … that receives an end of a fuse body … a terminal … that receives a conductor … and a fastening stem that extends from the mounting cuff and into the … terminal that receives the conductor. Claims 8 and 9 each depend directly on claim 1 and recite the mounting cuff and the terminal are machined (claim 8) or stamped (claim 9) from a single, contiguous piece of conductive material.”
During prosecution claim 1 was initially rejected and a restriction requirement was issued finding claims 8 and 9 directed to distinct species of the invention that needed to be claimed in separate applications. In response, the “fastening stem” limitation was added to claim 1. Claim 1 was then allowed and claims 8 and 9 were rejoined; each now being derived from the allowable generic claim 1 and no longer being directed to distinct species.
The district court construed the disputed term “fastening stem” of claim 1 to mean a “stem that attaches or joins other components” (and similarly construed analogous terms in other claims) and clarified that this construction requires the fuse end cap of claim 1 be constructed of more than a single piece of material. The parties then stipulated to a judgment of non-infringement, and plaintiff appealed the district court’s claim constructions.
The CAFC reviewed the district court’s claim constructions and interpretations of intrinsic evidence de novo. This review began with a recitation of the general rule that if a dependent claim reads on a particular embodiment of the claimed invention, the corresponding independent claim must cover that embodiment as well. Relatedly, the CAFC stated that a construction of an independent claim that renders dependent claims meaningless is generally disfavored and violates the doctrine of claim differentiation under which different claims are presumed to have different scope.
The CAFC noted that independent claim 1 of the ’281 patent recites a fuse end cap comprising three elements: a mounting cuff, a terminal, and a fastening stem. Dependent claims 8 and 9 further limit claim 1 by requiring that the end cap be formed “from a single, contiguous piece of conductive material.” The CAFC concluded that, under the doctrine of claim differentiation, claim 1 is presumed to cover the single, contiguous piece embodiments of claim 8 and 9.
The CAFC considered appellant’s reliance on case law that stands for the proposition that, notwithstanding this doctrine of claim differentiation, a construction that renders certain claims superfluous need not be rejected if that construction is consistent with the teachings of the specification. But the CAFC concluded that appellee’s construction, which did not limit claim 1 to multi-piece designs, was also supported by the specification.
While conceding that the specification of the ’281 patent refers to a “fastening stem” only with respect to the multi-piece “assembled end cap” embodiment, the CAFC cautioned that courts ordinarily should not limit “the claimed invention to preferred embodiments or specific examples in the specification.” The CAFC further concluded that limiting claim 1 of the ’281 patent to a preferred embodiment would be improper when nothing in the specification states that a fastening stem cannot be present in a single-piece apparatus, and because one can envision a fastening stem in a single-piece embodiment.
With respect to the prosecution history, the CAFC further rejected the district court’s inference that the examiner’s re-joinder of the dependent claims was based on a misunderstanding and did not indicate that the examiner understood claim 1 to cover single-piece designs.
The CAFC accordingly vacated the district court’s claim construction and judgment of non-infringement and remanded the case for the district court to adopt a new construction of “fastening stem” that allows for the independent claims to cover both single-piece and multi-piece designs.