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CAFC Updates


By April 4, 2022No Comments

Littelfuse brought a patent infringement action against Mersen alleging that Mersen infringes U.S. Patent No. 9,564,281 which is directed to a fuse end cap for providing an electrical connection between a fuse and an electrical conductor. After the district court construed the patent claims, the parties stipulated to a judgment of non-infringement. Littelfuse now appeals the district court’s claim constructions. In the course of the litigation, the district court construed the term “fastening stem” to mean a “stem that attaches or joins other components” and the phrase “a fastening stem that extends from the mounting cuff and into the second cavity of the terminal that receives the conductor” to mean “a stem that extends from the mounting cuff and into the second cavity of the terminal that receives the conductor, and attaches the mounting cuff to the terminal.” In further clarifying its constructions, the district court made clear that the claims do not cover a single-piece apparatus (i.e., an end cap formed from a single piece of material), making that point expressly in its order denying reconsideration of its claim constructions, stating that “the fuse end cap described in claim 1 is of multi-piece construction.” However, the CAFC finds that the recitation of a single-piece apparatus in dependent claims is persuasive evidence that the independent claims also cover a single-piece apparatus, and that the district court’s construction would not only render the dependent claims superfluous, but would mean that those claims would have no scope at all, a result that should be avoided when possible. The CAFC concludes that the claim construction of the “fastening stem” limitation that is most consistent with the claims, specification, and prosecution history does not confine the independent claims to embodiments in which the fuse end cap is formed from multiple pieces of material. For that reason, the CAFC vacates the court’s judgment of noninfringement and remands the case for the district court to adopt a new construction of the “fastening stem” limitations that allows for the independent claims to cover both single-piece and multi-piece embodiments. 


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