by Dennis Crouch
Littelfuse, Inc. v. Mersen USA EP Corp., 2022 WL 995611, — 4th — (Fed. Cir. Apr. 4, 2022)
The district court narrowly construed Littelfuse’s U.S. Patent No. 9,564,281–leading to an admission of non-infringement. On appeal, the Federal Circuit has vacated and remanded–finding that the proper construction provides a broader scope.
The patent claims an end-cap for a fuse and particularly requires “a fastening stem  that extends from the mounting cuff  and into [a] cavity  of the terminal .” Claim 1 does not expressly indicate whether these parts (cuff / stem / terminal) are made from a single piece of metal (unitary) or instead are multi-piece. Claims 8 & 9, do provide for unitary bodies that are machined/stamped “from a single, contiguous piece of conductive material.”
The district court construed claim 1 as covering only a multi-piece apparatus. Since Mersen’s fuses were clearly unitary, Littelfuse conceded the absence of literal infringement. In addition, Littelfuse had narrowed this portion of the claim during prosecution — that amendment also likely foreclosed a claim of equivalents.
On appeal, the Federal Circuit rejected this narrow claim construction on the following canons:
- Textualism: Look first to the language of the claim at issue. Here, claim 1 does not require a multi-piece arrangement.
- Claim Differentiation: Interpret an independent and dependent claims so that their coverage fits like nested dolls. Here, the district court interpreted claim 1 as excluding a unitary-body while dependent claims 8&9 require a unitary body.
- Consider the Prosecution History: Here, the examiner wrote in their reasons for allowance that claims 8 & 9 “require all the limitations of [claim 1].” This gives weight to the Claim Differentiation canon.
- Don’t Limit Claims to the Preferred Embodiment: Here, the only embodiment that included the stem/cuff/terminal arrangement was a multi-piece apparatus. But, “Nothing in the specification states that a fastening stem cannot be present in a single-piece apparatus. . . . One can envision a stem that projects from the side of the mounting cuff even in an embodiment in which the fuse end cap is formed from a single piece of material.”
These canons together led the Federal Circuit to reject the district court’s claim construction.
Not such an easy case: So far, I’ve suggested that this was an easy case. But, the district court also had good reason for its determination that the end-cap was a multi-part. In particular, embodiments of the specification appear to provide for two types of end-units. Unitary and multi-part. The unitary embodiments do not have the fastening stem — it is not needed because the cuff and terminal are made of the same piece of metal. On the other hand, the multi-part embodiments do show the fastening stem — it is needed in order to connect the cuff and terminal because they are separate pieces of metal. You can see this difference from the multi-part drawing (above) with the unitary drawing (below). The original claims did not include the fastening stem, but that limitation was added during prosecution in order to avoid prior art. That addition, according to the district court, shifted the claim meaning to only cover multi-part caps. The district court noted the dependent claims but suggested that it was a mistake by the examiner to allow those after the amendment.
On remand: The patent discloses a multi-part cap with a stem; and a unitary cap without a stem. The accused product is apparently a merger of these two – a unitary cap with a stem. The Federal Circuit has ruled here that the claims extend that far. On remand, the district court may consider whether the full extent of this expanded claim scope is supported under the written description and enablement requirements of 112(a).