The Northern District of Iowa recently held that a defendant’s motion for partial summary judgment of invalidity was barred after the PTAB issued final written decisions, regardless of when the motion was filed. The defendant filed its motion before the final written decisions were issued, but the court rejected the defendant’s argument that the timing of the motion insulated it from estoppel.
The case involved six patents, two of which were the subject of PGR petitions that the defendant filed while the district court litigation was ongoing. During claim construction, the defendant argued that certain claim terms were indefinite. The district court agreed with the defendant and found the terms indefinite as a matter of law. Based on the court’s constructions, the defendant filed a motion for partial summary judgment seeking a determination that some of the patents—including the patents subject to PGR—were invalid.
In response, the plaintiff filed two motions: one seeking reconsideration of the court’s indefiniteness ruling, and another requesting a stay of the litigation pending resolution of the PGRs. The court granted the stay and deferred ruling on the summary judgment motion, noting that the board’s decisions could clarify relevant issues.
Afterwards, the board issued final written decisions in the PGRs finding that none of the claims were unpatentable for indefiniteness. In so doing, the board provided guidance on how a skilled artisan would interpret the disputed claim terms.
After lifting the stay, and with the board’s final written decisions in hand, the court denied the defendant’s motion for partial summary judgment of invalidity, finding that statutory estoppel under 35 U.S.C. § 325(e)(2) applied. Because the defendant raised or could have raised indefiniteness in the PGR proceedings, the court found that the defendant was estopped from finding that those claims were invalid on that basis in the district court.
Notably, in opposing estoppel, the defendant argued that because its motion was filed before the board’s final written decisions—i.e., before estoppel applied—the court could have ruled on it earlier and can still rule on it now. The court rejected this argument, noting that the plain language of the estoppel statute provides an “unequivocal bar” that “does not contain any limitation that would allow a petitioner to avoid estoppel if it raised the issue before post-grant review.” The court further found the defendant’s position inconsistent with Federal Circuit precedent holding that, after a final written decision, the defendant is estopped from maintaining its invalidity position during appeal even though it had first raised the invalidity defense in district court before the post-grant review.
Further, the court noted that even if estoppel did not apply, it still would have denied the defendant’s motion. With the benefit of the board’s claim construction analysis, the court granted the plaintiff’s motion for reconsideration and revised its earlier construction. The newly construed terms were no longer indefinite, rendering the defendant’s invalidity arguments moot.
Practice Tip: When implementing an overall invalidity strategy, a patent infringement defendant should carefully consider the ramifications of a final written decision from the PTAB. In particular, statutory estoppel will prevent a defendant from advancing invalidity arguments in district court, and even during appeal, including arguments it made prior to the start of a post-grant proceeding.
Intirion Corp. v. Coll. Prods., Inc., No. 23-CV-4023 (N.D. Iowa Sept. 16, 2025)
