IP Law Daily, PATENT—Fed. Cir.: Video game developer secures revival of invalidity defenses in video-game controller patent dispute, (Jun 22, 2026)

By Mandavi Singh, LL.M.

The court found insufficient evidence that the disputed invalidity grounds could reasonably have been raised during an earlier inter partes review and rejected hindsight-tainted search evidence used to support estoppel.

The U.S. Court of Appeals for the Federal Circuit has reversed a district court order barring Valve Corporation from asserting two invalidity grounds against a video-game controller patent owned by a licensing entity. The appellate court found that the district court improperly estopped Valve under 35 U.S.C. §315(e)(2) from relying on prior-art grounds that allegedly could have been raised during an earlier inter partes review (IPR). The court concluded that the evidence was insufficient to establish that one ground was reasonably discoverable and that hindsight-tainted search evidence could not support estoppel of the second ground (Ironburg Inventions Ltd. v. Valve Corp., No. 24-2088 (Fed. Cir. Jun. 18, 2026)).

Background. The plaintiff-appellee, Ironburg Inventions Ltd. (Ironburg), a patent-holding and licensing company, owns U.S. Patent No. 8,641,525 (the ’525 patent), which is directed to video-game controllers featuring additional controls on the back of the controller. The defendant-appellant, Valve Corporation (Valve), is a video game developer, publisher, and hardware manufacturer best known for operating the Steam digital gaming platform and for producing gaming hardware products. Ironburg alleged that Valve’s Steam® Controller infringed the ’525 patent.

After Ironburg sued Valve in 2015, Valve filed IPR2016-00948, challenging the patent before the Patent Trial and Appeal Board (PTAB). During the course of related proceedings, a third party, Collective Minds Gaming Co. Ltd. (CMG), filed another IPR petition asserting two additional obviousness grounds. One relied on U.S. Patent Publication No. 2010/0298053 (Kotkin). The other combined U.S. Patent No. 6,760,013 (Willner), Japanese Patent Application No. H10-020951 (Koji), and U.S. Patent No. 5,773,769 (Raymond). Although the CMG proceeding was later terminated, Valve amended its district-court invalidity contentions to include those grounds.

The district court held that Valve was estopped from asserting the CMG grounds under §315(e)(2). Following an earlier appeal, the Federal Circuit remanded after holding that Ironburg bore the burden of proving that the disputed grounds reasonably could have been raised during the earlier IPR. On remand, the district court again found estoppel, leading to the present appeal.

IPR estoppel. The Federal Circuit reiterated its earlier holding in Ironburg Inventions Ltd. v. Valve Corp., 64 F.4th 1274 (Fed. Cir. 2023), that the patent owner bears the burden of establishing that a disputed invalidity ground reasonably could have been raised during the IPR. The court also cited Ingenico Inc. v. IOENGINE, LLC, 136 F.4th 1354 (Fed. Cir. 2025), which clarified that §315(e)(2) applies to invalidity “grounds” rather than individual prior-art references.

Kotkin. The Federal Circuit first addressed the district court’s conclusion that Kotkin was reasonably discoverable based on searches performed by Valve’s search vendor before the IPR petition was filed.

The district court relied on evidence showing that the search vendor had searched patent classifications containing Kotkin. The Federal Circuit found that the analysis was inadequate because the relevant searches generated more than 26,000 references. The court concluded that the mere presence of Kotkin within those results did not establish that a skilled searcher reasonably would have discovered it. Evidence in the record indicated that classification searches ordinarily are supplemented by keyword searches, citation searches, or other narrowing techniques. Because the district court relied on an insufficient evidentiary basis, the court reversed the estoppel ruling concerning the Kotkin ground.

Willner-Koji-Raymond. The Federal Circuit next considered the district court’s reliance on searches performed by Ironburg’s search vendor after remand.

Ironburg offered evidence that later searches could locate Koji and Raymond through combinations of classification and citation searching. The Federal Circuit, however, concluded that the search methodology was tainted by hindsight bias. Certain searches relied on forward-and-backward citation techniques that incorporated references arising after Valve filed its IPR petition. The court determined that such information could not properly inform the inquiry into what a diligent searcher would have discovered at the relevant time.

The court further found that a supplemental search undertaken to locate Raymond demonstrated the same defect. Testimony showed that the search was conducted specifically because Raymond had not previously been found, indicating that the search strategy had been shaped by knowledge unavailable at the time of the original IPR petition. Because the evidence was influenced by hindsight, it could not reliably establish discoverability. The Federal Circuit therefore reversed the district court’s estoppel ruling concerning the Willner-Koji-Raymond ground as well.

Judge Stark’s concurrence. Circuit Judge Leonard P. Stark filed a separate concurring opinion. While agreeing with the majority, he emphasized that proving discoverability under the Federal Circuit’s “skilled searcher” framework requires more than showing that a prior-art reference was merely accessible. Judge Stark observed that future cases would continue to refine the distinction between a reference’s accessibility, findability, and the discoverability of an invalidity ground based upon that reference.

Outcome. Finally, the Federal Circuit reversed the district court’s estoppel rulings concerning both invalidity grounds and remanded for further proceedings. Costs were awarded to Valve.

The Case is No. 24-2088.

Judge: Hughes, T.

Attorneys: Gregory S. Tamkin (Dorsey & Whitney LLP) for Ironburg Inventions Ltd. Patrick A. Lujin (Shook, Hardy & Bacon, LLP) for Valve Corp.

Companies: Ironburg Inventions Ltd.; Valve Corp.

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