IRONBURG INVENTIONS LTD. v. VALVE CORPORATION
Authored by: Jeremy J. Gustrowsky
In a second trip to the Federal Circuit involving a video game controller patent dispute, the court has provided important guidance on what it takes to prove that a patent challenger “reasonably could have raised” an invalidity ground during an inter partes review (IPR). The decision reverses a district court ruling that had blocked Valve Corporation from raising two invalidity grounds against Ironburg Inventions’ U.S. Patent No. 8,641,525, which covers a game controller with rear-mounted paddle controls.
The case revolves around the IPR estoppel statute, 35 U.S.C. § 315(e)(2), which prevents a petitioner from later asserting in court any invalidity ground it “raised or reasonably could have raised” during an IPR. After Valve’s initial IPR petition resulted in a final written decision, Valve sought to assert two new invalidity grounds in district court based on prior art that a third party (Collective Minds Gaming) had identified in a separate IPR petition: one ground based on U.S. Published Patent Application No. 2010/0298053 (Kotkin), and another combining U.S. Patent No. 6,760,013 (Willner), Japanese Patent Application No. JP-A H10-020951 (Koji), and U.S. Patent No. 5,773,769 (Raymond). The district court found Valve estopped from raising either ground.
On the Kotkin reference, the Federal Circuit held that the district court’s finding of discoverability rested on too thin a record. The lower court had reasoned that because Kotkin appeared within patent classifications that Valve’s own searcher (Landon IP) had searched, it was reasonably discoverable. But those classification searches returned over 26,000 references in a Japanese-language database alone. The Federal Circuit held that “something more is required for estoppel when a classification search alone returns an unreviewable number of search results.” While the court declined to mandate manual review in every case, it made clear that thousands of unfiltered hits do not equal “discovery” for estoppel purposes. Typically, keyword searches, citation searches, or other narrowing techniques would follow an initial classification search.
On the Willner-Koji-Raymond combination, the court tackled a different problem: hindsight bias in Ironburg’s evidence. Ironburg had hired Cardinal IP to perform searches in 2023, well after Valve’s 2016 IPR petition, to demonstrate that a diligent searcher could have found the references back then. The Federal Circuit found that the Cardinal searches were tainted by hindsight because early forward-and-backward citation searches would have pulled in patents and publications that did not exist at the time of the original IPR petition, including a 2023 Ironburg design patent that cited Raymond. The searcher then used results from these tainted searches to craft subsequent keyword and classification queries, infecting the entire search methodology. A late attempt by Cardinal to apply date filters only to one search string was “too little too late.”
The court also rejected a supplemental Cardinal search that had been specifically conducted to locate Raymond after the initial search treated it as only “peripherally relevant.” A project manager’s deposition testimony candidly admitted the supplemental search was undertaken “because there was another reference that had not yet been found,” which the Federal Circuit called “clear evidence of hindsight bias.”
Judge Stark’s concurrence offers additional helpful framing, distinguishing between a prior art reference’s “accessibility” and its “findability.” A reference buried among tens of thousands of classification hits may be accessible but is not necessarily findable. By contrast, a reference cited on the face of the challenged patent (as Willner was here) is plainly findable. Judge Stark also emphasized a two-step analysis under § 315(e)(2): first, whether the references were findable, and second, whether the invalidity ground itself would have been discoverable based on those references.
The decision is significant for patent litigators on both sides of IPR estoppel disputes. Patent owners seeking to invoke estoppel need to do more than show that a reference could theoretically be located within a broad classification. Challengers, meanwhile, gain ammunition to scrutinize whether the patent owner’s evidence of “discoverability” is actually a hindsight-driven reconstruction. On remand, the district court must now consider Valve’s invalidity arguments based on Kotkin and the Willner-Koji-Raymond combination on the merits.