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Explore the latest in patent, trademark, and copyright cases on the Merchant & Gould LLP blog. Stay informed with expert insights on intellectual property law updates.

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Last week, the U.S. Court of Appeals for the Federal Circuit issued a decision in <a href="https://www.cafc.uscourts.gov/opinions-orders/24-2088.OPINION.6-18-2026_2711717.pdf">Ironburg Inventions Ltd. v. Valve Corporation, No. 2024-2088 (June 18, 2026)</a>, reversing and remanding a district court’s application of IPR estoppel and further clarifying the evidence needed to prove that a prior-art ground “reasonably could have been raised” in IPR.

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Ironburg owns U.S. Patent No. 8,641,525, which is directed to video game controllers with elongated back controls that can be operated by the user’s non-thumb fingers. Ironburg accused Valve Corp. of infringing its patent. Valve previously challenged the patent’s validity by filing a petition for inter partes review (IPR), which was partially instituted and culminated in a final written decision in September 2017. In the district court, Valve sought to assert invalidity grounds that had not been included in its IPR petition. The district court held that Valve was estopped under 35 U.S.C. §&nbsp;315(e)(2) from raising those grounds because they reasonably could have been found and raised in the earlier IPR. Valve appealed.

The Federal Circuit reversed. First, the Court held that a patentee cannot prove IPR estoppel merely by showing that a reference would appear somewhere in a broad patent classification search. Here, the asserted reference was within classifications searched by Valve’s searcher, but those searches returned 26,333 references. The Court explained that when a search produces such a large number of results, “something more” is needed to show that the reference was reasonably discoverable.

Second, the Court held that the skilled-searcher inquiry must be judged as of the IPR petition date, without relying on hindsight-tainted searches. The Court emphasized that the question is what a skilled searcher exercising reasonable diligence would have found before the relevant IPR petition, not what a later searcher could find using later-developed information or techniques.

Finally, the Court reinforced that IPR estoppel applies to invalidity “grounds,” not isolated references. Reference findability is part of the inquiry, but it is not the whole inquiry. The majority explained that if one reference necessary to a multi-reference ground was not reasonably discoverable, then the ground itself could not reasonably have been raised.

In a concurrence, Judge Stark framed the inquiry as one requiring proof both that the references were findable and that the invalidity ground based on those references would reasonably have been discovered.

Coauthored by Joseph Dubis and Zachary Yeager

Federal Circuit Clarifies the Skilled-Searcher Test in Ongoing Valve Controller Patent Litigation

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