Addressing for the first time the standard and burden of proof for the “reasonably could have raised” requirement for inter partes review (IPR) estoppel to apply, the US Court of Appeals for the Federal Circuit concluded that a patent owner bears the burden of proving that an IPR petitioner is estopped from using invalidity grounds that a skilled searcher conducting a diligent search reasonably could have been expected to discover. Ironburg Inventions Ltd. v. Valve Corp., Case Nos. 21-2296; -2297; 22-1070 (Fed. Cir. Apr. 3, 2023) (Lourie, Stark, JJ.) (Clevenger, J., dissenting).

Ironburg sued Valve for infringing Ironburg’s video game controller patent. Valve responded by filing an IPR petition in 2016. The Patent Trial & Appeal Board partially instituted on three grounds but declined to institute on two other grounds (the Non-Instituted Grounds), as was permitted prior to the Supreme Court’s 2018 decision in SAS Institute Inc. v. Iancu. Valve did not seek remand pursuant to SAS, which would have allowed the Board to consider the Non-Instituted Grounds. In the district court litigation, Valve alleged invalidity based on the Non-Instituted Grounds and grounds Valve learned of from a third party’s IPR filed after Valve filed its IPR (the Non-Petitioned Grounds). Ironburg filed a motion asserting that Valve was estopped, pursuant to 35 U.S.C. § 315(e)(2), from asserting both the Non-Instituted Grounds and the Non-Petitioned Grounds. The district court granted Ironburg’s motion in full, removing all of Valve’s invalidity defenses. After trial, the jury returned a verdict finding that Valve willfully infringed the patent. Valve appealed.

35 U.S.C. § 315(e)(2) precludes an IPR petitioner from asserting invalidity during a district court proceeding based on “any ground that the petitioner raised or reasonably could have raised during that [IPR].” The Federal Circuit first addressed the legal standard needed to meet the “reasonably could have raised” requirement for IPR estoppel. The Court found that the “skilled searcher” standard used by several district courts is appropriate, as opposed to a higher “scorched earth” search standard. The “skilled searcher” standard is consistent with the § 315(e)(2) statutory requirement of discovering prior art references that “reasonably could have been raised.”

The Federal Circuit next addressed which party has the burden to prove what prior art references a skilled searcher reasonably would, or would not, have been expected to discover. The district court placed the burden on Valve, the party challenging the patent’s validity, and determined that Valve did not show how difficult it was to find the Non-Petitioned Grounds that Valve did not initially uncover. The Court noted that the third party that did find the Non-Petitioned Grounds may have used a “scorched earth” search, which would make its discovery of the Non-Petitioned Grounds irrelevant to estoppel. The Court concluded that the patent owner has the burden of proving what a skilled searcher reasonably would have found because the patent holder is looking to benefit from estoppel. The Court explained that this conclusion is consistent with the practice of placing the burden on the party asserting [...]

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