In a report published by IP Litigator, Partner Joshua Stern, Senior Associate Gilbert Smolenski and former Counsel Erik Halverson delve into the Ironburg Opinion issued by the Federal Circuit on April 3, 2023. The opinion set forth the current standards for arguing IPR estoppel in district court.
Excerpt: “It explained that placing the burden on patent owners is consistent with “general practice that a party asserting an affirmative defense bears the burden to prove it” and that Ironburg had not identified a persuasive basis to depart from that general rule. Specifically, it rejected Ironburg’s argument that the burden of proof should not rest with the patent owner because often a defendant “will aim to protect details of its search efforts by asserting attorney-client privilege relating to its undertaking.”
Two primary findings were made in the consideration of whether estoppel applied to the Non-Petitioned Grounds to the district court. Firstly, the petitioner is subject to estoppel assuming all other conditions of the statute are satisfied, and a skilled searcher conducting a diligent search could have been expected to discover invalidity grounds. Secondly, the panel held that patent owners, as opposed to defendants, are tasked with proving, by a preponderance of evidence, that invalidity grounds could be found by a skilled searcher executing a reasonably diligent search. Patent owners are responsible for carrying that burden in the case of affirmative defense as that is considered “general practice.” The Ironburg standards should be considered by patent owners and petitioner/defendants when developing strategies for arguing IPR estoppel in district court.
