Aftermath Of Ironburg – Practice Pitfalls And Pointers

A number of district courts, as well as the Court of Appeals for the Federal Circuit, have weighed in on whether and to what extent a patent challenger in an inter partes review (IPR) before the Patent Trial and Appeal Board may be estopped from making prior art based challenges in a district court litigation. In Ironburg Inventions Ltd. v. Valve Corporation, the Federal Circuit has clarified that the patent owner, not the patent challenger, bears the burden of proof on estoppel.

In Ironburg, after the conclusion of an inter partes review (IPR), the patent owner, Ironburg, argued that the patent challenger, Valve, was estopped from relying in district court on prior art that was not at issue in the IPR.