In Ironburg Inventions Ltd. v. Valve Corporation, [2024-2088] (Fed. Cir. 2026), the Federal Circuit reversed and remanded the district court’s grant of partial summary judgment in favor of the patent owner on the issue of IPR estoppel, finding that estoppel did not apply because it was not shown that a reasonably diligent  search could have been expected to discover the references at issue.

Valve challenged Ironburg’s patent in a  first IPR, and again in a second IPR.  After  the Final Written decision in the first IPR,  IPR Ironburg successfully asserted estoppel under 35 USC 315(e)(1), the Board finding that a skilled searcher  conducting a reasonably diligent  search could have been expected to discover the reference on which the second IPR was based.  A third party also filed an IPR against Ironburg’s patent, and Valve tried to amend its invalidity contentions in Ironburg’s infringement suit against it.  Ironburg moved for estoppel under 35 USC 315(e)(1), arguing that Valve should be estopped form asserting the grounds raised by the third-party IPR.  The District Court found that because the third party found the prior art, a skilled searcher could reasonably be expected to find the same prior art.

In a first appeal, the Federal Circuit held that the district erred in placing the burden on Valve to show that Valve reasonably could not have raised the third-party ground during the first IPR, when the burden was on Ironburg to show that estoppel applied to Valve.  The Federal Circuit further held that Ironburg failed to meet its burden by merely relying on the fact that the third party found the prior art, without any evidence about the third party’s diligence in finding the prior art. On remand, the district court again found Valve was estopped as to the prior art in the Valve’ second IPR and as to the prior art from the third party IPR.

Ironburg relied on searches by a private search company to show that the grounds in the prior IPRs would have been discoverable to a skilled searcher exercising reasonable diligence, and the district court determine that the prior art was reasonably discoverable.  In the present appeal, Valve argued: (1) that its pre-petition search evidence does not demonstrate that references were discoverable under a proper articulation of the skilled searcher standard, and (2) that Ironburg’s evidence from third-party searchers was irrelevant to the skilled searcher inquiry.

Regarding the skilled searcher inquiry, the Federal Circuit said the statutory language requires a focus on what reasonably, rather than possibly, could have been raised prior to the filing of a relevant IPR petition.  The Federal Circuit said when evidence is introduced that sheds light on what a skilled searcher may have discovered only after the time of the relevant IPR petition, such evidence is likely irrelevant to the skilled searcher inquiry.

The Federal Circuit identified two open questions regarding the skilled searcher inquiry:  First, whether the skilled searcher inquiry poses a question of law, reviewable de novo, or a question of fact, reviewable for clear error. Second what “discovery” within the skilled searcher inquiry entails.  However the Federal Circuit  neatly ducked both questions, finding that the reference was unfindable under any conception of what the skilled searcher.  

The Federal Circuit said that a reference was not discoverable merely because it is located in classifications that a searcher would believe to be relevant – at least where an unreviewably large number of references are returned by a skilled searcher’s diligent search.  This was in line with preponderant evidence of record in this case, which indicated that keyword searches or other narrowing techniques would be used after an initial classification search.  Because the district court was confronted with thousands of references in the search results yet still found that no narrowing was required for the reference to be deemed discovered, the Federal Court concluded the district court erred, warranting reversal of the finding of estoppel.

The Federal Circuit then addressed whether a search that was not date restricted to exclude references after the filing of the IPR Petition involved hindsight.  Because the searching included forward-and-backward searching the failure to exclude subsequent references which could contain backward citations could misrepresent what a reasonable search could find at the time the IPR was filed.  The Federal Circuit agreed, finding that the failure to date limit searches employing forward-and-backward searching taints the results of what a skilled searcher at the time of an IPR would discover.

Judge Stark wrote separately to highlight certain aspects, noting:

1. The patentee’s burden to show discoverability of invalidity grounds is not automatically satisfied by proving the findability of the prior art reference(s) on which the invalidity ground is based.
2. To prove estoppel, a patent owner must prove: (i) the prior art reference(s) at issue were findable by a skilled searcher conducting a diligent search and (ii) the skilled searcher also reasonably would have been expected to discover, based on the reference(s) found, the invalidity ground the challenger seeks to assert in court.
3. in at least some circumstances, “something more” than proving the mere accessibility  of a prior art reference is required in order to establish a skilled searcher performing a diligent search would have found the reference.
4. “Something more” than accessibility is not demonstrated when the only evidence in the record is that a skilled searcher would have undertaken a classification search that yielded, in addition to the reference now being asserted by the patent challenger, tens of thousands other references.
5. “Something more” may be satisfied the reference is expressly cited on the face of the patent being challenged.

in John Bean Technologies Corp. v. Morris & Associates, Inc., [2017-1502] (April 19, 2018), the Federal Circuit reversed the district court’s grant of summary judgment based on its finding of equitable estoppel, and remanded for proceedings consistent with this opinion.

In 2002, Morris wrote Bean that its recently issued U.S. Patent 6,397,622 was invalid over certain prior art, and demanding cessation of statements regarding infringement of the patent to Morris’ customers.  Eleven years later, Bean filed a request for ex parte reexamination, which after amending the existing claims to overcome the art identified by Morris, and adding new claims, issued in 2014.

Bean sued Morris on the reexamined U.S. Patent 6,397,622, and the district court granted Morris summary judgment based upon equitable estoppel.  Equitable estoppel which is an absolute bar to a patentee’s infringement action, consists of three elements: (1) the patentee engages in misleading conduct that leads the accused infringer to reasonably infer that the patentee does not intend to assert its patent against the accused infringer; (2) the accused infringer relies on that conduct; and (3) as a result of that reliance, the accused infringer would be materially prejudiced if the patentee is allowed to proceed with its infringement action.

The Federal Circuit noted the unusual nature of the case — namely that the finding of equitable estoppel was based on conduct before the issuance of the rights being asserted — the reexamination claims.  However relying upon the principles undergirding
the issuance of reexamination claims, i.e. that (1) reissue claims cannot be broader than the original claims; and (2) a patentee cannot assert reexamination claims to obtain damages prior to the issuance date of the reexamination certificate (unless they are identical in scope).  The Federal Circuit found that the amendments made during reexamination were both substantial and substantive. The Federal Circuit concluded that because the asserted claims did not exist at, or were substantively altered since, the time Morris wrote to Bean, Bean could not have engaged in misleading conduct or silence with respect to those claims.

The Federal Circuit allowed that there may be cases where the reexamined
claims contain fewer amendments such that the reexamined claims do not differ in
scope from the original claims, and might be considered identical for purposes of applying equitable estoppel, but found that is not the situation in the present case, and thus the district court abused its discretion in applying equitable estoppel to bar Bean’s infringement action.