Patent searches are a versatile tool that can be used as a preventative measure to avoid costly litigation and as a weapon to invalidate an allegedly infringed patent. As emphasized by a recent Federal Circuit decision, however, patent searches in the context of litigation are often only as valuable as they are thorough.

In Ironburg Inventions Ltd. v. Valve Corp., No. 2024-2088, 2026 WL 1755196 (Fed. Cir. June 18, 2026), the Federal Circuit addressed whether Valve was prevented from relying on certain prior art to invalidate a patent it was accused of infringing. There, Ironburg argued that Valve failed to raise the subject prior art in an inter partes review (IPR) Valve previously filed against one of the patents-in-suit and was thus estopped from relying on the newly asserted prior art in a district court action under 35 U.S.C. § 315(e).

Under 35 U.S.C. § 315(e), a petitioner in an IPR that results in a final written decision generally may not later assert in a civil action any invalidity ground that the petitioner “raised or reasonably could have raised” during that IPR. In other words, if the petitioner based its IPR on the results of a rudimentary patent search and that search failed to identify certain prior art, that prior art cannot later be asserted by the same petitioner when found by other means. Whether a more thorough patent search reasonably could have been expected to discover the additional prior art is evaluated through the lens of a “skilled searcher conducting a diligent search.” Significantly, the burden of proof to show prior art reasonably could have been raised belongs to the patent owner.

Turning back to Ironburg Inventions Ltd. v. Valve Corporation, Valve ultimately persuaded the Federal Circuit that while it was possible that the subject prior art could have been found earlier, Ironburg failed to meet its burden of showing that discovery of the prior art was reasonable. To do so, Valve pointed to the significant number of hits resulting from a classification search used by its search vendor to show it would be unreasonable for even a skilled searcher working diligently to review each of the several thousand hits. Because Ironburg did not provide evidence of how Valve’s vendor narrowed its search, the court allowed Valve’s reliance on the newly asserted art.

Yet the takeaway of this case is not only the importance of understanding which party carries the burden of proof. Rather, it is also the value of a thorough, well documented, initial patent search. Indeed, had the subject prior art been found before the initial IPR several waves of appeals and remands may have been avoided. Of course, no prior art search is perfect, but a thorough search as opposed to a rush job can solve problems before they arise.

The business lesson is straightforward. Prior art searches should not be treated as a check-the-box exercise. For companies preparing to enter a crowded space, evaluating a patent threat, or considering an IPR, the quality and documentation of the search can affect both legal strategy and cost. A more thorough search at the outset may be more expensive, but it can help identify stronger invalidity positions earlier, preserve strategic options, and reduce the risk of later fights over what could or should have been raised the first time around. Moreover, it is just as important to recognize when a more preliminary search may be appropriate, such as before pursuing patent rights.

Accordingly, companies should consider not only whether to conduct a prior art search, but also how to structure and preserve it. Keeping a clear record of the search methodology may prove valuable long after the search is complete.

If your company is considering competing in a crowded space, facing a patent demand, or considering an IPR challenge, early coordination with patent counsel can help ensure that prior art searching supports both immediate business decisions and long-term litigation strategy.