Is "Burying" Important Prior Art in a Large Number of Insignificant References Inequitable Conduct in USPTO Patent Prosecution?

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Several recent cases illustrate a continuing and evolving split among the different federal district courts as to whether a defense of inequitable conduct can successfully be based on “burying.”

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The U.S. Court of Appeals for the Federal Circuit (CAFC) in Therasense[1] set the current standard for inequitable conduct.  While the CAFC recognized burying examiners with a deluge of prior art references -- most of which have marginal value -- as a problem straining the USPTO’s resources and contributing to a backlog of administrative work, the Court did not decide in that particular case whether a defense of inequitable conduct can be successfully based on burying.  Burying here means submitting one or more highly material prior art references along with a large group of relatively insignificant references in an information disclosure statement (IDS), or series of IDSs.  To constitute inequitable conduct under Therasense, it would seem that the burying must be done with deceptive intent and the “buried" reference must be but-for material.   Several recent cases illustrate a continuing and evolving split among the different federal district courts as to whether a defense of inequitable conduct can successfully be based on “burying.” 

In a July 2023 decision by the U.S. District Court for the Northern District of Illinois,[2] Illinois Tool Works, Inc. (ITW) had sued its competitor Termax, LLC for infringing two patents relating to automotive component fasteners.  Termax filed a petition in the Patent Trial and Appeal Board (PTAB) for Inter Partes Review (IPR) of one of the two patents, and successfully invalidated the patent during the pendency of the district court case.  In the meantime, ITW prosecuted an application for a third patent in the USPTO.  In an IDS submitted during prosecution of that third patent, ITW submitted the PTAB’s final decision invalidating one of the two original patents-in-suit.  When the third patent was granted, ITW amended its complaint against Termax to allege infringement of the new (i.e., third) patent instead of the PTAB-invalidated one.  In the IDS in question, ITW submitted seven non-patent references including the PTAB’s final decision. 

With regard to ITW’s third patent, Termax alleged that ITW committed inequitable conduct by burying the PTAB’s decision invalidating the previously-asserted patent in a multiplicity of other references in the IDS, and by failing to draw the examiner’s attention to a particularly relevant part of the PTAB’s decision.  The district court found that the PTAB decision was plausibly but-for material.  However, the court also found that there was no obligation for ITW to highlight for the examiner the relevance of each cited reference. 

Further, the district court found that including the PTAB decision in an IDS among only six other references could not amount to burying, let alone burying with deceptive intent.   The district court did not reach the question of whether burying constitutes inequitable conduct, instead stating that that the CAFC has not established definitively whether or under what circumstances burying may constitute inequitable conduct.  

In PACT XPP Schweiz AG v. Intel Corp.,[3] PACT alleged that an Intel system infringed twelve of PACT’s patents relating to multi-processor computer chips that increase processing speeds and expand memory storage.   After the conclusion of a series of IPRs, appeals of the IPR decisions, and other litigation, PACT moved for summary judgment on Intel’s affirmative defenses, including inequitable conduct. 

Among other bases for its inequitable conduct defense, Intel asserted that PACT intentionally buried prior art references during USPTO prosecution of its applications for two of PACT’s asserted patents.  The U.S. District Court for the District of Delaware explained: “Intel's expert will testify that the reference was not cumulative of others provided to the PTO, and that it would have been material. Intel also cites evidence that despite the PTO’s repeated objections to PACT’s ‘voluminous’ information disclosure statements containing only marginally relevant or irrelevant citations, and PACTs awareness of the importance of the prior art in question, PACT continued to dump documents.”  Without actually deciding the issue on the merits, the district court concluded that this testimony by Intel’s expert sufficiently created a factual dispute and, on that basis, denied summary judgment and allowed Intel to present the defense at trial.    

In PACT, the Delaware district court discussed the CAFC’s decisions in Fiskars[4] and Molins[5], rejecting PACT’s argument that Fiskars precludes basing an inequitable conduct defense on burying, and relying on Molins for the proposition that burying is a cognizable form of inequitable conduct.    

As detailed in Bridgestone Americas Tire Operations, LLC v. Speedways Tyres Limited et al.,[6] Bridgestone is the largest tire company in the world. Speedways makes and sells a tire like Bridgestone's Champion Hydro ND tire—the Agristorm nD2 tire. Bridgestone sued for infringement of a patent relating to that tire, and Speedways counterclaimed that the patent is unenforceable due to inequitable conduct.  More specifically, Speedways alleged that Bridgestone submitted over 150 patent references and 50 other publications to the USPTO and failed to submit three other references.  Speedways also alternatively argued the prosecuting attorney tried to hide the most relevant patent references (the same three references) by submitting them among a large number of less relevant references.  Bridgestone moved to dismiss Speedways’ inequitable conduct defense.    

The district court granted Bridgestone’s motion to dismiss the inequitable conduct defense, concluding that Speedways’ allegation was inadequate.  The court stated that “hiding references in a sea of other references is not ‘with[olding] or misrepresent[ing]’ prior art references,” and Speedways did “not provide any legal authority for the proposition that hiding material prior art references in a sea of other prior art references satisfies the ‘intent to mislead’ element.”  The district court’s decision did not discuss the pure “failure to disclose” alternative pleading by Speedways.  Nonetheless, it is apparent that the district court regards burying as not being a cognizable basis for an inequitable conduct defense.

Avoiding a finding of burying in jurisdictions that accept it as a basis for an inequitable conduct defense appears to require avoiding the disclosure to the USPTO of too many references with too much inequality of materiality of the references.  For “how many is too many references,” it appears that the standard is that number of references that would likely overwhelm the examiner.  A recent PTAB decision suggests that it would be wise to hesitate before submitting more than 100 prior art references in an IDS.  In Hum Industrial Technology, Inc. v. Amsted Rail Company, Inc.,[7] the USPTO instituted an IPR where two of the relied-on references had been previously cited by the applicant among 98 references submitted in IDSs during prosecution of the original application but had not been relied upon in any rejections by the examiner. The PTAB’s rationale for its reliance in the IPR institution decision included a statement that an examiner’s initials on almost 100 references does not indicate sufficient evaluation of relevance by the examiner.  This potentially has a bearing on the CAFC’s treatment of this same issue in the Fiskars case as it contradicts the view stated in Fiskars that, "any cited reference that is initialed by the examiner on an IDS in the prosecution history has been adequately considered by the examiner."

These recent cases show that there exists an unresolved district court divergence of thinking on whether burying can be the factual basis for a defense of inequitable conduct.  Whether the defense so pled can survive the early pleading phase of a case may depend on where and in which district the allegation is made, at least until the CAFC more definitively addresses the question.