Federal Circuit: Only Minimal Evidence Needed to Satisfy Corroboration Requirement in Priority Contests

February 22, 2023

The US Court of Appeals for the Federal Circuit recently held that the Patent Trial and Appeal Board correctly considered evidence of multiple witnesses to be sufficient in corroborating actual reduction to practice when determining priority in interference proceedings, notwithstanding limited documentary evidence.

In Dionex Softron GmbH v. Agilent Technologies, Inc., the Federal Circuit affirmed a precedential decision issued by the US Patent and Trademark Office’s (USPTO’s) Patent Trial and Appeal Board (PTAB or Board), holding that substantial evidence supported the Board’s finding that actual reduction was sufficiently corroborated by the witness testimony of the coworkers.[1]

In an interference proceeding, the PTAB found that two of Agilent Technologies’ patent applications have priority over competing ones filed by Thermo Fisher Scientific unit Dionex Softron GmbH because Agilent proved a final reduction to practice prior to Dionex’s date of conception, and the PTAB thus concluded that priority is awarded to Agilent.[2]

Patent Interferences

A patent interference is an inter partes proceeding to determine which party was the first to invent commonly claimed subject matter.[3] Interferences are becoming rare because they only apply to pre–America Invents Act (AIA) patents, but they are a viable procedure for challenging the validity of an issued patent or otherwise allowable claims under virtually any theory of invalidity—provided that the challenged claims have an effective filing date of earlier than March 16, 2013.[4] Applications with an effective filing date of March 16, 2013, or later are not subject to interference proceedings.[5]

The only party that has standing to initiate or request an interference is an applicant with a pending patent application that contains allowable claims toward the same or substantially the same invention claimed in another pending application or unexpired patent.[6] In addition, a patent examiner can initiate an interference proceeding without formal prompting by another party if the claims are otherwise allowable.[7]

Once declared, the PTAB conducts the interference proceeding in two stages to determine the priority issues of multiple patent applications and see which party was the first to invent the commonly claimed (i.e., interfering) subject matter.[8] These two phases are known as the “preliminary motions phase” and the “priority phase.” During the preliminary motions phase, the patentability issues are decided, while during the priority phase, the administrative patent judges decide which party made the patent first.

The USPTO will consider prior art, support, and derivation.[9] It may also include limited discovery such as expert witness depositions regarding conception and reduction to practice.[10] The PTAB issues a decision on the validity or patentability of each challenged claim.[11]


A patent owner "bears the burden of establishing that its claimed invention is entitled to an earlier priority date than an asserted prior art reference."[12] A patent owner can demonstrate prior invention for a pre-AIA patent in one of two ways:

  1. Establish an earlier reduction to practice of the claimed invention before the critical date of the reference.
  2. Establish conception of the invention prior to the critical date plus reasonably continuous diligence to reduce the invention to practice after the critical date.[13]

An actual reduction to practice requires the following:

  1. Construction of an embodiment or performance of a process that meets all the limitations of the claims at issue.
  2. A determination that the invention would work for its intended purpose.
  3. Sufficient evidence to corroborate inventor testimony regarding these events.[14]

Conception must encompass all the limitations of the claims at issue and is the formation of "a definite and permanent idea of the complete and operative invention."[15] Conception and reduction to practice require a contemporaneous recognition of the invention represented in the claims—conception and reduction to practice cannot be established after the fact.[16]

Independent corroboration of evidence is required for both conception and reduction to practice. Previously it has been held by the Federal Circuit that an inventor's testimony may not corroborate unwitnessed evidence of the inventor, and the "testimony of one co-inventor cannot be used to help corroborate the testimony of another [inventor]."[17]


The Dionex decision provides more clarity as to the metes and bounds of the sufficiency of co-worker testimony in corroborating actual reduction to practice as well in regard to whether a negative inference should be drawn in the event of a lack of co-inventor testimony.

In 2018, both Agilent and Dionex applied for patents with the USPTO regarding a high-pressure liquid chromatography system to separate, identify, and quantify chemicals in sample mixtures.[18] The instituted interference was between Agilent’s US Patent Application No. 15/965,402 and Dionex’s US Patent Application No. 16/016,866.[19] In the interference, the Board identified Dionex as the senior party and Agilent as the junior party, thereby requiring that Agilent prove priority by a preponderance of the evidence.[20]

Later in the proceeding, Agilent and Dionex separately moved for judgment on the basis of priority due to their respective alleged dates of conception and reduction to practice.[21] The Board granted Agilent’s motion and denied Dionex’s motion, finding that Agilent proved conception as of May 1, 2007 and actual reduction to practice as of June 1, 2007, more than six months before Dionex’s earliest alleged conception date of December 4, 2007.[22]

Federal Circuit Ruling

In Dionex, the Federal Circuit, in its opinion, reviewed de novo the Board's legal conclusions concerning priority, conception, and reduction to practice. The Federal Circuit treated corroboration as a question of fact reviewed for substantial evidence and deferred to the Board’s resolution of evidentiary dispute, crediting seemingly minimal evidence to be sufficient. Finally, the Board's evidentiary determinations, including whether to draw an adverse inference, were reviewed for abuse of discretion.

In its analysis embraced by the Federal Circuit, the Board applied the rule of reason and found that the testimony of Wolfgang Kretz, one of Agilent’s two co-inventors, was sufficiently corroborated by two of his co-workers, Manfred Berndt and Martin Bäuerle, who had worked with Kretz during the relevant time.[23] Berndt and Bäuerle testified that Kretz successfully tested a prototype encompassing the claims at issue by June 1, 2007.[24]

Circuit Judge Leonard P. Stark wrote: “Under the flexible rule of reason approach, there was nothing inappropriate about the Board accepting” the testimony; although the inventor “may not have known every detail, [] omniscience is unnecessary under the rule of reason. . . . There is no per se requirement to infer that the testimony of an inventor who fails to testify would be harmful to the position of his co-inventor.”[25]

The Board rejected Dionex’s argument that it should draw a negative inference from the lack of testimony of the other co-inventor and the absence of contemporaneous documentary evidence. The Federal Circuit agreed with this seemingly low threshold of evidence and was highly deferential to the Board treating sufficiency of corroboration as a question of fact that it chose to review for substantial error, treating the drawing of negative inferences within the Board’s discretion.

Judge Stark wrote: “[T]he Board has discretion to determine whether to apply a negative inference based on what ‘is reasonable under the totality of evidence in the case’. . . . [There is] no mandate that the Board draw a negative inference whenever a party fails to present some types of documentary evidence an opposing party insists must exist.”[26]

Thus, the Federal Circuit treated corroboration as a factual finding reviewed for substantial evidence, while deferring to the Board’s resolution of evidentiary disputes, further developing the legal standard of a seemingly minimal threshold for corroboration.


This case sheds light on how the PTAB can use its discretion to weigh the evidence of inventor and co-worker testimony in corroborating the actual reduction to practice when determining priority. While testimonial evidence may not be ideal, here, the Federal Circuit concluded that, taken as a whole, substantial evidence supported the Board’s finding that Agilent’s actual reduction to practice was sufficiently corroborated and occurred before Dionex’s earliest conception date.

Although interferences are becoming less common, a number are still pending. The Dionex holding shows how inventor testimony can be sufficiently corroborated by other witness testimony, even without documentary evidence and without the testimony of every co-inventor. The Dionex holding is a beneficial opinion to consider for seemingly evidentiary deficient matters that involve corroboration of inventor testimony for an interference proceeding, i.e., the challenged claims have an effective pre-AIA filing date of earlier than March 16, 2013. It is also helpful the Dionex ruling in instances where a party swears behind a reference by showing prior conception and actual reduction to practice, which can occur for any pre-AIA application that is still pending or any interference.


If you have any questions or would like more information on the issues discussed in this LawFlash, please contact any of the following lawyers from Morgan Lewis’s post-grant proceedings team:

Dion M. Bregman (Silicon Valley)
Century City
San Francisco

[1] Dionex Softron GmbH v. Agilent Techs., Inc., 56 F.4th 1353 (Fed. Cir. 2023), Order at 11.

[2] Id.

[3] Morgan Lewis Insight, Patent Interferences (Apr. 21, 2021).

[4] Id.

[5] Id.

[6] Id.

[7] Id.

[8] Id.

[9] Id.

[10] Id.

[11] Id.

[12] In re Magnum Oil Tools Int'l Ltd., 829 F.3d 1364, 1375-76 (Fed. Cir. 2016).

[13] REG Synthetic Fuels, LLC v. Neste Oyj, 841 F.3d 954, 958 (Fed. Cir. 2016); see also Perfect Surgical Techniques, Inc. v. Olympus Am., Inc., 841 F.3d 1004, 1009 (Fed. Cir. 2019) (a patent owner "must show there was reasonably continuous diligence").

[14] Medichem, S.A. v. Rolabo, S.L., 437 F.3d 1157, 1169 (Fed. Cir. 2006).

[15] Kolcraft Enters., Inc. v. Graco Children's Prods., Inc., 927 F.3d 1320, 1324 (Fed. Cir. 2019).

[16] Mycogen Plant Sci. v. Monsanto Co., 243 F.3d 1316, 1335 (Fed. Cir. 2001).

[17] Medichem, 437 F.3d at 1171.

[18] Dionex, 56 F.4th 1353.

[19] Id.

[20] Id.

[21] Id.

[22] Id., Order at 4.

[23] Id. at 5.

[24] Id.

[25] Id. at 13.

[26] Id. at 14.