Cross-Examining the Expert at PTAB: A Deposition Playbook

A PTAB deposition is not a district court deposition. The time is shorter, the scope is narrower, and the transcript goes straight into the record without a trial in between. The judges on the panel will read it, sometimes quote it, and decide credibility based on it. That changes how the deposition should be prepared and how it should be conducted.

This is a playbook for cross-examining the opposing party's expert at the PTAB, organized around the mechanics, the prep, the question lines that work, the citation patterns in final written decisions, and the conduct boundaries the Board enforces.

The mechanics

37 CFR 42.53 governs depositions in PTAB proceedings. The default time limit is seven hours for cross-examination of a witness whose direct testimony is in declaration form, which is the standard format for expert testimony in IPRs. The seven hours is consumed by question-and-answer time only, not by breaks or by direct examination.

Scope is limited to the subject matter of the declaration. An expert who declared on claim construction, prior art, and a POSITA framework is fair game on those topics. The same expert is not fair game on prior litigation, prior testimony in unrelated matters, or general industry opinion, unless the connection to the declaration's subject matter can be drawn.

Location and format have shifted. Pre-pandemic PTAB depositions were typically conducted in person. The post-2020 default is remote videoconference, with paper or electronic exhibits served in advance. The Board has accepted remote depositions as the working norm, and most disputes about format are resolved by stipulation.

The transcript is filed as an exhibit. Either party may cite to it in the next round of briefing. The Board reads the cited portions as part of the final written decision drafting process, and a clean cross-examination admission can shape the credibility finding directly.

What goes into prep

Preparation starts with the declaration. Every paragraph that contains a conclusion needs a corresponding question line, traced back to whether the conclusion is supported by the cited art, the file history, or the expert's own qualifications. The declaration is the universe of fair-scope topics, and a careful read identifies the seams.

The second prep input is the expert's prior testimony. Every prior declaration the expert has filed is on the record somewhere. Every prior deposition that produced a transcript is potentially accessible. The cross-examination value of prior testimony is that contradictions between the prior position and the current declaration are the cleanest impeachment material available. The Board will note them in the FWD.

The third prep input is the exhibit set. Every reference the expert relies on, every figure, every claim chart should be identified in advance and marked for use at deposition. An expert who is confronted with a clean exhibit and asked a precise question gives a clean answer. An expert who is asked a vague question with no exhibit in front of them will dodge.

The fourth prep input, often skipped, is the expert's CV against the technology. POSITA challenges at the PTAB are answered through cross-examination on qualifications, and the qualifications questions should be scripted against the published CV and the technology subfield at issue.

Common question lines that work

POSITA framing. The expert defined the person of ordinary skill in the declaration. The cross-examination should test whether the expert's own qualifications match that definition, whether the defined POSITA would have had access to the cited references at the relevant date, and whether the expert applied the definition consistently across the obviousness analysis. A POSITA who has shifting capabilities depending on which conclusion the expert needs is the most common impeachment opportunity at IPR depositions.

Claim-by-claim probing. The expert's obviousness analysis is typically structured claim-by-claim or limitation-by-limitation. The cross-examination should walk through each limitation, identify the cited art for each, and test whether the expert can explain the combination without leaning on conclusory language. Where the expert relies on motivation to combine, the question line should pin down what specifically motivated a POSITA to make the combination at the priority date.

Contradiction with prior declarations. If the expert has filed prior declarations on the same technology, the same patent family, or the same defendant, the prior declarations are usable. The question line is straightforward: lay the foundation for the prior declaration, identify the relevant paragraph, read it in, and ask the expert to reconcile it with the current declaration. The Board treats unresolved contradictions as credibility hits.

Reliance on documents the expert did not read. Experts often cite to references they have read in summary form, through counsel, or through associates. Asking whether the expert read the document cover to cover, when, and what they understood from specific passages identifies the depth of the expert's actual familiarity with the cited art.

Compensation and engagement. Hourly rate, total hours billed, and the structure of the engagement are within scope. The PTAB does not exclude testimony on partisanship grounds, but disclosure of a heavy financial stake is part of the credibility record, and the answers will show up in the FWD's weighting discussion.

How depositions show up in final written decisions

PTAB final written decisions cite deposition transcripts directly. The citation pattern is "Ex. [number] at [page]:[line]," and the Board uses these citations to support credibility findings, to identify contradictions, and to explain why the testimony is being credited or discounted.

The clean cross-examination admission is the deposition's highest-value output. A direct admission, captured on the transcript, with a clean page-and-line cite, is the kind of material the Board can quote in the FWD. Conversely, a deposition that produces no clean admissions is a deposition that does not show up in the FWD, and that is a missed opportunity for the petitioner or patent owner whose lawyer conducted it.

The citation pattern is identifiable on WitnessLens. FWDs vary in how heavily they lean on deposition material, but the panels that engage with the cross-examination transcripts tend to write more detailed credibility analyses, and those analyses are the ones that survive on appeal.

What not to do

The Board has limited patience for harassing or out-of-scope questioning. The Federal Rules of Evidence apply at the PTAB through 37 CFR 42.62, and the Board polices scope through on-the-record objections under 37 CFR 42.53(f)(8), mid-deposition conference calls with the panel, and motions to exclude under 37 CFR 42.64. The practical risk is not the motion. The practical risk is that the panel reads the transcript later, sees the out-of-scope questioning, and discounts the credibility of the questioning party.

The other failure mode is the deposition that runs out of clock without getting to the key admissions. The seven-hour limit is real. Spending three hours on background and qualifications is three hours not spent on the merits. The best PTAB cross-examinations front-load the merits questions, get the admissions on the record early, and use the remaining time to seal off escape routes.

A third failure mode is treating the PTAB deposition like a district court deposition. The cadence is different. The transcript is read by judges, not by jurors. The premium is on precision and on clean, citable admissions, not on rhetorical flourish or witness intimidation. The most effective PTAB cross-examinations read like a clean technical interview that ended with the expert conceding a key point.

A note on the data

The citation-pattern observations above draw on PTAB final written decisions on WitnessLens, with deposition-citation density tracked across panels and across years. The procedural rules cited (37 CFR 42.53 and related Board guidance) are current as of the date of this post. Methodology details are on the methodology page.