When accused of patent infringement, how can you turn around and invalidate the other party? Attorney Shen Jinlong discusses U.S. invention patent invalidity challenges and what evidence is needed to support them.

Conclusion first: When sued for infringement of a U.S. utility patent, countering by invalidating the other party's patent is a completely feasible defense strategy. The core path is to file an inter partes review (IPR) or ex parte reexamination (EPR) with the United States Patent and Trademark Office (USPTO), relying mainly on evidence such as patent literature, public publications, sales records, and physical products to prove that the other party's patent lacks novelty or non-obviousness. In practice, the timestamps and public nature of evidence often determine success more than the quantity.

First, get this straight: an invalidation objection is not litigation, but an administrative proceeding.

Many clients, when they encounter a U.S. patent infringement lawsuit for the first time, react by thinking, “I’ll also go to court to sue him for patent invalidity.” This approach does not work in the United States. There is no separate “patent invalidity action” in which a court directly declares a patent invalid; final authority over patent validity rests with the USPTO. The path available to you is to initiate administrative proceedings within the USPTO, commonly Inter Partes Review (IPR) and Ex Parte Reexamination (EPR). IPR can only be based on patents or printed publications as evidence, and cannot rely on physical products or sales records to assert obviousness; EPR allows broader types of evidence, but the procedure is slower and offers less participation. Which route to choose depends on the form of the evidence you have.

For IPR, the 9-month and 12-month timelines must be calculated clearly first.

After an IPR petition is filed, the USPTO generally decides whether to institute within 6 months (Institution Decision). After institution, it issues a Final Written Decision within 12 months, and this 12-month period may be extended by up to 6 months for good cause. In practice, if infringement litigation has already begun, the defendant usually has to apply to the court for a stay within 30 days and wait for the IPR outcome. Many clients encountering this for the first time overlook this linkage: whether the IPR is instituted directly affects whether the court is willing to grant a stay. The key to institution is whether the petition can establish a reasonable likelihood that at least one claim of the opposing party is invalid. This threshold is not particularly high, but the evidence must precisely correspond to the technical features of the claims; speaking in generalities is useless.

Evidence Is the Linchpin: What Materials Can Truly Invalidate a U.S. Utility Patent

Patent documents published before the priority date are the strongest evidence. U.S. patents, foreign patents, PCT publications, and journal articles all count. Next are publications, including books, industry standards, product manuals, and even publicly available web archives. Sales records and physical products cannot be used directly in IPR to argue obviousness, but they can serve as supporting evidence in EPR or in court invalidity defenses. Timestamps are an ironclad rule: the evidence's publication date must be earlier than the opposing party's patent priority date; even one day earlier is sufficient, while one day later makes it worthless. We generally advise clients to first prepare an evidence timeline, clearly listing each item's publication date, source, and acquisition method, and then compare it claim by claim against the opposing party's claims. In addition, 37 C.F.R. §42.104 sets clear requirements for the contents of an IPR petition, including how the claims are challenged and how the evidence supports the challenge; if the format is wrong, it may not even pass institution.

Is the other party's patent still under examination? Then pursue EPR or directly submit prior art.

If the other party's patent has not yet been granted, or you merely want to annoy the other side at low cost, you may consider filing prior art with the USPTO (a Third-Party Submission), within the window after the other party's patent is published and before grant. This window is usually within 6 months from the publication date, or before the first Office Action is issued, whichever comes first. Another scenario is where the other party's patent has already been granted but you want to avoid the high cost of IPR; EPR can be filed anonymously and costs much less, but the USPTO does not necessarily institute it, and your subsequent level of participation is limited. Which route to choose depends on your business objective: whether you want to completely kill the other party's patent, or merely buy time and increase your negotiating leverage.

Pitfalls Beyond Evidence: Estoppel and Repeated Challenges

Inter partes review (IPR) has a powerful “estoppel” rule: if you challenge a claim in an IPR and fail, you cannot later challenge the same claim in district court or ITC proceedings based on any ground that you raised or reasonably could have raised during the IPR. That means your first filing must be on target. We have seen many clients rush to file an IPR with scattered evidence, only to have institution denied, which then forecloses their subsequent options. Therefore, before filing, you must prepare a complete claim chart, mapping each challenged claim to the evidence element by element. If there is a gap in the evidence chain, it is better to supplement the prior art search first rather than force the filing. For cross-border evidence requiring notarization, translation, and service, you may go through the overseas intellectual property support process to make the timestamps and public accessibility solid.

Costs and timeline: IPR is not a small amount, but it is cheaper than infringement damages.

The official fees for an IPR are calculated based on the number of claims, usually from several thousand to tens of thousands of U.S. dollars; attorney fees vary with complexity, ranging from tens of thousands to several hundred thousand U.S. dollars. In terms of timeline, from filing to final decision, it usually takes about 18 months. Compared with U.S. patent infringement litigation, where damages and attorney fees often run into millions of dollars, the cost-effectiveness of an IPR is clear. But the premise is that your evidence is strong enough and your objectives are clear enough. If you are merely trying to delay, the stay effect after IPR institution may not be what you hope for; the court has discretion. We generally advise clients, after receiving an infringement warning letter or complaint, to first conduct a quick patent validity assessment, and then decide whether to initiate invalidation proceedings, rather than filing right away.

How to Coordinate with Litigation: Stay, Settlement, and Licensing Negotiations

IPR and infringement litigation can proceed in parallel, but their timing must be coordinated. A common play is to file the IPR first while moving the court to stay the litigation; if the IPR is instituted, the likelihood that the court will grant a stay increases significantly. Even if the IPR ultimately does not wipe out all of the opposing party’s patent claims, knocking out a few key claims changes the leverage in settlement negotiations. In practice, many cases settle after IPR institution and before the final decision, because both sides see the risk. The key here is that the invalidity proceeding is not the goal; it is a means. Your business objective may be to keep selling products, to push down licensing fees, or to completely invalidate the opposing party’s patent. Different objectives require different strategies and different levels of investment in evidence. For those who need an overall strategy, you can refer toUS and EU trademark and patent filing page.the procedural connection approach within.

The Three Most Common Pitfalls for Chinese Sellers

Pitfall one: submitting Chinese-language evidence directly, without notarization and authentication and an English translation, which the USPTO will not accept. Pitfall two: the publication date of the evidence is unclear; for example, if exhibition materials list only the year but not the month and day, such evidence is basically useless in an IPR. Pitfall three: ignoring the other party's patent priority chain and assuming the filing date is the baseline; in fact, the other party may obtain an earlier priority date through a continuation or continuation-in-part, so your evidence timestamp must be pushed further back. We also repeatedly remind clients of these details in our intellectual property legal services in other countries. If you want to learn about the team's background, you can seeLawyer Shen Jinlong of this firmIntroduction to.

Attorney Shen Jinlong, of the foreign-related intellectual property team at Guangdong Zhiming Law Firm, focuses on U.S. and EU trademark, patent, and copyright matters. To assess U.S. patent invalidity and opposition strategies, please call 0755-25986969 to schedule a consultation.

Disclaimer: The content of this article is general legal information sharing and does not constitute legal advice for any specific case. U.S. patent invalidity proceedings involve complex factual determinations and application of law, and the outcome of an individual case depends on the specific evidence and procedural developments. It is advisable to consult a licensed attorney with experience in U.S. patent practice before taking any action.