When accused of patent infringement, one of the most powerful defenses is challenging the validity of the patent itself. If a patent is invalid, it cannot be infringed. Patent validity challenges attack the legal foundation of the patent, arguing it should never have been granted in the first place.
Grounds for Invalidity
Patents can be invalidated on several grounds. Lack of novelty (anticipation) means someone else already invented or disclosed the exact same thing before the patent application was filed. If even one prior reference shows every element of a patent claim, that claim is invalid.
Obviousness is the most common invalidity defense. Even if no single prior reference shows the entire invention, the patent is invalid if a person of ordinary skill in the field would have found the invention obvious based on combining existing knowledge. Over 70% of patents challenged at the Patent Trial and Appeal Board are found obvious.
Inadequate written description or lack of enablement means the patent document doesn't sufficiently explain the invention or teach others how to make and use it. The patent must provide enough detail that someone skilled in the field could recreate the invention without undue experimentation.
Indefiniteness challenges argue the patent claims are so unclear that skilled readers cannot determine what they cover. Vague claim language can render a patent unenforceable.
Prior Art Searches
Prior art is any evidence that the invention was already known before the patent application was filed. This includes earlier patents, published articles, products sold publicly, public demonstrations, and even oral descriptions in some cases. The most devastating invalidity defenses come from finding prior art the patent examiner missed.
Effective prior art searches go beyond simple database queries. They involve foreign patents (especially Japanese and European), trade publications, academic papers, industry conferences, archived websites, and sometimes testimony about what was known in the field. A single overlooked publication can invalidate an entire patent.
Inter Partes Review (IPR)
Inter partes review is a proceeding at the Patent Trial and Appeal Board (PTAB) that allows anyone to challenge patent validity based on prior art patents and publications. IPR has become the preferred method for challenging patents, with proceedings typically completed in 12-18 months compared to years for district court litigation.
IPR petitions must be filed within one year of being served with a patent infringement complaint. The PTAB only institutes review if there's a reasonable likelihood at least one challenged claim is unpatentable. About 60-70% of IPR petitions result in at least some claims being found invalid.
The standard for invalidity in IPR is "preponderance of the evidence"—more likely than not—rather than the higher "clear and convincing evidence" standard required in district court. This makes IPR an attractive option for defendants.
Post-Grant Review (PGR)
Post-grant review is similar to IPR but must be filed within nine months of patent issuance and can raise any invalidity ground, not just prior art. PGR is less commonly used because of the tight filing deadline, but it offers broader attack options for newly issued patents.
District Court Invalidity Defenses
Invalidity can also be raised as a defense in patent infringement litigation. The burden is higher in court—clear and convincing evidence—but juries sometimes favor defendants when shown strong prior art. District court allows invalidity defenses that IPR doesn't, including inequitable conduct, prior public use, and on-sale bar violations.
Inequitable conduct occurs when patent applicants deliberately withhold material information from the patent office or make misrepresentations. While difficult to prove, inequitable conduct renders the entire patent unenforceable, not just individual claims.
Parallel Proceedings Strategy
Many defendants pursue invalidity challenges in multiple forums simultaneously—filing IPR petitions while also asserting invalidity defenses in district court. Coordinating these parallel proceedings requires careful strategic planning. IPR findings can affect district court litigation, and vice versa.
Timing matters significantly. District courts often stay litigation pending IPR decisions, which can delay trial for years. This delay can benefit defendants who face weak infringement claims or need time to design around the patent.
Cost-Benefit Analysis
Patent validity challenges are expensive but often worthwhile. IPR petitions typically cost $250,000-$500,000 through completion. District court invalidity defenses add significant costs to already expensive litigation. However, successfully invalidating a patent eliminates all damages exposure and future licensing demands.
Consider the patent's remaining term, the strength of the invalidity arguments, the potential damages at stake, and whether other defendants might contribute to challenge costs. Some industries have formed joint defense groups to share invalidity challenge costs.
Getting Legal Help
Patent validity challenges require technical expertise in the patent's field and deep knowledge of patent law. Success depends on thorough prior art searches and persuasive legal arguments. An experienced patent litigation attorney can evaluate your invalidity options and develop the strongest possible challenge strategy.