Festo Alters Scope of Patent Equivalents—Again


In the ninth judicial decision in a lawsuit that was originally filed about 15 years ago, the U.S. Court of Appeals for the Federal Circuit, sitting en banc and after sifting through no less than 15 amicus briefs, laid down a new set of rules for determining the scope of a prosecution history estoppel. Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd., Case No. 95-1066 (Fed. Cir. Sept. 26, 2003).

As recently affirmed by the U.S. Supreme Court (in Festo VIII), whenever an applicant for a patent narrows the scope of his or her claims by amendment and the patent owner later tries to rely on the doctrine of equivalents to establish infringement, in order to avoid prosecution history estoppel, the patent owner must demonstrate that the amendment was not made for a reason "relating to patentability."

If he or she cannot, the application of prosecution history estoppel will prevent the scope of a patent claim from being expanded under the doctrine of equivalents to embrace a product or process that is only insubstantially different from the element that was amended. Once it is determined that an estoppel does apply, the insubstantially different element in the accused product or process will only be embraced as an equivalent if the patent owner can prove that "one skilled in the art could not reasonably be expected to have drafted a claim that would have literally encompassed the alleged equivalent."

This test could be met, the U.S. Supreme Court said in Festo VIII, if:

"[T]he equivalent [was] unforeseeable at the time of the [amendment]";

"[T]he rationale underlying the amendment [bore] no more than a tangential relationship to the equivalent in question"; or

"[T]here [was] some other reason suggesting that the patentee could not reasonably be expected to have described the insubstantial substitute in question."

The Federal Circuit in Festo IX reaffirmed these principals as stated by the U.S. Supreme Court and went on to set forth guidelines as to when each of these tests could be met. Before addressing the guidelines, the Federal Circuit addressed an overarching issue, holding that it is up to the court, not the jury, to decide whether the evidence is sufficient to overcome an estoppel: "Questions relating to the application and scope of prosecution history estoppel Ö fall within the exclusive province of the court."

Then, directing its attention to the first testówhen the equivalent would have been unforeseeable at the time of the...

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