United States: 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 … fall within the exclusive province of the court."

Then, directing its attention to the first test—when the equivalent would have been unforeseeable at the time of the amendment—the Federal Circuit said the demarcation of such evidence "is best left to development on a case-by-case basis." Nevertheless, the Court set forth "general guidance," noting that unforseability must be determined from the perspective of a hypothetical person of ordinary skill in the art. An allegedly equivalent element that was not known at the time of the amendment, the Court said, "would not have been foreseeable." An allegedly equivalent element that was known at the time of the amendment "would more likely have been foreseeable." If the element was also known in the field of the invention at the time of the amendment, the court said that the equivalent "certainly should have been foreseeable."

The Federal Circuit pointed out that the second test—the "tangential relation" test—examines "whether the reason for the narrowing amendment was peripheral, or not directly relevant, to the alleged equivalent." While the Court did not define the scope of this test any more precisely, it did state that an amendment made to avoid prior art that contains the equivalent is not tangential. The Court said that the tangential relation test must be determined solely based on the prosecution history record. Still, the Court left the door open to testimony from those skilled in the art "when necessary" to explain the meaning of the record.

The Federal Circuit observed that the third test—the "some other reason" inquiry—"while vague, must be a narrow one." The Court said the test may be satisfied by proof there was "some reason, such as the shortcomings of language, why the patentee was prevented from describing the alleged equivalent when it narrowed the claim." Proof that the equivalent was an "inferior and unacceptable design," however, is insufficient to meet this requirement. The Court also said that the proof should be limited to the prosecution history record "[w]hen at all possible," but did not explain when extrinsic proof would be permitted.