It is not necessarily true that “equivalents not within the prior art must be tangential to the amendment.” As here, an equivalent may be outside the scope of the prior art and the prior art may operate in the same way as the claimed invention. Nevertheless, amendments that emphasize a limitation of the claims in order to overcome the prior art, even if that limitation is not by itself distinguishing, may be sufficient to establish more than a bare tangential relationship. It is therefore best practice to argue and amend in a manner that targets the key distinctions with the prior art as specifically as possible. For example, it may be best to avoid sweeping generalizations, such as assertions that the prior art does not disclose a large quotation of the claim text, rather than pointing to the specific distinction meant to be highlighted.
Background / Facts: The patent being asserted here relates to inspection equipment for probe cards used to test chips on semiconductor wafers. Probe cards contain structures called probes, whose tips make contact with bonding pads located on the periphery of each chip. The claims, after an initial amendment, recite a digital viewing system to assess whether probes have become misaligned relative to each other by obtaining a digital image through a window “in a first state where said probe tip is driven in contact with said window with a first force.” In the accused products, a similar first image is obtained but without physical contact, when the probe tips are approximately five microns above the viewing window. However, the district court found that the accused products were equivalent to the claimed invention.
Issue(s): Whether prosecution history estoppel nevertheless bars the application of the doctrine of equivalents, in that the amendment bears more than a mere tangential relation to the equivalent in question.
Holding(s): Yes. “[A] tangential rationale for the amendment is not objectively apparent from the prosecution history.” The court noted that to distinguish the amended claim, in particular, from the prior art, the patentee stated that the claim “calls for the viewing system to obtain a digital image of the probe tip … in [first and second states in which] said probe tip is driven in contact with said window.” While it may be true that physical contact was not itself distinguishing as the prior art in fact disclosed a surface contacted by a probe, and “[i]t may be that [the patentee] did not need to surrender a lack of physical contact between the probe tip and window in either state to overcome [the prior art] … [t]he dispositive fact is that [the patentee] chose to do so.”