The rule of foreseeability in filing history estoppel

Prosecution history estoppel is an antagonistic tool against the doctrine of equivalents. As Phil Collins sang in 1981, “words can only say so much”, and this difficulty is recognised when describing an invention. This forms the basic concept of the doctrine of equivalents. Through the doctrine of equivalents, a patentee can moderately extend the claim scope to equivalents of the recitation of the claims (eg, via the 'function-way-result' test). As the doctrine of equivalents may blur the boundaries of the claim scope, prosecution history estoppel becomes a useful tool to draw a clearer line between what is covered by the patent and what is not.

In the United States, in 2007 the US Court of Appeals for the Federal Circuit affirmed that prosecution history estoppel applies to any amendments made to overcome patentability-related rejections during prosecution of the patent at issue (Festo Corp v Shoketsu Kinzoku Kogyo Kabushiki Co). The court followed the rule of foreseeability, which addresses the long-running argument of complete bar versus flexible bar of prosecution history estoppel. Briefly, where amendments are made during prosecution, equivalents foreseeable at the time of the amendments shall be deemed surrendered from the doctrine of equivalents.

The Taiwanese Judicial Yuan published the draft Elements of Patent Infringement Determination in 1994. Although the draft has never been officially enforced and some judges refuse to follow it, it still forms the basis of patent infringement determination in general practice in Taiwan. The Elements of Patent Infringement Determination define 'prosecution history estoppel' as “preventing the Patentee from using Doctrine of Equivalent to re-claim the scope limited or obviated during prosecution”. This definition is almost exactly the same as that in the United States. However, the determination does not clearly distinguish between the complete bar or the flexible bar for prosecution history estoppel. That said, in practice, under the Elements of Patent Infringement Determination, an equivalent surrendered by prosecution history estoppel is indefinite. Therefore, the IP Court's practice must be examined in this regard.

Recent decision
In November 2014, in Fu-Er Technology Ltd v HTC Co Ltd, the IP Court affirmed the rule of foreseeability. Fu-Er Technology Ltd is the exclusive licensee of Taiwanese Patent 237264, entitled “A Multi-Function Semi-conductor storage Device And Method For Booting A Computer Using Thereof”. Fu-Er Technology sued HTC Co Ltd and Senao International Co Ltd for patent infringement. The court agreed with the defendants’ assertion and concluded that the accused products were equivalents of the claimed invention surrendered in view of prosecution history estoppel. Therefore, although the accused products fell within the claim scope under the doctrine of equivalents, the defendants had not infringed the plaintiff's patent.

Claim 1 of the patent at issue claimed a multi-function semiconductor storage device. During the prosecution, the plaintiff limited claim 1 by adding the following limitation to overcome rejections:

said semi-conductor storage media module (1) being at least divided into two storage spaces; wherein one of the two storage spaces is for storing information relevant to said multi-function semi-conductor storage device; said storage spaces at least correspond to a memory disc; said memory disc supports at least one device protocol of UFI protocol, SFF8020I protocol, SFF8070I protocol, [Small Computer System Interface (SCSI)] Transparent Command Set protocol, Reduced Block Commands (RBC) T10 Project1240-D protocol, ZIP disc protocol, and MO disc protocol.

In comparison, the portable devices of the first accused product supported media transfer protocol (MTP), which is an extension of picture transfer protocol. However, MTP pertains to data transfer protocol, but not device protocol. The plaintiff alleged that MTP began in 2007 and therefore was not foreseeable at the time of the amendments. However, the court held that claim 1 had been amended to limit the device protocol feature, but not data transfer protocol. Therefore, MTP was not an unforeseeable equivalent of device protocol at the time of the amendment. Similarly, the SCSI transparent command set protocol of the second and third accused products also pertained to data transfer protocol and had been surrendered in view of prosecution history estoppel.

A previous IP Court case regarding prosecution history estoppel and foreseeability took place in 2011. The November 2014 decision affirms the rule of foreseeability in determining equivalents surrendered in view of prosecution history estoppel. The recent decision is also the latest IP Court case on the rule of foreseeability. The patentee may still appeal the IP Court's decision, but in any case the rule of foreseeability will be increasingly discussed in prosecution history estoppel cases.

It is unsurprising that the IP Court is gradually aligning its practice with that of the United States for an issue that rarely arises in Taiwan. Such decisions remind applicants to consider carefully amendments during prosecution to ensure that such amendments are relevant to patentability. On the other hand, for those claiming non-infringement or design-arounds, amendments made during patent prosecution can be a major help.

In the past, applicants have recited claims as widely as possible at the start of filing to allow them a reasonable degree of bargaining power during prosecution by gradually limiting the claims. From the perspective of prosecution history estoppel, this strategy would be considered improper because every amendment would cause loss in the equivalent scope of the patent. Therefore, applicants should recite their claims with the proper scope at the start of filing in order to avoid amendments during prosecution. Even if the claim scope does not look broad, preserving the integrity of the equivalent scope is more important in litigation.

This is an Insight article, written by a selected partner as part of IAM's co-published content. Read more on Insight

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