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The doctrine of file history estoppels: the patentee shall not claim the abandoned patent rights on the basis of the doctrine of equivalents if the patentee narrowed the scope of patent rights due to amendments, corrections, or the like, during patent prosecution and maintenance.  

The Patent Infringement Judgment Points (2016 edition) indicated that if the patentee narrowed the patent scope by taking an action such as amendments, correction, or response, and foresaw such action resulting in the abandonment of a part of the patent right. Under such circumstances, permission for the patentee to claim the abandoned patent scope based on the doctrine of equivalent, which does not comply with the intention of the doctrine of equivalents. In other words, the doctrine of equivalents does not apply to the abandoned patent scope, but applies to the patent scope remaining in the patent. In particular, the patent scope abandoned by the patentee shall be determined by the purpose or grounds of the action such as amendments, correction, or response. If the purpose for narrowing the patent scope is related to the patentability of novelty and inventive steps to distinguish from the prior art, the abandoned patent scope is regarded as the patentee's intention to give up. Hereby, the file history estoppel of the application will be involved.  

In Heraeus precious metals north Smerica Conshohocken LLC v. Giga solar materials corp. (2017 Mingzhuanshangzi No. 28 Civil Judgment1), the Taiwan Intellectual Property Court considered that if the patentee had the intent to narrow the scope of the claim for avoiding the issues of novelty or inventive steps, it would introduce the file history estoppels.  

Heraeus precious metals north Smerica Conshohocken LLC (patentee, plaintiff of the civil litigation and appellant) is the owner of the Taiwanese Invention Patent No. I432539 titled “CONDUCTIVE PASTE FOR FORMING A SOLAR CELL ELECTRODE” (the '539 patent). The patentee filed a lawsuit and claimed that the object produced by Giga solar materials corp. (defendant and respondent) fell within the scope of the '539 patent. However, the Intellectual Property Court dismissed the lawsuit.  

Main Technical Features related to the file history estoppel  

Claim 1 of the '539 patent: “A conductive paste for use in forming a solar cell electrode by firing at 500 to 900℃, wherein the conductive paste comprises: a solar cell electrode comprising a conductive powder of silver as a main component,…”.   

During the examination, the plaintiff added the limitation, by firing at 500 to 900℃, into Claim 1 to narrow down the claim scope so as to distinguish with the Citations 2-4, wherein the ranges of the firing temperature of Citations 2-4 are 370-440℃, 500~850 ℃, and 600～800℃ separately.   

The infringing object: the firing temperature of the infringing object at issue is 920℃. 

Main issue of this case  

Does the technical feature of "500 to 900℃" amended by the plaintiff under the examination be interpreted as the plaintiff's intention to abandon the claim scope of "below 500℃ and above 900℃"?  

Intellectual Property Court’s Opinion  

Applying the file history estoppels against the doctrine of equivalents is not without any restrictions. The certain conditions, i.e. “the relevance”, “the expectation”, and the like, will be all considered; the following points are made accordingly.  

The plaintiff’s purpose of amending the claim scope to “at 500 to 900℃” is definitely for distinguishing from the combination of Citations 2 to 4, which is a consideration of the inventive steps and related to patentability.

That is, the reason for the additional amendments is not "unknown reasons", but deliberately to distinguish it from the citations. Therefore, the relevance therebetween is not "low correlation". The file history estoppels deem to be involved and the doctrine of equivalents deems to be limited.    

The scope of claims in patent applications is not solely on the basis of the claim language, but upon giving claims their broadest reasonable interpretation “in light of the specification as it would be interpreted by one of ordinary skill in the art.” Hereby, the reasonable scope of claims shall not be interpreted by the patentee’s subjective thoughts. 

Also, the plaintiff does not deny that prior to the '539 patent, many patents disclosed that the setting temperature of the sintering furnace is above 900℃. Namely, those of ordinary skill in the art at the time of the invention are well known for the aforesaid features and the firing temperature in excess of 900℃ can be expected. Thus, the scope of above 900℃ shall be regarded as the abandoned part via the file history estoppels after the amendment is made thereby.    

Obviously, Taiwan takes the doctrine of file history estoppels with flexibility. Introducing the file history estoppels against the doctrine of equivalents still has some restrictions, which consider the reason of “the relevance with the patentability”, “the expectation of the skilled person”, etc. Also, those explanations shall be interpreted in the broadest reasonable scope by the skilled person in the art rather than by the patentee’s subjective thoughts.

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