1. The interpretation of patent claims is a matter of law because such interpretation involves the defining of the scope of patent right, the court therefore should decide by its ex officio power if both parties argued upon such interpretation. By contrast, to compare the interpreted scope of the patent right at issue with the product at issue and to decide whether the product at issue has fallen within the scope of the patent right at issue, is a matter of fact. Because the application of doctrine of equivalents involves a widening of the literal scope of patent claims, the assertion for applying the doctrine of equivalents shall be initiated by the patentee in accordance with the principle of debate. On the other hand, the doctrine of estoppel is a ground for interfering the enforcement of patent right by the patentee, the allegation of the doctrine of estoppel shall be initiated by the defendant based upon the principle of debate, and shall be decided according to the relevant file wrapper of prosecution history.

2. The application of the doctrine of estoppel is limited to supplements, amendments, corrections, responses and replies by the patentee during the patent prosecution, and is related to the limitation of the patent claims based upon its patentability. The so-called “limitation of the patent claims based upon its patentability” includes the limitation for overcoming prior arts, and for complying with other requirements related to the allowance of the patent filings (such as enabling requirement, written disclosure and so on), and the application thereof is to examine the reasons alleged by the patentee when the supplements, amendments, corrections, responses and replies were submitted, so as to specifically decide whether they were made based upon its patentability. In the case that the alleged reasons were ambiguous, the supplements, amendments, corrections, responses and replies were deemed relevant to its patentability. However, the doctrine of estoppel is not applicable if the patentee has proved that the supplements, amendments, corrections, responses and replies were unrelated to the patentability. In addition, in the case that the supplements, amendments, corrections, responses and replies made by the patentee were relevant to its patentability but without limiting the patent claims, there is still no applicability of the doctrine of estoppel. Further, the scope of application based upon the doctrine of estoppel is merely limited to the portions restricted or deleted by the patentee, rather than limiting the applicability of the doctrine of equivalents upon the unrestricted or undeleted portions of the technical features, in order to properly protect the equivalent scope of the patent right and to refrain from unreasonably determining the scope given up by the patentee. Nevertheless, regarding the burden of proof for alleging the amended but not disregarded scope of equivalents as favorable facts [for example, the equivalent scope (such as pioneer technology) is not foreseeable while making the supplements, amendments, corrections, responses and replies; the interconnections between the equivalent scope and the reasons for the supplements, amendments, corrections, responses and replies are very little; or it is hardly able to reasonably expect that the patentee could disclose the equivalent scope at the very beginning] was to be taken by the patentee.

3. According to the academic deliberation and discussion, the doctrine of estoppel is divided into “the doctrine of estoppel for interpreting patent claims” and “the doctrine of estoppel for the application of doctrine of equivalents”, wherein the former indicates that the doctrine of estoppel is not only a defense, but also a limitation of the patent claims while considering both the party’s interest and the public interest, the court therefore can review the specification and drawings and must examine the file wrapper of prosecution history while interpreting the patent claims, and the patentee is not allowed to re-assert the abandoned portion during the patent infringement litigation. The latter on the other hand, considers that the doctrine of estoppel was originated from the principle of faith and trust, so as to limit the equivalent scope asserted by the patentee and narrow down the technical features, instead of re-interpreting the patent claims in light of the file wrapper of prosecution history and further limiting the literal scope of the patent right. Therefore, while there is no literal infringement and doctrine of equivalents is thereby applied for further judgment, whether the doctrine of estoppel is to be applied is considered for the first time in accordance with the assertion of the defendant. With regard to the manners of conducting the determination, one is to determine the application of the doctrine of estoppel after the product at issue was determined to be applied with doctrine of equivalents, while the other is to decide directly that the product at issue did not fall within the equivalent scope of the patent claims when the doctrine of estoppel was apparently applicable to the accused product. This court adopts the latter point of view in the present civil litigation, and firstly decides whether the product at issue has any portion of its technical features not being literally read upon the patent claims so as to apply the doctrine of equivalents, and to apply the doctrine of estoppel thereafter.