“…Specifically, if the tool's age reaches a given limit, it is taken down, and a pre-established maintenance procedure is performed (during this period the tool is unavailable for production). In semiconductor manufacturing, PM is not necessarily carried out exactly at the age recommended by the manufacturer; rather, it is customary to identify acceptable time intervals, or "time windows", in which PM can be performed (see [10], [15]). To accommodate this flexibility, the model proposed herein may consider "overtime" for a tool, implying that it works beyond the age recommended by the manufacturer but not beyond the time window.…”