Wright Williams & Kelly
TECHNICAL ALERT #12 All versions of TWO COOL® make the same assumption about the way rework is handled. This assumption is the same one that was used in SEMATECH revision B. The current equation for determining the maximum wafer (unit) shipments is:
This equation assumes that product can only be reworked once per process step. Product failing after rework is then considered scrap and the user must adjust the equipment yield to reflect this loss. This equation has the effect of cutting shipments in half for a rework rate of 100%. We would like to solicit your input as to whether this equation accurately reflects your operating environment. A second possible equation is as follows:
This equation makes no assumption about the number of times the product can be reworked. This equation has the effect of reducing shipments to zero for a rework rate of 100%. SEMI guideline E35 contains no definition of redo or rework.
Techalert149707

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