Wright Williams & Kelly
TECHNICAL ALERT #12
All versions of TWO COOL® make the same assumption about the way re-work 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 re-worked once per process step. Product failing after re-work 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 re-work 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 re-worked. This equation has the effect of reducing shipments to zero for a re-work rate of 100%.
SEMI guideline E35 contains no definition of re-do or re-work.