Wright Williams & Kelly

TECHNICAL ALERT #12
FOR ALL USERS OF ALL TWO COOL® VERSIONS


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:

Maximum Ships = (Throughput * Available Hours)/(1 + re-do rate)

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:

Maximum Ships = (Throughput * Available Hours) * (1 - re-do rate)

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.

Techalert14-9707


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