Chip Manufacturing Process (Cont.)
The IC manufacturing process takes the following steps (cont.):
- Then, the wafers are diced into dies or chips, each of which is the individual rectangular sections.
Dicing enables you to discard only those dies that contain the flaws, rather than the whole wafer.
- The yield is the percentage of good dies from the total number of dies on the wafer.
In the previous figure, one wafer produced 20 dies, of which 17 passed testing.
(X means the die is bad.)
The yield of good dies in this case was 17/20, or 85%.
- These good dies are then bonded into packages and tested one more time before shipping the packaged parts to customers.
One bad packaged part was found in this final test.
The cost of an integrated circuit can be expressed in three simple equations:
Cost per die = Cost per wafer / ( Dies per wafer × Yield )
Dies per wafer ≈ Wafer area / Die area
Yield = 1 / ( 1 + Defects per area × Die area )n
The second equation is an approximation, since it does not subtract the area near the border of the round wafer that cannot accommodate the rectangular dies.
The final equation is based on empirical observations of yields at integrated circuit factories, with the exponent n related to the number of critical processing steps.