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Chip Scale Review November • December • 2016


carried out on key variables to understand

their impact on cost (

Table 1


Cost model assumptions include

the following: 1) Direct costs only—

no overhead or pricing margins; and 2)

Factories are assumed to be well-balanced

and fully utilized.

Table 2

shows the cost

breakdown of wet bench technology relative

to the ImmJET 6-chamber tool, which is the

more cost-effective of the two. The type of

contributing cost is also included. Note that

the percentage of cost for the new technology

is split almost evenly between material and

capital. This is because the equipment price

is more expensive than a traditional wet

bench, but less material is required to clean

the same number of wafers. The wet bench

is a more material-heavy process, not only

due to the larger bath, but due to the filter

requiring continual replacement – and the

filter represents a material cost.

Sensitivity analysis

The analysis of baseline assumptions

revealed that the wet bench is more

expensive than the 6-chamber ImmJET

tool. To verify these findings, material

costs (related to both the bath and the

filter) were analyzed for sensitivity. There

are multiple ways to look at chemical

costs with regard to a process that uses

a substantial volume of chemical as a

consumable. This analysis looks at the

trade-offs from the perspective of the

number of wafers cleaned by a set number

of gallons, and also by the refresh rate of a

bath for a set number of wafers. It should

be noted that the yield for both processes

was assumed to be the same. Because the

use of single-wafer processing typically

results in higher yield than a batch process,

the results in this analysis are conservative.

The two charts in

Figure 4

show the

cost of the strip step for the 6-chamber

tool compared to a wet bench, at different

refresh rates. The blue circle indicates the

baseline assumptions. These charts make it

clear that even if the 10-gallon refresh rate

is a high assumption and fewer gallons can

be used to completely clean 500 wafers, the

Table 1:

Cost model assumptions (ImmJET vs. wet bench).

Table 2:

Strip + filter costs by activity.

E-Tec Interconnect AG,

Mr. Pablo Rodriguez, Lengnau Switzerland

Phone : +41 32 654 15 50

, E-mail:

Figure 4:

Cost sensitivity to chemical usage. (Note:

y-axis scale is the same for both charts.)