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36

Chip Scale Review November • December • 2016

[ChipScaleReview.com]

spin-rinse-dry station where the surface is

completely cleaned and becomes particle-

free using an IPA rinse.

Because there are numerous types of

dry film resists, the selection of a solvent

appropriate for the film being dissolved is

important. For the work reported in this

paper, a Dynastrip™ solvent technology

was selected given its compatibility with

all advanced packaging applications, such

as plated bumps and redistribution line

metallurgies. This family of chemistries

has excellent performance with dry film

resists, as well as wet spin-on resists.

The Dynastrip solvent is compatible

with copper, all solder types, and with

t he unde r l y i ng pa s s i va t i on l aye r s .

Because it can be recirculated within the

equipment, and has a high bath loading

capability, it contributes to a low cost-of-

ownership, as is demonstrated in the cost

analysis section of this paper. It should

be noted that other chemistries have

been used successfully. However, there

are differences in the chemical costs,

chemical life, and process parameters.

One of the significant operational cost

drivers using a wet bench or traditional

single-wafer process is the frequency of

filter changes caused by the significant

buildup of partially dissolved resist material

in the system. To address this, ImmJET

technology includes a Triple Strainer that

collects this material. The Triple Strainer is

automatically flushed with solvent to clear

the buildup of residuals. With two strainers

in tandem, one strainer can be actively

processing while the other is self-cleaning,

thereby enhancing process efficiency and

eliminating the cost for filter replacements.

Cost-of-ownership

Activity-based cost modeling is a detailed,

bottom-up approach to understanding cost. A

process flow is broken down into individual

activities, and the cost considerations for every

activity are analyzed. These considerations

include the time required for the activity,

labor dedicated to the activity, material costs

(both consumable and permanent), tooling

costs, all capital-related costs, and yield loss.

The goal of the study was to compare

ImmJET to three industry standard methods:

wet bench, batch spray, and single-wafer strip

equipment. A summary of the initial analysis

is shown in

Figure 3

. Because the wet bench

is the most commonly used of the three

alternatives, the scope of the cost analysis

presented in this study compares the new

solution versus a traditional wet bench strip

approach (

Figure 3

). This analysis focuses on

a single-step in a process flow, so rather than

adding or removing steps, as often happens

when two technologies are compared, all of

the adjustments are within the parameters

of a single step. Industry data was used to

determine the parameters for the current

industry method, such as equipment price,

bath refresh rate, and throughput. However,

because every factory is different, in addition

to selecting baseline assumptions for the

industry method, a sensitivity analysis was

Figure 3:

Cost-of-ownership comparison.

P RoHS