3. The case
The layout design problem presented in Yang and Kuo
[10] is adopted for the present study. It is an IC packaging
plant. The detail of IC fabrication process is not discussed
in this paper for a concise presentation. Interested readers
are referred to Xiao [26] for a detailed discussion of the IC
fabrication process.
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T. Yang, C.-C. Hung / Robotics and Computer-Integrated Manufacturing 23 (2007) 126–137 127
The IC packaging plant usually adopts the process
layout strategy that clusters the same tool type to form a
workstation. A product traverses all the workstations in
the same sequence. For the case study problem, there are
ten departments (workstations) whose names and area size
information are depicted in Table 1.
The case study is based on an existing layout design.
Understandably, the company would like to know whether
the existing design is an effective one. The experience
learned from this study will provide guidelines for the
company’s future layout design problem, as well as for
identifying potential layout improvement opportunities.
In Yang and Kuo [10], a set of potential ‘good’ layout
alternatives were generated by commercial software,
entitled Spirals [3]. According to the flow distance
criterion, the top 17 layout design alternatives were
generated and selected for further analysis. The existing
layout design was the 18th alternative choice. A preliminary
study was conducted to determine the design criteria
among the area experts that subsequently led to three
quantitative and three qualitative design attributes. The
quantitative attributes included material handling distance
(in ‘meters’), adjacency score and shape ratio, which are the
direct outputs of Spirals. They are referred to as C1, C2
and C3, respectively, hereafter.
The handling distance was measured by the sum of the
products of flow volume and rectilinear distance between
the centroids of two departments. The adjacency score is
the sum of all positive relationships between adjacent
departments. There is a positive relationship between each
two consecutive departments along the process routing.
Shape ratio is defined as the maximum of the depth-towidth
and width-to-depth ratio of the smallest rectangle
that completely encloses the department. The shape ratio is
always greater or equal to one. For a layout design
problem, we endeavour to minimize both the shape ratio
and flow distance, while maximizing adjacency score.
There are three qualitative attributes—flexibility, accessibility
and maintenance. They are referred to as C4, C5 and
C6, respectively, hereafter. Flexibility involves two aspects:
the first is the capability to perform a variety of tasks under
a variety of operating conditions; second is the flexibility of
future expansion. Accessibility involves material handing
and operator paths. Finally, the maintenance issue involves
the required space for maintenance engineers and tool
movement. The qualitative attributes are evaluated using
an analytic hierarchy process (AHP). Readers are referred
to Yang and Kuo [10] for details of the AHP evaluation
process, as well as the block layout figures of the 17 design
alternatives. The performance ratings for the 18 alternatives
with respect to the six attributes are summarized in
Table 2: decision matrix.
Yang and Kuo [10] adopted a data envelopment analysis
(DEA) approach in solving the case study problem. DEA is
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Table 1
Layout data
No. Department name Size (m2)
1 Wafer sawing 89.21
2 Die bond 181.51
3 Wire bond 577.38
4 Molding 599.57
5 Dejunk/trimming & curing 183.71
6 Electro deflash/solder platting 500.13
7 Marking 199.94
8 Forming and singulation 186.40
9 Lead scanning/inspection 110.78
10 Packaging 51.09
Table 2
Decision matrix