The Operation Management Assignment

Published Date: 02 Nov 2017

Introduction

The company that we choose for the Operation Management assignment is Unisem (M) Berhad (Unisem). In order to observe and collect details information of the Unisem and to complete the assignment, our group members went for a visit to the Unisem manufacturing site in Simpang Pulai, Perak on 8th of March 2013.

Unisem Group is a global provider of semiconductor assembly and test services for many of the world’s successful electronics companies. Unisem Group now having six factories in the five countries which are two in Malaysia and the other four are in China, Indonesia, USA and UK with approximately 10,000 employees worldwide. Unisem Group also is the listed company in Malaysia on The Main Board of K.L.S.E and the headquartered is in Kuala Lumpur, Malaysia. Unisem Group offers an integrated suite of packaging and test services which are wafer bumping, wafer probing, wafer grinding, a wide range of lead frame and substrate IC packaging including leaded, QFN, BGA and Flipchip packages and high end RF and mix signal test services.

Unisem was incorporated in 1989 and commence operations in 1992 with built up area of 570,000 ft and factory floor space with a minimum class 5000 clean room as an independent subcontract integrated circuit (IC) packaging and test house in Simpang Pulai, Perak. Unisem had about 3500 employees to operate the daily operation of the company. The company also awarded the Supplier Awards which are TriQuint, EXAR, SIGe, Mind speed, and AATI. Besides that, Unisem also received certification on Quality Management System (QMS). There certification are ISO /TS 16949 IN 2009 and ISO 14001 in 2004. Unisem also received certification on Certificate of Green Partner with Sony and Certificate of Green Activity with Canon.

Unisem provides full turnkey solutions that include wafer probe, wafer Grind, packaging, test, tape & reel, drop shipment, QA analysis and research & development. Unisem has the capability of packaging and testing a wide range of leadframe packages, which are expected to remain as the most effective solutions for the applications under 100 leads. In order to meet customers’ immediate demand, Unisem will continue to work closely with the customers to develop the next generation of packages which focusing on their effort on packages with their engineering and equipments capability.

The vision of the Unisem is to be a leading global multinational company providing comprehensive turnkey assembly and test services for the evolving needs of the customers, and a model corporate citizens in the communities in which they operate.

In order to achieve the vision, Unisem mission had committed to:

(i) Provide total customers satisfaction (ii) Be a caring company and employer of choice (iii) Generate profits and accelerate growth (iv) Develop long term win-win partnership with our business associates (v) Adhere to good corporate governance and support environmental, social and economical development of the community. (vi)Uphold and live our core values. The core values are referring to Team work, Commitment, Trust, Proactive, Caring.

The business strategy that used by Unisem is unit selling point. The products that produce by the Unisem must confirm that the overall product is in 99.9% good condition. If the products are not in the 99.9% they will deny the product and will not send to the customers as to remain their reputation and trust. Once Unisem receive the order, unisem will confirm the order and will delivery to the customers and almost 78% that the product will delivery to the customers on time and accurately. Besides that, Unisem also provide 24 hours of shipping. The company had two shift times which are 7am-7pm and 7pm-7am. The company had 2 shift times shipping is to fulfil the time of delivery for customer and also avoid the late delivery time. Unisem also keep upgrading their level packaging time on time. This not only will keep the product safe but also will increasing the confident of customer to the Unisem as the product will not easily destroy when the product is delivery to the customers. There is some of the strategy that used by Unisem to compete with others competitor.

Lastly, for the other information that Unisem had about 64% sales in North America, 22% sales is in EURO and14% of customers is in Asia. Besides, Unisem has a customer base comprising primarily fabless companies and also to a lesser extent design houses. They also had a small proportion of integrated device manufacturers.

Production Process

Diagram of Production process flow (steps) and description

Unisem have separate the process line become 2 parts, the front of line process and the end of line process. In Unisem, they are using the mass customization process strategies. Unisem’s output is basically customized based on the customers’ specific conditions (make-to-order) and the output is usually in high volume. From this point, so we know Unisem is using mass customized process.

Front of Line Process

There are 7 steps involved in the front of line process. The steps are shown in Figure ():

Figure (): the diagrams for front of line process

Step 1: Drop ship from customer

Unisem will start their process when marketing department had received customer’s order. In this step, marketing department will pass the input such as probe and wafer to the operation department for further production process. The back-grinding process begins after marketing department received the wafer. The back-grinding is a process that the back of the wafer is grinded to make it thinner, after that polished to improve heat transfer and reliability. During this process, all the condition must meet the customers’ requirement.

Step 2: Wafer Mount

After the back-grinding process, wafer was cleaned and polished. Wafers are sent to the next process, wafer mounting. In this step, wafer mounted to the wafer frame by using the Mylar films (membrane) to maintain the wafer location. Wafer mounting is one of step during the die preparation of a wafer. During this step, wafer is mounted on a plastic tape that is attached to ring.

Step 3: Wafer Saw

Wafer sawing process will be going on after wafer mounted. Wafer sawing process is a process to saw a wafer to require the dimension. Its involved many variables such as width of the saw streets, the die size, and the metal compositions of wafer have to be considered when formulating the saw parameters. In this step, wafer is cut into unit of dies without cutting the membrane. The failure perform of this process properly may cause mechanical damage to the dies.

Step 4: 2nd optical inspection

After the back-grinding, wafer mount and wafer saw process, the dies have completed. The dies are observed in microscope in 100% to select out the defected dies, afterward worker will inked them. The result for the wafer in this step maybe fails. The dies are pass the 2nd optical inspection will be continues to next step, die attach whereas fail will have to back to step 2.

Step 5: Die Attach

Die attach is the process of attaching the silicon chips to the die pad or die cavity of the support structure. There are two types of die attach process, one is adhesive die attach and other is Eutectic die attach. Adhesive die attach uses adhesives such as polyimide, epoxy and silver-filled glass as die attach material to mount the die on the die pad or cavity. Other, Eutectic die attach, which is commonly employed in hermetic packages, uses a eutectic alloy to attach the die to the cavity. A eutectic alloy is an alloy with the lowest melting point possible for the metals combined in the alloy. Dies are transferred to the lead frames, which is the support structure and attached with the epoxy in this step.

Step 6: Wire Bond

Dies are using to interconnect with the support structure, lead frame with wires in this step. Wire bonding is the process of providing electrical connection between the silicon chip and the external leads of the semiconductor device using very fine bonding wires.

Step 7: 3rd Optical Inspection

After the wire was bond on to the dies, the other inspection should have. In this step, the sample size of dies to sort out the bonding and attached defects. The dies had to test either the attach process or the wire bond process was completed to the production or not. If the production was fail, they need to re-attach the dies and re-bond the wire. After checked, conformal coating will going in this steps also, to coat layer of liquid glass to protect the device from moisture and pressure for customers’ requirements. After this, the production will sent to the end of line process.

After the dies have completed from the front of line process, the continue process, end line process will going on and take over the production from the front line process and start the process to produce successful production.

End of Line Process

There are 11 steps are involved in the end line process. These steps show as following:

Figure (): the steps for end of line process

Step 1: Molding

The molding process is using the black plastic materials that encapsulate semiconductor chips to protect them from light, heat, humidity, dust, physical shock. The units are encapsulated by compound that is non-conductor to protect the die and the wire bond.

Step 2: Slurry

After the molding process, the next step is slurry process. In this step, it will clean the lead of the units by blast frame of chip with medium level such as mixture of glass powder and other material with water.

Step 3: Laser mark / Pad print

In this step, the chips have to go on laser mark or pad print process. It is the process for marking a label on the surface or the bottom. The mold compound usually using the laser mark machine for labelling process. After that, there is a label to define when and where this chip had produced.

Step 4: Post mold cure

Post mold cure process is contributes to the electrical and mechanical properties of Novalac molding materials and affects how those properties change with thermal and humidity environments. In this step, the process is cure the units by using oven to harden the mold compound and to cure the ink mark on the surface if the unit use pad print.

Step 5: Plating

When the post mold cure process is finished, the plating process is next. In this process, an electrolysis process to solder the lead frame. The temperature to heat in this process is very high.

Step 6: QA Gate

After the planting process, the production will send to the other department for examine the quality and the conditions. All the production with pass in good conditions will be send to step 7, and the fail production will have to back to step 1.

Step 7: Trim / Form

After selected the pass production in the QA Gate, trim/form is needed to the next step production. In this step, the production will have to singular the unit from the lead frame. After that, there is an open and short test to test the production again. The test is randomly taking some sample to test by the software.

Step 8: Final Visual Inspection

After the test, the last inspection is ready. In this step, they will do inspection on the units to make sure the production are correct marking, no lead damage, good mold compound, and have a good lead.

Step 9: Pack

After the final inspection, the productions have to pack nicely before ships to customers. They put the devices in pack for easy and safe delivery thought transportation. They pack the amount of the total production according to the order and unit by the customers.

Step 10: Ship

The final step is shipping the goods by logistics. Before shipping, the productions department have to check with all the conditions such as customer specification and order unit. Afterward, they need pass it to the logistics department. Logistics department will double check and confirm to the productions again before sending the goods to customers.

Analyze Strength and Weaknesses

During the company visitation, we discover Unisem is using mass customization process strategy in their production and operation line. The mass customization is a strategy that mixed with the process focus, product focus and repetitive focus. By combining the flexibility and efficiency of both process and product focus will result in producing large quantity and large variety of products. Besides that, this strategy also called "made-to-order" because the products and services are delivered based on customer’s desire and wants.

Strength

The major advantages of mass customization are that the product can be customized through customer’s desire and wants. It is cost effective due to the company only produce according to what the customer’s design. Unisem is helping customers to creating chips based on their desire such as the function to carry out in a Smartphone or a television. Once the customization process is complete, Unisem will start to produce it according to the amount of the customer’s order, usually in high volume.

Another strength that we found during the visitation is that each of the operators is well train in each of the process stages. As the human resource manager explain to us, the operators will be send for training each 6 months to ensure they are still remember what their task and improve their skills. Besides, the maintenance department will send out technician to schedule check the machinery 6 times in a year to ensure the machines are operating. Each of the technicians will also train by the information technology department each 6 months.

Weaknesses

In spite of the customers can design their product and Unisem produce it but the layover time will be the disadvantages of mass customization. Usually designing a product takes longer time like 4 to 5 weeks compare to non-customize product. Meanwhile, the customers need to design the products they want earlier so that they can launch their own product in time. Furthermore, customize product are not returnable if the customers does not satisfy with it because the product already made to suite your desire.

There is a weakness for Unisem is that their production department did not show to process flow. The diagram display of the process flow is important because sometimes the workers might forgotten what to do in the next step so they can quickly refer to the process diagram so that they won’t get caught by the supervisors.

Other than that, the company does not own a power generator in case power supply failure happens. When power supply failure happens, it may delay all the production and goods delivery time. When goods are delivery late to the customers, this may result in voiding their company’s reputation. Besides, when power supply failure happen, all of the machine have to set again the settings because mostly setting will back to default automatically.

Facility Layout

Unisem building

Parking lot

Visitor room

Guard house

Garden

Factory Layout of Unisem (M) Berhad

Unisem is commence operations in 1992 with built up area of 570,000 ft² factory floor space with a minimum class 5,000 clean room .The map above shows the factory layout of Unisem and all its facilities location. First of all, the location of its guard house is on the left side of the premise main entrance while the parking lots are located outside the guard house. Visitor room is just beside the guard house which is the place to give visitor or customer to wait or rest. The Unisem building is located centre and both side of the block of the Unisem building.

The middle building has a reception desk, shoes locker room, discussion room, management department, meeting room, and a raw stock. Left hand side of the Unisem building is warehouse and right hand side is the manufacture factory. The combination of Unisem building became a U shape which also represents the symbol of Unisem. In year 2001, the Unisem have expanded the building and build another block of building behind the U shape building.

Office Layout

In this office layout, A and B is human resources department. Human resource department is placed with the responsibility of ensuring that it plans adequately for Unisem future engagements that will involve people and this department also responsibility of planning future Unisem goal in relation to people or clarifying these same goals to all staff members. C is finance department which play an important role in managing money, gathering payments and collecting receivables, paying bills and utilities on time and ensuring the company keeps a positive net worth value. D is the executive director office is which the room for the chief of operation in Unisem.

Meanwhile E and F is the marketing department which finds the best way to reach Unisem customers, and works with the rest of the company to help determine the new product needs of the market. Other than that, G and H are the purchasing department, and the role of purchasing department is to maintain uninterrupted flow of materials to support the development schedules. And to procure materials economically at a cost consistent with the quality and service required. However, generally all purchases may be attempted at the lowest cost. The middle of the office is the place for general clerk and personal clerk. Besides, we can assume that the Unisem is applying open system concept such as human resource manager are together in the same room with all those human resource staff as well as other’s department. Lastly, the conference room is at the right beside the human resource department.

Front of Line Manufacture Layout

First of all, there is the pass box at the left side of the layout; the pass box is the box that transferring wafer from outside to the manufacturing department without infects any dust. Other than that, the red colour is the wafer probe machine, which is the machine to produce wafer mounted to wafer frame using Mylar film (membrane) to maintain wafer location. The wafer probe machine cut wafer into units of dies without cutting the membrane. After wafer probe machine finish process and go to die attach machine. The die attach machine (Blue colour) are transferred the die to the lead frames and attached with the epoxy. After that it go through the final process of front of line manufacture which is wire bond. The wire bond machine (light green) interconnected the die to the lead frames by using gold wires. After the wire bonding finish, product will be sent to the end of line manufacture.

End of line manufacture layout

Plating machine

Molding machine

Changing room

In this end of line manufacture layout we can notice that changing room is the place for worker to change their personal shoe to rubber shoe. The purpose of wearing rubber shoe is can be discharge the static electricity in the manufacture room and it is meant for the workers safety. The front of line product will sent to here to continues the process. Molding machine encapsulated the units by compound non-conductor to protect the die and the wire bond. After cleaning the lead of the units by blast frame of chip with medium, the next things is the worker will mark the label on the surface of the mold compound by using laser. Finally it come to the final stage of the product which is after cure the units using oven to harden the mold compound and cure the ink mark on the surface if the unit use pad print. Plating machine is an electrolysis process to solder the lead frame and the entire finish product will be sent to the warehouse.

Warehouse Layout

The warehouse layout is to optimize tradeoffs between handling cost and cost associated with warehouse space. In the warehouse layout we can notice there is quality assurance room to inspection on the units to make sure correct marking, no lead damage, good mold compound & good lead and the goods are functionality. Besides that, the quality assurance room also responsible in packaging the devices in pack so that it is easy and safe for delivering trough transportation. After check and order picking the entire finish products are ready to be ship to customer.

Analyze the Strength and Weaknesses

Based on the Unisem we had investigated, we found out that Unisem used the combined layout in their facility layout strategy. They are using process and product-oriented layout in order to concerns where several products are produced in repeated number with no likelihood of continuous production. This layout involving the fabrication of parts and assembly, fabrication tends to employ the process layout, while the assembly areas often employ the product layout. This combination in order minimize imbalance in the fabrication or assembly line and produce desired volumes at the least of total cost needed.

Strength

There are some advantages of combine of both types of layouts to the company. For the first advantage of process layout, the breakdown of one machine does not interrupt the entire production flow since there are multiple machines enables to transfer in the department. For example, when one of the die bonder has breakdown, another die bonder will be transferred in order to continuous proceeding without any further delay and stoppage. The second advantage for process layout which is the full utilization of machines and fewer machines are required. It’s mean that variety of products can be made without any changes in the arrangement of machine. Therefore, this may cause the lower of investment and lower cost in the number of machines.

On the other hand, the advantage of product layout also encourages smooth production run in the end of line process which from the dies until finished goods. Therefore, it will help to reduce or almost eliminate the work-in-progress goods. Goods that are kept in the warehouse are usually finished goods and absence of work-in-progress inventories. With the straight line production flow, it may reduce the material handling cost and able to produce in a faster way. Thus, it can generate a large volume of products in a short time. Other than that, by using the product-oriented layout enables to produce low variable cost. Other than that, it is easier supervision by generalist supervisors. By reducing the manufacturing, it is recommend often use less skilled labor in purpose to reduce the cost and lesser training requirement.

Weaknesses

However, the disadvantages of process layout arise when the material handling are inefficient and slow due to the backtracking and long movements occur. The orders need to take longer time move through the system and become more complexities because of difficult scheduling and routing, changing the number of setups, and unique material handling. These procedures cannot be mechanized and lead to high cost. The second disadvantage which is higher labor skills resulting higher cost and work in process inventories are higher due to greater storage space required. The increasing of high labor skill needs will increases the required of training and experience as well, and the higher work in process levels increase the capital investment.

On the other hand, there are also some weaknesses of using this product layout. The company made large initial capital investment to establish the production process. Expensive special purpose equipment needs to be rent or purchase for the process purpose that need to focus to make a single product. High volume of product is required in order to meet the breakeven point in long term and able to cover the cost.

Study Area’s Literature Review

Literature Review (A genetic algorithm and queuing theory based methodology for facilities layout problem)

Based on the research conducted by Dhamodharan Raman , Sev V. Nagalingam and Bruce W. Gurd .The research are genetic algorithm and queuing theory based methodology for facilities layout problem .This study aims on facility layout problems while considering various aspects which vary with the shape of the facilities, nature of production demand, nature of material flow, and number of floors. Based on the research shows that the process of obtaining optimal solutions involves two steps: Modelling approaches for facility layout problem, and solution approaches for facility layout problem. Modeling is using to define the problem and consider the factors that are imperative in developing layouts. Solution approach are affect by genetic algorithm , there are three types of algorithm which is exact algorithms, heuristic algorithms, and meta-heuristic algorithms. Furthermore, the researcher have classified and analyzed such models and approaches to provide a qualitative justification for utilizing queuing theory and GA in our methodology.

Literature Review (Unequal area flexible bay facility layout using ant colony optimization)

Based on the research by Sadan Kulturel-Konak and Abdullah Konak. The research are unequal area flexible bay facility layout using ant colony optimization. This study aims on ant colony optimisation approach is proposed to solve the facility layout problem with unequal area departments and flexible bays, which is one of the commonly used layout representations in industry practice. Optimal approaches to the facility layout design can only solve problems with a limited number of departments.The researcher also do the experiments shown that considering orientation of the facility and dummy departments can significantly improve block layout solutions based on the flexible bay structure. In addition, further research is needed to apply the flexible bay structure in problems with irregular shaped departments and facility areas.

Literature Review (Managing change in the workplace)

From the research that conducted by Dan Roberts, he said that an efficient workplace not just about the facilities planning and facilities management but also the office furniture layout. Managing the facilities layout can boost employee’s morale but it needs a lot of planning and effort to achieve a successful facilities management. The research also according to a business journal that written by Don Greeson, the executive vice president at Hurbson Office Supply in Syracuse and he said that:"a company that doesn’t have a facilities management plan is in touble" (Greeson) Other than that, according to Bob Mcaleer, senior vice president of marketing for Stephens Office Interiors in Syracuse also said that:"the concept of the facilities management should center around managing a work area in order to maximize the results and productivity from that particular work station." (Greeson) Therefore, the modern facilities design has to be plan well so that may result in better operation performance, production process and happier employee.

Literature Review (Managing Facilities)

From the research that conducted by Peter Rowley, he said that facilities management cover a broad range of activities like buildings structure, maintenance management, space management, security, cleaning, working environment, space management, and project management. The facilities management must be well manage so that all the facility will support together to achieve efficient and effective economic operation of the organization’s business. Besides that, space forecast is important as the needs to estimate the spare for storage of goods and equipments. Furthermore, there should be using the "fit factor" as it means the structure and the shape of the building must be limit to a degree the space utilization so that can obtain for more spaces. At last, the company should concern about the safety and health that applies in a workplace. Providing a good working environment and a suitable temperature like ventilation systems, adequate fire exits, number of toilets and it location, first aid provision, suitable lighting and cleaning will result in better of management the facility. Therefore, by managing well in these areas will improve the operation flow systems.

Literature Review (Towards measuring the effectiveness of a facilities layout)

Based on the research by Raman, he stated that facilities layout has significant contribute towards manufacturing productivity in terms of cost and time in a manufacturing system. There are 10-30% of material handling cost can be reduced by having an effective facilities layout. Thus, there is a necessity to develop a measurement method to determine the effectiveness level of layout considering several key factors simultaneously. A measurement model considering a set of three layout effectiveness factors and they are facilities layout flexibility, productive area utilization and closeness gap. The facilities layout flexibility considers improving flexibility for arrangement and operation. Secondly, the productive area utilization considers improving the effectiveness of utilized area. Lastly, the closeness gap considers minimizing the material handling cost and the total production time by bringing closer the highly interactive facilities and departments.

Literature Review (Plant Layout: Capital Improvement without Capital Expenditure)

According to Najarian, he stated that reconfiguration of a plant for smoother and more rapid work flow is a cost-effective means to achieving the just-in-time benefits of increased capacity and throughput, faster cycle time, lower work-in-process inventory, reduced set-up time, and smaller lot sizes. Just-in-Time (JIT) methods such as cellular manufacturing, focused factories within a factory, and flexible assembly are ways to make current capacity responsive to volume growth and perhaps more importantly to product line complexity. Change presents the opportunity to add value through reconfiguration of the factory. The potential for manufacturing value-added will lead to increased profitability. There are five "Ds" of plant layout namely as design for time and quality, distance reduction, density rationalization, delivery rationalization, and decentralization. Just-in-Time era is making it an attractive option to improving operations and achieving greater capacity. Setting a payback target and doing the pre-project financial analysis and projections are the first steps. Careful monitoring and control of design and execution will ensure realization of added value.

Literature Review (Managing the Workplace of the future)

Based on the research conducted by Pekala, Nancy (2001), this research is aims to finding out the variable of facilities that will affect the company’s’ performance. The example for the independent variables such as meeting venues, office venues, workplace that work, non-territorial venues and productivity matters as the dependent variable. In this research, it’s examine the productivity can have a large effect on the process line with lower cost on the relationship between the facility layout (the venues of the facility). Based on the research, it’s shown that the production has significant influences by the variables of facility layout. While the worker can perform better since the venues of workplace is near to other venues which the relevant department with the production line such as refreshment place, meeting venues, and office venues. Worker can use the timeless to do the tasks with fully communication. Furthermore, the result also shows that the productivity was having a great result with the accessories of layout were clear and useful.

Literature Review (Managing Stakeholder Expectations in Facility Management using Workplace Management and Commitment Making Techniques)

This research is conducted by Ari Pennanen, 2005. The purpose for this research is to enable the facility management to define workplace strategy basing on organizations strategy and operations. Based on this research, is trying to find the result in facility planning the workplace strategy is subject to the conditions of continuous change and uncertainty. Furthermore, the theory of workplace planning is constructed on the basis of production and commitment making concept in order to link workplace to organization’s strategy. Besides that, this research also test the relationship between the decision or strategy making is relevant with some dependent variables such as concept of commitment and theory of workplace planning. Based on this research, its show that significant influences its independent variable and the dependent variable. The conclusion for this research is the theory of workplace planning not only for production, but also is with the organization’s general strategy. Lastly, the workplace planning is understandable since a workplace affects the productivity, while the working environment represents a large share of the usage.

Literature review (The influence of work-cells and facility layout on the manufacturing efficiency)

Based on the research by Seyed-Mahmoud Aghazadeh; Saeedreza Hafeznezami; Lotfollah Najjar; Ziaul Huq. The purpose of this research is to analyse the use of product-oriented layout and work cell planning and to understand how improvements on layout design could positively impact in the future efficiency. In this research a model was developed and measured using 26 weeks of data during the transformations. In finding, they find that there is strong correlation between the variables improved at both the cell structure and product structures of the facility and improve in efficiency of the manufacturing facility. The higher efficiency of the layout has allows the facility able to handle the much larger workload and decrease the short run and long run costs. The outcomes of the research also allow to redesign the facility as to maximise efficiency but however there is a limitation which is the time of a product remain in each cell on assembly line did not had effect on the overall output. Lastly, as a conclusion this research is useful for the manufacturers who having low variability in their product and having the ability to use work-cell layout within their facility.

Literature review (Use of a Robustness Index for Flexible Facility Layout Design in a Changing Environment)

Based on the research of Victor B. Kreng and Chih Ming Tsai, the conditions for production are commonly assumed to be constant for overcoming facility layout problems. There are various factors such as processes, products, machinery equipment will change unavoidably. Introduction of new equipment, process changes, modification of product mix and utilization of space and facilities are key factors that a layout needs flexibility. Furthermore, facility layout has to keep up with dynamic environments since production conditions vary very rapidly to the point that managers are unable to accurately forecast the changes in advance. Flexible layout explained as one with the capability to deal with changing production conditions in the future and must remain at its peak as the product mix fluctuates and in previous research flexibility focused on the minimum lost cost and minimum expected cost but it is not true about flexibility. As according to the definition of flexibility stated by Webster and Tyberghein, flexibility must take account of both low-cost and robustness. It is essential to understand how to use an index to measure the flexibility of each layout, so the layout can deal with environmental changes more effectively. As a conclusion, to achieve flexibility, many factors should be taken into consideration and not just the cost.