Qin Y. Micromanufacturing Engineering and Technology

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3. They provide unified interface definitions and

enable or simplify the task of integrating dif-

ferent systems, even if they are provided by

different suppliers.

Standardization activities are performed

throughout all layers of the shop-floor IT – usu-

ally based on specific needs. There exists a variety

of organizations that provide platforms for stan-

dardization that have to be considered in the

shop-floor IT environment – some of them target-

ing on specific industries (e.g. Semiconductor

Equipment and Materials International – SEMI

[5]), some of them approaching cross-industry

topics (e.g. Manufacturing Enterprise So lutions

Association – MESA international [6]), others

focusing on specific technologies (e.g. Internet

Society – ISOC [7]). The following sections give

a rough overview of selected organizations and

standard collections in the shop-floor IT area –

both on the factory-automation layer and on the

equipment-automation layer.

General Production IT Standards

Several organizations have made a number of

attempts over the last few years to create extensive

standard frameworks or reference models describ-

ing approaches to realize a pervasive production

IT landscape that integrates well with the overall

IT landscape within the enterprise and thus sup-

ports the goal of process optimization described at

the beginning of this chapter. One approach that

shaped the discussion for several years, especially

in the early 1990s, was the ‘Reference Model for

Computer Integrated Manufacturing (CIM)’ [8].

This describes a hierarchical IT architecture that is

built up from six levels based on the scheduling

and control hierarchy and has been designed as a

guideline for establishing a vertically integrated

production-IT landscape. Although the concept

has not yet been implemented to its full extent,

it served as a basis for many successors. In 1997

MESA [6] presented a definition for MES, which

is still considered to be valid, and its potential

scope by describing a set of 11 functional groups.

The scope of a concrete MES solution was defined

to be a subset of the potential scope based on the

user’s priorities and requirements. A few years

later, in 2000, ISA-95 Part I was published. This

is based on the concepts of CIM (especially the

scheduling and control hierarchy) and focuses on

the specification of interface between business sys-

tems and manufacturing operations and control

systems. Furthermore, ISA-95 integrates the func-

tional groups defined by MESA to describe the

functionalities of the manufacturing operations

and control, i.e. the MES, level. ISA-95 Part II

[9] and Part III [10] followed later and comple-

ment Part I with the detailed specification of the

data model on the one hand and the activity

model and dataflow specification for the

manufacturing operations and control level on

the other. VDI 5600 [2] is currently the latest

standard in this series. It comes from a task-

oriented view of the MES that rather reflects the

user’s perspective than the system perspective and

updates and extends the MESA MES model.

Equipment Interface Standards

An important prerequisite for implementing sev-

eral requirements described in the preceding sec-

tions is the ability to communicate with process

equipment in order both to remotely control the

equipment and to acquire a variety of data from

the equipment, such as operational data, machine

data and process data. As a factory usually houses

equipment from a variety of suppliers, the effort

to connect them to the production IT environment

of a given factory is comparably high, as a specific

connector has to be implemented for each equip-

ment type. This is where the idea of the definition

of a standard IT interface for equipment, as

shown in Fig. 24-5, comes into play.

One of the standard frameworks that is fre-

quently used to integrate equipment with higher

levels of the production IT landscape is the OPC

[11] framework. However, an industry-specific

framework from the semiconductor industry has

been selected for further discussion, as it provides

a more comprehensive approach, which can

serve as a generic example. Figure 24-6 (based

on [12]) gives a compressed overview of the

standards framework that is widely used in the

CHAPTER 24 Manufacturing Execution Systems for Micro-Manufacturing 391

semiconductor industry. The communication

protocol defined by E5 lays the foundation of

the standard framework. Today, it is usually

bound to a TCP/IP-based message transport layer

according to E37 (HSMS-SS), which enables com-

munication with equipment using a unified mes-

sage form at. While this protocol basically allows

for the communication of a host system with an

equipment instance, it leaves the supplier with a

high degree of freedom regarding the actual

implementation of the interfa ce. For this reason,

the effort for integrating equipment into the shop-

floor IT still turned out to be rather high. Further-

more, different interface implementations pro-

vided largely varying capabilities that needed to

be taken into account. To overcome these limita-

tions, additional standards have been added on

top of E5. The ‘Generic Model for Communica-

tions and Control of Manufacturing Equipment’

(GEM) defines the semantics of the interface, i.e.

the behavior of the equipment from the IT inter-

face perspective. This step led to a significant

reduction of the effort required for the integration

of equipment and allowed for the introduction of

standard compliance tests. E30 is complemented

by a standard for recipe management and stan-

dards for specific equipment models. While E30

contains specifications that have to be considered

for all types of semiconductor equipment, specific

equipment models comprise equipment charac-

teristics and behavior definitions that have to be

implemented in addition to GEM for specific

equipment types only, for example transport sys-

tems: these take the specific needs based on the

equipment type into account.

The standard framework is completed by the

family of GEM300 and a couple of auxiliary stan-

dards. As the transition from 200 mm to 300 mm

wafer processing was accompanied by the

demand for a higher level of automation, the

requirements for additional automation capabili-

ties on top of E5 arose and led to the definition of

these standards, such as the capabilities to manage

carriers or to track substrates. Additionally, there

was an increasing need to acquire data from pro-

cess equipment. The family of Equipment Data

Acquisition (EDA) standards has been created to

meet these requirements. The EDA stack is imple-

mented in parallel with the GEM/SECS interface,

is limited to data acquisition and allows an arbi-

trary number of clients to acquire data from

equipment based on web technologies.

FIGURE 24-6 Equipment interface standard framework – as defined by SEMI

392 CHAPTER 24 Manufacturing Execution Systems for Micro-Manufacturing

CONCLUSIONS

Today, it is virtually unthinkable to ope rate state-

of-the-art manufacturing facilities without a vari-

ety of IT systems supporting production. Several

classes of IT systems can be found over the differ-

ent layers of these facilities – from enterprise

resource planning systems as an example on the

enterprise management layer down to program-

mable logic controller-based applications on the

manufacturing processes layer. The term MES

usually refers to a collection of integrated soft-

ware applications that is located between those

two layers – on the manufacturing operations

and control layer. On the one hand the MES

ensures the right level of information transfer

between upper and lower layers and thereby sup-

ports the integration of processes on the shop

floor into the overal l business process framework.

On the other hand the MES provides a rich set of

functionalities to optimize operations on the shop

floor in different dimensions, such as product

quality, resource utilization and the adherence

to delivery dates. A variety of standards have been

created in different industries to enable and sim-

plify the set-up of the MES environment. Looking

at the potential provided by an MES, the rele-

vance of this topic in the area of micro-

manufacturing will continue to grow in the future.

REFERENCES

[1] Enterprise-control system integration, Part I: Models

and terminology. ANSI/ISA-S95.00.01-2000. Instru-

ment Society of America, Research Triangle Park,

NC, USA (2000).

[2] Manufacturing execution systems – production man-

agement systems. VDI 5600 Blatt 12006-08. Verein

Deutscher Ingenieure. Published by: Beuth Verlag

GmbH, 10772 Berlin, Germany (2006).

[3] Specification for definition and measurement of

equipment reliability, availability and maintainabil-

ity (RAM). SEMI E10. Semiconductor Equipment

and Materials International, 3081 Zanker Road,

San Jose, CA, USA (2004).

[4] Specification for definition and measurement of

equipment productivity. SEMI E79. Semiconductor

Equipment and Materials International, 3081 Zan-

ker Road, San Jose, CA, USA (2006).

[5] Semiconductor Equipment and Materials Interna-

tional – SEMI [Last access: 30.10.2007]; http://

www.semi.org.

[6] Manufacturing Enterprise Solutions Association –

MESA International [Last access: 30.10.2007];

http://www.mesa.org.

[7] Internet Society – ISOC [Last access: 30.10.2007];

http://www.isoc.org/.

[8] Williams, T. J., (ed.), A reference model for com-

puter integrated manufacturing (CIM), a description

from the viewpoint of industrial automation, Instru-

ment Society of America, Research Triangle Park,

NC, USA (1989).

[9] Anonymous, Enterprise-control system integration,

Part II: Object model attributes. ANSI/ISA–

S95.00.02-2001. Instrument Society of America,

Research Triangle Park, NC, USA (2001).

[10] Anonymous, Enterprise-control system integration,

Part III: Activity models of manufacturing operations

management. ANSI/ISA-S95.00.03-2005. Instru-

ment Society of America, Research Triangle Park,

NC, USA (2005).

[11] The OPC Foundation [Last access: 30.10.2007];

http://www.opcfoundation.org/.

[12] M. Meier, P. Dreiss and J. Seidelmann, Potentials and

limitations of standardization of shop floor IT based

on examples from semiconductor industry, PPS Man-

agement 12 (2007) 4, Gito Verlag mbH, Klixstr. 1 A,

13403 Berlin, Germany (2007).

CHAPTER 24 Manufacturing Execution Systems for Micro-Manufacturing 393

Sustainability of Micro-

Manufacturing Technologies

Arnaud De Grave, Stig Irving Olsen, Hans Nørgaard Hansen and

Mogens Arentoft

INTRODUCTION

The common view in the field of the environ-

mental impact of micro-products is that small-

size products involve the use of less material,

require less production energy and produce less

waste material, and hence are more environ-

mentally friendly. This view is not fully valid

and there are many benefits in applying tools

for sustainability in micro-product development.

When looking at any technology, at least three

different levels are of interest to consider in the

complete product development scheme:

1. The final product is defined as the product that

is closest to the requirements of the end-user. It

is fairly easy to define it in the case of, e.g.,

hearing-aid equipment, but less evident in the

case of an MEMS RF switch used in a mobile

phone antenna. The size of the production chain

of such a product can involve many sub-con-

tractors and in terms of environmental aspects

all the steps have to be taken into account.

2. Some parts are not included in the final pro-

duct, e.g. the waste from manufacturing. These

parts are called ‘intermediate parts’. Examples

of such parts can be the excess material from

an injection molding runner system for feeding

of the molds, parts especially designed for

ease of handling and assembly, or even the

sections of a silicon wafer that are ground

before packaging, this excess thickness being

required for mech anical stability during pro-

duction.

3. The production system is mainly considered as

the manufacturing process chain, but the system

also includes the necessary material production

chain and the recycling and disposal chain.

This categorization is especially pertinent in

the case of micro-products, where the intermedi-

ate parts can represent up to 98% of the product

component, as, for example, is the case of micro-

injection-molded components.

In the following, first the technical aspect of

environmental assessment over the lifecycle is

described, then the aspect of how to use the

knowledge so obtained in product development

is presented.

LIFECYCLE ASSESSMENT

Theory

Lifecycle assessment (LCA) is a valuable tool for

the environmental assessment of products. The

principles of LCA form the backbone of DFE,

EcoDesign, etc., in product development [1].

LCA has been developed to analyze and assess

the environmental impact attributable to a prod-

uct through the whole lifecycle of that product,

i.e. the extraction of resources, conversion into

materials, production, use and disposal, as well

CHAPTER

394

as transport and infrastructure. LCA therefore

covers not only the production, but also all

supportive functions during the life of the pro-

duct. The inclusion of the supportive functions

demanded by a product in the assessment extends

to include all types of impact that a company (or a

product) is responsible for – not only within the

manufacturing chain, but also in all stages in the

life of the product. In a quest for sustainability

these are important aspects to include in product

development, since this is the stage at which deci-

sions can be taken concerning the environmental

impact of the product.

The importance of LCA as a tool to assess the

environmental sustainability of products and

manufacturing is increasing in the European

Union. Examples are the use of LCA in the

EcoDesign of Energy using Products Directive

(2005/32/EC) and the requirements for LCAs

in some of the recen tly published calls for the

European Seventh Framework program for re-

search and technological development.

LCAs involve the following steps:

1. Choice of product and identification of service

(the functional unit);

2. Establishing boundaries for the system;

3. Collection of data;

4. Environmental assessment;

5. Interpretation.

The initial step in all LCAs is to define the

goal and scope of the study [2] – w hat is the aim

of the study? What is the object of investigation,

the so-called functional unit? What are the sys-

tem boundaries for the investigated system, e.g.

should the production of the manufacturing

equipment be included? The chain of processes

in the system will be defined t hus, also identify-

ing the processes for which data need to be col-

lected. LCA is made in an iterative way, initially

starting with the m ost easily available data and

making a screening analysis with focus on the

materials, energy and chemicals used. The next

steps imply the use of more detailed data on the

inputs and outputs for each process. Figure 25-1

provides a schematic overview of the lifecycle of

a product and the data needed for carrying out

the analysis.

One important issue is the type of data

needed to be gathered in order to have a perti-

nent way of evalu ating the process chain. This

data falls mainly into two categories: process

data and material-use data. Many problems

arise from the difficulty of gathering the neces-

sary data.

Process Data. The easiest parameter to collect is

the energy – electrical or thermal – consumed in

the production of a specified amount of product,

usually 1 kg of product or, e.g., 1000 pieces. This

may be measured directly at the manufacturing

equipment or averaged from the energy consump-

tion at the facility. It is important to know the

type of energy and whether, e.g., it is produced

FIGURE 25-1 An LCA flow.

CHAPTER 25 Sustainability of Micro-Manufacturing Technologies 395

internally as waste energy from other processes.

Energy is consumed both in the manufactur-

ing process as well as during handling and

assembly.

Outputs (emissions, waste and products) from

the processes should be inventoried. Of course the

product is an important output serving as a refer-

ence for all other data, but also all types of waste

(solid, liquid or gaseous) from the processes

should be measured. This is, e.g. waste material

(the difference between what is in the product and

what is consumed as raw material). There will

probably also be some emissions from the process,

e.g. welding fumes. In the initial steps of the

LCA, data of the latter type may be hard to

acquire. If more than one product is produced

by the same process this is important also, since

the environmental impact from the process should

be allocated between the products.

Material-use Data. Data on the use of materials

is important, not only because of the environmen-

tal impact associated with the extraction of mate-

rials, but also to keep track of the losses during

manufacturing proces ses.

The total amount of raw materials consumed

in the process should be registered (i.e. what goes

in through the factory gate), and including also

the amount of internal recycling. The type and

quality of raw material is important, since differ-

ent materials cause different impacts during

extraction and differ significantly in scarcity.

Chemicals (for etching, cleaning, metal working

fluids, etc.) should be registered both in terms of

the consumption as well as the losses as emissions

or waste. Chemicals may cause toxic impact on

humans and the environment.

In the lifecycle impact assessment the inven-

tory is translated into environmental imp act

such as climate change, acidification and toxi-

city. T he environmental impact of different

options, e.g. choice of materials, disassembly

options, etc. can be compared or environmental-

improvement options can be identified, or it

can be identified whether a choice to reduce

environmental impact in one part of the l ifecycle

creates a greater environmental impact i n other

parts of the lifecycle, see also Fig. 25-1.Amore

detailed explanation of LCA methodologies can

be found in [1].

A range of software tools is available for mak-

ing the more detailed LCAs, e.g. GaBi, SimaPro,

LCAiT, TEAM, etc. Demo versions are often

available on the internet.

Application of LCA in

Micro-manufacturing

Micro-components are ofte n assumed to be

more environmentally friendly than their macro-

counterparts, although this may be challenged,

and in some cases even contradicted, as proposed

in [3,4] (Fig. 25-2).

In micro-manufacturing, LCA has been used

predominantly in the MEMS sector. The rapid

development of technologies and limited avail-

ability of data in the MEMS industry make com-

plete LCAs difficult to produce and they are quite

quickly outdated. One example is the manufac-

ture of a PC, for which the energy requirement in

the late 1980s was approximately 2150 kWh,

whereas in the late 1990s efficiency was improved

and only 535 kWh were necessary [5]: the use of

old data could result in erroneous results. Looking

at the overall environmental impact, this four-fold

increase in efficiency has been overcompensated

for by an increase in the number of computers

sold, from approximately 21 million to more

than 150 million [5]. The latter provides an exam-

ple of a rebound effect, showing that economic

and social aspects may have a huge implication for

the overall environmental impact.

A major trend is that shrinking product

dimensions increase the requirements of the pro-

duction environment to prevent pollution of the

product. This involves energy-intensive heating,

and ventilation and air-conditioning systems.

A clean room of class 10,000, for example,

requires approximately 2280 kWh/m

per year,

whereas a class 100 requires 8440 kWh/m

per

year. The same increase in requirements is rel e-

vant for supply materials such as chemicals and

gases. The demand for greater purity levels

implies more technical effort for chemical puri-

fication, e.g. additional energy consumption and

396 CHAPTER 25 Sustainability of Micro-Manufacturing Technologies

possibly more waste. Most purification technol-

ogies are highly energy intensive, e.g. all of the

distillation processes, which are used often in

wet chemical purification, account in t otal for

about 7% of the energy consumption of the

chemical industry of the USA [6]. Chemicals

used in large volumes in the semiconductors

industry are hydrofluoric acid (HF), hydrogen

peroxide (H

) and ammonium hydroxide

(NH

OH). These materials are used in final

cleaning processes and require X LSI grades

(0.1ppb).Sulfuricacidisalsousedinlarge

amounts, but it is a less critical chemical and

mainly requires an SLSI level purity [6].LCA

studies of electronics show that by far the great-

est energy consumption and waste are generated

in the production of the smallest components

(microchips and integrated circuits) [7].

Micro-manufacturing of other types of pro-

ducts also puts higher requirements onto the qual-

ity and purity of the materials. Exploitation and

loss of scarce resources is a concern, since the

consideration of economics is a primary obstacle

in the use of precious or rare materials in every-

day products. When products become smaller and

the components that include the rare materials

reach the micro- or nano-scale, economy is not

the most urgent issue, since it will not significantly

affect the price of the product. Therefore, devel-

opers will be more prone to use materials that

have the exact properties that they are searching

for. While an increased usage of such materials

may be foreseen due to the expected widespr ead

use of micro- and nano-technological products,

the recycling will be more difficult. An issue apart

from the loss of resources is that the extraction of

the rarest materials uses more energy and gener-

ates more waste than are associated with more

abundant materials. Table 25-1 illustrates the

energy intensity of a range of materials, i.e. how

much energy has been used for the production of

1 kg.

ECODESIGN/DFENVIRONMENT

Framework (from Reuse to Recycle)

First of all, it has to be stated that EcoDesign and

Design For Environment (DFE) are synonymous.

These frameworks take into account recycling,

remanufacturing, reuse and lifecycle assessment

FIGURE 25-2 Illustrating that LCA identifies environmen-

tal hot-spots in the lifecycle and how this information can be

used in, e.g., DFE to make environmental improvements.

The scissors show where the reduction in impact is greater,

therefore where effort should be targeted [1].

CHAPTER 25 Sustainability of Micro-Manufacturing Technologies 397

(LCA) during the design phases of the product, as

shown in Fig. 25-2. It is widely acknowledged that

the more is known about a product the less it can

be changed. This classical remark is also valid in

the case of DFE and has been pointed out in [8].

One of the key ideas in sustainability and Eco-

Design is to reduce the use of materials. This can

be done through process optimization, reuse of

the product or part of it, or when this is not pos-

sible, through considering the recycling of mate-

rial. Reused parts can be in the same field (broken

parts being replaced by remanufactured parts,

upgrade of systems...) or in some other unrelated

fields (a common example is the protection of

boats in docks of harbors by the use of old car/

truck tires). DFE can be seen as a cradle to favor

the use of many DFx components such as Design

for Recycling (DFR), Design for Remanufacture

(DFRm),DesignforAssemblyand for De-assembly

(DFA and DFD), Design for Manufacturing

(DFM) and the combination DFMA. Figure 25-3

shows the fram ework of DFE.

DFE also involves other objectives. For exam-

ple, the manufacturing chain should aim at caus-

ing the least possible environmental impact, an

issue which is more specifically addressed by the

concept of Env ironment Benign Manufacturing

(EBM) [9] and LCA of manufacturing processes.

From [10], DFE relies on eight axioms:

1. Manufacture without producing ha zardous

waste;

2. Use clean technologies (not in the ‘clean room’

meaning, but by taking care of minimizing the

impact in terms of pollution, etc. and also using

clean energy, such as windmill power, when-

ever possible);

3. Reduce product chemical emissions;

4. Reduce product energy consumption;

5. Use non-hazardous recyclable materials;

6. Use recyclable material and reuse components;

7. Design for ease of disassembly;

8. Product reuse or recycle at end of life.

Although originating from DFE of electronic

devices, it is quite clear that these axioms are of a

level of abstraction sufficiently high so as not to be

technology dependent and are well adaptable to

micro-scale mechanically based technol ogies.

They can be applied in the case of such micro-

systems as MEMS, and manufactur ed using VLSI

technologies. MEMS are just a portion of the

diversity of micro-products: they attract a lot of

media attention and are often seen as examples.

In this case, assembly and disassembly are related

to packaging and are dealing with the issue of

recycling chips. MEMS can also be applied in

any kind of non-silicon product development

and have to be seen as guidelines and checklists.

Many tools within the DFE family have been

developed through the years, from either acade-

mia or industry. A thorough overview of them is

given in [1]. Standardization work has resulted in

some EcoDesign guidelines, as in [11]. These tools

TABLE 25-1

Energy Intensity of the

Selected Materials (modified

from [7])

Material Energy Intensity of

Materials (MJ/kg)

Glass 15

Lead 54

Ferrite 59

Steel 59

Plastics 84

Copper 94

Epoxy resin 140

Aluminum 214

Tin 230

Nickel 340

Silver 1570

Gold 84,000

FIGURE 25-3 The Design for Environment (DFE) frame-

work.

398 CHAPTER 25 Sustainability of Micro-Manufacturing Technologies

are sometimes generic, and sometimes created by

one industry specifically for its needs and range of

products. They are not specific to particular tech-

nologies, although the electronic and mechanical

industries have been known for developing differ-

ent set of tools. In the case of micro-products,

often lying at the crossing between the miniatur-

ization of mechanical manufacturing and the non-

standardized use of micro-electronic manufactur-

ing processes, tools coming from both fields can

be used, albeit not optimally.

The new ISO TR 14062 tries to integrate envi-

ronmental aspects into the complete scheme of

product design an d development. Even if it does

not specifically target micro-technologies, its

management pe rspective brings valuable knowl-

edge to improve product design. [12] presents

some examples of cases to demonstrate what is

possible and provides details of some tools.

How to Apply to Micro-

manufacturing Technologies

To be capable of targeting the specifics of micro-

products, several issues have to be overcome. One

of the difficulties of micro-products development

is a lack of knowledge, on manufacturing pro-

cesses, solution principles and development meth-

ods. This lack of knowledge applies to an even

greater extent in the field of reliability and end-

of-life behavior. There are no known databases

for LCA in micro-technologies and therefore it is

very difficult to secure all the necessary informa-

tion to be able to take reliable design decisions

concerning the environment.

Most DFE components make a tremendous use

of handling and assembly. Unfortunately, han-

dling and assembly is a large issue that still, to a

high extent, remains to be solved at the micro-

scale, as seen in earlier parts of the present chapter

and as reported in [13], for example. The maturity

of the knowledge in the field of handling and

assembly for micro-components is still far from

being suitable for industrial applications. In the

case of an MEMS device, the concept of disassem-

bly does not really apply. Indeed, these devices are

often monolithic or embed ded, thus making it

difficult to separate the parts and materials. More-

over, the trend in micro-technologies is greatly

oriented towards the integration of functions

and co mponents. For instance, in two-component

injection molding, there is a strong bond between

the two polymers, or between the metal insert and

the polymer. Indeed, it is the goal of such a tech-

nology to create such a strong bond, hence going

against DFD principles.

Remanufacturing poses even more problems

than reassembly, due to the relative repositioning

accuracy a nd the skimming/trimming inherent

in the process. The amount of material may even

not be sufficient to allow a remanufacturing

operation.

Micro-components and DF

Intermediate Parts

On the one hand it is perhaps impossible to apply

remanufacturing concepts to micro-components,

but on the other these concepts can possibly be

applied to the intermediate parts.

For a typical micro-injection-molded part, the

runner system and other wasted parts can amount

to 95 to 98% of the total mass, due to the mini-

mum volume of a shot possible on available

hardware that was not specifically made for

micro-injection molding. Such parts can be seen

in Fig. 25-4. The effects of recycling of polymer,

both with and without fiber reinforcement, have

been studied in [14]. Even if the mechanical char-

acteristics of a part decrease with the number of

injection cycles, it is possible to design a piece with

a mechanical limit that allows a number of recy-

cling cycles. Stress/strain curves in relation to the

number of successive injections or recycled poly-

mer are available in the literature.

After a certain amount of injections, it is shown

that there is a loss in mechanical properties

(mainly due to fiber degradation), but these char-

acteristics may still be in the range of use for

some other design. Moreove r, by starting with

mechanical properties greater than necessary it

is possible to stay within expected limits after a

number of injections. Of course, a careful choice

of material is needed in order not to select a very

CHAPTER 25 Sustainability of Micro-Manufacturing Technologies 399

unenvironmentally friendly material, hence losing

on the one hand what is won on the other.

A DFE way of solving this problem could be the

use of carbon nano-tube reinforced polymers.

Indeed, nano-tube polymer composites not only

behave differe ntly in use, but also in manufactur-

ing processing [15]. Of course, such composites

will also require LCA and health-hazard studies.

The recycling of carbon nano-tubes is usually tar-

geted at recycling them without alteration or cost-

related issues. Environmentally-benign ways of

recycling polymer-based composites with nano-

tubes are investigated in [16,17]

Micro-factories

Likewise, it may be assumed that environmental

impact can be reduced by reducing the size of the

factory. However, few studies have as yet been

established to assess the actual environmental

impact of micro- factories and thus sustain this

assumption. Presupposing that the aim is to

develop environmentally-sustainable manufac-

turing methods, the need to examine the environ-

mental aspects of micro-factories is therefore

evident, as is the application of LCA as a tool.

The concept of the micro-factory is to create

small-sized production centers for small-sized

products in a ‘diverse-types-and-small-quantity

production’. It is based on the idea that the

manufacturing and manipulation processes are

often much bulkier than the parts that they pro-

duce and this is even more true for micro-compo-

nents. The manufacturing of micro-components is

very demanding. Indeed, it often requires a special

working environment not only for the handling

and assembly of the parts, but also for their pro-

duction. The maintenance of this working envi-

ronment (white- or clean-rooms with controlled

atmosphere and pressure for instance) is very

expensive, both in economic terms and in respect

of environmental impact.

One of the benefits of the micro-factory

approach is, of course, that the footprint is smal-

ler, hence inducing a lower cost in land occupa-

tion and, more importantly, atmo sphere control,

if need be. It is also assumed that there is a sub-

stantially lesser use of energy.

The example of the DTU (Technical Univers ity

of Denmark) micro-factory [18] can be used.

This system is targeting at hearing-aid and medi-

cal devices needing micro-components both in

polymer and in metal. The manufactur ing pro-

cesses chain can be seen in Fig. 25-5. It includes:

micro-injection molding, metal micro-forming,

die making, handling operations, and assembly

operations.

Unfortunately, there are often some difficul-

ties in data gathering, some of which to a certain

degree can be overcome by collecting data

continuously: using power meters, registering

the use of chemicals and raw materials, and

FIGURE 25-4 Relative size of micro-injection-molding components.

400 CHAPTER 25 Sustainability of Micro-Manufacturing Technologies