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577 Chapter 24 SUSTAINABLE DEVELOPMENT OF MICROELECTRONICS INDUSTRY THE ROLE OF METALS IN FUTURE INTERCONNECTION TECHNOLOGIES Hansjoerg Griese a , Jutta Müller a , Herbert Reichl b , Karl Heinz Zuber b a Green Electronics, FhG-IZM ,Berlin b Research Center for Microperipheric Technologies, TU Berlin 1. LEVERAGE OF ELECTRONICS The enormous potential of microelectronics technology and the importance of the microelectronics sector for nearly all leading industry segments according to the accumulated gross national product of Europe is illustrated in figure 24-1. The microelectronics industry, with 55000 Jobs and a revenue of about $25 billion, supplies the leading industry segments like communications or the automotive industry and thus contributes to as much as 80,000,000 Jobs and part of the Gross National Product amounting to $4800 billion. Hence, we define the ratios of microelectronics via components, systems and revenue of leading industries to the GNP of Europe from 1:2:7:50:200 (Griese, 2001). 2. ENVIRONMENTAL IMPACT OF ELECTRONICS The waste stream of electrical and electronic equipment (WEEE) is a complex mixture of materials and components. In combination with the constant development of new materials and chemicals having environmental effects, this leads to increasing problems at the end of the life of electronic products. The rapid growth of WEEE is of concern. In 1998, 6 million tons of waste electrical and electronic equipment were generated in the European Union (4% of the municipal waste stream). The volume of WEEE is expected to increase by at least 3–5% per annum. This means that in five years 16–28% more WEEE will be © 2006 Springer. Printed in the Netherlands. A. von Gleich et al.(eds.), Sustainable Metals Management, 577-592.

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Page 1: [Eco-Efficiency in Industry and Science] Sustainable Metals Management Volume 19 || Sustainable Development of Microelectronics Industry

577

Chapter 24

SUSTAINABLE DEVELOPMENT OF MICROELECTRONICS INDUSTRY THE ROLE OF METALS IN FUTURE INTERCONNECTION TECHNOLOGIES

Hansjoerg Griesea, Jutta Müllera, Herbert Reichlb, Karl Heinz Zuberba Green Electronics, FhG-IZM ,Berlin bResearch Center for Microperipheric Technologies, TU Berlin

1. LEVERAGE OF ELECTRONICS

The enormous potential of microelectronics technology and the importance of the microelectronics sector for nearly all leading industry segments according to the accumulated gross national product of Europe is illustrated in figure 24-1.

The microelectronics industry, with 55000 Jobs and a revenue of about $25 billion, supplies the leading industry segments like communications or the automotive industry and thus contributes to as much as 80,000,000 Jobs and part of the Gross National Product amounting to $4800 billion. Hence, we define the ratios of microelectronics via components, systems and revenue of leading industries to the GNP of Europe from 1:2:7:50:200 (Griese, 2001).

2. ENVIRONMENTAL IMPACT OF ELECTRONICS

The waste stream of electrical and electronic equipment (WEEE) is a complex mixture of materials and components. In combination with the constant development of new materials and chemicals having environmental effects, this leads to increasing problems at the end of the life of electronic products.

The rapid growth of WEEE is of concern. In 1998, 6 million tons of waste electrical and electronic equipment were generated in the European Union (4% of the municipal waste stream). The volume of WEEE is expected to increase by at least 3–5% per annum. This means that in five years 16–28% more WEEE will be

© 2006 Springer. Printed in the Netherlands. A. von Gleich et al.(eds.), Sustainable Metals Management, 577-592.

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578 Chapter 24

generated and in 12 years the amount will have doubled. The growth of WEEE is about three times higher than the growth of the average municipal waste within the EU (European Parliament, 2002).

MicroelectronicsRevenue appr. 25 B$Jobs appr. 55.000Revenue per Job appr. 450.000 $

Electronic ComponentsRevenue appr. 50 B$Jobs appr. 150.000Revenue per Job appr. 330.000 $

Electronic SystemsRevenue appr. 176 B$Jobs appr. 1.200.000Revenue per Job appr. 150.000 $

Leading Industry Segments:•Machinery•Electrical Industry•Automotive Industry•Communication Industry•Computer IndustryRevenue appr. 1.150 B$Jobs appr. 11.500.000Revenue per Job appr. 100.000 $

AccumulatedGross National Products

4.800 B$

from microelectronics to GNPRatios 1 : 2 : 7 : 50 : 200

Jobs appr. 80.000.000Revenue per Job appr. 60.000 $Revenue of

Leading Industriesappr.1.150 $B

Sources: GMM / VDE-TrendanalyseICE Mid-Term Status 1998Statistisches Handbuch für den Maschinenbau 1997Extrapolations

Figure 24-1. Leverage of microelectronics – direct contribution to revenues and Gross National Product.

2.1 Materials and Chemical Content

Only 3% of this waste is in the real sense electronics – mainly printed circuit boards (PCBs). PCBs can contain almost every chemical element from the periodic table in various compounds. Figure 24-2 gives some examples.

They contain not only inert materials like glass and ceramics but also highly toxic substances like special heavy metals, such as mercury, lead, cadmium or beryllium oxide. Some substances, like the flame retardant tetrabrome-bisphenol-A (TBBA), are probably not very toxic themselves but are predecessors of toxic reaction products formed during use or at the end-of-life.

Because of its hazardous content, electrical and electronic equipment causes major environmental problems at the end of life, if not properly treated. As more than 90% of WEEE is landfilled, incinerated or recovered without any pre-treatment, a large proportion of various pollutants found in the municipal waste stream in the developed countries comes from WEEE.

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SUSTAINABLE DEVELOPMENT OF MICROELECTRONICS INDUSTRY 579

Flammhemmer (FR)(zum Beispiel TBBAund A t i t i id)Epoxidharze mit FR

dFüllstof fe

Keramik(Al2O3, BaTiO3, AlN)

PE, ABS, PVC, PBT, etc.(meist mit Fl h t )

Glas (inkl. Bleiglas)

Elekt rolyt

Cadmium, Lithium, tDot iertes Silicium

Ag, Pd, Ni, Au, M(als Beschichtungen)

Organische Beschichtuund Pigmente

Bleioxid

BerylliumoxidQuecksilber

Spuren von F /Di i

Cadmium, Lithium, etc

Flame retardant(e.g. TBBA and Sb2O3)

Epoxy resinswith f lame retardants and

PE, ABS, PVC, PBT etc.(most ly f lame retarded)

Ceramics(Al2O3, BaTiO3, AIN)

Glass(incl. leaded glass)

Electrolytes

Cadmium, Lithium etc.

Doped silicon

Ag, Pd, Ni, Au, Pb, S(as plat ing)

Organic surfaces andpigments

Lead oxide

Beryllium oxide

Mercury

Traces of furanes anddioxines

Figure 24-2. Material content of printed circuit boards.

2.2 Environmental Assessment

A number of methods exist for quantification of the environmental impact of electronic products (Graedel, 1995).

Some – like the Eco Indicator 95 mentioned later in this paper – are based on life cycle-oriented approaches and summarize various effects (like ozone depletion, acidification of surface water, etc.) during the phases of production, usage and disposal of a product to derive a single number that quantifies its impact. It is also possible to quantify all impacts during the product life by a common unit, e.g., as energy. Life cycle-oriented assessment is usually very time consuming and requires a lot of information, which is not easily accessible or sometimes even unknown.

The TPI (Toxic Potential Indicator) assessment method, also used later on in this paper, concentrates on material properties and material specific legal regulations like workplace threshold values. Impacts over different life phases can be assessed only indirectly but the assessment is fast and based on well-defined data (Middendorf, 2000; Nissen, 2001).

2.3 Miniaturization and Environment

In the development of electronic components and devices, increasing miniaturization is the basic tendency. The key technology in this field is the assembly and packaging technology. A major step was the transition from Through Hole Technology (THT) to Surface Mounting Technology (SMT), which allowed closer spacing of the miniaturized components.

To assess the environmental impact, material toxicity of the miniaturized products and energy demand during production must especially be regarded. The toxicity impact of the miniaturized components is small. Although highly integrated

Tiller

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580 Chapter 24

ICs are expected to reach a share of 20% of the IC market, they will account only for 5% of the tonnage and only about 3% of the toxic potential of all ICs. The older generations of components will dominate the composition and amount of noxious substances because of their higher weight. Regarding raw material and energy flows, the miniaturized technologies have a higher impact (about 26%). This is caused by the higher content of silicon and precious metals (Nissen, 2001).

Generally speaking, we can suggest that boards with the same function unit become more environmentally friendly by miniaturization. However, shorter innovation cycles and an exponential growth of product numbers compensates the positive effect of miniaturization at least partly (this is sometimes referred as the rebound effect).

2.4 Regional Differences in Environmental Issues

In different regions of the world there are differences in aims and strategies for environmental protection in microelectronics (Pfahl, 2000).

The activities of US electronics companies are mostly driven by existing regulations and by cost reduction. Therefore, they are focused on the production process: replacing certain regulated materials, reducing energy consumption and the amount of material.

In Europe, regulations already announced as well as market forces lead to activities in design of products for the environment and life-cycle-assessment. This means that proactive actions play an important role in Europe.

In Japan, the influence of the government on the environmental behavior of electronics companies is still very high. In cooperation with nationally important companies, the long-term strategy is fixed and steps to get there are harmonized. Therefore, products for the global and domestic market are in focus. Lead-free soldering and halogen-free plastics have received much of their global dynamics from these activities.

Contrary to the US, the European Commission has announced three legal directives to reduce the environmental impact of electrical and electronic equipment. The draft has been divided in three parts: – The first dealing with collection and handling of electronic waste. – The second restricts the use of certain hazardous substances. – The third is a directive on the design and manufacturing of electronics.

The most important part in our context is the second one. In article 4 of the proposed directive, substances like lead, chromium VI, mercury and cadmium but also certain materials like poly-biphenyl-bromine or poly-bromide-diphenyl-ether will be substituted from 1.1.2006 on (European Parliament, 2002).

3. EXAMPLES

The following two examples show specific environmental problems caused by the use of metals in microelectronics and the ways to deal with them.

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3.1 Lead Containing Solder in Electronic Products and its Alternatives

There are world-wide efforts to substitute lead in electronic devices and there is an attempt in the EC to launch a directive referring to this (European Parliament, 2002). Japanese vendors such as Hitachi, Matsushita Electric and Toshiba have already announced the full implementation of lead-free soldering. Matsushita brought a portable MD player onto the market in October 1998, which adopts a Sn-Ag-Bi solder for the PCB assembly. The (planned) roadmap of the Japanese efforts to implement lead-free soldering is shown in table 24-1 (Suga, 2002).

Table 24-1. Time line towards lead-free electronics (Suga 2002) Component- Start development of full component supply with lead-free finishes 2001’ end - Full supply available of components with lead-free terminals 2003’ end - Full supply available of lead-free components 2004’ end Equipment- Introduction of lead-free solders 2002 - 2003 - Full adoption of lead-free solders in new products 2003’ end - Full lead-free production for new and old products,

with exception of legal exemptions 2005’ end

3.1.1 Toxic Potential of Lead

Tin-lead solders are well known, used worldwide and easy to handle for small enterprises and so 80–90% of electronics are soldered by tin-lead. Boards as well as components are suitable for the temperatures required to melt this alloys.

Even though lead is only used in small amounts on PCBs, due to its toxicity it is one of the weak points in respect to the boards’ environmental impact. The examination of a PCB example shows that only 7% of the material is SnPb but it contributes around 25% of the environmental impact of the PCB.

With simultaneous consideration of the strongly increased numbers of electronic products, that was one reason for world-wide efforts in research and development to substitute lead in electronic devices.

Figure 24-3 shows lead dissemination through water circulation. Discarded printed circuit boards come into contact with acid rain (acidified as the result of air pollution) and lead is dissolved and contaminates the groundwater. The polluted groundwater reaches the human body as drinking water. This leaching potential of lead is much higher than that of all other solder materials.

It has been known for more than a hundred years that lead affects the human nervous system and causes a range of serious problems. It is reported that the growth rate and intelligence of children that ingest lead are adversely affected. Low doses can accumulate. Lead is also known to be teratogenic and there is evidence that it is carcinogenic and mutagenic (Merian, 1991).

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Figure 24-3. Leaching of lead from discarded printed circuit boards (Source: Panasonic).

3.1.2 Lead in Electronics: The Interconnection System

Most of the lead on PCBs is obtained in the interconnection system consisting of the surface finishes of the board and the component leads or terminals and of course, the solder itself.

Some components such as varistors, thermistors or multilayer capacitors contain smaller amounts of lead and there are no alternatives at present. Therefore, a transition to lead-free electronic devices has to aim at the most heavily used parts, which will be the solders and surfaces finishes, and replace them.

A soldered contact, for example a surface mounted “J-Lead” in figure 24-4, consists of the component contact area and its finish, the solder, conducting area of the board with finish and the intermetallic compounds between them. This whole interconnection system including the surfaces and the component terminals must be considered if the solder is to be replaced.

Thus, are there alternatives for lead containing solders: less toxic, commercially available, easily processable with the same equipment? Today we can say yes, but associated with a lot of problems. The main point is that there is no simple binary or ternary eutectic solder available that meets all the requirements at the same time.

In table 24-2 possible lead-free solders are listed in comparison to tin-lead. The melting temperatures differ a lot. Most of the activities are now directed towards tin-silver-copper, tin-silver and tin-copper. Tin-bismuth plays no important role until all lead is phased out of the solder partners, because it forms a lead alloy with a very low melting point, for example in contact with tin-lead coated component surfaces.

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finish (e. g. pre tinning)

barrier layer

intermetallic compounds

componentcontact area

solder

conductorsubstrate

Figure 24-4. Electronic interconnection system.

Table 24-2. Lead free solders used by Japanese electronics industry (Suga, 2000)

3.1.3 Environmental Impact of Solders

The implementation of a new lead-free interconnection technology should not lead to unwanted new environmental burdens. To prevent this, the environmental impact of possible substitutes has to be considered during the selection of a new technology. This is especially important because the choice of different solder alloys also has influence on the finishes of the printed circuit board and of the package leads, as described above. The environmental impact of the different manufacturing processes must be taken in account, too (Griese, 2000). The main question is: are the

Alloys category Recommendedcomposition Remarks

Sn-3.5AgSn-(2-4)Ag-(0.5-1)Cu SnSn--3Ag3Ag--0.5Cu0.5CuSn-0.7Cu + Additives

(Ag, Au, Ni, Ge, In)Sn-3.5AgSn-(2-4)Ag-(0.5-1)Cu SnSn--3Ag3Ag--0.5Cu0.5CuSn-(2-4)Ag-(1-6)Bi,including the ones with1-2% of In

Incompatible with Sn-Pbplated components when itcontains some amount of Bi.

Sn-(8-9)Zn-(0-3)Bi SnSn--8Zn8Zn--3Bi3Bi

Handle carefully Sn-Zn incorrosive environment.Ni/Au finishes preferred forCu electrode at high temp.

Low temp. Sn-(57-58)Bi SnSn--57Bi57Bi--1Ag1Ag Incompatible with Sn-Pbplated components

Sn-3.5AgSn-(2-4)Ag-(0.5-1)Cu SnSn--3Ag3Ag--0.5Cu0.5CuSn-0.7Cu + Additive(Ag, Au, Ni, Ge, In)

Incompatible with differentsolder alloys in reworking.

Manual/Robot(Thread Solder)

Process

Wave

Needs temperature controlas Sn-Ag melts at high temp.

Medium &high temp.Reflow

Sn-Pb plating metals oncomponents might causefillet-lifting and damage toboards

Alloys category Recommendedcomposition Remarks

Sn-3.5AgSn-(2-4)Ag-(0.5-1)Cu SnSn--3Ag3Ag--0.5Cu0.5CuSn-0.7Cu + Additives

(Ag, Au, Ni, Ge, In)Sn-3.5AgSn-(2-4)Ag-(0.5-1)Cu SnSn--3Ag3Ag--0.5Cu0.5CuSn-(2-4)Ag-(1-6)Bi,including the ones with1-2% of In

Incompatible with Sn-Pbplated components when itcontains some amount of Bi.

Sn-(8-9)Zn-(0-3)Bi SnSn--8Zn8Zn--3Bi3Bi

Handle carefully Sn-Zn incorrosive environment.Ni/Au finishes preferred forCu electrode at high temp.

Low temp. Sn-(57-58)Bi SnSn--57Bi57Bi--1Ag1Ag Incompatible with Sn-Pbplated components

Sn-3.5AgSn-(2-4)Ag-(0.5-1)Cu SnSn--3Ag3Ag--0.5Cu0.5CuSn-0.7Cu + Additive(Ag, Au, Ni, Ge, In)

Incompatible with differentsolder alloys in reworking.

Manual/Robot(Thread Solder)

Process

Wave

Needs temperature controlas Sn-Ag melts at high temp.

Medium &high temp.Reflow

Sn-Pb plating metals oncomponents might causefillet-lifting and damage toboards

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584 Chapter 24

lead-free solders more environmental friendly in comparison to tin-lead? We will try an answer in the following paragraphs.

Table 24-3 shows different aspects of the environmental impact of interconnection systems in electronics that have been examined covering different phases of the life cycle. Results are summarized in table 24-4 and described below. The TPI (Toxic Potential Indicator), used here to give an overall rating, was developed at the Fraunhofer Institute for Reliability and Microintegration (IZM) as a fast screening method to evaluate the environmental impact of materials or products by their chemical contents (Middendorf, 2000). All lead-free solders have a better TPI rating than SnPb37. Even the use of the relatively poorly rated silver is favourable, because only a small quantity is used in the solder.

Table 24-3. Regarded categories of the environmental impact Material Properties TPI screening Acute toxicity Ecotoxicity TPI Toxic Potential Indicator

Toxicological data Toxicological data

Calculated from legal threshold values

Direct effects Toxic effects in ecosystems

Life Cycle Impact Metal production Manufacturing Material recycling Disposal EcoIndicator 95 Energy demand,

noxious auxiliary materials

Compatibility with copper and precious metal refining

TCLP Toxicity CharacteristicLeaching Procedure of US-EPA

Impact of mining, transportation,refining of raw materials

Impact of the production process

Effect of material on recycling processes

Leaching behaviour during disposal

Table 24-4. Overview of the environmental impact of lead free solders compared to SnPb.

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SUSTAINABLE DEVELOPMENT OF MICROELECTRONICS INDUSTRY 585

The direct effect on humans or mammals in general is summarized as ”acute toxicity. An effect in this category especially mentioned for silver is Argyria, a discoloration of the skin caused by the deposition of silver particles, usually with no other harmful effects.

„Ecotoxicity“ means the toxic effects on the environment, e.g., on certain groups of organisms (like plants or bacteria) or in certain compartments (water, soil, air). Compared to lead, all substitutes have advantages, especially tin/copper and tin/zinc solders have good properties (Merian, 1991).

The environmental impact of metal production was measured by the EcoIndicator95 method. The impact of ore mining, transportation and refining (energy consumption and emissions) are summarized to assess the metals. The lead-free solders have remarkably good ratings, only bismuth is rated relatively poorly because it is assumed to be produced mainly together with the noxious lead (Merian, 1991). Nevertheless, the rating of SnBi58 is better than SnPb37.

The manufacturing processes were coarsely rated according to the assumed energy demand and use of auxiliary materials (flux, cleaning agents, inert gases). It

and cleaning agents are an environmental minus. The material recycling capability is (up to now) assessed as the compatibility of

the solder components with copper refining and precious metal refining as pathways of electronic scrap recycling. According to the statements of copper smelters, especially the Bismuth rating is negative, because it contaminates the copper even in low concentrations.

To characterize the disposal performance of the solders, the US-American „Toxicity Characteristic Leaching Procedure“ TCLP1311 was carried out (Griese, 2000; Blackburn). Leaching behavior of SnPb solder is very poor compared to all alternatives. For copper, the leaching from the soldered joints is likely to be negligible compared to the copper PCB-layers. Zinc leaching has not been examined up to now.

At a glance, table 24-4 shows the potential for environmentally beneficial replacement of lead in the electronic interconnection systems but also indicates the need for in-depth studies to choose the appropriate solder.

3.1.4 Lead-Free Surface Finishes

– Up to now, the mainly used surface finish is SnPb Hot Air Solder Leveling (HASL). Alternative lead-free surface finishes are

– Chem. Ni/Au – Chem. Ni/Pd/Au – Chem. Sn – Chem. Ag –

The Ni/Pd/Au surface was not included in the following considerations because the market for palladium is very unstable and its costs are difficult to calculate.

still has to be quantified more precisely. Of course, the higher melting temperatures of SnAg, SnAgCu and SnCu solders lead to higher energy demand. For SnZn, the flux

Organic solderability protectants (OSP)

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For an average of 50% of the produced PCBs, the surface finishes have to change if the lead ban becomes reality. In Asia, where consumer electronics are produced, the low-cost HASL finishes with lead are applied more. The alternatives not only have to comply with technical/ technological requirements but should be more environmentally compatible than the conventional HASL SnPb layers.

In table 24-5 the different surface finishes are characterized by their layer thickness, the resulting masses of the several materials per square meter of PCB and their layer properties.

Table 24-5. Characterization of the lead-free finishes in comparison with the SnPb HASL layers Surfacefinish

Density (layer material)in g cm-3

Layer thickness (µm) and mass* in mg cm-2

Layer properties

HASLSnPb37

Sn: 7.2 Pb: 11.3

25 / 54.7 Not bondable, multiple solderable, T-stress

Chem.Ni/Au

Ni: 8.9Au: 19.3

5 /0.1 / 11.6 Bondable, multiple solderable, flat layers

Chem. Sn 7.2 1 / 1.8 Not bondable, multiple solderable, flat layers

Chem. Ag 10.5 0.1 / 0.3 Bondable, multiple solderable, flat layers

OSP 1 (est.) <0.5 / 0.2 multiple soldering difficult, not bondable, flat layers

* Assumption: One quarter of the surface is metallized All of the lead-free surfaces are very thin in comparison to the SnPb HASL

layers and therefore the layer masses are very small. Table 24-6 shows an overview on various aspects of the environmental impact of

the different surface finishes along their whole life cycle: the screening assessment by means of the TPI, the assessment of the environmental impact in the raw material production by means of the energy consumption, the assessment of the environmental impact in the finish manufacturing by means of energy and water consumption and some short remarks about the environmental impact in the end-of-life phase.

The screening assessment by means of the TPI shows that the HASL and Ni/Au layers are relatively high (poorly rated) in comparison to the Sn-, Ag- and OSP layers. The reasons are the high toxicity and mass of lead in the HASL and Ni in Ni/Au layers.

For the environmental impact of the first life cycle phase – the raw material production – the energy consumption is considered. For the production of the precious metal Au a high energy demand is necessary. This means that the environmental impact for this process is very high.

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Table 24-6. Environmental impact of lead-free surface finishes compared to HASL ManufacturingSurface

FinishTPI* E RM**

E in 106 J/m2

non-c./ convWater consumptionin l/m2 non-c./ conv

End of Life

HASLSnPb37

51.7 9615 2.48 1.51 50.5 40.3 Pb leaching

Ni-leachingNi/Au 47.2 73312 5.08 - 83.9 -Au-Recycling

Chem. Sn 0.2 432 3.28 5.93 73.7 35.6Chem. Ag 1.1 907 - 3.26 - 21.6 OSP 0.17 40 (est.) 1.42 0.83 31.3 21.6 No Recycling

*in 104 TPI/m2 PCB, ** for raw materials, in 103J/m2 PCB(conv: conveyorized, non-c: non-conveyorized) Environmental compatibility rating: Dark grey = very poor, grey = poor, white = good

For the assessment of the environmental impact of the manufacturing, the water and energy consumption have to be considered. These results were taken from the PWB Project Surface Finishes of the EPA in the USA [4]. There is a distinction between the non-conveyorized and the conveyorized process because of the large differences between them. For further examination of the environmental process impact, all the chemicals of the processes have to be included.

As shown in table 24-6, five surface finishing processes consume less water than the reference HASL, non-conveyorized process, including the conveyorized versions of the HASL, chem. Ag and Sn technologies, along with both versions of the OSP process. Two surface finishing processes consume more water than the reference process, the non-conveyorized version of chem. Sn and Ni/Au. The rate of water usage is primarily attributable to the number of rinse stages required by the processes. In general, the application of the conveyorized process is generally better than the non-conveyorized process, i.e., they consume less water.

Referring to the energy demand, table 24-6 shows that three of the process alternatives consumed less energy than the reference HASL, non-conveyorized process. Both the non-conveyorized and conveyorized versions of the OSP process, along with the conveyorized HASL process, consume significantly less energy than the reference process. The reductions were primarily attributable to the efficiency of these three processes and their short operating times. On the other hand, the long operating time in the case of the Ni/Au process is responsible for the relatively high energy consumption.

For a screening assessment of the environmental impact during the end-of-life phase, especially the disposal behavior of soldered PCBs, the leaching of the layer materials (only for metals) was examined by means of Toxicity Characteristic Leaching Procedure (TCLP). The results emphasize the well known solubility of Pb but also show a high Ni solubility.

Summarizing all facts of the surface finishes from an environmental point of view, the OSP finishes are rated best, whereas the NiAu finish should only be applied if required for technical reasons.

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3.2 Environmentally-Friendly Gold Coating

The copper of the conducting paths on printed wiring boards has to be protected against contamination. In microelectronics, Au layers are gaining more and more importance as a universal surface finishing. These layers are deposited by an

First an immersion gold layer with a thickness of less than 0.1 µm is generated in a charge exchange process. This thin gold layer has to be reinforced by a subsequent

State of the art for this kind of gold coating is the application of baths containing

The administrative regulations based on the German water balance act (Wasserhaushaltsgesetz) as well as the professional association of the chemical industry in Germany, demand to replace cyanide by less harmful substances whenever it is possible.

Additionally, old bath solutions have to be detoxified before disposal, which can lead to high costs. Oxidation by sodium hypochlorite is widely used but this method also implies additional risks. In the bath, toxic chloro-organic compounds may be formed with organic substances, such as tensides and the AOX-threshold value has to be observed in this case.

Further weak points of the cyanide gold bath are its difficult handling, its low thermal stability and its nickel ion sensitivity. Finally, these baths are not well compatible with the masking process materials because of their alkalinity.

These are various reasons for developing a new bath and the corresponding coating technology with the aim of obtaining a technically, economically and ecologically optimized bath.

As a first step towards the substitution of cyanide, the literature on complex formation was surveyed to find compounds that form sufficiently stable complexes with Au (I)-cations. Further important properties were solubility in water and stability at temperatures up to 80° C.

The pre-selection led to a number of organic sulphur, phosphorous and nitrogen compounds. Already at this early state of development, the environmental impact of these compounds was assessed and compared to cyanide. For this, the Toxic Potential Indicator was investigated. The results are shown in table 24-7.

According to the results of the ecological assessment, 2,3-Dimercaptopropane-1-sulfonic acid and histidine are the preferable substances, but 2,3-Dimercaptopropane-1-sulfonic acid was rejected due to its high cost. In table 24-8 the detailed threshold values and classifications of cyanide and histidine are listed.

electroless chemical process on chemically coated nickel layers on the copper.

chemical reduction process for bondability reasons. The key components of such a coating bath are a complexing and a reducing agent. While the complexer keep the cations of gold in solution, they are reduced only at the active surface by the reducing agent and deposited there.

cyanide as complexing agent and as free cyanide. But the highly toxic cyanide ispotentially dangerous for health and the environment, if released during an accident.Therefore, its use requires high expenses for safety and environmental protection.

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Table 24-7. Complexing agents and their environmental assessments Compound TPI per mg Potassium Cyanide 67,5Trimethylphosphine (TMP) 35,6Mercaptosuccinic acid (MA) 33,52,3-Dimercaptopropane-1-sulfonic acid 1,6 Histidine 0,0

Table 24-8. Threshold values and classifications of cyanide and Histidin Complexer MAK-

value[ml m-3]

Waterpollutionclass

LD50(or. rat) [mg kg-1]

R-description acc. to German Hazardous Subst. Declaration

Cyanide 5 3 5 Highly toxic in case of inhalation, contamination, swallowing

Histidine - 0 > 15000 Maybe harmful in case of inhalation, contamination, swallowing

After selection of the complexer, the suitable environmentally-friendly reducing agent has to be determined. For some industrially used reducing agents, the TPI was also calculated (see table 24-9), but the selection of an appropriate reducing agent depends strongly on the complexer used. The combination must provide sufficient chemical stability of the solution.

Table 24-9 shows that thiosulfate and ascorbic acid have a good environmental compatibility and should be preferred. For the combination with histidine, thiosulfate was selected.

Before the gold-free worn out solution with the organic complexer can be disposed of, the organic load must be reduced, even if the constituents are not toxic. Otherwise, the self-cleaning capacity of natural waters could be exceeded. The limit is 600 mg·l-1 COD (chemical oxygen demand) for the plating industry in Germany.

Table 24-9. Reducing agents Compound TPI per mg Hydrazine 77.9 Formaldehyde 20.4 Thiosulfate 0.0 Ascorbic acid 0.0

In general, biological degradation is preferable to chemical treatment of waste water with high concentrations of organic compounds. The constituents can be removed thereby without additional chemical agents. Microorganisms use the pollutants as a source of carbon and/or energy. The pollutants are metabolized to CO2, water and biomass and thus eliminated from the water. The biodegradation of a cyanide-free plating bath solution could be shown as decrease of COD over time (Zuber, 2001).

The new cyanide-free bath for gold coating has excellent technical properties and the plating process is more environmentally compatible than the currently used bath. The substances are biodegradable and less toxic, the bath works at a lower operating temperature and the plating rate is higher.

Continued examinations are concentrated on the corresponding recycling process. The chemical principle of deplating, compared with plating, is shown in

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590 Chapter 24

figure 24-5 together with typical carbon contents of the solution, which indicate its suitability for biodegradation after use.

AuRed.

e-

CA-Au+CA-

CA-

Red. CA-

CA-

CA-

Ox.

CA-Au+CA-CA-

CA-

CA-

Ox.

e-

Total 16,8 g l -1 C in 0,1-mmixed solut ionFor comparison: Usual growthmedia contain ca. 4 g l-1 C !Cost ef fect ive and resourcesaving waste water treatmentby biological degradat ion

ComplexingAgent :2,4 g l-1 C

Oxidizer:7,2 g l-1 C

pH-Correctant:7,2 g l-1 C

Plating Deplating

Figure 24-5. Biodegradable organic carbon content of gold plating and deplating solutions.

The aim is to make energy consuming, centralized gold smelting obsolete for the recycling of gold-containing electronic devices and to replace cyanide in the present recycling process. The recycling product (gold complex) can be used directly in the chemical industry, as shown in figure 24-6.

Precious Metal Refining

Chemical Industry

Plating Bath Supplier

PWB Manufacturer

Consumer

Recycler

Copper Smelter

Possible new

Pathways

Figure 24-6. Industrial gold cycle.

Even more important than the described technological development was the successful cooperation of the involved technologists and practitioners with environmental scientists that led to this result. The inclusion of environmental assessment at an early stage of the process development besides technical and economical optimization, leads to process-integrated environmental protection and is profitable for the industry as well as for the environment.

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SUSTAINABLE DEVELOPMENT OF MICROELECTRONICS INDUSTRY 591

4. SUMMARY

Electronic products contain numerous noxious substances, among them many metals, in components and boards. In general, the amount in a single electronic device is comparatively low in absolute numbers and even decreasing due to miniaturization.

However, the enormous growth of production numbers and the short innovation cycles compensate this positive tendency and lead to rising burdens for the environment by discarded products. Additionally, there is the significant impact of the complex production processes, such as raw material extraction or microchip production and others.

Therefore, there are efforts in many countries to evaluate and control the environmental impact of microelectronics. By careful optimization of microelectronic products and processes, as described in the two examples in this paper, the harmful impact on the environment can be minimized during the ongoing rapid development of production numbers and new technologies in microelectronics.

Facing the product numbers and growth rates forecasted for the developing countries by the ICT-Industry, all materials, especially toxic metals in electronic components, need to be closely examined. However, this examination should not primarily aim at legal regulations and the ban of materials, but on product responsibility and the environmental awareness of the producers.

REFERENCES

Blackburn, W. B.; Newcomer, L. R.; Kimmell, T. A.: “Performance of the Toxicity Characteristic Leaching Procedure”. Wilson Laboratories, S-Cubed, U. S. EPA

European Parliament: Texts Adopted at the sitting of Wednesday 10 April 2002 PART ONE.Paper P5_TAPROV(2002)04-10 PROVISIONAL EDITION PE 316.565.

Graedel, T. E.; Allenby, B. R.: Industrial Ecology. Prentice Hall, Englewood Cliffs, USA 1995

Griese, H; Müller, J.; Reichl, H.; Somi, G.; Stevels, A.; Zuber, K. H.: EnvironmentalAssessment of Lead-Free Interconnection Systems. Proc. Symp. on Lead Free Interconnect Technology, SMTA, Boston/Massachusetts, June 13 - 14, 2000

Griese, H.; Müller, J.; Nissen, N. F.; Reichl, H.; Zuber; K. H.: International Trends to Environmentally Compatible Electronics. Proc. Workshop on Environmental Management in Electronics Industry, New Delhi, February 9th-10th, 2001

Merian, Ernest (Ed.): “Metals and Their Compounds in the Environment”. VCH Verlagsgesellschaft mbH, Weinheim (FRG), 1991

Middendorf, A.; Nissen, N. F.; Griese, H.; Müller, J.; Pötter, H.; Reichl, H.; Stobbe, I.: EE-Toolbox – A modular assessment system for the environmental optimization of electronics.Conf. Record 2000 IEEE Int. Symp. on Electronics and the Environment, San Francisco/CA, May 8-10, 2000

Nissen, N. F.: Entwicklung eines ökologischen Bewertungsmodells zur Beurteilung elektronischer Systeme. Dissertation Elektrotechnik der Technischen Universität Berlin, 2001

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Pfahl, R. C.,: Green Electronics: Trends in the US. Joint Int. Congr. EGG2000+, VDE Verlag Berlin, Offenbach, September 11-13, 2000

Suga, T: JEITA Lead-free Soldering Roadmap. Draft July 2002 Zuber, K. H.; Griese, H.; Hannemann, M.; Müller, J.; Schmidt, R.: Environmentally-Friendly

Plating and Deplating of Gold in PCB Manufacturing. Proc. Micro System Technologies 2001, Düsseldorf, March 27-29, 2001