Design for eXcellence

Unit 5: Design for environment

Section 3: DfE and board materials and processes

In this last section, we looked at the materials of the solder used in assembly; we will start this section by reviewing environmental issues caused by solvents in the related areas of cleaning and fluxes. We will then progress to another problem with consumables that is shared by assembly and fabrication, before dealing with a wider group of environmental concerns specific to the board, the laminate itself and the materials and by-products of the fabrication process.


Section Contents


Cleaning

Introduction of fluorocarbon solvents

Rosin flux residues require cleaning, especially when activated fluxes have been used, and cleaning was very commonly carried out, especially throughout Europe and the USA, driven by a perception held by military customers that all flux residues are potentially harmful. The original approach used a variety of solvents but these gave problems:

Some solvents present health hazards and/or have low TLV limits.

An occupational exposure standard (OES) is the concentration of an airborne substance, averaged over a reference period, at which according to current knowledge there is no evidence that it is likely to be injurious to employees if they are exposed by inhalation day after day to that concentration. Chemical manufacturers are required to issue product safety information which will contain OES information, although it may be given in terms of the US threshold limit value (TLV) which for practical purposes is the same.

Fluorocarbons had been developed during the 1930s as refrigerants, and in the late 1960s were introduced for the cleaning of electronic assemblies. The particular compound most commonly used was 'CFC-113', 1,1,2-trichloro-1,2,2-trifluoroethane1. This material:

For these reasons, fluorocarbons rapidly became the preferred means of cleaning, despite their expense. The solvents were marketed under a variety of trade-names, of which Arklone and Freon were the best-known in the UK.

1 The numbering system used for CFCs and similar compounds is confusing, but there is an explanation at http://www.epa.gov/ozone/geninfo/numbers.html.

Ozone depletion

Following scientific evidence of the damaging effect on the stratospheric ozone layer, which protects us from the harmful effect of the sun's radiation, over 100 countries agreed, in the Montreal Protocol of September 1987 (amended in London, June 1990 and at Copenhagen, November 1992), to phase out man-made ozone-depleting chemicals as quickly as possible. Not only was CFC-113 affected, but another of the common chlorinated solvents (1,1,1-trichloroethane, or methyl chloroform, and sold as Genklene or Chlorothene) was also covered by the resulting European-wide regulations, where phase-out was scheduled by the mid-1990s. The Protocol and its associated EC regulations imposed control on the supply to the market of the substances rather than their use as such, but the effect is the same, to force electronic companies to seek different ways of approaching the problem, and these materials have now essentially become unavailable.

The Ozone Depletion Potential (ODP) is the ratio of the impact on ozone of a chemical compared to the impact of a similar mass of CFC-11, and indicates the relative ability of substances to damage the Earth's ozone layer. There are two groups of chemicals, classified according to ODP:

Class I materials, those with significant ODP, have already been phased out. HCFCs and other halogenated materials with some ODP are subject to increasing restrictions and will also be phased out, those with the highest ODP values first. For example, the commonly used HCFC-141b ceased production on 1 January 2003.

If you are interested in researching this in more detail, a good starting point in the US Environmental Protection Agency website at http://www.epa.gov/docs/ozone/.

2 For a complete listing, see http://www.epa.gov/ozone/ods.html (Class I) and http://www.epa.gov/ozone/ods2.html (Class II).

Other issues

The list of environmental issues involved with cleaning materials is in fact much more extensive than mere ozone-depletion, although it is that aspect which has been nearest the headlines. A fuller list includes:

The Environmental Protection Act 1990 controls emission from large cleaning operations (the trigger levels for which are constantly reducing) and, through Water Authority consents, is also affecting the ability of a company to discharge even treated effluent. Legislation in the EPA and elsewhere, regulates how many materials, including spent solvents, may be carried, transferred, stored, treated and disposed of. These regulations are likely to get tighter and involve higher costs in the future.

3 Probably the most unfriendly material from the GWP perspective is sulphur hexafluoride. Used as a cover gas in magnesium production and casting, as a dielectric gas and insulator in electric power equipment, as a fire suppression discharge agent in military systems, and formerly as an aerosol propellant, this has a GWP of 22,200 and a life of 3,200 years!

Hazards in cleaning

Almost all cleaning options have some potential to harm operators if not properly controlled to minimise risk. Precautions taken have to be reasonably practical but also to take into account technical, cost and environmental issues. Three aspects of Health and Safety hazard are generally considered:

Alternatives to CFCs

As with the replacement for tin-lead solder, there is no immediate drop-in replacement for the CFCs used in cleaning. The nearest to such a material, n-propyl bromide, was developed too late in the day, and its use has been somewhat controversial. Although it has an ODP rating of zero, is relatively cheap, non-flammable and fits a range of applications, it is somewhat toxic, with an OEL of 50 ppm, and some concern that this will reduce. In consequence, there has been no change to the four basic approaches to the withdrawal of CFCs that were proposed at the outset:

  1. Use a volatile organic solvent in a process similar to CFC vapour cleaning using either non-flammable HCFC solvents or flammable solvents with a lower global warming potential.

  2. Use an organic solvent with a high boiling point, either evaporating the solvent at elevated temperature or choosing a water-miscible material which can be rinsed with water and dried once the solvent has completed its task of removing the 'soil' - this is referred to as a 'semi-aqueous' process.

  3. Use water as a solvent, either in combination with detergent to remove rosin flux residues or in conjunction with water soluble fluxes. Some components are not compatible with water or are difficult to clean because of fluid entrapment in small crevices. Water-soluble fluxes are more active than rosin fluxes, providing a larger process window, but even traces need to be removed because they are acid.

  4. Use a no-clean process.

A somewhat unexpected problem with a number of the processes, especially those based on water/saponifier combinations, is that the lead from solder will actually dissolve in the solvent, whereas this was not a problem with CFCs. This points out the need to consider every aspect of the process when evaluating a proposed change!

With no 'drop-in replacement' for CFCs available, much attention has inevitably been focussed on removing the need for cleaning. Figure 1 gives an example of a review carried out by a user of the cost and difficulty of alternative cleaning approaches, from which the no-clean option can clearly be seen to be desirable, if less easy than using CFCs.

Figure 1: Difficulty : cost ratio for different cleaning methods, Source: Nortel

Difficulty : cost ratio for different cleaning methods

No-clean processes

No-clean processes are not the same as not cleaning! In the latter case there will be flux residues, and they may or may not be deleterious to the long term reliability of the end product. A no-clean process involves selecting flux materials which will be effective in use but whose residues are:

Of these, the major issues in recent years have been associated with pin testability and cosmetic acceptability, and work continues on solder ball elimination and maximising the process window.

No-clean systems

No-clean systems have been formulated for both wave-soldering and reflow soldering. The basis for both is a flux which has a higher proportion of either solvent (for wave soldering) or rheology modifiers (for reflow soldering) and a lower concentration of both flux base and activator. Moreover both flux base and activators are chosen so that their decomposition products are not harmful.

The ultimate of no clean is 'no residue', where the flux is expended entirely during the process of producing the solder joint. This also presents the ultimate challenge for the user! The issues with all no-clean/no residue processes relate to process control, so that solderability is achieved and, the joint satisfactorily wetted, before the protective qualities of the flux are dissipated.

Inert soldering

It has been known for some time that reducing the oxygen level of the environment leads to reduced oxidation and gives a number of benefits with wave soldering:

It is this solution which can be used with both wave soldering and reflow soldering to enhance the process performance of fluxes that would otherwise be ineffective because of their reduced content of fluxing agents.

It may be thought that no-clean/no residue inevitably leads to using an inert atmosphere, but there is always a cost penalty associated with the use of nitrogen. Whilst nitrogen forms 79% of the air we breath, its extraction involves considerable energy expenditure, and it is costly both to store and transport. Careful consideration has therefore to be given to the nitrogen usage of machines:

With wave soldering, the benefits are more immediately apparent and the costs less, particular as it is feasible and cost-effective to inert the soldering area alone. With reflow soldering, the use of nitrogen atmosphere is also claimed to improve wetting times and allow a lower reflow temperature to be used, which:

In practice, convection reflow systems have a high gas usage, and the cost is difficult to justify. Nor is it possible to inert just the reflow zone: because of the extended time at high temperature during the reflow process, the whole of the oven has to be filled with nitrogen, and the percentage of oxygen maintained at a low level (certainly less than 50 ppm).

There is of course always the prospect of using no flux at all, and the search for this is intensifying. The problem has always been that component solderability is variable, and some degree of pre-cleaning inevitable if wetting is to be reliable and joints made at high first-time yields. Alternative metallisations and methods such as plasma cleaning are currently under evaluation.

Choosing a cleaning method

When selecting the most appropriate cleaning method for any given set of circumstances, there are many trade-offs, as Figure 1 has already indicated in terms of cost and relative difficulty. The United Nations Environment Programme support this link, at which Protonique offer guidance to users, especially those in developing countries.

Self Assessment

To gain further insight into the choices available, consider the cleaning needs of two types of assembly house making:

What are the cleaning options available? Review what you know about the options, and only then use the link above to check your conclusions and the logic of your argument. Notice how, for the second assembly house, the recommendations given may change according to the assumptions that you make about the level of reliability required of the products.

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Volatile Organic Compounds (VOCs)

Volatile Organic Compounds (VOCs) are used widely in products from paints, primers and coatings, to underarm deodorant and cleaning fluids, but have been found to be a major contributory factor to ground level ozone. Whilst ozone in the upper atmosphere helps protect us from the sun's dangerous ultra-violet rays, ozone at ground level is a highly reactive gas that, according to studies by the US Environmental Protection Agency, 'affects the normal function of the lung in many healthy humans.'

These studies show that breathing air with ozone concentrations above air quality standards aggravates symptoms of people with pulmonary diseases and seems to increase rates of asthma attacks. There is also evidence that prolonged exposure to ozone causes permanent damage to lung tissue and interferes with the functioning of the immune system. As you will find at http://www.epa.gov/oar/oaqps/gooduphigh/, ozone is "good up high, bad nearby".

Ozone has been a difficult pollutant to control because it is not emitted as such, but is actually formed in the atmosphere through a photo-chemical process in which VOCs react with oxides of nitrogen in the presence of sunlight. For this reason, controlling VOCs is an effective way of minimising ozone levels. In fact, the EPA definition of a VOC is any volatile organic compound which participates in atmospheric photo-chemical reactions.

The original concerns started with CFC awareness, accelerated by photo-chemical smog incidents. California was the first state to enact laws limiting the VOC content in paints and coatings, setting a precedence for US federal regulation.

The 1990 Clean Air Act Amendments required that VOCs emitted into the atmosphere be calculated and disclosed to the EPA. Effective from 1993, the legislation aimed at reducing the quantity of VOCs released into the atmosphere over a three year period, placing the burden of proof on the consumer to document their emission level.

Whilst the rules vary, they generally apply to all companies using or storing more than 5 tons per year, and 'major stationary sources' have to obtain an operating permit for equipment dealing with chemicals. A major stationary source is one with the 'potential to emit' more than 10 tons per year of any one hazardous air pollutant, or 25 tons per year of any combination of pollutants. Note that this 'potential to emit' refers to the amount that would be used with the equipment running at full capacity, and not the actual usage.

In the USA, not only VOCs, but also oxides of nitrogen, carbon dioxide, carbon monoxide, sulphur dioxide, and particulate matter need to be tracked, and there are swingeing penalties for non-compliance. The situation in the USA is currently more tightly regulated than in Europe, but the aims and strategies are comparable, and there is continuing regulatory activity to reduce emission levels. For example in the UK, a 10 tonne limit was set in the Environmental Protection Act (Solvent Emissions Directive) (England) Direction 2002 , and similar legislation in other regions.

In the printing industry, almost everything using chemicals is covered: printing presses, film processors, plate processors, and proofing presses: in the electronics industry, all companies of a significant size will be obliged to comply with VOC restrictions. Other than affecting cleaning strategies, the major impact if VOC regulation comes from their being a important constituent of fluxes. Note particularly that calling flux 'water-washable' only means that the residues may be removed by aqueous processing: such fluxes are not necessarily VOC-free, and will probably contain some solvents at the time of application.

Actions needed by the assembler are:

This is an area where there have been a number of improvements in materials. For example Cookson Electronics have reported the successful development of VOC-free foam and spray fluxes for wave soldering. However, in order to remove all water from board surfaces, components and holes, the amount of flux and the pre-heating process parameters are critical. In combination, the process window for lead-free soldering with VOC-free fluxes is narrower than that for SnPb soldering with VOC-based fluxes.

Self Assessment Questions

Explain to your colleagues why VOCs may have an impact on their health and on the processes carried out by your assembly partners.

Compare your answer with this one.

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Waste generation and disposal

Items which are consumed, but do not form part of the product that is wanted by the end customer include:

An environmental audit of any manufacturing facility will inevitably uncover a number of such issues.

Manufacturing paperwork

Responses to the waste generation challenge include at least the intention of implementing a 'paper-less workplace', in which the information requirements of the factory management system are recorded electronically rather than in hard copy. The difficulty here is winning acceptance of this, especially among people with a traditional quality management system approach, and the very real challenge of developing systems that are both foolproof and totally secure. In this context, 'security' relates to the continued integrity of data during unexpected power down, the ability of the system to sort information and select only that which is correct, and the security of the system against unauthorised attempts to corrupt it.

Packaging during manufacture

There is an opportunity for suppliers and users to work together to reduce waste: the collection of waste for recycling is not only economically effective but a useful housekeeping measure!

A particular problem has been noted in relation to tapes used for component placement, where the packaging forms a large percentage of the bulk of the total delivery! The alternative, of bulk packaging of small components in reusable containers, has attracted some attention. Earlier methods of bulk packaging were not satisfactory, because of feeder jamming problems: cassettes (Figure 2), where a factory-filled container is mated with a one-at-a-time dispenser, are seen as effective in both reducing waste and increasing the time between component feeder replenishment. After the cassette has been placed on an appropriate feeder, the bottom opening is opened by means of the manual slide.

Figure 2: Bulk case for transferring components

Bulk case for transferring components

The trays used for large components also present a challenge for the recycling-conscious engineer. Here the problem is not just one of economic collection for return to vendor, but is compounded by the very wide range of different tray types (several hundreds) and the length of the distribution chain from the original packager, typically in the Far East.

Packaging

Packaging has to be environmentally friendly, and this has proscribed the use of foams expanded with CFCs and discouraged the use of paper products produced with chlorine-containing bleaches. Given that paper products are generally recyclable, there is a discernible trend towards their use in preference to expanded foams, but where alternatives are considered, due notice must be taken of the frequent need for packaging to be part of the static protection for a product.

Given that some packaging is inevitable, then the company must establish a policy for the recycling of waste. This means that the manufacturer bears responsibility for making sure that packaging materials are recycled or, if this is not practicable, at least that they are capable of being recycled by the end-user.

The primary legislation is the European Packaging and Packaging Waste Directive (94/62/EC), interpreted in the UK by the Packaging (Essential Requirements) Regulations 1998, which set the rules for what can be used for packaging, and the Producer Responsibility Obligations (Packaging Waste) Regulations 1997, which sets targets for recovery and recycling of waste.

Currently the UK is meeting its recovery and recycling targets, but new EU Directives are likely to set higher and more challenging targets:

In fact, in September 2002, the European Parliament voted to increase the minimum recycling targets by weight for packaging from the 55% proposed by the commission to 65% and decided that these targets should be met by December 2006 - two years earlier than the environment committee would prefer.

If you would like to research this topic further, suggested starting points are:

4 For the purposes of the packaging directive, recovery of packaging waste includes incineration with energy recovery (energy from waste) and recycling, including composting. Recycling of packaging waste does not take place until the recycled material has been put back into productive use.

Product recycling

In a parallel move, responsibility is also being passed back to the manufacturer to have available and promote a policy of recycling the product as well as its packaging. These issues affect a business in every aspect from marketing and design to manufacture, distribution and servicing, and can be expected to have a major impact on the design and construction of products for the 21st century.

WEEE contains a number of measures on recycling, with encouragement to minimise the number of types of plastic used, use materials which can be easily recycled, and design and make parts which are easier to repair, upgrade, re-use, dismantle and re-cycle. There is also a requirement to minimise the use of certain dangerous substances, with a time-scale to phase out lead and other 'hazardous' materials, and this issue is dealt with in the next section.

Under WEEE regulations, producers have to set up (and bear the costs of) waste recovery systems, and must supply information to users, recyclers and the authorities. There are targets for collection (to be reassessed), and increasing targets for component, material and substance re-use and recycling.

Self Assessment Questions

Explain to your assembler's facilities manager:

Compare your answer with this one.

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Board fabrication issues

As far as board materials and processes are concerned, the environmental aspects fall into two areas:

In summary, it may be said that the current situation has improved, compared with that obtaining several years ago.

Aiming for an environmentally board fabrication plant

WWW Research

Rather than give you the answer immediately, we should like you to visit the US EPA site http://www.epa.gov/epahome/search.html and search for the term "Printed Wiring Board". You will find a modest number of hits, including a number of case studies. Take half an hour or so to skim through these documents and make notes on the main issues involved.

What conclusions can you draw from this study?

Review your answer as you read on.

The primary conclusion you can draw from your study is that this is an area that has received considerable attention in recent years for both safety and environmental reasons, seeking to reduce the total amount of water used and to eliminate processes with adverse environmental and health hazards.

The replacement of electroless copper has been promoted for two reasons. Firstly many of the formulations involve formaldehyde, a carcinogen, and secondly the processes consume large amounts of water. As a result, many manufacturers have adopted alternative 'direct metallisation' techniques, although there is now an electroless copper process that does not use formaldehyde. Probably the most attention has been given to direct metallisation systems based on palladium, but carbon/graphite treatment and conductive polymers are also in use.

You will know from your study of HASL that there are many environmental implications of this process. Not only does it use heat, but the coating contains lead, and the fluxes used are aggressive. The EPA study on this is particularly interesting because it provides comparative information for six different surface finishes, and there is no single winner.

For example, all the processes use hazardous materials5, some of which are subject to regulatory requirements, and one or more of which are materials that present a risk to the aquatic environment. Perhaps more surprising is the very wide range in the consumption of water and energy, with a range of 7:1 in water consumption and 10:1 in energy consumption for different processes applied to the same test board. ENIG is seen to be not as environmentally benign as some other surface finishes, a fact also borne out by the Cookson Electronics life-cycle analysis.

5 Specific hazardous materials, apart from the lead, are thiourea used in the immersion tin process and related urea compounds used in the nickel/gold and nickel/palladium/gold processes, all of which are believed to be carcinogenic to humans.

Other areas where savings can be made, both in cost and to the environment, involve the regeneration of materials such as spent etchants and the recovery and reuse of other materials. A case has also been made for the use of plasma de-smear to replace the permanganate process.

PCB manufacturers also have waste streams that are associated with photoresist: the spent developer solution, containing uncured resist and potassium carbonate; the spent stripper solution, containing cured mask, known as 'skins', and a high percentage of amines; the rinses from these processes; and the skins filtered from the stripper solution during processing to extend stripper life.

The main opportunities for cost-saving relate to the expensive concentrate used for stripping, where recycling the majority of the stripper can save substantial costs. Removing the skins, and separating them from fluids that have been trapped, is one of the challenges, where centrifuge methods have proven of value.

The critical area is that of water usage. When water used to be freely available, 'total loss' systems were prevalent,. Here the total volume of discharge was unimportant, provided that heavy metals and other contaminants were present in sufficiently low concentration. With more recent shortages of water, and its high cost, there is much emphasis on saving water consumption.

The techniques for this are generally relatively straightforward, but need a lot of attention to detail. Many savings can be made simply by implementing drag-out reduction and rinse water reduction techniques; the next step is the more capital-intensive work of re-circulating cooling water and use ion exchange technology to purify wastes. As with the semiconductor industry, correct processing can also help metal reclaim.

One of the problems in any attack on water usage is a lack of awareness of how much water is being used and discharged, and of the consequent cost to the business. One useful idea is that of a 'water mass balance', based on the principle of conservation that the amount of water entering a site must equal the amount of water, in all its various forms, that leaves the site. Based on the survey of water used, a water mass balance is a key technique for identifying where water is used, and where it might be wasted. Even relatively small continuous usages of water can have a substantial impact on costs: bear in mind that you are charged both for the water you consume and for the effluent you discharge.

If you are faced with the problem of implementation, register at Envirowise (formerly the DTI's Environmental Technology Best Practice Programme) http://www.envirowise.gov.uk/ for several relevant publications:

Other problems relate to devising effective techniques of removing persistent organic species from spent liquor, operational baths and rinse water. In particular, there are concerns about chelating agents such as EDTA (ethylene diamine tetra-acetic acid), which take up heavy metals during the process. There are also concerns about materials used as brighteners, photochemical strippers, surfactants and surface-modifying compounds.

A promising procedure is to use ozone and hydrogen peroxide either together or individually in the presence of short wavelength (254 nm) ultraviolet radiation. This generates highly reactive hydroxyl radicals that destroy virtually all organic substances, and have a greater oxidising potential than hydrogen peroxide or ozone separately.

Flame retardancy additives

Fire kills, which is why flame retardants are used in almost all polymers. In the context of PCB assembly this obviously affects the board, but also impacts on the materials used for area array packages (often laminates) and the moulding compounds used to protect semiconductors. Nor must we forget the largest single use, which is in equipment housing.

Flame retardants traditionally use bromine compounds6, in particular polybrominated diphenyl oxides (PBDPO), often in combination with antimony trioxide. The halogens are only weak fire retardants, and antimony trioxide by itself is not a fire retardant, but when combined they become very effective. During burning, antimony trioxide promotes charring of the resin, which reduces the formation of volatile gases. At the same time, the heat of combustion promotes cross-linking between the antimony and the polymer, which creates a more stable thermoset. Also, at above 315C, bromine forms hydrogen bromide, which reacts with the antimony trioxide to form antimony trihalides and oxyhalides that trap free radicals, inhibiting ignition and pyrolysis.

6 For more information, visit the European Brominated Flame Retardant Industry Panel web site at http://www.ebfrip.org/.

These are really good additives, so what is the problem? The difficulty is what happens at the end of product life. When materials treated with bromine flame retardants are recycled, they can generate dioxins and furans, materials that are extremely toxic even in low dosage. Whilst this problem can be overcome by increasing the process temperature, there is a second more intransigent problem, the contamination of the environment by the halogenated flame retardants themselves. These are released during both manufacture and recycling or disposal of products containing them, and have been found widespread in both fish and humans.

As a result of this concern, some materials are in the process of being banned, and others will need to be replaced. The main impact will be on equipment housings. Here there are a number of alternatives: aromatic bromine compounds that cannot generate dioxins or furans during combustion; phosphate esters; melamine and inorganic fillers. There is also the possibility of using inherently flame-retardant polymers such as modified polyphenylene oxide (PPO).

For boards, the most commonly used flame retardant is tetrabromobisphenol A (TBBPA). However, whilst this is still permitted under RoHS provisions, this decision can be revisited at any time. Possible substitute materials include various phosphorus and zinc compounds, and inorganic fillers.

The two phosphorus-containing alternatives are organic phosphates, which may be dissolved in the epoxy system and create foams that extinguish flames, and particles of red phosphorus itself. Being relatively large (20-30m) these are visible during microsectioning, and there is a concern that laser ablation might evaporate the particles, leaving holes in the structure. Overall, there are concerns about the toxicity of phosphorus materials, their comparative lack of stability, and the fact that they leach easily into the water table.

Laminate manufacturers have in the past used a variety of inorganic fillers such as mica or clay, or the more 'sanitised' fillers aluminium hydroxide and magnesium hydroxide. However, in order to make a laminate flame retardant the percentage of filler has to be sufficiently high to leave little fuel to burn. Levels as much as 50% by weight have been reported. These high loadings adversely affect board properties, making the laminate stiffer and more brittle, reducing impact strength and tensile strength, and increasing water absorption.

Of the other approaches in development, zinc compounds have been used in some halogen-free formulations, with zinc borate the most widely used. This behaves like aluminium trihydroxide: when heated, both decompose to release water that forms an envelope around the flame, and also absorbs energy, lowering the temperature.

Alternative approaches are to use materials that are inherently flame-retarding, and silicone compounds have been evaluated for this: they have high heat resistance, are not toxic, and do not generate toxic gases during combustion. Lau also reports success with finely-dispersed silicon in polycarbonate resin, but this material is primarily for use in housings.

In summary, this is a topic that is likely to see substantial development in the years to come particularly as the Japanese are starting to promote 'halogen-free' in the same way that earlier workers promoted lead-free. The only difference is that the colour of choice, indicating that the material contains no halogens, is likely to be blue rather than green.

Notwithstanding the commercial implications, we have to be careful that we do not overreact to environmental pressures in this area. It has been commented that US consumer products are generally much less flammable than their equivalents in Europe, because they contain more brominated compounds. In fact, because of pressure to remove these materials from enclosures, it has been estimated that as many as 100 people have died as a result of fires in electronic equipment!

End-of-life recycling

We have already seen that WEEE has a number of measures on recycling, with producers having to arrange channels for recovery of end-of-life product. Also we discovered that the problem runs into hundreds of millions of units as regards CRTs. The question now arises as to what one can do with the associated printed circuit boards.

Activity

What is the scale of the problem as regards boards as distinct from final electronic products? What is in or on a board that would make it worth processing? And what can you turn a PCB into?

After exercising your imagination on the last two of these questions, try a web search using the terms recycling +"printed circuit boards".

Review your answer as you read further.

Whilst data on the total amount of electronic scrap produced is available, for example from Industry Council for Electronic Equipment Recycling (ICER) http://www.icer.org.uk/, data for scrap boards is less readily available. However, an interesting 'scoping study' on what one can do with scrap boards may be found at this website.

50,000 tonnes of PCB scrap is produced each year in the UK and of this only around 15% is currently subjected to any form of recycling. The remaining 85% is consigned to landfill. Currently, the only board waste being recycled is the proportion having an inherent value because of its precious metal content and this is limited to recovery of the metal content via smelting.

Goosey and Kellner, August 2002

We can recover all the metallic elements on a printed circuit board such as the copper (and any nickel) and the tin and lead from the solder. There may also be smaller quantities of precious metals, such as gold, palladium and silver. Flame retardants can also be recovered. However, there may be hazards associated with certain types of components, containing mercury or beryllia.

But what is worth recovering? Certainly gold, palladium, silver and copper can earn revenue, but the other metals recovered are hardly in worthwhile quantities. However, whilst most populated boards and bare boards with a precious metal content have a value that exceeds the cost of processing, in other cases the costs of refining may exceed the intrinsic value of the metal.

The normal process for recycling a board starts with disassembly and component recycling where possible. Certainly any hazardous components need to be removed before the board is shredded and granulated by machine, separating metals from the plastic and fibres that constitute the majority of the board. Metals can then be recovered by a variety of separation processes and passed to refiners, and the plastic and fibre residue either incinerated or sent to landfill. The current way in which this is organised is indicated schematically in Figure 3.

Figure 3: Flow chart for recycling an electronics assembly, Goosey and Kellner

Flow chart for recycling an electronics assembly, Goosey and Kellner

Unfortunately, economic forces mean that much of this work is currently exported to countries such as China, where labour costs are lower and health and safety restrictions less onerous. More sophisticated approaches, specifically looking at hydrometallurgical treatments, are being investigated by Imperial College and at Cambridge, with the aim of providing a solution before 2006.

Of course with printed circuit boards there are one or two alternatives. For example, you can turn your spare boards into coasters or even into a golf club (http://www.circuit-pro.com/), although one wonders how much new resin is used and solid waste produced during the fabrication process for the latter. There is also a limit to the number of coasters and golf clubs that could realistically be produced!

In the US, the non-metals portion of circuit boards is currently being used in several industries to enhance products. In plastic lumber, it gives strength to the "wood"; in concrete, it adds strength, making the concrete lighter, and providing an insulation value ten times that of standard concrete. It is also being used in the composite industry as filler in resins to make everything from furniture to awards plaques - "This unique product gives the appearance of marble and granite".

Plastic drum recycling

Somewhat more immediately successful than the initiatives for PCB recycling is the plastic drum recycling project, which is trying to reduce the environmental impact of the 12M new 25 litre drums consumed in the UK each year, each containing 1-2 kg of plastic. The project has both to research the way these drums are distributed throughout the UK, from the point of view of collecting and recycling the materials, put together appropriate recycling schemes, and then propose how this can be done, given that there may well be toxic residues in the drums.

Probably the most difficult aspect is creating new products for the recycled material. A number of products have been identified that can be made from 100% recycled material, plus some colorant. By compacting drums, so that 72 drums can be crammed onto a single pallet, it has been possible to cut transport costs, and there is a commercial market for the material - 100/tonne is paid for granulated material designated for use in subsoil drainage.

A final comment

Reviewing a number of these recycling projects, it is clear that their success or otherwise depends critically on economic factors, and that these may change according to the marketplace. Such changes have been behind the demise in recent years of initiatives to collect waste paper, where an oversupply led to collapse in the market price, making separate collection appear uneconomic.

But does this equation fully take into account the environmental cost? This is a topic we should be exploring in a wider context in the next section.

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