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Environmental and Public Health Issues

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Industry Overview

The electronics industry, compared to other industries, has been viewed as “clean” in terms of its environmental impact. None the less, the chemicals used in the manufacture of electronic parts and components, and the waste generated, create significant environment issues that must be addressed on a global scale due to the size of the electronics industry. The wastes and by-products derived from the manufacture of printed wiring boards (PWBs), printed circuit boards (PCBs) and semiconductors are areas of interest that the electronic industry has vigorously pursued in terms of pollution prevention, treatment technology and recycling/reclamation techniques.

To a large degree, the incentive to control the environmental footprint of electronic processes has migrated from an environmental impetus to a financial domain. Due to the costs and liabilities associated with hazardous waste and emissions, the electronics industry has aggressively implemented and developed environmental controls that have greatly reduced the impact of its by-products and waste. In addition, the electronics industry has taken a proactive approach to incorporate environmental goals, tools and techniques into its environmentally conscious businesses. Examples of this proactive approach are the phase-out of CFCs and perfluorinated compounds and the development of “environmentally friendly” alternatives, as well as the emerging “design for the environment” approach to product development.

The manufacture of PWBs, PCBs and semiconductors requires the use of a variety of chemicals, specialized manufacturing techniques and equipment. Due to the hazards associated with these manufacturing processes, the proper management of chemical by-products, wastes and emissions is essential to assure the safety of the industry’s employees and the protection of the environment in the communities in which they reside.

Table 1, table 2 and table 3 present an outline of the key by-products and wastes that are generated in the manufacturing of PWBs, PCBs and semiconductors. In addition, the tables present the main types of environmental impact and the generally accepted means of mitigation and control of the waste stream. Primarily, the wastes that are generated affect industrial wastewater or the air, or become a solid waste.

Table 1. PWB waste generation and controls

Process steps

Hazardous
waste/materials

Environmental
impact

Controls1

Material
preparation

None

None

None

Stack and pin

Heavy/precious metals
Epoxy/fibreglass

Solid waste2
Solid waste2

Recycle/reclaim
Recycle/reclaim

Drilling

Heavy/precious metals
Epoxy/fibreglass

Solid waste2
Solid waste2

Recycle/reclaim
Recycle/reclaim

Deburr

Heavy/precious metals
Epoxy/fibreglass

Solid waste2
Solid waste2

Recycle/reclaim
Recycle/reclaim

Electroless
copper plating

Metals

Corrosives/caustics

Fluorides

Wastewater

Wastewater/air

Wastewater

Chemical precipitation

pH neutralization/air scrubbing
(absorption)
Chemical neutralization

Imaging

Solvents

Corrosives
Solvents

Air

Air
Solid waste2

Adsorption, condensation or
incineration
Air scrubbing (absorption)
Recycle/reclaim/incineration

Pattern plating

Corrosives

Metals
Fluorides

Wastewater/air

Wastewater
Wastewater

pH neutralization/air scrubbing
(absorption)
Chemical precipitation
Chemical precipitation

Strip, etch, strip

Ammonia
Metals
Solvents

Air
Wastewater
Solid waste2

Air scrubbing (adsorption)
Chemical precipitation
Recycle/reclaim/incineration

Solder mask

Corrosives
Solvents

Solvents/epoxy inks

Air
Air

Solid waste2

Air scrubbing (adsorption)
Adsorption, condensation, or
incineration
Recycle/reclaim/incineration

Solder coating

Solvents

Corrosives
Lead/tin solder, flux

Air

Air
Solid waste2

Adsorption, condensation or
incineration
Air scrubbing (adsorption)
Recycle/reclaim

Gold plating

Corrosives
Corrosives
Metals
Metals

Air
Wastewater
Wastewater
Solid waste2

Air scrubbing (adsorption)
pH neutralization
Chemical precipitation
Recycle/reclaim

Component
legend

Solvents

Solvents/inks

Air

Solid waste2

Adsorption condensation or
incineration
Recycle/reclaim/incineration

1. Use of mitigation controls depends upon discharge limits in the specific location.

2. A solid waste is any discarded material regardless of its state.

Table 2. PCB waste generation and controls

Process steps

Hazardous
waste/materials

Environmental
impact

Controls

Cleaning

Metals (lead)

Wastewater

pH neutralization, chemical
precipitation, recycle lead

Solder paste

Solder paste (lead/tin)

Solid waste

Recycle/reclaim

Adhesive
application

Epoxy glues

Solid waste

Incineration

Component
insertion

   

Plastic tapes, reels and tubes
are recycled/reused

Adhesive cure and
solder reflow

     

Fluxing

Solvent (IPA flux)

Solid waste

Recycle

Wave soldering

Metal (solder dross)

Solid waste

Recycle/reclaim

Inspection and
touch-up

Metal
(lead wire clippings)

Solid waste

Recycle/reclaim

Testing

Scrapped populated
boards

Solid waste

Recycle/reclaim
(boards smelted for precious
metal recovery)

Reworking and
repairing

Metal (solder dross)

Solid waste

Recycle/reclaim

Support
operations—stencil
cleaning

Metal
(lead/tin/solder paste)

Solid waste

Recycle/incineration

 

Table 3. Semiconductor manufacturing waste generation and controls

Process steps

Hazardous
waste/materials

Environmental
impact

Controls

Lithography/etching

Solvents
Metals
Corrosives/Caustics
Corrosives
Sulphuric acid
Fluorides

Solid waste
Wastewater
Wastewater
Air
Solid waste
Wastewater

Recycle/reclaim/incineration
Chemical precipitation
pH neutralization
Air scrubbing (absorption)
Recycle/reprocess
Chemical precipitation

Oxidation

Solvents
Corrosives

Solid waste
Wastewater

Recycle/reclaim/incineration
pH neutralization

Doping

Poison gas (arsine,
phosphine, diborane,
boron trifluoride,
boron trichloride,etc.)
Metals (arsenic,
hosphorus, boron)

Air



Solid waste

Substitution with liquid
sources/incineration
(afterburner)

Recycle/reclaim

Chemical vapour deposition

Metals

Corrosives

Solid waste

Wastewater

Incineration

pH neutralization

Metallization

Solvents
Metals

Solid waste
Solid waste

Incineration
Recycle/reclaim

Assembly and testing

Solvents
Metals

Solid waste
Solid waste

Recycle/reclaim/incineration
Recycle/reclaim

Cleaning

Corrosives
Fluorides

Wastewater
Wastewater

pH neutralization
Chemical precipitation

 

The following are generally accepted means of mitigating emissions in the PWB, PCB and semiconductor industries. The controls of choice will vary according to engineering capabilities, regulatory agency requirements and the specific constituents/concentrations of the waste stream.

Wastewater Control

Chemical precipitation

Chemical precipitation is generally used in the removal of particulate or soluble metals from wastewater effluents. Since metals do not naturally degrade and are toxic at low concentrations, their removal from industrial wastewater is essential. Metals can be removed from wastewater by chemical means since they are not very soluble in water; their solubilities depend upon the pH, metal concentration, type of metal and the presence of other ions. Typically, the waste stream requires pH adjustment to the proper level to precipitate out the metal. The addition of chemicals to wastewater in an effort to alter the physical state of dissolved and suspended solids is required. Lime, caustic and sulphide precipitation agents are commonly used. The precipitating agents facilitate the removal of dissolved and suspended metals by coagulation, sedimentation or entrapment within a precipitate.

A result of chemical precipitation of wastewater is the accumulation of sludge. Therefore, dewatering processes have been developed to reduce the weight of the sludge by means of centrifuges, filter presses, filters or drying beds. The resultant dewatered sludge can then be sent off for incineration or landfill.

pH neutralization

pH (the hydrogen-ion concentration or acidity) is an important quality parameter in industrial wastewater. Due to the adverse effects of pH extremes in natural waters and on sewage treatment operations, the pH of industrial wastewater must be adjusted prior to discharge from the manufacturing facility. Treatment occurs in a series of tanks that are monitored for the hydrogen-ion concentration of the wastewater effluent. Typically, hydrochloric or sulphuric acid is used as neutralizing corrosives, and sodium hydroxide is used as a neutralizing caustic. The neutralizing agent is metered into the wastewater effluent to adjust the pH of the discharge to its desired level.

Adjustment of pH is often required prior to the application of other wastewater treatment processes. Such processes include chemical precipitation, oxidation/reduction, activated carbon sorption, stripping and ion exchange.

Solid Waste Control

Materials are a solid waste if they are abandoned or discarded by being disposed of; burned or incinerated; or accumulated, stored or treated before or in lieu of being abandoned (US Code of Federal Regulation 40, Section 261.2). Hazardous waste generally exhibits one or more of the following characteristics: ignitability, corrosivity, reactivity, toxicity. Depending upon the characteristic of the hazardous material/waste, various means are used to control the substance. Incineration is a common treatment alternative for solvent and metal wastes generated during PWB, PCB and semiconductor manufacturing.

Incineration

Incineration (afterburner) or thermal destruction has become a popular option in handling ignitable and toxic wastes. In many instances, ignitable wastes (solvents) are used as a fuel source (fuel blending) for thermal and catalytic incinerators. Proper incineration of solvents and toxic wastes provides complete oxidation of the fuel and converts combustible material to carbon dioxide, water and ash, thereby leaving no liabilities associated with residual hazardous waste. The common types of incineration are thermal and catalytic incinerators. The selection of the type of incineration method is dependent upon the combustion temperature, fuel characteristics and residence time. Thermal incinerators operate at high temperatures and are widely used with halogenated compounds. Types of thermal incinerators include rotary kiln, liquid injection, fixed-hearth, fluidized bed and other advanced design incinerators.

Catalytic incinerators oxidize combustible materials (e.g., VOCs) by injecting a heated gas stream through a catalyst bed. The catalyst bed maximizes surface area, and by injecting a heated gas stream into the catalyst bed combustion can occur at a lower temperature than thermal incineration.

Air Emissions

Incineration is also used in control of air emissions. Absorption and adsorption are used as well.

Absorption

Air absorption is typically used in the scrubbing of corrosive air emissions, by passing the contaminant through and dissolving it in a non-volatile liquid (e.g., water). The effluent from the absorption process is typically discharged to a wastewater treatment system, where it undergoes pH adjustment.

Adsorption

Adsorption is the adherence (by means of physical or chemical forces) of a gas molecule to the surface of another substance, called an adsorbent. Typically, adsorption is used to extract solvents from an air emission source. Activated carbon, activated alumina or silica gel are commonly used adsorbents.

Recycling

Recyclable materials are used, reused or reclaimed as ingredients in an industrial process to make a product. Recycling of materials and waste provides environmental and economic means of effectively addressing specific types of waste streams, such as metals and solvents. Materials and wastes can be recycled in-house, or secondary markets may accept recyclable materials. The selection of recycling as an alternative for wastes must be evaluated against financial considerations, the regulatory framework and available technology to recycle the materials.

Future Direction

As the demand for pollution prevention increases and industry seeks cost-effective means to address chemical use and waste, the electronics industry must evaluate new techniques and technologies to improve the methods for hazardous-materials handling and waste generation. The end-of-pipe approach has been replaced by design for the environment techniques, where environmental issues are addressed over the full life cycle of a product, including: material conservation; efficient manufacturing operations; the use of more environmentally friendly materials; recycling, regeneration and reclamation of waste products; and a host of other techniques that will assure a smaller environmental impact for the electronics manufacturing industry. One example is the large amount of water that is used in the many rinsing and other processing steps in the microelectronics industry. In water-poor areas, this is forcing the industry to find alternatives. However, it is essential to make sure that the alternative (e.g., solvents) does not create additional environmental problems.

As an example of future directions in the PWB and PCB process, table 4 presents various alternatives for creating more environmentally sound practices and preventing pollution. Priority needs and approaches have been identified.

Table 4. Matrix of priority needs

Priority need (decreasing
order of priority)

Approach

Selected tasks

More efficient use,
regeneration and recycling of
hazardous wet chemistries

Extend life of electrolytic and
electroless plating baths.
Develop chemistries and
processes to allow recycling
or in-house regeneration.
Eliminate formaldehyde from
materials and chemistries.
Promote onsite recycling and
reclamation/regeneration.

Research to extend baths.
Research in-line
purification/ regeneration.
Research alternative
chemistries.
Modify government regulations
to promote recycling.
Educate line production on
drag-in/drag-out problems.

Reduce solid waste generated
by scrap PWBs, leads and
components in the waste
stream.

Develop and promote
recycling of scrap PWBs,
leads and components.
Develop new process-control
and performance tools.
Improve the solderability of
PWBs.

Develop infrastructure to
handle recycled material.
Establish enhanced
process-control and evaluation
tools  usable by small and
medium-sized businesses.
Deliver consistently clean,
solderable boards.

Establish better supplier
relationships to enhance the
development and acceptance
of environmentally friendly
materials.

Promote supplier,
manufacturer, customer
partnerships to implement
environmental materials.

Develop a model hazardous
materials management
system for small and
medium-sized PWB
companies.

Minimize the impact of
hazardous materials use in
PWB fabrication.

Reduce lead solder use when
possible and/or reduce the
lead content of the solder.
Develop alternatives to solder
plating as an etch resist.

Change specifications to accept
solder mask over bare copper.
Validate quality of lead
plating alternatives.

Use additive processes that
are competitive with existing
processes.

Develop simplified,
cost-effective additive
material and process
technologies.
Seek alternative sources and
approaches for additive
process capital equipment
needs.

Collaborate on projects to
establish novel additive
dielectrics and metallization
technologies and processes.

Eliminate hole smear in PWB
fabrication.

Develop no-smear resins or
drilling systems.

Investigate alternative
laminate and pre-preg
materials.
Develop the use of laser and
other alternatives to drilling
systems.

Reduce water consumption
and discharge.

Develop water use
optimization and recycle
system.
Reduce the number of
cleaning steps in PWB
manufacture.
Eliminate parts handling and
preparation to reduce
recleaning.

Modify specifications to reduce
cleaning requirements.
Investigate alternative
parts-handling methods.
Change or eliminate
chemistries that require
cleaning.

Source: MCC 1994.

 

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Contents

Preface
Part I. The Body
Part II. Health Care
Part III. Management & Policy
Part IV. Tools and Approaches
Part V. Psychosocial and Organizational Factors
Part VI. General Hazards
Part VII. The Environment
Part VIII. Accidents and Safety Management
Part IX. Chemicals
Part X. Industries Based on Biological Resources
Part XI. Industries Based on Natural Resources
Part XII. Chemical Industries
Part XIII. Manufacturing Industries
Electrical Appliances and Equipment
Metal Processing and Metal Working Industry
Microelectronics and Semiconductors
Glass, Pottery and Related Materials
Printing, Photography and Reproduction Industry
Woodworking
Part XIV. Textile and Apparel Industries
Part XV. Transport Industries
Part XVI. Construction
Part XVII. Services and Trade
Part XVIII. Guides

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