Environmental and Public Health Issues

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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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Environmental and Public Health Issues

Contents

Microelectronics and Semiconductors References