Laura J. Turbini

Examining the environmental impact of lead-free soldering alternatives

In 1999, the Surface Mount Council identified the issue of lead-free electronics as an emerging area for concern and evaluation. This was triggered by the initial European Unions (EU) proposal for a Directive on Waste from Electrical and Electronic Equipment (WEEE) and by the Japanese focus on environmental marketing and on recycling, which has resulted in timetables for lead elimination. The present EU directive on the elimination of lead from electronics by 2008 has added further urgency to this issue. From an industrial ecology perspective, it is essential to evaluate the environmental impact of the proposed alternatives and to compare this with that of the present Sn/Pb solder. Industrial ecology is the multidisciplinary study of industrial systems and economic activities, and their links to fundamental natural systems. Based on this definition, it is important to study the environmental impact of lead-free electronics through their entire life cycle. Factors such as alloy availability, processing considerations, energy use and potential ground water contamination must be considered. Based on these criteria, lead-free products are not more environmentally friendly than the present electronics soldered with Sn/Pb. Thus, the focus of future regulation should be on recovery and recycling of the metals at end-of-life as required in the WEEE rather than the elimination of lead-based solder.

A Product and Process Selection Model with Multidisciplinary Environmental Considerations

Introduction of product designs and process innovation requires a company to evaluate complex cost and environmental tradeoffs. In the past, these have not included environmental costs. This paper describes the first known analytical approach to capture comprehensively measurable corporate environmental impact considerations for the product life cycle. A mixed integer programming model is developed to select product and process alternatives while considering tradeoffs of yield, reliability, and business-focused environmental impacts. Explicit constraints for environmental impacts such as material consumption, energy consumption, and process waste generation are modeled for specified assembly and disassembly periods. The constraint sets demonstrate a new way to define the relationship between disassembly configurations and assembly activities through take-back rates. Use of the model as an industry decision tool is demonstrated with an electronics assembly case study.

Use of surface insulation resistance and contact angle measurements to characterize the interactions of three water soluble fluxes with FR-4 substrates

Soldering flux chemistry and its interaction with the printed wiring board have been important reliability concerns for a number of years. Post Vietnam investigation of military hardware revealed corrosion in some areas. The test method most frequently used to assess the corrosion potential of flux residues is surface insulation resistance (SIR) testing. This paper gives some background on surface insulation resistance testing and reports on its application to three different water soluble fluxes. The appearance of surface dendrites is linked to test procedures that allowed water condensation on the board surface. Subsurface conductive anodic filament formation is associated with the use of fluxes which contained polyglycols. The use of contact angle measurements to assess the effect of the soldering flux residues on the board is demonstrated.

Conductive anodic filament enhancement in the presence of a polyglycol-containing flux [PWBs]

Under certain environmental conditions, printed wiring boards (PWB) respond to applied voltages by developing subsurface deposits of copper salts extending from anode to cathode along separated fiber/epoxy interfaces. These deposits are termed conductive anodic filaments (CAF). In this work, the dimensions and growth patterns of a CAF has been determined by serial sectioning. The CAF growth pathway is characterized and the spatial distribution of the copper salts is quantified with scanning electron microscopy (SEM). The chemical composition of the CAF is determined using energy dispersive X-ray analysis (EDX). The failure phenomena known as CAF poses serious long term reliability risks in electronic applications where the PWB is exposed to adverse and hostile environments or those with closely spaced conductors. Recent ion chromatography results indicate a correlation between the polyglycol and halide content of the soldering flux, and a substrates susceptibility to CAF formation.

The implications of activity based environmental impact allocation

This paper presents the motivation for allocation of effluents and wastes to the electronic product and process design responsible for them. The environmental impact allocations are based on the relationships between the process flow inputs and outputs and their activity levels. The method is demonstrated on two generic printed wiring assembly designs. The demonstration presents the allocation of the costs and effluent generation for various operations ranging from kitting to shipping. This activity based flow allocation approach is helpful in implementing inventory surveys for life cycle analysis and quantitative modeling of environmental impacts.

Evaluation approach for environmental impact and yield trade-offs for electronics manufacturing product and process alternatives

This paper develops an approach to evaluate environmental impact and yield trade-offs in electronics manufacturing over the life cycle of the products studied. A mathematical model is described which provides sensitivity analysis of the revenue and cost trade-offs constrained by operational parameters, government regulations, and environmental goals.

Designing for technological obsolescence and discontinuous change: an evaluation of three successional electronic products

Product displacement has been occurring for many years and will continue to challenge the market as technological advances result in product obsolescence. While opportunities do exist to incorporate environmentally conscious design and engineering criteria into the product development process, much of the ultimate environmental success is dependent upon closing the product life cycle, through reuse (upgrade and/or repair), re-manufacture and recycling. This paper reports on the analysis and evaluation of three successional audio video home electronic products: the VHS Video Cassette Recorder (VCR), the Laser Disc Player (LD) and the Digital Video/Versatile Disc Player (DVD). The newly released DVD player has rendered the LD player obsolete and will soon render the VCR obsolete. This paper investigates potential environmental improvements to the DVD player through design strategies for upgrading a successional product and for reducing its end-of-life impact.

Characterization of Conductive Anodic Filament (Caf) by X-Ray Microtomography and by Serial Sectioning

X-ray microtomography is used to nondestructively section printed wiring boards in which conductive anodic filaments (CAFs) had grown, Quantification of the spatial distribution of copper is compared for microtomography and for serial sections obtained in SEM with backscattered electrons. The agreement between the techniques is excellent and indicates that microtomography may be used confidently to follow the subsurface growth of CAFs.

Analysis of Catastrophic Field Failures Due to Conductive Anodic Filament (CAF) Formation

Under certain environmental conditions, printed wiring boards (PWB) respond to applied voltages by developing subsurface deposits of copper salts extending from anode to cathode along separated fiber / epoxy interfaces. The formation of these deposits, termed conductive anodic filaments (CAF) require high humidity (80%RH) and high voltage gradient (5V/mil). The humidity exposure during the storage environment may cause the failure in the use environment. CAF formation is enhanced by the use of certain hot air solder leveling (HASL) fluids and / or water soluble flux constituents. In this work, two catastrophic field failures were analyzed. Both failures were related to boards produced in a manufacturing process, which included HASL. One CAF failure occurred between a component through-hole and power plane held at a potential difference of 40V with a 0.005″ nominal spacing. The other occurred on an inner layer of a multi-layer board (MLB) between a via and ground plane held at a potential difference of 320V with 0.015” nominal spacing. The nature of the CAF was analyzed using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). Ion chromatography (IC) was used to identify residue extracted from a failed board. The failure phenomena known as CAF poses serious longterm reliability concerns in electronic products exposed to adverse and hostile environments, especially those with closely spaced conductors.

Towards quantifying the effect of lead legislation on electronic product and process design

In this paper we demonstrate the use of the Emerging Product Process and Consideration of Environment (EPPACE) mixed integer programming model to evaluate the effect of a lead tag or limits placed on availability of lead on economic decisions for product and process design. The paper concludes with directions for future study. Other questions that might be answered using the EPPACE model are discussed.