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This report, presented as the keynote paper at Surface Mount International, is the culmination of joint efforts to assess the use of lead in electronics assembly. The study, which will be presented in two parts, involved the collaboration of the following participants: B. R. Allenby and J. P. Ciccarelli, AT&T, Basking Ridge, New Jersey; I. Artaki, J. R. Fisher and D. Schoenthaler, AT&T Bell Laboratories, ERC, Princeton, New Jersey; T. A. Carroll, Hughes, El Segundo, California; D. W. Dahringer, Y. Degani, R. S. Freund, T. E. Graedel, A. M. Lyons and J. T. Plewes, AT&T Bell Laboratories, Murray Hill, New Jersey; C. Gherman and H. Solomon, GE Aerospace, Philadelphia, Pennsylvania; C. Melton, Motorola Inc., Schaumburg, Illinois; G. C. Munie, AT&T Bell Laboratories, Indian Hill, Naperville, Illinois; and N. Socolowski, Alpha Metals, Jersey City, New Jersey.

The lead‐free soldering process has been confounding the PWB fabricators when they set out to select the right materials for lead‐free soldering. This paper discusses the compatibility of currently available laminate materials for lead‐free assembly.

This paper has been written to provide a review of material characteristics. Problem areas are highlighted and methods for choosing each type of material for compatibility with lead‐free soldering process are described.

When lead is banned and taken out of the traditional tin‐lead solder, there are other metal alternatives to alloy with tin such as silver, bismuth, copper, and zinc, etc. The melting point of these lead‐free alloys is higher than the conventional tin‐lead solder. Consequently, the reflow temperature of the lead‐free solder can now reach 240‐250°C. As the reflow temperature is elevated, it will pose a severe reliability challenge to the laminate materials. The compatibility of currently available commercial laminate materials for lead‐free assembly are discussed in this paper.

The value of this paper is that it provides information and solutions relating to the selection of the most appropriate materials for use in lead‐free soldering and assembly.

The purpose of this paper is to show production process developments and innovations that resolve many of the issues faced with certain process steps for printed circuit board (PCB) manufacturing following “green” practices.

Several key PCB manufacturing processes have been developed or studied with respect to new environmental legislations and practises.

The introduction of new legislations designed to protect the environment require changes to laminate materials, solders, and PCB manufacturing techniques. The effect of new laminate materials on the desmearing and metallising processes have been assessed and recommendations given. The effect of increased thermal stress on plated copper has been assessed. Developments in adhesion enhancement for black oxide alternatives have been made and are presented with their suitability for the newer green laminate materials. The development of a new laminate manufacturing technique to reduce environmental impact is introduced. The capabilities of different surface finishes in relation to new lead‐free soldering techniques is investigated and presented.

This is a short paper covering several major PCB processing steps and covers experiences and development results.

The paper details how “green” PCB manufacturing affects some key processes, developments to improve results and environmentally friendlier innovations in laminate manufacturing techniques.

The purpose of this paper is to investigate the laser soldering of fine pitch quad flat package (QFP) devices using lead‐free solders and solder joint reliability during thermal cycling.

QFP devices were selected as the test vehicles and were soldered with four alloy types, Sn37Pb, Sn3.5Ag, Sn3.8Ag0.7Cu and Sn3.8Ag0.7Cu0.03Ce. The experimental samples were QFP‐256 devices with lead‐free solder paste on the printed circuit boards. The packages were dried for 24 h at 125°C prior to reflow soldering. Soldering experiments on the QFP devices were carried out with an infrared (IR) reflow soldering oven and a diode laser (DL) soldering system. Reflow soldering was performed at peak temperatures of 210°C (SnPb), 240°C (SnAgCu and SnAgCuCe) and 250°C (SnAg), as determined on the boards. Pull testing was adopted to evaluate the tensile strength of the four solders using an STR–1000 micro‐joint strength tester.

The tensile force of the QFP micro‐joints increased as laser intensity increased when it was less than an “optimal” value. The maximum tensile force of the QFP micro‐joints was gained when the laser intensity had increased to 2,165, 2,127, 2,165 and 2,064 W/cm², depending on the alloy used. The thermal fatigue performance of three lead‐free solder joints, SnAgCuCe, SnAgCu and SnAg, was determined to be superior to that of the eutectic SnPb alloy. After soldering without thermal cycling tests, the fracture morphology of soldered joints exhibited characteristic toughness fracture with both of the soldering methods. After 700 thermal cycles, the fracture mechanism was also toughness fracture, nevertheless, the dimples became large. The fracture morphology of the soldered joints subjected to 1,500 thermal cycles indicated brittle intergranular fracture on the fracture surface and no intense plastic deformation appeared before fracture with IR soldering. For DL soldering, the pull fracture model of the SnAgCuCe was completely ductile in the soldered joint with 1,500 thermal cycles.

The paper usefully investigates the influence of laser intensity on the tensile strength of different soldered joints and the solder joint reliability during thermal cycling.

Over the last few years, the emergence of new European draft legislation has focussed electronics industry attention on the likely ultimate proscription of lead in electronics assembly. Much work has already been undertaken to identify the possible alternatives to conventional tin‐lead solders and to evaluate their performance benefits and limitations in comparison with the traditional materials. Although, some companies are already offering products manufactured using lead‐free products, there is still a widespread lack of activity in many areas. With this none‐too‐distant deadline rapidly approaching, Envirowise has sponsored this paper as part of its coordinated activities to assist the UK electronics industry and to promote environmental efficiency and best practice. This paper details the current situation with respect to the drivers towards the adoption of lead‐free assembly before giving an overview of the current situation. This paper concludes with details of sources of further information.

The purpose of the present study was to review the thermo-mechanical challenges of reflowed lead-free solder joints in surface mount components (SMCs). The topics of the review include challenges in modelling of the reflow soldering process, optimization and the future challenges in the reflow soldering process. Besides, the numerical approach of lead-free solder reliability is also discussed.

Lead-free reflow soldering is one of the most significant processes in the development of surface mount technology, especially toward the miniaturization of the advanced SMCs package. The challenges lead to more complex thermal responses when the PCB assembly passes through the reflow oven. The virtual modelling tools facilitate the modelling and simulation of the lead-free reflow process, which provide more data and clear visualization on the particular process.

With the growing trend of computer power and software capability, the multidisciplinary simulation, such as the temperature and thermal stress of lead-free SMCs, under the influenced of a specific process atmosphere can be provided. A simulation modelling technique for the thermal response and flow field prediction of a reflow process is cost-effective and has greatly helped the engineer to eliminate guesswork. Besides, simulated-based optimization methods of the reflow process have gained popularity because of them being economical and have reduced time-consumption, and these provide more information compared to the experimental hardware. The advantages and disadvantages of the simulation modelling in the reflow soldering process are also briefly discussed.

This literature review provides the engineers and researchers with a profound understanding of the thermo-mechanical challenges of reflowed lead-free solder joints in SMCs and the challenges of simulation modelling in the reflow process.

The unique challenges in solder joint reliability, and direction of future research in reflow process were identified to clarify the solutions to solve lead-free reliability issues in the electronics manufacturing industry.

The European Commission has decided that from the second half of 2006 only lead‐free solder pastes will be permitted for use in the electronics industry. Earlier results of testing showed that lead‐free solder pastes may not be appropriate for both printed‐circuit‐board (PCB) and hybrid‐circuit applications, because of the materials' compatibility with the soldering process and with the solder pads. The basic properties of the investigated pastes show which of the tested solder pastes can be used for both applications. After selection of the appropriate solder pastes, reliability tests were conducted. The surface insulation resistance was tested for both the hybrid circuits and PCBs, whereas the mechanical strength of the soldered joints of components was only tested for the PCBs.

The purpose of this paper is to characterize the motivations used into migrating to lead‐free solder by providing examples and directions for those making the material change.

This work achieves its objective of identifying which electronic industry actions towards lead‐free soldering have been successful and why. The research reported the various motivating factors considered in adopting lead‐free electronics. To that end, the authors researched industry literature and discussed approaches with various companies and agencies. The scope of this paper is largely the board‐component level soldering process and companies involved in the international electronics industry.

The motivation to migrate to lead‐free solder has been and continues to be multi‐faceted. Issues include regulatory, commercial, and technical. Processing with lead‐free solder is successful, so the electronics industry's move towards environmentally compatible processes will meet regulated dates for change.

A company can learn how to incorporate environmental improvement principles resulting from the migration to lead‐free solder. Using that migration as a case study, the company can realize additional benefits by applying these principles to other product lines. Those interested in developing environmentally friendly products and processes can adopt the lessons that this paper identifies. Incorporation of lead‐free techniques, rather than resistance to change, is the result of adopting the lessons.

The paper presents a synopsis of the electronic industry's migration to lead‐free products and processes. It compares motivations for change that other studies have not compared. Manufacturers searching for direction and example to meet waste minimization goals will find the paper useful in providing such.

To present an overview of the current status of the RoHS directive and its implications for the printed circuit board (PCB) industry.

A review paper detailing the requirements of the RoHS directive, the materials that are proscribed, where they are found and the impacts on PCB fabrication and assembly.

The main implications of RoHS for the PCB industry are related to the proscription of lead and the move to lead‐free assembly. Tin‐lead HASL finished boards will no longer be allowed and new laminates may be needed to accommodate the higher soldering temperatures associated with lead‐free assembly. There is growing pressure to move away from the use of brominated flame retardants, even though the standard materials used in FR4 type laminates are not proscribed.

Manufacturers need to be aware of the implications of the RoHS directive, not just in terms of compliance but also from a materials selection and reliability perspective.

The paper details how the RoHS directive impacts PCB manufacturing and assembly and highlights the changes needed to enable reliable lead‐free assembly within the context of legislative compliance. Actions necessary to ensure compliance are also detailed.