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As technologists and engineers prepare for and address important changes to chemical content of electronic products, it would be useful to understand the drivers, context, and trends for this activity. This introductory chapter will provide a brief overview of environmental legislative and regulatory trends that are influencing the movement to lead-free electronics and will attempt to set the stage for thinking about future challenges.

The search for a global Pb-free replacement for Sn-Pb eutectic alloy has been an evolving process as the threat of a regional lead ban became a reality in July 2006. Over the twelve years from 1994 through 2006, the manufacturing, performance, and reliability criteria for Pb-free solder joints have become increasingly complex as relationships between the solder alloy, the circuit board materials and construction, and the component designs and materials have been revealed through widespread experimentation by companies, industrial consortia, and university researchers. The focus of this chapter is to examine the primary criteria used to develop the current generation of Pb-free solder alloys, the tradeoffs made between various properties once these primary criteria were satisfied, and the open questions regarding materials and processes that are as yet unanswered.

In general, the process flow for lead-free surface mount assembly process is similar to the conventional SnPb soldering process. Often the same equipment set used for SnPb can be used for lead-free reflow soldering. However, there are some differences that must be taken into account. The material set used for lead-free soldering is different and typically higher reflow temperatures are required. This chapter will review the different aspects of the discuss its impact on design, equipment, process and materials. surface mount assembly process with respect to lead-free solder and

Lead-free wave soldering is already in mass production in Asia and developing in Eastern Europe and the Americas, however lead-free wave is still the most challenging process to implement (together with lead-free BGA/CSP and PTH rework) and manufacturers around the world are challenged to qualify equipment and processes that will produce a quality lead-free product.

With tin-lead soldering, there is a long history of soldering experience from hand soldering to wave soldering to surface mount technology. The development of lead-free solder manufacturing experience has been a relatively recent occurrence. For lead-free rework the developments that have occurred have not been reviewed in a comprehensive manner.

Lead-free solder joint reliability is a multi-faceted and challenging topic. Lead-free solders such as eutectic SnAg and SnBi have been used successfully in niche applications for many years. With the advent of no-lead (Pb) legislation, a multitude of soldering alloys has been proposed for mainstream electronic applications. The high number of lead-free alloy options remains a major factor slowing the development of reliability databases, test standards, acceleration factors and life prediction models. While the electronics industry has over fifty years of experience working with a single, main stream alloy -near-eutectic SnPb solder -the engineering community now faces the daunting task of qualifying product assemblies for an increasing variety of lead-free solders such as SnAgCu, SnAg, SnAgBi, SnBi, SnCu, SnZn alloys of near-eutectic or other compositions, some with known additive elements (e.g., nickel, cobalt, germanium) and others with proprietary compositions.

In response to the European Union (EU) Restriction of Hazardous Substances (RoHS) and other countries’ impending lead-free directives, the electronics industry is moving toward lead-free soldering. Total lead-free soldering requires not only lead-free solder paste but also lead-free printed circuit board (PCB) finish and lead-free component/packages. Transitioning tin-lead (SnPb) soldering to totally lead-free soldering is a complex issue and involves movement of the whole electronics industry supply chain. In reality, there is a transition period.

Printed wiring board manufacturing yields and subsequent product reliability are significantly impacted by the properties and characteristics of the laminate materials used. The selection of laminate materials is more critical for achieving higher temperature lead-free solder alloy assembly yield targets and long term product reliability requirements. The SAC305 tin-silvercopper alloy (3.0 percent silver and 0.5 percent copper) recommended for lead-free assembly reflow processing and rework has a melting point about 40°C higher than the melting point of eutectic tin-lead.

In the move to lead-free electronics, one of the main aspects of printed wiring board (PWB) fabrication that has received attention is the surface finish. The surface finish of the PWB represents the last major step in fabrication before component assembly and, as such, represents the interface between the external board circuitry and the bonding medium (i.e. solder). The use of lead-free solders requires higher assembly temperatures and places increased demands on the surface finish if it is to survive multiple reflow cycles. In PWB fabrication, the surface finish can serve several interrelated functions, including:

This chapter will review the current and developing standards, which affect lead-free soldering. Developments in standards for lead-free soldering are not complete and are progressing with new discoveries and developments. The majority of the chapter will cover IPC standards with reference to other standards, which are considered relevant and known.