TABLE OF CONTENTS To accomplish a lead-free soldering environment, not only the solders used for forming solder joints but also the surface finishes of pads on printed circuit boards (PCBs) and leads of components have to be lead-free. This is based on the considerations of both environmental safety and joint reliability issues. At this stage, an Sn-Pb surface finish is widely used in the electronics industry. Figure 14.1 shows the PCB surface finishes technology adoption status in the United States, published by IPC Technology Marketing Research Council.1 Although Sn-Pb hot-air solder leveling (HASL) still remains the dominant choice since 1998, its usage has definitely been declining with time even before the heat on lead-free soldering was felt by the industry.
In Fig. 14.1, several lead-free surface finishes are cited, including organic solderability preservative (OSP), Ni-Au, and Pd. Because the pressure on lead-free soldering is increasing at a tremendous rate, many new lead-free surface finish technologies have emerged since the late 1990s. In this chapter, the options on lead-free surface finishes will be introduced, with the chemistry, process, and performance of the most promising choices discussed. Since the same surface finish may be used on products varying considerably in design and application, the considerations for selecting a surface finish need to address a wide range of possible applications, including solderability, compatibility with solder alloys, solder joint reliability, wire bondability, connector abrasion resistance, electrical contact resistance, shelf life,...
