| Abstract |
Surface finishes are applied to printed wiring boards (PWBs) to prevent oxidation of exposed copper on the board, thus ensuring a solderable surface when components are added at a later processing stage. The most widely used surface finishing process in PWB manufacturing is hot air solder leveling (HASL). In this process, tin-lead is fused onto exposed copper surfaces. This process may pose potential health and environmental risks due to the use of lead, and the HASL process also generates significant quantities of excess solder that must be recycled. In addition, HASL does not provide a level (planar) soldering surface for fine pitch components. Several emerging surface finishes viewed as viable alternatives to HASL have been developed in recent years. These finishes eliminate the use of lead in the surface finishing process and produce a planar surface. For these reasons, the Design for the Environment (DfE) PWB Project team selected the surface finishing process as the focus of a study to identify technologies that perform competitively, are cost-effective, and pose fewer potential environmental and health risks. This Guide presents first-hand accounts of the problems, solutions, and time and effort involved in implementing alternative surface finish technologies. The information presented summarizes telephone and e-mail interviews with PWB manufacturers and assemblers currently using these technologies, and the suppliers of the alternative technologies. With the information from these interviews, manufacturers considering a switch to an alternative technology can benefit from the lessons learned by those who already have made the change. Five technologies are discussed in this Guide: immersion silver; immersion tin; organic solderability preservative (OSP); electroless nickel/immersion gold; and electroless nickel/electroless palladium/immersion gold. |
