The term lead-free has caused a certain degree of trepidation among board shops and assembly houses across the entire spectrum of electronic packaging. RoHS legislation has reached its full realization date as of July 1st, 2006, requiring engineers and manufacturers to provide quick solutions for both the manufacturing and reliability of lead-free assemblies. Despite all of the misgivings about the transitory period between the initial stages of lead-free implementation and the eventual maturation point, there are some steps from a technical and manufacturing perspective that can be taken to mitigate lead-free conversion. By now, any remotely interested party to the lead-free transition has heard the catch phrase "lead-free is not a drop in process." This is an established truism intrinsic to most manufacturing processes, and is perhaps more relevant in the case of lead-free due to the number of manufacturing sectors that are involved.

For instance, the selection of a lead-free solder can be daunting, as illustrated by the choice of solder alloys displayed in Table 2-1. These candidates were the result of a study cited by NCMS(1) in an attempt to narrow down the selection process to 8 alloys from a larger pool of 79. Even so, this is not an exclusionary or comprehensive list by any means, with other alloys having been introduced by other consortiums and organizations. The alloys are further classified into three general application categories: Reflow Solder,
Wave Solder, and Rework Solder.

Each of these solders has unique physical attributes, beyond their inherent melting points, that would be of interest to the manufacturing sector while converting to a lead-free process. Inadequate wetting ability can affect the performance specifications of a PCB assembly if it does not meet the criteria for solder joint coverage. Wetting and issues relating to higher temperature application of the lead-free solders can be controlled, and their effects mitigated, by adjusting reflow profiles, wave profiles, conveyor speeds, flux selections, and other parameters that are within the scope of the specific manufacturing process.

PC board finishes contribute to lead-free uncertainty as well, and add a second-level factor to the interaction with the solder. Some of the more popular board finishes include:

Component leads are also available in a variety of plated metals, from pure tin to the more expensive Nickel-Palladium finishes. SAC (Tin-Silver-Copper), SnAg, Ni, and Pd round out a list of the more popular component finishes currently available.

There are numerous lead-free choices available for manufacturers. Yet despite the massive number of possibilities, the manufacturing sector has been able to adapt lead-free processes while its supporting infrastructure is being built and its material selections are narrowing. Process incompatibilities can often be slow, costly, and painful to resolve, but there is no lack of effort in the industry to do so, with many studies showing improved results in making the lead-free transition.

With such a broad range of metallurgical selections for solder, PCB finishes, substrates, component types, and component finishes, there is a need to extract reliable information to pose as a guideline for lead-free packaging at various levels. At the EMPF training center, we offer a comprehensive approach to lead-free training that will allow participants to gain an understanding of the technical issues surrounding the implementation of lead-free solders in an electronics manufacturing environment. Students will acquire the technical insight necessary to select the proper choices of components, alloys, substrates, finishes, designs, and environmental tests to achieve a level of reliability needed for various applications.

Most importantly, the EMPF offers hands-on training that gives students first-hand experience with the manufacturing issues surrounding the implementation of lead-free processes. Students will learn:

• Market drivers and pressures for lead-free implementation
• Legislative initiatives, including RoHS and WEEE

• Lead-free solder alloys
• Board Finishes
• Substrate impact
• How lead-free alloys affect components
• How to select the appropriate lead-free materials

• Understanding the process variables required for lead-free manufacturing
• Designing experiments for the introduction of lead-free processes in a manufacturing facility
• SMT reflow
• Wave soldering
• Hand soldering for rework and repair
• Reliability
• Designing for harsh environments
• Thermal cycling behavior of lead-free solder joints
• Shock and combined environment behavior of lead-free
• Modeling for reliability
• Mitigating the effects of tin whiskers

• Critical findings from ACI experience
• Failure modes
• Largest causes of variability

Remember, adequate preparation in lead-free processes will allay potential problems that may arise in future designs. For more information on lead-free training, or other classes available from the EMPF, including IPC certifications, please contact the registrar at (610) 362-1295, via email at registrar@empf.org, or find course descriptions on the web at http://www.aciusa.org/courses .

References:
1 NCMS Lead-Free Alloy study 1993-1998