With the impending 2006 deadlines approaching, many electronics manufacturers have already begun the implementation of lead free soldering. Many other companies are still in the early transition stages. Component manufacturers and board fabricators have already begun supplying lead free finishes on their components and boards. Eventually, lead finishes will become extinct, forcing the entire electronics manufacturing industry to switch to lead free.

Electronics manufacturers need to recognize that there are no drop in / “turn key” replacements for solders containing lead. While lead free soldering utilizes the same tools as lead soldering, there are differences in the process and resulting product which require careful analysis prior to implementation.

The introduction of lead free alloys has created many new issues and concerns for the electronics manufacturing industry. Lead free soldering will affect all segments of electronics manufacturing, from commercial and military to international and domestic production. The EMPF has designed a lead free manufacturing course which addresses the issues and concerns encountered. This course provides information on how to introduce lead free soldering into your production environment. Classroom lecture, coupled with a hands-on lab, allows students to go through all the steps of automated and manual processes in lead free manufacturing.

The course will cover the following:

Lead free soldering background
Students learn the rationale behind the implementation of lead free soldering, environmental issues, and the current legislative status in Asia, Europe, and the United States. This course includes discussions on customer expectations, concentrating on the differences between the consumer and aerospace markets (including military products). These discussions will give students insight into the pressures on electronics suppliers, as well as component and equipment manufacturers.

Material concerns
Lead free soldering requires higher processing temperatures for reflow, wave, and hand soldering operations. Manufacturers must pay close attention to the moisture sensitivity of the boards and components used during manufacturing. The Glass Transition Temperature (Tg) of the board materials is another concern. In some cases, the exposure to higher temperatures exceeds the Tg of the board. The higher processing temperatures can cause board defects such as delamination, popcorning, and warpage. Recommended bake-out times for hardware, prior to soldering with lead free solders, are reviewed.

Another major concern that will be discussed is flux contamination. Flux removal becomes more difficult with the increase in process temperatures. Aggressive cleaning processes and chemistries are needed in order to remove flux residues.

Solder joint appearance
Lead free solder connections tend to have a different appearance than solder connections made with their tin lead (SnPb) counterparts. Solder connections using lead free solder often show signs of dewetting or may be grey or porous in appearance. The use of more aggressive fluxes and an inert environment such as nitrogen help improve the degree of wetting and the overall appearance of the solder connections. Icicles and solder peaks are another anomaly typically associated with lead free hand soldering. Increasing tip temperatures will eliminate icicles and solder peaks. Students perform final inspection of the test boards in accordance with the requirements of IPC-A-610.

Reliability and failure analysis
The failure mechanisms observed in lead free solder joints may be different from that observed in tin lead solder joints. Grain coarsening cannot be used as an indicator of environmental conditions. Higher reflow temperatures and different physical properties of the alloy may change the failure mechanism of the joints and surrounding areas. Additionally, investigations should include an expanded area when evaluating cross-sections.

• Fatigue cracks
• Gold enbrittlement
• Land/fillet lifting
• Tin whisker formation and detection
• Intermetallic growth
• Solder microstructure
• Flux residue
• Solderability
• Black pad

Students are familiarized with the effects of high temperature processing on plastic and laminate materials and taught how to mitigate the negative effects of high temperature processing. Process indicators such as lead free ball grid array (BGA) voiding, solder microstructure, and package delamination, are also discussed. For the hands-on failure analysis portion of the class, students are encouraged to provide lead free hardware for possible elemental analysis utilizing the SEM’s energy dispersive spectroscopy (EDS) system.

Reliability data collected by the Lead Free Component Focus Group and other lead free transition programs is discussed in detail to aid the student in the selection of reliable materials and package designs. Completion of the reliability and failure analysis sections of the course will provide students with the knowledge needed to make effective decisions regarding solder joint reliability, materials selection, and lab analysis of lead free solder joints.

Laboratory analysis
During the lab portion of the course, students run a variety of test vehicles using various board finishes, lead free solder alloy combinations, processing methods, temperature profiles, and atmospheric conditions. Students participate in the screen printing, component placement, reflow, wave hand soldering, and rework processes. Students will gain an understanding of the similarities and differences between lead and lead free solder alloy processing.

Equipment maintenance
Lead free solders are known to cause corrosion of wave solder pots due to the high tin content of the solder. In addition, the increase in process temperatures tends to damage the belts and panels on the reflow ovens and the tips on soldering irons. Students will learn how to properly maintain equipment and reduce damage.

The Lead Free Manufacturing course at the EMPF is ideal for companies that have already made the conversion to lead free, as well as those who are still in transition. Please contact the EMPF registrar at (610) 362-1320 for course schedule and pricing.

For more information concering Lead Free processes and surrounding issues, please stop by ACI's new Lead Free Manufacturing Page to download articles contributed to ACI by some of the industry's most knowledgable individuals and organizations, as well as material generated by ACI, and documents on the legislation surrounding the Lead Free issue.