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Lively discussions charge lead-free solder implementation summit
BY JULIA GOLDSTEIN
SAN JOSE, CALIF. – The Microelectronics Packaging and Test Engineering Council (MEPTEC), in association with San Jose State University, held a technical summit on lead-free solder implementation on January 10. The summit, chaired by Professor Guna Selvaduray of San Jose State University, was well-attended by representatives from various segments of the industry. The event stimulated many discussions on the subject, but whether that translates into concrete action remains to be seen.
Both organizers and speakers at the summit stressed its goal to focus on implementation, as legislative and customer requirements – particularly from Japan – are driving lead-free solder. Because of this, it is anticipated that U.S. manufacturers will need to address a lead-free solution soon. Discussion in regard to the validity of pursuing lead-free solder, though perhaps subject to debate, was not the topic of the day.
To share or not to share?
Keynote speaker Maniam Alagaratnam (LSI Logic) focused on the importance of various segments of industry working together and openly sharing information to reach a single solution. But such a goal will not be easy to achieve. Several audience members commented that they will not publish their data unless the rest of the industry will share its data, as well. Some also cautioned that data should only be shared with customers and not with competitors.
Technical Presentations: The morning session included five technical presentations that addressed a myriad of lead-free issues. Thavarajah Manickam gave a presentation on an approach used by LSI Logic to implement a lead-free package for a Japanese OEM. David Suraski (AIM) discussed requirements for a lead-free solder and presented data on some promising alloys. He showed data suggesting that a Sn/Ag/Cu/Sb near-eutectic alloy is very promising. Ongoing work by a group of companies was presented by Swaminath Prasad (ChipPAC). Various combinations of packages and lead-free alloys were tested, with Phase I results suggesting that a tin/bismuth system is the best choice. James Heneke (Dexter Materials) described the results of a successful search for die attach and encapsulation materials capable of withstanding high (260°C) reflow temperatures.
Finally, Bance Hom (Consultech) discussed the history of IC lead finishing and why the industry should return to pure tin. She also summarized Carsem's evaluation of matte tin plating. Overall, it appears that many materials exist that can potentially meet the requirements of lead-free packaging. However, there isn't universal agreement as to what the solution should be. It was emphasized during the summit that multiple solutions are often required, dependent on both the application and the customer.
Break-out Sessions: The afternoon discussion sessions were divided into four topics: reliability and standards, materials and supplier issues, basic data and design, and processing and equipment issues. The discussions in these sessions were lively and could have extended well beyond the 90-minute time limit before the whole group reconvened.
The report by the reliability and standards group discussed the need for uniform standards for lead-free alloys, an effort that needs to be driven by the standards organizations (JEDEC, EIA, EIAJ, AEC). Members of this group also stressed the need to collect data on these alloys; they suggested an industry/university collaboration to achieve this.
The session on materials and supplier issues reported on the current state of the industry. Areas in which the industry is ready to provide lead-free solutions include solder materials, mold compounds and die attach epoxies. The industry doesn't have solutions for lead finish coatings and PCBs, both of which are critical to lead-free implementation. The group mentioned that flip-chip bumping and solder die attach are areas in which there is currently low demand for lead-free solutions.
Participants reporting on basic data and design concluded that no set of usable data exists for lead-free alloys today, and that data is not complete for lead, either. The group suggested that a transitional stage is in order, in which a handful of alloys would be chosen for initial evaluations.
The session on processing and equipment issues focused on plating for lead finishing, solder reflow profiles and requirements for reflow ovens. They also mentioned the need for retraining operators and revising inspection criteria.
Some topics overlapped at several of the sessions, including how to define a lead-free system. (Do all components throughout the system have to be lead-free? Should there be a maximum threshold level for residual lead that is not intentionally added?) Another problem that received repeated mention was whiskering in tin-bearing alloys, originally mentioned during the technical talks.
Future summits
Another issue discussed at the summit was whether to join existing consortia, such as NEMI or HDPUG, or start a new consortium. According to the participants, it would be sensible to make use of existing resources, but at the same time the desire for a Silicon Valley-based group was emphasized. In either case, it is important that the dialogue begun in the lead-free summit continue.
To that end, another summit is tentatively scheduled for June 2001. People who are responsible for lead-free implementation in their organizations, particularly those located in the greater Bay Area, should make an effort to attend. For information on future lead-free summits, please contact Bette Cooper (MEPTEC): 650-988-7125;
E-mail:[email protected]; www.mepteconline.com.