ISMI Evaluation of Lead-Free Flip Chip Technology

Davis, Brett
(Zephyr Environmental Corp., Austin, TX)

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Zephyr Environmental Corporation (Zephyr) was retained in 2011 by International Sematech Manufacturing Initiative (ISMI) to identify any remaining technical challenges with the transition to lead-free solder for Level 1 bumps in Flip Chips. The primary focus of the project was to determine whether or not the semiconductor industry should continue to aggressively pursue renewal of the European Union (EU) Restriction of Hazardous Substances (RoHS) regulation’s Exemption 15, which allows leaded solder in Level 1 bumps. The project began with interviews of experts from the leadership of ISMI’s Assembly Packaging Council and of university researchers. Based upon the interviews, a mini-survey of ISMI member company experts was initiated to obtain their perceptions of remaining challenges to a full transition to lead-free bumps. The survey results suggested that there was some, but not universal, concern that technical issues remain for complete transition of Flip Chip Level 1 bumps to lead-free solders. Failures due to higher reflow temperatures, under-fill issues, intermetallic compound formation, current induced voids, shear stresses, low-k delamination and mechanical shock susceptibility are the main concerns. Electro-migration, solder physical/chemical properties, and thermal-mechanical fatigue are lesser concerns, especially in consumer products applications. The ISMI Working Group (WG) for this project met in Dresden, Germany. Based upon member share presentations and RoHS “recast” information provided by the Fraunhofer Institute, the WG recommended that the WG be continued into 2012 to coordinate industry collaboration, both on the technical challenges of transition and on any future need for an exemption renewal or narrowing request, as well as to keep other stakeholders informed and involved. This presentation will explain the reasoning for this recommendation and will serve as part of the stakeholder outreach effort.

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