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Polyimide Restructuring: Application for Printed Leadfree Bump Integrity Improvement
Keywords: Polyimide, Leadfree, Bump
Polyimide is a widely used passivation layer on top of a semiconductor die. In flipchip, this is used as a barrier to protect the die from stress brought about by the difference in coefficient of thermal expansion between the silicon, the bump, the underfill, and the substrate. Use of polyimide has become even more popular with the use of the more brittle lowK dielectric on nanoscale die technology. A trade off however is that the polyimide has shown weakness in adhesion to the underfill compared to the conventional SiN/USG passivation layer. An added value for the polyimide use is that when designed properly it can also provide additional protection to the bump which can be useful now as leadfree bump is getting more and more attention with the speculation that ROHS eutectic bump exemption is coming to an end by 2010. The industry is now searching for an economical leadfree bump solution. Several technologies being developed focuses on plated bump technology as this has a more robust UBM layer compared to printed bump UBM, however, the plated bump is more expensive than printed bump. This paper will discuss how the polyimide layer when restructured can offer extra protection to the printed leadfree bump, including discussions on how the polyimide can be restructured to improve its adhesion to the underfill.
Roden Topacio, Member of Technical Staff

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