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Stencil printing technology for 100m flip chip bumping

: Manessis, D.; Patzelt, R.; Ostmann, A.

Global SMT and Packaging 4 (2004), Nr.2, S.10-14
ISSN: 1474-0893
Fraunhofer IZM ()

Stencil printing remains the technology route of choice for flip chip bumping because of its economical advantages over traditionally costly evaporation and electroplating processes. This paper deals with all processing facets of 6 wafer bumping of peripheral array structures at 100m pitch. Both type 7 (2-11m) and type 6 (5-15m) pastes of eutectic composition Sn63/Pb37 in conjunction with electroformed stencil technology have been successfully employed for wafer bumping. Bumping using 30m stencil thickness has yielded bump heights of 42.3±3.8m and 43.6±3.5m for type 7 and type 6 pastes, respectively. Alternative stencil design scenarios are exploited and it turns out that staggered designs provide effective solutions for aperture decoupling and optimization of overprinted paste volumes for peripheral ultra fine pitch configurations. Furthermore. the present study provides insights into the fundamental understanding of the printing performance of very fine pastes and con tributes in defining the narrow process windows of type 6 and type 7 pastes for wafer bumping, it is shown that type 6 paste is more appropriate than type 7 for the stencil aperture dimensions used in the present study.