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A cost-effective alternative technology for wafer bumping - Electroless Ni/Au UBM deposition and ultra fine pitch printing of solder paste

: Boettcher, L.; Ostmann, A.; Manessis, D.; Aschenbrenner, R.; Reichl, H.

International Microelectronics and Packaging Society -IMAPS-:
International Conference and Exhibition on Device Packaging. Vol.1 : Co-located with the Global Business Council, GBC 2006 Spring Conference
ISBN: 978-1-62748-108-3
International Conference and Exhibition on Device Packaging <2, 2006, Scottsdale/Ariz.>
Fraunhofer IZM ()

The continuous trend of microelectronics packaging industry for further miniaturization of electronic products has relied heavily on the fast evolution of Flip Chip wafer bumping technologies. Electroless Ni/Au deposition for Under Bump Metallization (UBM) in conjunction with Stencil printing of Sn-Pb and lead-free solder pastes offers a cost-effective alternative technology for wafer bumping and therefore it has become increasingly accepted in industry. Electroless Ni-P in combination with immersion Au deposition is a low cost maskless process for the fabrication of under bump metallization (UBM) for flip chip applications. Stencil printing of solder paste for flip chip wafer bumping offers among others the advantages of cost-effectiveness and compatibility with pre-existing printing equipment in a surface mount assembly line. Previous studies have shown the capabilities of solder paste stencil printing technology for flip chip wafer bumping at Ultra Fine pitches (<120 m). They have promoted the state-of-art in stencil manufacturing and printing by using very thin laser-cut and electroformed stencils (up to 30m) with very fine apertures (up to 40m × 90m) [1], [2].