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Latest developments in bumping technologies for flip chip and WLCSP packaging

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


IEEE Components, Packaging, and Manufacturing Technology Society:
33rd IEEE/CPMT International Electronic Manufacturing Technology Symposium, IEMT '08 : 4-6 Nov. 2008, Penang
Piscataway, NJ: IEEE, 2008
ISBN: 978-1-4244-3392-6 (print)
ISBN: 978-1-4244-3393-3
Art. 5507876
Electronic Manufacturing Technology Symposium (IEMT) <33, 2008, Penang>
Fraunhofer IZM ()

Stencil printing of solder paste remains the technology route of choice for flip chip bumping because of its economical advantages over traditionally costly evaporation and electroplating processes. Fraunhofer IZM printing group has developed stencil printing processes to meet the current trends in wafer bumping roadmaps with continuous increase of I/O's and reduced bumping pitch. Mainstream wafer bumping has been performed by using innovative Type 5 (15-25 m) and Type 6 (5-15n) pastes with both Sn-Pb and Pb-free compositions from 300m up to 100m pitches for peripheral pad configurations and up to 120m for area array configurations. At R&D level, IZM has advanced stencil printing very close to its technological limits at pitches even down to 50m Innovative electroformed and laser-cut with nano-treatment stencils have been manufactured with an extreme thinness of 20m for bumping wafers at Ultra fine pitches (UFP) of 100m, 80m and 60m. Specifically, for 100m pitch bumping , both type 7 (2-11 m) and type 6 (5-15m) pastes of eutectic composition Sn63/Pb37 have been successfully employed. Bumping using 25 m electroformed stencil thickness has yielded bump heights of 42.3±3.8m and 43.6±3.5m for type 7 and type 6 pastes, respectively. A newly prototype developed type 8 paste (2-8m) has been used for the first time to bump chips with peripheral contacts at 80m and 60m pitch. Bumping at 80m pitch with nano-treated laser-cut stencil has yielded bumps of 28m in height. For bumping at 60m pitch, a 20m thick electroformed stencil was used with 35m × 80m oblong apertures. Printing at 60m pitch has yielded very promising results and has proved the capability of electroformed technology to manufacture accurate and robust thin stencils. The bump height at 60m pitch was measured to be 28 ± 3m. Paste-in-Resist technology has been developed as an alternative to stencils in order to overcome the manufacturing difficulties of making extremely small apertures. Paste is printed in resist