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Lead Free Solder / UBM Phase Reactions in Electroplated Bumps

: Engelmann, G.; Jurenka, C.; Wolf, M.J.; Dietrich, L.

Reichl, H. ; Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration -IZM-, Berlin:
Micro System Technologies 2005 : Micro Electro, Opto, Mechanical Systems & Components International Conference & Exhibition, October 5-6, 2005, Munich, Germany
Poing: Franzis, 2005
ISBN: 3-7723-7040-3
International Conference on Micro Electro, Opto, Mechanical Systems & Components <2005, München>
Fraunhofer IZM ()

Lead-free solder application in flip chip interconnection systems require an increase in knowledge in the field of under bump metallizations (UBMs), solder materials, board metallizations as well as in the interactions between these components. Common UBMs have been tested with various lead-free solder systems to study the formation and growth of intermetallic compounds (IMCs) during liquid and solid phase reaction. Due to a high rate of IMC formation connected to the consumption of the UBM these UBMs are often not recommended for lead-free bumps of devices with very small solder joints in elevated temperature (150 °C) applications. In such cases it would be advantageous to use UBMs showing a limited formation of IMCs at the interface UBM/solder to maintain the plasticity of the interconnect and the adhesion of the UBM to the diffusion barrier. As an example for such an UBM the sputtered Al/Ni(V)/Cu thin film UBM was evaluated for the use of SnAgCu solder.
In the present study bi- and monolayer UBMs as well as the solder material were electrodeposited (index: ed) as this process had been evaluated to meet the requirements of small bump fabrication and realization of fine pitch for flip chip devices.