Residue-Free Solder Bumping Using Small AuSn Particles by Hydrogen Radicals

Eiji HIGURASHI  Daisuke CHINO  Tadatomo SUGA 

Publication
IEICE TRANSACTIONS on Electronics  Vol.E92-C  No.2  pp.247-251
Publication Date: 2009/02/01
Online ISSN: 1745-1353
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Recent Advances in Integrated Photonic Devices)
Category: 
Keyword: 
solder bumping,  AuSn,  plasma reflow,  hydrogen radicals,  solder particles,  flux residues, 

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Summary: 
An AuSn reflow process using hydrogen radicals as a way to avert the cleaning of flux residues was investigated for its application to solder bumping. AuSn particles (manufactured by a gas atomizer) smaller than 5 µm, which are difficult to reflow by conventional methods that use rosin mildly activated (RMA) flux, were used for the experiments. In this process, the reduction effect by the hydrogen radicals removes the surface oxides of the AuSn particles. Excellent wetting between 1-µm-diameter AuSn particles and Ni metallization occurred in hydrogen plasma. Using hydrogen radicals, 100 µm-diameter AuSn bumps without voids were successfully formed at a peak temperature of 300. The average bump shear strength was approximately 73 gf/bump. Bump inspection after shear testing showed that a fracture had occurred between the Au/Ni/Cr under bump metallurgy (UBM) and Si substrate, suggesting sufficient wetting between the AuSn bump and the UBM.