Residual stress and interfacial reaction of the electroplated Ni-Cu alloy under bump metallurgy in the flip-chip solder joint

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Pure Ni, the Ni-Cu alloy, and pure Cu layers as the under bump metallurgy (UBM) for a flip-chip solder joint were deposited by electrolytic plating. For the pure Ni layer, residual stress can be controlled by adding a wetting agent and decreasing current density, and it is always under tensile stress. The Ni-Cu alloys of different Cu compositions from similar to20wt.%Cu to 100wt.%Cu were deposited with varying current density in a single bath. The residual stress was a strong function of current density and Cu composition. Decreasing current density and increasing Cu content simultaneously causes the residual stress of the metal layers to sharply decrease. For the pure Cu layer, the stress is compressive. The Cu layer acts as a cushion layer for the UBM. The residual stress of the UBM strongly depends on the fraction of the Cu cushion layer. Interfacial reaction of the UBM with Sn-3.5 wt.% Ag was studied. As the Cu contents of Ni-Cu alloys increased, the dissolution rate increased. Several different intermetallic compounds (IMCs) were found. The lattice constants of alloys and the IMC increase with increasing Cu contents because the larger Cu atoms substitute for the smaller Ni atoms in the crystallites. The Cu content of the IMC are strongly dependent on the composition of the alloys. Ball shear tests were done with different metal-layer schemes. The failure occurs through the IMC and solder.
Publisher
SPRINGER
Issue Date
2004-09
Language
English
Article Type
Article
Keywords

LEAD-FREE SOLDERS; THIN-FILMS; TECHNOLOGY; INTERCONNECTS; RELIABILITY; PERFORMANCE; SYSTEMS; SN

Citation

JOURNAL OF ELECTRONIC MATERIALS, v.33, no.9, pp.948 - 957

ISSN
0361-5235
DOI
10.1007/s11664-004-0021-1
URI
http://hdl.handle.net/10203/85613
Appears in Collection
MS-Journal Papers(저널논문)
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