Abstract
With the shrinkage of size, porous Cu3Sn has become a new potential threat of the reliability in Cu pillar microbump. The formation of porous Cu3Sn is caused by the decomposition of Cu6Sn5 after Sn atoms in solder depletion. Besides, the stress introduced by the phase transition from η-Cu6Sn5 to η′-Cu6Sn5 will promote the formation of porous Cu3Sn. In this paper, uniform Ф10 µm Cu/Sn and Cu/Ni (~ 0.6 μm)/Sn microbumps have been fabricated by multilayer electrodeposition and the effect of the Ni layer on the growth behavior of porous Cu3Sn was investigated by comparing IMCs’ (Intermetallic Compound) evolution in Cu/Sn and Cu/Ni/Sn bumps aged at 170 °C and 200 °C. The ~ 0.6 μm Ni barrier layer can effectively retard the Cu atoms diffusion, which can hinder IMC from overgrowth. Moreover, the results of X-ray diffraction indicate that the ability of the Ni layer can stabilize Cu6Sn5 phase and weakens the tendency of the porous Cu3Sn formation. Under the conjoint action of retarding the growth of IMC and stabilizing Cu6Sn5 phase, the Ni layer can inhibit the formation of porous Cu3Sn efficaciously.
Highlights
Three-dimension integrated circuit (3D IC) is a promising solution for smaller size and high performance mobile devices.[1,2,3] In 3D IC packaging, the size of Cu microbump has scaled down dramatically and in recent years more attention has been paid to several microns.[4,5,6] When the size of Cu pillar bumps reduces to several microns, the physical characteristics of the solder joint will change significantly, which raises new potential threats.[7, 8] During the reflow and solid-state aging process, the excessive growth of intermetallic compound (IMC) would deplete the Sn solder[9]
The formation of porous Cu3Sn is contributed the decomposition of Cu6Sn5, which is caused by the overgrowth of intermetallic compounds (IMC) and the stress introduced by the phase transition of Cu6Sn5
Uniform Ф10 μm Cu/Sn and Cu/Ni (~0.6 μm)/Sn microbumps have been fabricated by multilayer electrodeposition and the effect of the Ni layer on the growth behavior of porous Cu3Sn was investigated by comparing the evolution of IMC in Cu/Sn and Cu/Ni/Sn bumps aged at 170 °C and 200 °C
Summary
Three-dimension integrated circuit (3D IC) is a promising solution for smaller size and high performance mobile devices.[1,2,3] In 3D IC packaging, the size of Cu microbump has scaled down dramatically and in recent years more attention has been paid to several microns.[4,5,6] When the size of Cu pillar bumps reduces to several microns, the physical characteristics of the solder joint will change significantly, which raises new potential threats.[7, 8] During the reflow and solid-state aging process, the excessive growth of intermetallic compound (IMC) would deplete the Sn solder[9]. Few literatures have investigated the effect of Ni barrier layer on Cu6Sn5 phase transition, so a purposive research needs to be carried out, which play an important role in retarding the formation of porous Cu3Sn. Here, Cu/Sn and Cu/Ni/Sn microbumps of 10 μm were fabricated by multilayer electroplating and the thickness of Ni layer was ~ 0.6 μm. The inhibiting effects of the Ni barrier layer on the growth of porous Cu3Sn in 10 μm microbumps is deeply clarified
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