Tingbi Luo

Microstructure and mechanical properties of Sn–Zn–Bi–Cr lead-free solder

In this paper, Traces of Cr were added into Sn-8Zn-3Bi solder alloys to study the influences of Cr on mechanical properties and high temperature reliability of solder alloys by room temperature tensile test and high-temperature aging treatment. With observation of microstructure and fracture surface analysis, the strengthening mechanisms of Cr in solder alloys were discussed. Experiments show that: the microstructure was refined after traces of Cr added and two kinds of intermetallic compound (IMC) formed. Therefore the addition of Cr improved the plasticity of Sn-8Zn-3Bi alloy. The elongation reached up to 50.96% after 0.1% Cr added; and the fracture mechanism converted from quasi-cleavage fracture into ductile fracture. But after more than 0.3% Cr added, the brittleness of the alloy increased. During 0, 4, 9, 16 days aging, the mechanical properties of Sn-8Zn-3Bi-0.3Cr alloy were improving slightly with aging time. Through the microstructure analysis it was found that the Sn-Zn-Cr phase was transited after aging and Zn in alloy was consumed, so that primary Zn phase was reduced and microstructure was improved.

Formation and growth of interfacial intermetallic layers of Sn-8Zn-3Bi-0.3Cr on Cu, Ni and Ni-W substrates

In this paper, the formation and growth of intermetallic compounds (IMCs) of Sn-8Zn-3Bi-0.3Cr solder on Cu, Ni and Ni-W substrates have been investigated. For the Cu substrate, only Cu₅Zn₈ intermetallic compound was observed. For the Ni substrate, a Ni₅Zn₂₁ film formed at the interface due to the fast reaction between Ni and Zn. For the Ni-W substrate, a thin Ni₅Zn₂₁ film appeared between the solder and Ni-W layer, whose thickness decreases with the increase of W content. An amorphous bright layer was also found to form below the Ni₅Zn₂₁ layer as aging time extended, which is caused by the diffusion of Zn into Ni-W layer.

Enhanced Ni3Sn4 nucleation and suppression of metastable NiSn3 in the solid state interfacial reactions between Sn and cone-structured Ni

Interfacial reactions of Ni micro cones with Sn at solid state temperatures from 373 K to 473 K were studied and compared with Sn/flat Ni diffusion couples. Due to its morphological characteristics, cone-structured Ni enhanced the nucleation of Ni3Sn4, resulting in thicker Ni3Sn4, which is also smaller in grain size and different in texture. At lower annealing temperatures (<423 K), cone-Ni also strongly suppresses the nucleation of metastable NiSn3. The stripe-like micromorphology and special texture of Ni cones are believed to be the reasons for enhanced Ni3Sn4 nucleation.

Formation and growth of intermetallic compounds of Sn-2Ag-2.5Zn on Cu and Ni substrates

The formation and growth of intermetallic compounds of Sn-2.0Ag-2.5Zn solder on Cu and Ni substrates after soldering and subsequent aging process have been investigated in this study. Ni films were electrodeposited on copper substrates. The interfacial micrographs of solder joints prepared at 250°C for 15s and aged for 24h, 96h and 216 h respectively. Double-layer IMC composed with Cu5Zn8 and Ag3Sn was observed at the interface of Sn-2Ag-2.5Zn and Cu couple, which was compact and acted as a barrier layer to confine the further growth of Cu-Sn IMC. On Ni barrier layer, a thin Ni3Sn4 film appeared between the solder and Ni-W layer, which is thin and smooth. After aging process, the thickness increased slowly and steadily, which revealed that Ni barrier layer acts as a promising barrier layer.

Studies on microstructure and mechanical properties of Sn-Zn-Bi-Cr lead-free solder

In this paper, Traces of Cr were added into Sn-8Zn-3Bi solder alloys to study the influences of Cr on mechanical properties and high temperature reliability of solder alloys by room temperature tensile test and high-temperature aging treatment. With observation of microstructure and fracture surface analysis, the strengthening mechanisms of Cr in solder alloys were discussed. Experiments show that: the microstructure was refined after traces of Cr added and two kinds of intermetallic compound (IMC) formed. Therefore the addition of Cr improved the plasticity of Sn-8Zn-3Bi alloy. The elongation reached up to 50.96% after 0.1% Cr added; and the fracture mechanism converted from quasi-cleavage fracture into ductile fracture. But after more than 0.3% Cr added, the brittleness of the alloy increased. During 0, 4, 9, 16 days aging, the mechanical properties of Sn-8Zn-3Bi-0.3Cr alloy were improving slightly with aging time. Through the microstructure analysis it was found that the Sn-Zn-Cr phase was transited after aging and Zn in alloy was consumed, so that primary Zn phase was reduced and microstructure was improved.