Coupling effect in Pt/Sn/Cu sandwich solder joint structures
ABSTRACT The interaction between Sn/Cu and Sn/Pt interfacial reactions in Pt/Sn/Cu sandwich joint structures was studied. We found the interfacial Sn/Pt reaction to be greatly influenced by the opposite Sn/Cu reaction. The PtSn4 interfacial compound formation rate was very sluggish compared with that of the single Sn/Pt reaction case. On the other hand, the growth rate of the Cu6Sn5 compound at the Sn/Cu interface was not affected by the opposite Sn/Pt reaction, which has a rate similar to that of the single Sn/Cu reaction case. However, the morphology of the Cu6Sn5 grains was different than in the single Sn/Cu reaction case (i.e. it had the conventional scallop-type shape). In the sandwich case, the Cu6Sn5 grains had a column-like appearance. The column-like morphology of the Cu6Sn5 grains is due to the small interfacial energy, γsolder/Cu6Sn5, caused by the dissolution of Pt from the molten solder. Also, we found that the Pt dissolution would also cause a reduction in the solubility of Cu in the molten solder. The above two parameter changes lead to a diminishing of the ripening flux among Cu6Sn5 grains. Hence, smaller Cu6Sn5 grains would not be depleted and the separation distance between Cu6Sn5 grains would not be widened.
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ABSTRACT: Platinum does not oxidize easily, and has slow reaction rates with Sn-based solders. Due to these two positive attributes, a single platinum layer has the potential to replace both the oxidation protection layer and the diffusion barrier layer in the underbump metallurgy of flip-chip devices. To evaluate this potential further, the dissolution rate and the wetting properties of Pt were investigated in this study. It was found that Pt did have a dissolution rate less than half that of Ni, currently the most popular barrier layer material. The wetting properties of Pt were not as good as those of Ni but were nevertheless still acceptable for industrial applications. In short, as far as the dissolution and the wetting characteristics are concerned, Pt is an effective top surface layer for use in underbump metallurgy.Journal of Electronic Materials 12/2008; 38(1):25-32. · 1.64 Impact Factor
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ABSTRACT: Purpose – The purpose of this paper is to identify the solder joint with optimal mechanical properties among Cu/Sn/Cu, Ni/Sn/Ni and Cu/Sn/Ni solder joints. Design/methodology/approach – Solder joints with the same specimen shape were prepared by reflow. The microstructures were observed and analyzed by scanning electron microscopy and tensile testing was carried out to investigate the mechanical properties. Findings – The mechanical properties of solder joint correlate closely with the intermetallic compounds (IMC) layer structure and the dissociative IMC particles in the solder bulk. Under the influence of the opposite Cu bar, the Cu/Sn/Ni has a duplex IMC layer structure at the Ni side, involving a thin Ni-Cu-Sn IMC layer and a faceted (Cu,Ni)6Sn5 layer. The mechanical connection of the duplex IMC layers is weak due to the pores in the layers. The Cu/Sn/Ni fractures in the IMC layers in a brittle mode under tensile testing. Comparatively, the Ni/Sn/Ni also has duplex Ni3Sn4 layers, and they connect firmly with each other. The tensile fracture of the Ni/Sn/Ni occurs in the solder bulk in a ductile mode, as well as for the Cu/Sn/Cu. Compared with the Cu/Sn/Cu solder bulk, the solder bulk of the Ni/Sn/Ni and the Cu/Sn/Ni have higher ultimate tensile strengths, because the strengthening effect of the dissociative Ni3Sn4 and (Cu,Ni)6Sn5 particles on the solder bulk is stronger than that of the Cu6Sn5 particles. Among Cu/Sn/Cu, Ni/Sn/Ni and Cu/Sn/Ni, Ni/Sn/Ni has the optimal mechanical properties. Originality/value – The paper offers insights into the significant influence of base material matching on the microstructure and mechanical properties of solder joints.Soldering and Surface Mount Technology 02/2011; 23(1):40-46. · 0.82 Impact Factor
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ABSTRACT: Co/Sn/Cu sandwich couples formed by electroplating were examined to investigate the interaction between Cu and Co across the Sn layer for various Sn thicknesses from 75μm to 580μm. At the Sn/Cu interface, both Cu6Sn5 and Cu3Sn are formed. Unlike in a binary Sn/Cu couple, Cu6Sn5 has a spiked structure for couples with a thinner Sn layer. At the Co/Sn interface, two phases, CoSn3 and (Cu,Co)6Sn5, were simultaneously observed after reaction at 200°C. Remarkably, the CoSn3 reaction layer was much thinner than that in the binary Sn/Co couple. Furthermore, only the (Cu,Co)6Sn5 phase was formed at 150°C. This finding indicates that CoSn3 growth is significantly inhibited in Co/Sn/Cu sandwich couples due to the Cu substrate. KeywordsLead-free solders-interfacial reactions-Co-CuJournal of Electronic Materials 01/2010; 39(8):1303-1308. · 1.64 Impact Factor