Effect Of Oriented Electroplating Copper And Nickle Layer On The Interface Reaction

The increasingly development of three-dimensional(3D) has attracted much attention since it has high package density, parallel processing, short wire length and so on. With advantages such as well mechanical and electronic behavior, copper micro-bump is regarded as a replacement of conventional solder micro bump. Under this miniaturization trend, the interfacial reaction between copper bumps and Tin solders would alter during bonding and the serving process, especially the growth behavior of interfacial IMC in micro bumps would greatly be influenced by the grain orientation of micro-bumps which will be anisotropic with limited grains.Texture of substrate has marked influence on the nucleation and growth of intermetallic compounds. A lot of researches focus on the interfacial reaction between the single crystal substrate and the solder have been carried out. However, single crystal substrate is not economical and impracticable, that is why the electroplating polycrystalline Cu substrate with preferred texture was prepared. Cu-Sn and Ni-Sn bonding interfaces with different preferred orientations are observed. Thus, effect of preferred orientation of deposition coating on growth of intermetallic compound is systematically investigated.By controlling the additive, current density, power type, etc. in the eletroplating, copper film and nickel film with preferred orientation can be obtained. With using additive P-68, the preferred orientation of copper film is evidently shown as(220). The preferred orientation of nickel film turns from(111) to(200) as the current density increases. Under the direct-current conditions, nickel film(200) crystal plate shows obvious preferred orientation. While under the pulsed conditions,(111) crystal plane shows.Diffusion coefficient of atom differs from crystal plane. So while there is preferred orientation in coating, the atomic diffusion shows anisotropy. The arrangement of(200) plane is more closely spaced than(220) plane, which makes the atomic diffusion more difficult in(200) plane, and has a smaller diffusion coefficient than(220) plane. There is obvious facet in IMCs grains at the interface of Cu(200)-Sn, which doesn’t appear in Cu(220)-Sn. The facet is arranged to form a polygonal pattern by different angles and fine pores formed between grains. Cu3 Sn preferentially nucleates bewteen Cu(220) and Cu6Sn5.There are flaky IMCs of different size and same thickness formed on Ni(220)-Sn interface, while the IMCs on Ni(220)-Sn interface are massive and uniform equi-axed grains. The former Ni/Sn atomic ratio is bigger than the latter one, the common Ni-Sn intermetallic compound Ni3Sn4 is formed with sufficiently aging. With large lump IMCs layer consuming the whole interface, holes and cracks appeared since on Ni(220)-Sn interface, which will have impact on mechanical and electrical properties of the bonding interface.