Influence Of Joint Size And TiO₂ Nanoparticles Dopant On Interfacial Reaction Of Micro-solder Joints

To high density microelectronic devices, the geometrical size of solder joints(BGA joints or Flip-chip joints) shrinks from millimeters to tens of microns. As a result, the percentage of the volume of the brittle intermetallic compounds(IMC) layer in solder joints trends to become higher, and possibly only a few IMC grains is interconnected with solder joints interface. At the micro-scale, the microstructure, interfacial IMC evolution and mechanical parameters of solder joints have obviously size effect, which were great influence on the design of microsolder joint structure, the reliability analysis of electronic products, and life assessment. During the process of service, the decreasing of the solder joints size makes the interfacial IMC evolution to have a more important impact on the reliability of solder joints. Therefore, the research on the size change effects of solder joints on interface reaction is significant for the electronic industry.In this paper, the Sn-3.0Ag-0.5Cu/Cu and Sn-3.0Ag-0.5Cu-TiO2/Cu joint interfaces, with three different size of pads have been studied. The research systematically investigates the influence of size effect and TiO2 nanoparticles dopant on the IMC growth and microstructure of interconnect interface in reflow and aging processes. The main conclusions obtained are as follows:The influence of size effect and TiO2 nanoparticles dopant on liquid-solid interface reaction in Sn-3.0Ag-0.5Cu/Cu micro solder joints in reflow process has been investigated. Results show that the thickness of interfacial IMC layer and the number of willow-shaped IMC decrease with the decrease of the size of pads. Meanwhile, the thickness of IMC layer decrease when Ti O2 nanoparticles is added into the Sn-3.0Ag-0.5Cu micro solder joints. Both reducing the size of pads and TiO2 nanoparticles doping could decrease the IMC layer growth exponents, and restrain the growth of IMC layer. In reflow process, size effect influences the growth of IMC layer probably due to the difference of the size of bonding pads, which makes the Cu element concentration near the interface region to be different, and thus makes the growth rate of the interface IMC to be different. A grain boundary pinning mechanism for inhibition of the IMC growth in aging process due to TiO2 nanoparticles addition is proposed. In addition, the size of pads could influence the effect of TiO2 doping on the IMC growth. The experimental results show that the smaller the size of pads, the effect of TiO2 doping restraining the growth of IMC is more significant.The influence of size effect and TiO2 nanoparticles dopant on solid-solid interface reaction in Sn-3.0Ag-0.5Cu/Cu micro solder joints in 100 i, 120 i, and 150 i aging process have been investigated. Results show that interfacial IMC layer thickness decrease with the decrease of the size of pads in aging process. Interfacial IMC layer growth rate exhibites in direct proportion to the size of the pads. Meanwhile, the thickness of IMC decrease when TiO2 nanoparticles is added into the micro-solder joints. In aging process, both reducing the size of pads and TiO2 nanoparticles doping could increase the activation energy of interfacial IMC layer, and thus reduce the atomic diffusion rate, so as to inhibit the excessive growth of the IMC. In aging process, size effect influences the growth of IMC layer probably due to the difference of the diffusion rate of elements at the micro-solder joint interface with different size of bonding pads. A heterogeneous nucleation mechanism for retarding the IMC layer growth due to TiO2 nanoparticles addition is proposed.