Investigation On The Fabrication And Mechanical Properties Of Sn-Bi/Carbon Nanotubes Composite

Due to the increasing chip heat dissipation in microelectronic packaging, developing thermal interface material (TIM) with high thermal conductivity and high connection strength become an urgent need. In this paper, Sn-Bi/carbon nanotubes (Sn-Bi/CNTs) composite was fabricated based on electrodeposition method. The micro morphology, structure, element composition and melting point of Sn-Bi/CNTs composite were characterized by using scanning electron microscope (SEM), transmission electron microscope (TEM), energy spectrum analysis (EDS) and differential scanning calorimeter (DSC), respectively. Characterization results showed that the codeposition of CNTs and Sn-Bi was achieved and there was no significant effect on the melting point with the addition of CNTs.The single lap joint samples of Sn-Bi/CNTs composite were obtained by two different processes. The results of joint shear tests showed that the strength of lap joint was quite different by using different processes. The tensile test samples of Sn-Bi/CNTs composite were prepared by cold press and sintering, and the influence of different pressing pressure on the tensile properties of Sn-Bi/CNTs composite was studied. The results showed that the higher pressing pressure was conductive to improve the tensile strength. Then the single lap joint tests and tensile tests were preformed to characterize the mechancial properties of Sn-Bi/CNTs composite with CNTs concentration of Omg/L,5mg/L,25mg/L and 125mg/L, respectively. The results showed that when the concentration of CNTs is 0-25mg/L, the joint strength and tensile strength of Sn-Bi/CNTs composite were increased with increasing the concentration of CNTs, which indicated that adding the CNTs can improve the mechanical properties of Sn-Bi/CNTs. Particularly, when the concentration of CNTs is 25 mg/L, the joint strength and tensile strength of Sn-Bi/CNTs composite reached the maximum value. And the joint strength and tensile strength of Sn-Bi/CNTs composite was about 1.6 times and 1.25 times of pure Sn-Bi, respectively. However, the mechancial properties of Sn-Bi/CNTs composite deteriorated when the concentration of CNTs continued to increase, which is mainly due to the agglomeration of CNTs. Fracture analysis showed that CNTs can refine the grain size of matrix, and CNTs mainly exist in the form of bridging and pull-out.The mechanical parameters of Sn-Bi/CNTs composite with different content of CNTs were obtained based on theoretical models of fiber reinforced composite in this study, and a single lap joint finite element model was built by using ANSYS software. Comparative analyses of the influence of the content of CNTs and the joint geometric parameters on joint strength were studied respectively. The results indicated that joint strength largely effect by the thickness of lap joint, and was increased with increasing the content of CNTs. When the content of CNTs is 1.2vol.%, the joint strength of Sn-Bi/CNTs composite was-126.6% higher than Sn-Bi. The random distribution and uniform distribution mesoscopic models of Sn-Bi/CNTs composite were established to study the effect of distribution and content of CNTs on stress distribution and elastic modulus. Simulation results showed that the composite was strengthened due to the stress-sharing effect of CNTs. However, stress concentration was found in the end of CNTs, which the initial failure may occur. The elastic modulus of uniform distribution model was inceased with increasing the content of CNTs, and there is a limit value. The average elastic modulus of random distribution model was larger than that of uniform distribution model, but the deviation was great.