Ultrasonic Irradiation Assisted Fabrication Of Nanosized SiC Particles To Enhance The Solder Of SnCu Composite

Mainly due to cost issues, the eutectic SnCu alloy is becoming one of the mostinterested lead-free solders in the electronic packaging industries. Nevertheless, theeutectic SnCu alloy requires improving its mechanical properties, such as shear,tensile and creep behaviors. Thus, further enhancement of mechanical properties,including thermal properties brings about more concerns. Adding reinforcedparticles in conventional eutectic SnCu alloy solder is one effective way. Due togood thermal conductivity, low coefficient of thermal expansion, excellentheat-resistant quality and stable chemical properties, nano-SiC particles areconsidered to be the one of the excellent reinforcing particles. In this study, wefabricated SiC-SnCu composite solder under high-intensity ultrasonic irradiation.The microstructures and its properties were investigated as functions of SiC contentand ultrasonic power, respectively.In the experiment, the microstructures were firstly investigated. With theincrease of nano-SiC content from0to0.3wt.%, the dendrite arm spacing wasrefined because heterogeneous nucleation and dispersed distribution occurred in thecomposite solder, but it was coarsened when the SiC content further increased from0.4to0.8wt.%, owing to the agglomeration and floatation of nano-SiC particles. Itgot finer with increasing ultrasonic power from66to198W. But the dendrite armspacing was coarsened after the ultrasonic power further increased.The melting point, coefficient of thermal expansion (CTE) and Vickersmicrohardness of the SiC-SnCu composite solder were also investigated.Differential Scanning Calorimeter (DSC) results showed that the melting point ofthe composite solder had been reduced about2.5℃, so the present solderingprocess can also be applied to the composite solder. CTE of the composite solderwith0.5wt.%SiC had been reduced23.2%compared to the original eutectic SnCusolder. The microhardness of the composite solder with0.3wt.%SiC prepared by165W power ultrasound increased about21.3%when compared that to the originalSnCu solder.Eventually, the SiC-SnCu composite solder ball was remelted and soldered to aCu pad by a sirocco-circumfluence reflow soldering system. After7days agingunder150℃, the intermetallic compounds (IMCs) at the interface of the SiC-SnCu/Cu joints were investigated. Compared with the SnCu/Cu joints, theIMCs thickness of the former reduced31.9%, owing to the addition of nano-SiCparticles. Furthermore, BGA shear test results showed the composite solder jointwith0.3wt.%nano-SiC particles achieved the maximum shear strength of30.92MPa, which was improved43.4%compared to the original SnCu solder joint.