A Reliability Study of Nanoparticles Reinforced Composite Lead-Free Solder

Abstract

This work looks at the development and investigation of a reinforced composite solder with low melting point. The composite solder was prepared by adding Sn-3.0Ag-0.5Cu nanoparticles into Sn-58Bi solder paste. The Sn-3.0Ag-0.5Cu nanoparticles were manufactured using a self-developed Consumable-electrode Direct Current Arc (CDCA) technique. The test FR-4 Printed Circuit Board (PCB) with Cu pad and Electroless Nickel Immersion Gold (ENIG) surface finish were fabricated, and fifty SR1206 chip resistors were mounted on pads of test PCB with the reinforced composite solder paste by using conventional surface mount technology. The differential scanning calorimetry (DSC) was used to analyze the constituent of the composite solder joint after reflow. A scanning electron microscope (SEM), transmission electron microscope (TEM) and optical microscope (OM) were employed in order to observe the morphology of nanoparticles; the microstructure of reinforced composite solder joint; the crack initiation and propagation in solder joint; and the fracture mode after shear test. The thermal cycling (TC) was carried out with a temperature range of 40C and 125C. The contact resistance of the solder joint was measured during thermal cycling, and the shear test of solder joints was performed before and after 500 thermal cycles. After the shear test, all fracture surfaces were inspected to identify the fracture mode of the composite solder joint. The results of the experiments detailed in this work indicate that the shear strength of the composite solder increased 2 times in comparison to Sn-58Bi. Meanwhile, the thermomechanical fatigue (TMF) resistance of the composite solder with 1 mass% nanoparticles was 16 times stronger than Sn-58Bi and 4 times stronger than Sn-3.0Ag-0.5Cu. However, the tendency of forming micro-cracks between nanoparticles and solder matrix and the fracture within solder was increased for solder joints with more than 3 mass% nanoparticles after thermal cycling. [doi:10.2320/matertrans.MJ201002]