Surface Metallization,wetting And Brazing Of SiC_p/Al Composites For Electronic Packaging

High volume fraction?HFC,?50%?SiC_p/Al composites have been widely used in electronics,automobile and aerospace due to high thermal conductivity,strength,enhanced specific modulus and compatible coefficient of thermal expansion?CTE?.However,the Al₂O₃ film and exposed SiC particles were considered to be the two main brazing barriers of the HFC SiC_p/Al composites,resulting in a poor joint quality.In order to overcome this problem,most researchers chose to carry out surface metallization?such as Ni and Cu plating?.However,the joint strength decreased with the increase of brazing temperature in the brazing experiments,which can be mainly attributed to the difference between the thermal expansion coefficient of the substrate and the coating,leading to the decrease of the bonding force between the coating and the substrate.In this paper,70%SiC_p/Al composite was selected as the substrate,and the various concentrations of Si C particles?0 to 3,6 and 9 g/L in bath?were incorporated in the Ni–P coatings to fabricate Ni-P-SiC composite coatings.Moreover,the microstructures,phase composition,physical and mechanical properties of the Ni-P-Si C coatings were investitaged and analyzed,and three commercial Sn-based brazing filler?Sn,Sn-3.5Ag,Sn-3.5Ag-0.5Cu?were used to study the wetting and brazing of SiC_p/Al composites.The experimental results showed that the Si C content in the coatings increased obviously and the XRD diffraction peaks were enhanced with the SiC concentration increasing from 3 to 9g/L.A new phase Ni3 P formed in the coating during the heat treatment at 400 °C.The critical load?Lc?of the Ni-P-SiC composite coating on the SiC_p/Al composite reached the maximum of84.9 N while heat-treated at 200 °C,and it decreased with the increase of SiC content.The thermal diffusivity gradually increased as the temperature increased;however,the thermal diffusivity reduced firstly and then climbed with the increase of SiC content.From the wettability experiments,the contact angles of the three kinds of Sn-based brazing fillers on the coated SiC_p/Al composites increased with the SiC concentration increasing from 0 to 3,6 and 9 g/L.The contact angles of Sn,Sn-3.5Ag and Sn-3.5Ag-0.5Cu on the Ni-P-3SiC coated SiC_p/Al composites are 43°,49° and 30 °,respectively.The interface reaction between the brazing filler and the composite coatings can greatly improve thewettability of the systems.The SiC particles added into the coating cannot participate in the interface reaction.When the Sn-3.5Ag and Sn-3.5Ag-0.5Cu solders were used as brazing fillers,the shear strength values of brazed joints of Ni-P-3SiC coated SiC_p/Al composites were respectively 28 MPa,33 MPa,30 MPa and 38 MPa,indicating that appropriate amount of SiC particles were incorporated in the Ni–P coatings can enhance the joint strength.