Studies On Electroless Ni Alloy Plating And Sodering Of The SiCp/Al Electronic Packaging Composites Of High SiC Content

High SiC volume SiCp/Al composites are widely used in electronic packaging and aerospace areas, due to their excellent properties of low and adjustable coefficient of thermal expansion (CTE), high thermal conductivity (TC) and specific modulus and so on. Soldering of the SiCp/Al composites is a critical step to fulfil the electronic packaging, before that, surface metallization of them is necessary. Electroless Ni-P alloy plating is most employed to do that. Therefore, research on electroless Ni-P alloy plating and soldering of the high SiC volume SiCp/Al composites is an essential issue as the composite materials applied in electronic packaging.SnCl2 and PdCl2 based baths were used to sensitize/activate the SiCp/Al composites, respectively. Plannar views and distributions of the sensitized/activated points on the surfaces of the composites were studied. After sensitizing for 1.0 min, Al alloy surfaces of the composites are etched appropriately without large and/or deep corrosion pits. The Sn(OH)2 precipitates distribute uniformly to ensure the homogeneous distribution o f the Pd activation particles on the composite surfaces.H2PO2- based bath was used to electroless deposit Ni-P alloy film on the sensitized/activated SiCp/Al composites. Surface morphologies of the composites and their effects on the Ni-P alloy depositing process and bonding action of Ni and P atoms in the Ni-P alloy were studied. The inhomogeneous distribution of the Sn/Pd activating points results in preferential deposition of the Ni-P alloy particles on the Al alloy and rough SiC particle surfaces and in the etched caves. The Ni-P alloy film has an amorphous structure where chemical bonding between Ni and P atoms exists. After a continuous Ni-P alloy film formed, electroless Ni-P alloy plating is not affected by surface morphology and characteristics of the SiCp/Al composites any longer, but by the electroless plating process itself. The Ni-P alloy film follows a linear growth kinetics with an activation energy of 68.44 kJ·mol-1.In the soldering structure between the SiCp/Al composites and the Kovar alloy, a continuous (Au,Ni)3Sn2 intermetallic (IMC) layer is formed at the interface between the Ni-P alloy film and the Au-Sn eutectic solder. Meanwhile, large ξ’(Au5Sn) bulks and rod-like (Au,Ni)3Sn2 particles are formed adjacent to the IMC layer. After annealing at 200℃, the rod-like (Au,Ni)3Sn2 particles disappear gradually, the (Au,Ni)3Sn2 layer turns to be denser and thicker and its interface with the Au-Sn solder becomes smoother. The hermeticity of the sample soldered at 350℃ for 25 min is as high as 1×10-10 Pa·m3·s-1. The interface of the solder joint is testified to be reliable after the thermal shocking test.