Study On Brazing Of Aluminum Matrix Composites For Electronice Packing

High volume fraction SiC particle reinforced aluminum matrix composites (SiC/Al composites) exhibit low coefficients of thermal expansion, low density and good conductivity for heat. Therefore, it is hopeful for the materials to be new electronics packing materials instead of Kovar alloys. However, the materials have poor weldability, which restricts their applications in electronics packing. Kovar alloys can be ring welded and laser welded easily, but SiC/Al composites can not be welded with these method for their special microstructure. One of the resolvent is that brazing Kovar alloys with SiC/Al composites firstly, and then joint Kovar alloys with ring welding.The soldering between SiC/Al composites and Kovar alloys, brazing of SiC/Al composites, brazing between SiC/Al composites and Kovar alloys and electroless nickel for SiC/Al composites are investigated in this paper. The microstructures of joints, appearance of fractures and electroless nickel coatings are analyzed by OM, SEM, EDS and TEM. The results are show as following:Soldering between SiC/Al composites with nickel coating and Kavor alloys was conducted at 420℃for 5min with Zn-Cd-Ag-Cu filler alloy in Ar atmosphere. Solder beams with complete metallurgical bonding and dense structure are obtained. The shear strength of joints is 225MPa, and fracture occurs at the surface of SiC/Al composites close to nickel coating.Brazing of SiC/Al composites was carried out at 560℃for 3min with Al-24Cu-5Si-1.5Mg-0.5Ni filler alloy in vacuum. Brazing seams without gas pore, impurity and microcracks are obtained. In addition, filler metal is not only bonded with aluminum matrix metallurgical, but also wet SiC particles well. Precipitates with three distributions, twins and dislocations exist in brazing seams. The maximal shear strength of joints is 102.3MPa, and fracture including cleavage plane and transient fracture zone. Brazing between SiC/Al composites and Kavor alloys is conducted at the same weld parameters. Continuous fragile layers are formed between filler metal and Kovar alloys, and cracks are formed easily in the layers due to residual stress.Electroless deposition of nickel on the surface of SiC/Al composites in alkaline bath was conducted, and continuous nickel coatings with dense structure, good adhesion and 4.07%(wt.%)phosphorus are acquired. When the Electroless deposition time is 20min, the thickness of nickel coatings is 6μm.In the end, the electronics packing components made of brazed SiC/Al composites and Kavor alloys were tested for resistance to air loss after electroless deposition of nickel and aurum. The leakage rate is less than 1×10-8Pa·m3/s, which meets the requirement of electronics packing. The study supports processing technique for substituting traditional materials with composites completely in the industry of electrical radio detector.