Spray forming, also called spray casting or spray deposition, is the inert gas atomization of a liquid metal stream into variously sized droplets (10-500 microns) that are then propelled away from the region of atomization by the fast flowing atomizing gas. The droplet trajectories are interrupted by a substrate which collects and solidifies the droplets into a coherent, near fully dense preform. By continuous movement of the substrate relative to the atomizer as deposition proceeds, large preforms can be produced in a variety of geometries including billets, tubes and strip at flow rates of 5-30kg/min.
Spray formed Si-Al alloys for electronic packaging applications
Alloys containing up to 70wt%Si are being manufactured by spray forming. These alloys offer a unique combination of low thermal expansion, high thermal conductivity and low density, and are under investigation for electronic package thermal management applications in the avionics, satellite and other industries. The research concerns the characterisation of the key mechanical and microstructural properties of Al-70Si alloy(AlSi70 alloy in China); the optimisation of spray forming; and the enhancement of alloy properties by ternary alloy additions and novel variants of the spray forming process.
Main characteristics of controlled expansion alloys(also called Al/Si alloy for electronics packaging and housings)
1. Pre-select coefficient of thermal expansion(CTE) in the range of 7~17ppm/℃,so it can be tailored to all sizes and shapes for different applications.
2. High thermal conductivity.
3. Low density and lightweight.
4. Outstanding thermo-mechanical stability.
5. Uniform and isostropic microstructure,no porority and holes.
6. Primary silicon distribute well,no macro segregation,finely and equiaxed grains(average grain size is about 10μm), relative density could reach up to 100%
7. Easy of machined(e.g.CNC/EDM),platability and weldability.
8. Higher specific stiffness eminently suitable for a wide range of applications
9. Environmentally friendly,present no disposal problem
10. Excellent electrical conductivity(Perfect EMI/RFI shielding performance)
11. Higher cost advantage in comparation to copper-molybdenum and copper-tungsten.
Grade Content Density CTE Thermal Conductivity Tensile Strength Yield Strength Poisson's Ratio Elongation Elastic Modulus g/cm³ ppm/℃ W/m.K MPa MPa % GPa AlSi27 Al-27%Si 2.6 17 175 170 130 0.29 3.8 91 AlSi42 Al-42%Si 2.55 13.5 143 200 187 0.29 1 105 AlSi50 Al-50%Si 2.5 11.5 140 220 210 0.28 <1 108 AlSi60 Al-60%Si 2.46 9 125 181 181 0.27 <1 121 AlSi70 Al-70%Si 2.43 7.5 120 138 138 0.25 <1 131
Controlled expansion Si/Al alloy properties
parameters of China's electronic packaging manufacturer