Pressureless Infiltration Fabrication And Interfacial Modification Of 3D-SiC/Al Interpenetrating Composite For Electronic Packaging

High volume fraction SiC_p/Al composites have attracted considerable attention in application researches of high-density,high-power,high-frequency integrated circuits and become highly promising candidates for electronic packaging due to their excellent comprehensive properties of high thermal conductivity,low thermal expansion coefficient,low density,and especially their performance designability.However,the increasing development of microelectronic systems in the miniaturization,integration and high performance imposes ever more demanding requirements on the composite.In this thesis,the high SiC volume fraction 3D-SiC/Al-Si-Mg interpenetrating composites with high thermal conductivity and low thermal expansion were prepared by pressureless infiltration technique,by optimizing the interfaces between SiC and SiC as well as between SiC and Al in the composite and reducing the interfacial thermal resistance of the composites.SiC powders were modified to reduce the influence of such as SiC crystal defects and its irregular geometric shape on the properties of the resulited 3D-SiC/Al-Si-Mg composite.In the preparation of 3D-SiC preforms through SiC powders coated with polycarbosilane?PCS?,PCS plays different roles in either forming or sintering process.In the forming process,PCS acts as a binder and SiC particles are bonded together.In the sintering process,PCS is converted into SiC by high temperature pyrolysis to act as a solid sintering aid and the SiC particles are sintered into 3D-SiC preforms.?1?A high thermal conductivity?TC? and low thermal expansion coefficient?CTE? 3D-SiC/Al-Si-Mg IPC with three dimensional mutually interpenetrated structure has been successfully constructed using excessive Si content Al-15Si-10Mg alloy pressurelessly infiltrated into unoxidized 3D-SiC preform.The results showed that both SiC ceramic and Al alloy phases distribute evenly and form a three-dimensional mutually interpenetrated structure in the obtained interpenetrating composite.No clear brittle and harmful Al₄C₃ phase was found in the composite.The obtained interpenetrating composite contains 67vol%of SiC and has the properties of a density of 3.01 g/cm³,a relative density of 99.2%,a thermal conductivity of 224.5 W/?m·??,a thermal expansion coefficient?RT?300?? of 7.04×10^-6?^-1 and a bending strength of 277 MPa.T6 treatment further improved the overall performance of the composite having the properties of a thermal conductivity of 233.6 W/?m·??,a thermal expansion coefficient?RT?300?? of 7.03×10^-6?^-1 and a bending strength of 288 MPa.?2?Mechanical failure of components used in microelectronic systems is attributed to thermal stress involving temperature fluctuations,which can be eliminated by matching the CTE of the component parts.Low thermal expansion coefficient and high thermal conductivity 3D-SiC/Al-Si-Mg IPCs with monomodal or multimodal SiC distribution were fabricated by pressurelessly infiltrating Al-15Si-10Mg into high loading 3D-SiC preforms made from either a single size of SiC particle or mixed SiC particles with different sizes of F220,F800 and F1000 mesh,respectively.The effect of monomodal and multimodal SiC distribution on the thermal conductivity,thermal expansion coefficient and bending strength of the interpenetrating composites were carefully studied.3D-SiC/Al-Si-Mg IPCs with optimized multimodal SiC distribution showed better comprehensive properties than 3D-SiC/Al-Si-Mg IPCs with monomodal SiC distribution.The highest thermal conductivity of 233.2 W/?m·??and bending strength of 283 MPa as well as lower thermal expansion coefficient of 6.32×10^-6?^-1 were obtained for the bimodal 3D-SiC_F220/800/Al-Si-Mg IPC having a total 73% volume fraction of F220 and F800 SiC.The use of finer F1000 SiC particles in the high loading 3D-SiC preforms could lead to finer SiC particles not well filling in the free space left by coarse SiC network and the forming of agglomerates,which result in the microstructural nonuniformity,excessive Mg₂Si and retained pores in the prepared interpenetrating composites causing the weakening of strength and thermal conductivity of the interpenetrating composites.A significant reduction in thermal expansion coefficient?RT?300?? of 5.68×10^-6?^-1 was achieved with trimodal 3D-SiC_{F220/800/1000}/Al-Si-Mg interpenetrating composite having a total 79% volume fraction of F220,F800 and F1000 SiC.?3?A new theoretical model to calculate the thermal expansion coefficient of 3D interpenetrating composite based on the thermal elasticity has been proposed which fits well with the experimental thermal expansion coefficient data of the interpenetrating composites.?4?The interfacial characteristics of the 3D-SiC/Al IPCs,including interfacial bonding between SiC reinforcement and Al alloy in composites as well as the structure and composition of interface,carry a great weight in determining the thermophysical and mechanical properties of the composite.Interface in the 3D-SiC/Al-Si-Mg IPC was modificated by using two different kinds of aluminum alloy Al-15Si-10Mg and Al-9Si-6Mg to infiltrate into the 3D-SiC preforms either unoxidized or preoxidized in air at 1000?,1100? and 1200? for 2 h,respectively.The results showed that desired interface can be achieved in both interpenetrating composites made with those two aluminum alloys,as demonstrated by their excellent comprehensive properties.When the Al-15Si-10Mg alloy with excessive Si content is used for infiltration,interface in 3D-SiC/Al-Si-Mg IPC fabricated with the unoxidized 3D-SiC preform is directly bonded through atomic matching without any interfacial reaction.The pre-oxidation of3D-SiC preforms has negligible effect on the thermal expansion coefficient of composites,but the thermal conductivity and bending strength are weakened.When the Al-9Si-6Mg alloy with a lower Si content is used for infiltration,interface zone with a thickness around 200 nm forms in the 3D-SiC/Al-Si-Mg IPC fabricated with the 3D-SiC preform preoxidized at 1000?.The reaction-bonded interface is composed of AlN and MgAl₂O₄,which have better interfacial affinity with SiC and can isolate SiC effectively from liquid Al against the formation of detrimental Al₄C₃ phase.The composite has the properties of a thermal conductivity of 219.5 W/?m·??,a thermal expansion coefficient?RT?300?? of 7.66×10^-6?^-1 and a bending strength of 318 MPa.