New Lightweight Low-expansion, High Thermal Conductivity Electronic Packaging Materials

Electronic packaging materials used in aerospace vehicles should notonly meet the basic need of low thermal expansion coefficient (TEC) andhigh thermal conductivity (TC), but also the need of hermeticity andstrength, and lightweight is the precondition to use. High-siliconaluminum alloys used as lightweight electronic packaging material cannot only realize the design of physical properties by changing thecomposition of alloy, but also have excellent comprehensive properties.Its low expansion coefficient can be obtained by increasing Si content,however, alloy brittleness increases and thermal conductivity decreaseswith the increase of Si content, which restricts its application.High-silicon aluminum alloy materials with lightweight, low thermalexpansion coefficient and high thermal conductivity, studied in this paper,is important developing direction in electronic packaging materials usedin aerospace, the researches on its scientific theory and preparationtechnology have important scientific and practical significance.This dissertation based on the study of military industry project:electronic packaging material of high-silicon aluminum alloys withlow-density, low thermal expansion coefficient and high thermalconductivity, in order to solve problems occurred in the preparation anduse of electronic packaging material of high-silicon aluminum alloys, themain researches are as follows:Binary high-silicon aluminum alloys were prepared by powdermetallurgy and vacuum canning hot-extrusion process, and the effect ofextrusion temperature, powder size and Si content on microstructure andproperties of material was comprehensively studied. The results show that:binary high-silicon aluminum alloy with lower Si content solves theproblem of brittleness and gains better thermal conductivity, but it dosenot satisfy the need of the TEC and tensile strength of electronicpackaging material.In order to improve the tensile strength and decrease the TEC, SiC_pand SiO₂ with low TEC and cost addition were put into binaryhigh-silicon aluminum alloy matrix to prepare particle reinforcing Al-Si matrix composites. The microstructure and properties of SiC and SiO₂particle reinforced Al-Si matrix composites prepared by hot-extrusion andhot-press respectively were studied, TEC and TC were verifiedrespectively by Turner, Kerner and EMA (Effective MediumApproximation) models. The TEC of the composites decreases, at thesame time, the TC of them decreases rapidly and the tensile strength cannot be tested because of the bad formability of materials, they can alsonot meet the using need of electronic packaging materials.In order to gaining the best comprehensive properties,high-temperature air-oxidation and high-energy milling pretreatmentprocesses, introduced in this paper for the first time, were applied toincrease the oxygen content of Al-Si alloy powder, combined withvacuum canning hot-extrusion process to fabricate SiO₂ and Al₂O₃dispersion strengthening composites. The oxidation thermodynamics andkinetics condition of Al-Si alloy powder were discussed, thethermodynamics condition of oxidation, priority oxidation andnonoxidation were calculated and drew, the effect of oxidation time,milling time, the ratio of ball to powder and Si content on powder oxygencontent, material microstructure and properties were comprehensivelystudied.At last, all processes used in fabricating high-silicon aluminum alloycomposites were synthetically analyzed and compared, It can beconcluded that: the comprehensive properties of the composites preparedby powder after high-energy milling process are the best, all propertiescan entirely meet the need of electronic packaging materials, and theparameters of milling process were optimized. In this paper, thethermodynamics condition of oxidation, priority oxidation andnonoxidation has been established based on the investigation of theoxidation thermodynamics and kinetics condition of Al-Si alloy powder.A novel low-density, low thermal expansion coefficient(TEC) and highthermal conductivity(TC) electronic package material was developed.