| Ceramic Ball Grid Array（CBGA）packaging technology is currently the most widely used and largest market-share secondary packaging technology for chips.It offers advantages such as small device size,high chip utilization,low parasitic inductance,and high reliability.However,there is a poor match in the coefficient of thermal expansion（CTE）between ceramic substrates and plastic substrates such as epoxy resin,leading to issues such as thermal mismatch and solder joint cracking failure under high-temperature environments or thermal cycling.A reliable solution is to develop multi-layer ceramic substrate materials with a high coefficient of thermal expansion（HICTE）to mitigate thermal stress between the three components.Furthermore,with the development of electronic components towards lightweight,miniaturization,and high integration,there is a significant increase in power density within the components,leading to higher thermal conductivity requirements for the substrate.High thermal conductivity materials are needed to promptly dissipate the heat generated by the chips to ensure the normal operation of electronic devices.Therefore,this dissertation aims to develop ceramic substrate materials that combine both high coefficient of thermal expansion and high thermal conductivity to meet the reliability requirements of CBGA packaging.The intrinsic thermal expansion and thermal conductivity of solids are both related to the scale of lattice vibrations’anharmonic effects,and the intrinsic high thermal conductivity and high thermal expansion of the lattice are inherently contradictory.However,for polycrystalline ceramics,it is possible to regulate their non-intrinsic thermal conductivity and thermal expansion by adjusting the microstructure,achieving practical applications with both high thermal conductivity and high expansion properties.Therefore,this dissertation aims to achieve this by exploring novel intrinsic high thermal conductivity materials,including Li2Si O3,Li4Si O4,and Li2Si2O5（referred to as Li-Si-based）,Li2Si O3-Al2O3（Li-Al-Si,LAS-based）,LAS-K2O-B2O3-Si O2,LAS-Li F,and Mg（Zn）Al2O4 spinel-based ceramic materials.This is done by adjusting the ceramic’s coefficient of thermal expansion through additives,glasses,multiphase composites,or solid solution relaxation lattice structures,while also adjusting non-intrinsic factors affecting phonon scattering to minimize non-intrinsic phonon scattering,ultimately obtaining ceramic substrate materials that combine both high thermal conductivity and high thermal expansion.The main dissertation of this dissertation includes:（1）Comprehensive analysis of the thermal conductivity mechanism of Li-Si-based ceramics through crystal structure and microstructure.First-principles calculations and predictions of the phonon spectra and theoretical thermal conductivity of Li2Si O3 lattice were performed,confirming that the interaction between low-frequency optical phonons and acoustic phonons is the main source of lattice thermal resistance.The phonon mean free paths and Raman spectra half-widths of various ceramics were systematically compared.Li2Si O3 ceramic exhibited the lowest Raman spectra half-width and the highest phonon mean free path,resulting in the highest thermal conductivity of 8.325W/（m·K）.The thermal expansion and dielectric properties mechanism of Li2Si O3 and Li2Si2O5 ceramics were analyzed through the P-V-L complex chemical bond theory and experimental measurements.Li2Si O3 showed the best comprehensive performance among the compared ceramics,with a thermal expansion coefficient of 8.0～8.5×10-6/K,low dielectric loss（0.00253）,and moderate dielectric constant（6.9）,making it a potential candidate for high thermal conductivity and high expansion CBGA packaging ceramic substrate materials.（2）Optimization of ceramic’s comprehensive performance by adding additives.The addition of Al2O3 to Li2Si O3 improved the microstructure of the ceramic,increased the phonon mean free path,and enhanced the thermal conductivity to 11.836 W/（m·K）,with a thermal expansion coefficient of around 10×10-6/K.In LAS ceramics,the addition of 3wt.%K2O-B2O3-Si O2（KBS）glass as a sintering aid reduced the sintering activation energy and temperature to 900℃.However,the thermal conductivity of LAS-3KBS ceramics decreased to 8.6 W/（m·K）due to the addition of glass,although it improved the microstructure uniformity and denseness,increasing the flexural strength to 270 MPa.Li F additives could lower the sintering temperature of LAS ceramics and improve their thermal properties.LAS-2Li F ceramic achieved a thermal conductivity of 11.36 W/（m·K）at a sintering temperature of 940℃.Additionally,Li F addition relaxed the lattice structure of Li2Si O3,increasing the thermal expansion coefficient of LAS ceramics to11～12×10-6/K.（3）Evaluation of Mg（Zn）Al2O4 spinel as an alternative high thermal conductivity ceramic substrate material.Zn1-xMgxAl2O4 solid solution ceramics sintered at 1550℃exhibited a thermal conductivity ranging from 6.777 W/（m·K）to 18.499 W/（m·K）,with a thermal expansion coefficient increased from 4.5～6.5×10-6/K to 5.8～8.5×10-6/K due to lattice relaxation.The addition of 4 wt.%KBS glass reduced the sintering temperature of Mg（Zn）Al2O4 ceramics to 1450℃,resulting in a thermal conductivity of 18.496W/（m·K）for Zn Al2O4-4KBS ceramics.The amorphous phase of KBS is mainly distributed within the network structure of grain boundaries,with the ceramic material’s coefficient of thermal expansion following that of the matrix phase.Additionally,the dense microcrystalline structure and high Young’s modulus of the matrix can elevate its flexural strength to 294 MPa.LAS additives could also lower the sintering temperature to 1450℃and improve the thermal properties of Mg（Zn）Al2O4 ceramics.LAS existed as crystalline and amorphous phases within the ceramics,not directly participating in reactions with the main phase.The addition of 5 wt.%and 10 wt.%LAS increased the thermal conductivity of Zn Al2O4-5LAS and Mg Al2O4-10LAS ceramics to 13.531W/（m·K）and 16.791 W/（m·K）,respectively,with a thermal expansion coefficient of 8～10×10-6/K and high flexural strength of 168 MPa and 212 MPa,respectively.（4）Thermo-mechanical simulation of the ceramic materials in CBGA structure packaging substrates using finite element analysis.Ceramic substrates with high thermal conductivity ensure the normal operating temperature of the chips,while a high coefficient of thermal expansion significantly reduces the thermal stress on solder balls and bumps,enhancing the reliability of electronic devices.Compared to KYOCERA A484 Al2O3 ceramic substrates,ceramic substrates effective in reducing thermal stress have a thermal expansion coefficient in the range of 8～12×10-6/K. |
