Study On LTCC Substrate Materials With Low Thermal Expansion

Low temperature co-fired ceramic?LTCC?technology is an ideal choice for achieving the high-density packaging of electronic parts and components.The coefficient of thermal expansion?CTE?value of current LTCC substrate materials is usually between 5?8 ppm/?.Excessive CTE value will make the thermal mismatching between the substrate materials and chips serious,and will damage the reliability of packaging.Therefore,it is very important to conduct research on LTCC substrate materials with low thermal expansion.In this work,La₂O₃-B₂O₃ glass-ceramics and B₂O₃-SiO₂ glass with low softening point were used as sintering aids,and were composited with low CTE ceramic fillers to develop LTCC substrate materials with low CTE value?<4.5 ppm/??.The sintering behavior and characteristics of composites were studied.The structure,crystalline phase composition,thermophysical property and crystallization behavior of La₂O₃-B₂O₃-CaO?LBC?and La₂O₃-B₂O₃-CaO-P₂O₅?LBCP?glass-ceramics were studied,and the influence of La₂O₃/B₂O₃ ratio on the characteristics of glass-ceramics were discussed.The results suggested that the change of La₂O₃/B₂O₃ ratio would have effect on the network structure of glass-ceramics.The increase of La₂O₃/B₂O₃ ratio would reduce the glass transition and softening temperature of glass-ceramics,and improve the amount of crystalline phase of La BO₃.But this would also increase the spontaneous crystallization tendency of glass-ceramics.Besides,the crystallization activation energy of glass-ceramics increased with the rising of La₂O₃/B₂O₃ ratio,and the nucleation rate during the crystallization process was also involved.LBC glass-ceramics were combined with Al₂O₃,and the sintering behavior and properties of composites were discussed.It was proved that LBC glass-ceramics could help the low-temperature sintering and densifying of Al₂O₃,and no interfacial reaction was discovered during the sintering process.The properties of composites depended on both the composition of glass-ceramics and the content of Al₂O₃.LBCP glass-ceramics and cordierite were used to develop another kind of composite.Slight interfacial reaction between glass-ceramics and cordierite was spotted,and the main crystalline phases of composites were cordierite and LaBO₃.Too high or too low glass/ceramic ratio would have negative effect on the densification of composites.The addition of cordierite as well as the decrease of La₂O₃/B₂O₃ ratio could reduce the CTE value of composites.Dense composites sintered at 850oC showed good properties which meet the requirements of LTCC substrate with low thermal expansion:dielectric constant about 4.8?7.5,dielectric loss about 2.0×10^-3,the minimum CTE value to 4.12 ppm/oC and good chemical compatibility while co-firing with Ag electrode.Amorphous B₂O₃-SiO₂?BS?glass with low softening temperature was synthesized,and the properties of BS glass were studied.It was found that BS glass had low density,low CTE value and ideal dielectric properties.Then BS glass was composited with Al₂O₃,and the influences of glass/ceramic ratio and sintering process on the sintering behavior and properties of composites were researched.The compositions of BS glass/Al₂O₃ composites maintained their characteristics during the sintering process,and the sintering and densifying process of composites could occur at low temperature.High glass/ceramic ratio and sintering temperature would have positive effect on the rise of densities of samples.?-spodumene was added into composites while the glass/ceramic mass ratio was fixed.Interfacial reaction was still not found,and the rise of?-spodumene content would benefit the densification as well as the reduction of CTE value of composites.Based on the results,glass/ceramic composite system with advantages in comprehensive properties comparing with current commercial products was developed,which had low dielectric constant of 6.2,low dielectric loss of 1.9×10^-3,proper CTE value of 3.57 ppm/°C and high flexural strength of 156 MPa.