Study On Properties And Structure Of High Strength Calcium-silicon LTCC

Low Temperature Co-fired Ceramics（LTCC）materials of glass/ceramic system had been widely studied and applied in various fields due to their good mechanical and thermal properties.In order to meet the market requirements for miniaturization and high integration of LTCC technology products,when the strength requirement had exceeded the maximum strength that the device structure design could achieve,it was necessary to increase the strength of the material itself to improve the strength of the product.Therefore,combined with the current situation of the industry and product demand,this paper chose CaO-B₂O₃-Al₂O₃-Si O₂ as the main component of the base glass,and Al₂O₃ as the ceramic filler.According to the experimental requirements,the experimental formula was perfected to prepare high-strength LTCC materials.In terms of composition changes,the effects of CaO and La₂O₃ content changes on the structure and properties of high-strength and low-temperature co-fired ceramics were studied.On the basis of the above experiments,the effects of different heat treatment regimes on the crystallization ability and properties of low temperature co-fired ceramics were studied.The experimentally prepared CaO-B₂O₃-Al₂O₃-Si O₂glass/Al₂O₃-based low-temperature co-fired ceramics had excellent properties,the sintering temperature could be reduced to 830℃,and the performance was relatively good.When the sintering temperature was 890℃,the flexural strength could reach219.45 MPa.The main research results of this paper were as follows:（1）The effect of CaO on low-temperature co-fired ceramics was complex.When the content of CaO was less than 40 wt.%,the content of CaO increases,which would introduce free oxygen,destroy the glass network structure,and reduce the viscosity of the glass.When the CaO content was more than 40 wt.%,Ca²⁺would form larger anion groups with[Si O₄]tetrahedron,which hindered the migration of ions and increases the viscosity.The increase of CaO content would promote the precipitation of Ca Si O₃ and Ca₂Si O₄ and the transformation of Ca Si O₃ to Ca₂Si O₄,which was beneficial to the improvement of strength and density,but at the same time led to the increase of thermal expansion coefficient.（2）La³⁺existed only in the glass phase around the crystal phase.When the La₂O₃content was less than 2.9 wt.%,La³⁺would destroy the glass network structure and promote the generation of non-bridging oxygen in the glass.When the La₂O₃ content was greater than 2.9 wt.%,the aggregates of La-related elements increased,hindering the migration of ions.With the increase of La₂O₃,the activation energy of crystallization first decreased and then increased.Affected by glass phase,crystal phase and glass’s wetting to Al₂O₃,the density and thermal expansion coefficient increased gradually,and the strength first increased and then decreased.The strength of the La-doped sample was higher than that of the non-La-doped sample,and the highest strength is 219.45 MPa.（3）The heat treatment system was mainly to control the crystallization to change the structure and properties of the low temperature co-fired ceramics.The types of crystal phases inside the low temperature co-fired ceramics under different heat treatment regimes were basically the same.When the holding time was short and the sintering temperature was low,only a small amount of crystal phase was precipitated inside the sample.The increase of sintering temperature would intensify the transformation ofβ-Ca Si O₃ toα-Ca Si O₃,and promote the increase of size and number of Ca Al₂Si₂O₈ and Ca₂Si O₄ crystals.The increase of the holding time would promote the crystallization and make the crystal grow more completely.The experiment showed that the influence of sintering temperature was greater than that of holding time.Considering the performance and cost,the optimal heat treatment system was the sintering temperature of 890℃and the holding time of 1 h.The comprehensive performance of the samples prepared under this heat treatment system was the best.