| With the rapid development of microelectronics technology, the electronic system is developing towards the direction of very large scale, high integration, multifunction and miniaturization. In the chips' second level package with ceramic ball grid array package (CBGA), the difference of thermal expansion coefficient (CTE) between the substrate and the printed circuit board (PCB) need to be prevented, because this can cause the failure of solder joint and damage the chips. We need to study the high coefficient of thermal expansion of the low temperature co fired ceramic (LTCC)substrate material.In the mature BaO-B2O3-SiO2 (BBS) glass-ceramics system, there is still the problem of poor linearity of the coefficient of thermal expansion curve. Firstly, by replacing CaO with BaO in part through the literature research's enlightenment, which is that CaO-B2O3-SiO2 glass has high linearity of thermal expansion coefficient curve,we study the barium borosilicate glass ceramics and the results show that the linearity of material's thermal expansion coefficient curve is better. On this basis, the new system of calcium borosilicate glass ceramics based on the performance of replacing CaO with BaO totally needs to make the study. This is a material of calcium borosilicate glass mixed quartz sand, which sintered at 950? by traditional solid-state method. We need to research the effect of material crystal content, the flexural strength, thermal expansion coefficient, dielectric properties and microscopic properties etc by conducting the experiment of different composition. We found that the main crystalline phase is quartz and wollastonite, the increase of the content of CaO inhibited the precipitation of cristobalite phase, the volume change caused by phase transition between a-cristobalite and ?-cristobalite reduced, so the sample obtained a high linearity of thermal expansion coefficient curve. Wollastonite, as the new crystalline phase, will greatly enhance the flexural strength of the glass ceramics, when its structure is the acicular crystal structure in triclinic. The result showed that the sample has a lower coefficient of thermal expansion because wollastonite's CTE value is small and is about 6.5 ppm/?. When CaO content is 40wt%, calcium borosilicate glass ceramics has good properties. The flexural strength of 222.5MPa is high, the CTE value is 9.39 ppm/?, there are a high linearity of thermal expansion coefficient curve and excellent dielectric properties. When the quartz sand content is 35wt%, the thermal expansion coefficient increased to 11.8 ppm/?, which can meet the requirements of CBGA package. Flexural strength is 150MPa. At the same time, it is found that the excessive CaO or Si02 will deteriorate the microstructure, increase the number of pores and decrease the performance of glass ceramics.Finally, the calcium borosilicate glass ceramics' crystallization kinetics, sintering kinetics and the theoretical calculation of thermal expansion coefficient are studied in deep. The Kissinger method and Ozawa method are used to calculate the the crystallization activation energy E and crystallization index of n respectively. It is found that excessive CaO content cause the increasing of activation energy and the change of crystallization mode from the surface crystallization to body crystallization. The result by calculating sintering activation energy showed that CaO inhibite the precipitation of quartz and cristobalite. So the transformation between quartz and cristobalite caused decrease of activation energy. This reduced the degree of difficulty in sintering shrinkage. Compared with the actual value, the mathematical value of CTE by the oxide method and the crystal phase method is used to calculate the gap between the actual value and the mathematical value. It is found that the crystal is the key of calculating the thermal expansion coefficient. The error by oxide method is too large. The crystal phase method can be used for the design and prediction of new glass ceramic system. |
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