Background
Electronic products are widely applied in modern life, electronic components are the most basic constituent units of the electronic products, the precision requirement of the electronic components is high, and in order to ensure that the electronic components are not interfered by external environment, ensure the working precision and prolong the service life, the electronic components are required to be installed on a ceramic packaging base and packaged. A common electronic component is a piezoelectric vibrating piece; in addition, in the application field where the requirements for the temperature sensitivity and the temperature control accuracy are high, the ceramic package base is required to package the piezoelectric vibrating reed and also package the temperature detecting element together to form the resonator device having the temperature compensation function, wherein the temperature detecting element may be an integrated circuit chip and a thermistor element having the temperature detection function.
The traditional resonator device with the temperature compensation function is formed by packaging a piezoelectric vibrating piece and a temperature detection element in the same cavity of a ceramic packaging base together, but by adopting the scheme structure, the size of the ceramic packaging base is large, the development trend of miniaturization is not adapted, and meanwhile, the problems that the piezoelectric vibrating piece and the temperature detection element are mutually interfered in the assembling and processing process and the like can occur. Therefore, more and more temperature compensation functional resonator devices adopt ceramic package bases with upper and lower cavity H-shaped structures.
The structure of the H-shaped ceramic packaging base mainly comprises: a substrate; the first frame body is arranged on the upper surface of the substrate and forms a first cavity with the substrate; the second frame body is arranged on the lower surface of the substrate and forms a second cavity with the substrate; the bonding pad for the piezoelectric vibrating piece is arranged on the upper surface of the substrate, exposed out of the first cavity and used for mounting the piezoelectric vibrating piece; the temperature detection element pad is arranged on the lower surface of the substrate, exposed out of the second cavity and used for mounting a temperature detection element; and electrode terminals provided on the side of the lower frame not connected to the substrate, the electrode terminals including electrode terminals for the piezoelectric vibrating reed and electrode terminals for the temperature detection element. The pad for the piezoelectric vibrating reed is electrically connected to the electrode terminal for the piezoelectric vibrating reed via a wiring pattern a, and the pad for the temperature detecting element is electrically connected to the electrode terminal for the temperature detecting element via a wiring pattern B. Wherein, the substrate and the second frame body are usually made of alumina ceramic materials; the first frame body can be made of metal materials or aluminum oxide ceramic materials. The frequency characteristic of the piezoelectric vibrating reed can change along with the change of the environmental temperature, in the application field with high requirements on temperature sensitivity and temperature control precision, the temperature change in the first cavity directly influences the performance of the resonator device, the temperature detection element can detect the temperature change in the first cavity and send information to the control circuit, and the control circuit controls and adjusts the voltage for driving the piezoelectric vibrating reed according to the temperature change, so that the stable signal output of the resonator device is ensured.
In the conventional H-type ceramic package base, the substrate and the second frame are made of alumina ceramic material, and the thermal conductivity of the substrate and the second frame is 18-32W/(m · K), and the cover plate covering the first cavity is made of metal material, such as kovar material, and the thermal conductivity of the cover plate is 70-80W/(m · K), and under the condition that the thermal conductivity of the cover plate is higher, the conduction rate of the heat in the first cavity toward the cover plate side is greater than that toward the second cavity side, so that the temperature detected by the temperature detection element is greatly different from the actual ambient temperature of the piezoelectric vibrating reed, and the temperature detection element cannot monitor the temperature change in the first cavity in real time, and the adjustment of the voltage for driving the piezoelectric vibrating reed by the control circuit has delay, and the stability of the output signal of the resonator device is finally affected. Therefore, there is a need for improvements in ceramic package base materials to increase their thermal conductivity.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a ceramic packaging base with high heat conductivity.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a ceramic package base is mainly composed of alumina, and the ratio of the length of grain boundaries between alumina grains in the base to the length of grain boundaries between all the grains in a unit area is 0.6-0.9 (hereinafter, the length of grain boundaries between alumina grains is referred to as the length of alumina grain boundaries; and the length of grain boundaries between all the grains is referred to as the length of total grain boundaries).
In the present invention, the susceptor contains alumina as a main component, and means that the alumina content in the susceptor is 70% by weight or more.
The present invention can improve thermal conductivity by limiting the ratio of the length of the alumina grain boundary to the total grain boundary length to be in the range of 0.6 to 0.9, because: when the ratio of the length of the alumina crystal boundary in the base to the length of the total crystal boundary is less than 0.6, the aluminum-magnesium spinel and other impure phases have high ratio, and the heat conduction among the alumina crystal grains is reduced; when the ratio of the two is more than 0.9, it means that the ratio of other crystal phases is reduced, that is, the ratio of Si, Mg, Ca, etc. added is reduced, which results in reduced adhesion between alumina and reduced strength of the porcelain.
Further, the difference between D90 and D10 of the alumina grains in the susceptor is 2.24 to 4.48 μm.
The difference value between D90 and D10 of alumina crystal grains in the base is limited to be 2.24-4.48 mu m, so that the existence of abnormally large crystal grains can be reduced, the possibility of crack damage caused by the excessively large crystal grains is reduced, the base is prevented from being cracked due to crack concentration, and the strength of the porcelain body is improved.
When the size of the alumina crystal grains is larger, the sintering temperature can be greatly increased, so that the strength of the porcelain body is reduced; when the size is too small, the heat transfer efficiency is lowered due to the increase of grain boundaries. Furthermore, the average grain diameter of the alumina crystal grains in the base is 2.1-3.5 μm, which is beneficial to improving the strength and the heat conduction efficiency of the alumina base.
In addition, the porosity of the base after sintering also influences the heat conductivity of the ceramic packaging base through experiments, and the heat conductivity of the base is reduced along with the increase of the porosity. According to the invention, the thermal conductivity of the base is further improved by optimizing the proportion of each component in the base formula.
Further, the ceramic packaging base comprises the following components in percentage by weight: al (Al)2O3 88-96%、SiO22.0 to 6.4 percent of magnesium oxide, 0.3 to 2.5 percent of MgO and 0.5 to 4.6 percent of CaO.
The ceramic packaging base of the invention has the following functions of the components:
SiO2MgO and Al2O3Forms viscous flow liquid phase at high temperature, and the liquid phase has strong surface wetting force and small surface tension compared with solid phase, so that the alumina crystal grains are easy to grow graduallyAnd close to reduce the content of pores, the blank forms a more compact stack. Along with the rise of the temperature, the liquid phase is recrystallized, and crystal grains are deposited and grown, so that the blank is further compact, the porosity is reduced, and the thermal conductivity is improved.
Function of MgO:
in the invention, MgO can be added with Al2O3Formation of magnesium aluminate spinel (MgAl) at high temperatures3O4) And in Al2O3The grain boundary forms a nail, the movement rate of the grain boundary is inhibited, pores on the grain boundary are fully eliminated, and the method has a remarkable effect of promoting the densification of the blank. Wherein the MgO content is limited to 0.3 to 2.5 wt%, and if the MgO content is less than 0.3 wt%, Al cannot be effectively used2O3Magnesium aluminate spinel (MgAl) is formed at grain boundary3O4) The difference of the growth rate of the crystal grains is obvious, which shows that the crystal grains grow abnormally, and air holes are not effectively eliminated; if the MgO content is higher than 2.5 wt%, the sintering activation energy of the ceramic is increased, the sintering temperature is raised, and simultaneously the proportion of the grain boundary between non-alumina grains is increased, and the strength of the ceramic is obviously reduced.
The function of CaO:
at the same temperature, SiO2The viscosity of the MgO glass phase is higher, while the addition of 0.5-4.6 wt% CaO leads to a significant reduction in the viscosity of the glass phase and an improvement in the liquid phase relative to Al2O3The infiltration improves the elimination efficiency of the air holes.
Further, the ceramic packaging base also comprises the following components in percentage by weight: cr (chromium) component2O30.5-2.5% and Mo 0.2-1%. Cr (chromium) component2O3Mo and Mo act as pigment in the ceramic, and proper amount of Cr is added2O3The sintering temperature can also be reduced.
The invention also provides a preparation method of the ceramic packaging base, which comprises the following steps:
(1) mixing the raw materials of all the components to obtain a ceramic packaging base material composition;
(2) ball-milling and uniformly mixing the ceramic packaging base material composition, the solvent and the dispersant, and then adding the resin and the plasticizer for uniform mixing to obtain a mixture;
(3) carrying out tape casting on the mixture obtained in the step (2) to prepare a green body;
(4) and (4) punching the green body obtained in the step (3), filling holes through a via hole, laminating, printing metal slurry, and sintering to obtain a ceramic packaging base.
Further, the solvent comprises at least one of toluene, xylene, butanone and isopropanol.
Further, the dispersing agent comprises at least one of stearic acid and span.
Further, the resin comprises at least one of PVB and acrylic resin.
Further, the plasticizer comprises at least one of castor oil, PEG, DBP, DOP.
Compared with the prior art, the invention has the beneficial effects that:
according to the invention, the ratio of the length of the alumina crystal boundary to the length of the total crystal boundary is optimized to improve the heat conductivity coefficient of the ceramic material in the packaging base, so that the conduction rate of heat in the first cavity of the packaging base to the second cavity side is improved, the difference between the temperature detected by the temperature detection element and the actual environment temperature of the piezoelectric vibrating piece is reduced, and the stability of the output signal of the resonator device is ensured.
Detailed Description
To better illustrate the objects, aspects and advantages of the present invention, the present invention will be further described with reference to specific examples. It will be understood by those skilled in the art that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The compositions of the ceramic package bases of examples 1 to 15 and comparative examples 1 to 4 are shown in table 1.
TABLE 1
The method for preparing the ceramic package bases of examples 1 to 15 and comparative examples 1 to 4 includes the steps of:
(1) mixing the raw materials of the components according to the proportion shown in the table 1 to obtain a ceramic packaging base material composition;
(2) ball-milling and uniformly mixing the ceramic packaging base material composition, toluene and stearic acid, and then adding PVB and PEG for uniform mixing to obtain a mixture;
(3) carrying out tape casting on the mixture obtained in the step (2) to prepare a green body;
(4) and (4) punching the green body obtained in the step (3), filling holes through a via hole, laminating, printing metal slurry, and sintering to obtain a ceramic packaging base.
And (3) carrying out performance test on the prepared ceramic packaging base, wherein the test method comprises the following steps:
firstly, measuring the heat conductivity coefficient: after ball milling, the slurry is punched and sheared into slices after casting forming, the slices are sintered into slices with the thickness of 0.2-0.3mm by a kiln, and the heat conductivity coefficient of the porcelain body is measured by adopting a hot plate method; wherein the heat conductivity coefficient is more than or equal to 28W/(m.K) which is up to the standard;
② ceramic strength: laminating the tape-casting film to 3cm thick, cutting into 4 x 55cm cuboids, sintering in a kiln to obtain a test standard sample, and testing three-point bending strength of the porcelain body; wherein, the strength of the porcelain body is more than or equal to 420MPa, which is up to the standard;
testing the grain size and the grain boundary length: after FE-SEM inspection, the grain size and grain boundary length were analyzed using nano measurer software.
The test results of examples 1 to 15 and comparative examples 1 to 4 are shown in Table 2.
TABLE 2
From the results of examples 1 to 15 and comparative examples 1 to 4, it can be seen that the present invention, which defines the ratio of the alumina grain boundary length to the total grain boundary length to be in the range of 0.6 to 0.9, ensures a high thermal conductivity of the ceramic base material.
From example 2 and example 15, it is understood that the average grain size of the alumina crystal grains is slightly smaller, resulting in a slight decrease in the thermal conductivity of the ceramic base; from the results of examples 11 and 14, it is understood that the average grain size of the alumina crystal grains is large, and the strength of the ceramic base is lowered. Therefore, the average grain diameter of the alumina crystal grains in the base is preferably 2.1-3.5 μm, so that the base has higher strength and heat conduction efficiency.
From the results of comparative examples 2 to 4, it can be seen that the ceramic strength is significantly reduced when the difference between D90 and D10 of alumina grains is large, while the ceramic strength is reduced when the difference between D90 and D10 of alumina grains is small, because the grains are too uniform, the packing density is reduced, the ceramic density is not high, and the ceramic strength is reduced, therefore, the difference between D90 and D10 of the alumina grains of the present invention is preferably 2.24 to 4.48 μm.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.