A calcium aluminum borate microcrystalline glass material with low thermal expansion coefficient and its preparation method

Abstract

This invention belongs to the field of electronic ceramics and their manufacturing, and relates to a calcium aluminum borate microcrystalline glass material with a low coefficient of thermal expansion and its preparation method. This invention uses CaCO3, Al2O3, and H3BO3 as raw materials, obtaining a glass material through high-temperature melting and water quenching, followed by granulation and sintering to obtain a microcrystalline glass material with CaAl3BO7 as the main crystalline phase. The glass material, after melting and holding at 1300℃ for 1 hour and water quenching, and then sintering at 850–950℃, exhibits excellent dielectric properties and low thermal expansion characteristics: the dielectric constant is between 7.41 and 9.14; the sample sintered at 925℃ with a 10wt.% excess of H3BO3 has a Q×f value as high as 28561 GHz (@15.725 GHz), a flexural strength of 140 MPa, and a coefficient of thermal expansion of 3.08 × 10⁻⁶. ‑6 With a coefficient of thermal expansion of 1 / K, which is similar to that of silicon semiconductor materials, it can meet the thermal-electric-mechanical performance requirements of microwave dielectric ceramic substrate materials, and has the potential to be used as a packaging substrate material.

Description

Technical Field

[0001] This invention belongs to the field of electronic ceramics, specifically relating to a microcrystalline glass material with low thermal expansion coefficient and low dielectric constant and its preparation method. Background Technology

[0002] Against the backdrop of 5G / 6G communication technology evolving towards higher frequency bands and chips and modules developing towards high-density integration, microwave dielectric materials face stringent challenges in multi-dimensional performance optimization. To meet the operational requirements of modern communication systems in complex environments and wide temperature ranges, materials must simultaneously achieve low dielectric constants (ε). r The synergistic control of low dielectric loss (tanδ) and low coefficient of thermal expansion (CTE) is achieved; among which, the CTE parameter plays a decisive role in achieving thermal compatibility between microwave dielectric substrates and semiconductor devices; taking single-crystal silicon, a typical semiconductor material, as an example, its CTE value at room temperature is 3.0~3.5×10 -6 / K, the microwave dielectric material that is compatible with it needs to control the CTE to a similar level so that the interface thermal stress can be effectively relieved through the thermal expansion matching mechanism within the application temperature range. When there is an excessively large CTE difference between materials, the thermal stress caused by temperature changes may lead to failure problems such as bonding interface peeling and chip cracking, which in turn affects the long-term reliability of the device.

[0003] From the perspective of dielectric performance mechanism analysis, low dielectric constant materials can significantly reduce the distributed capacitance per unit length of transmission lines, thereby effectively reducing signal transmission delay and dielectric loss. Under the action of high-frequency electric fields, low dielectric materials have shorter polarization relaxation times, enabling faster charge response and thus improving signal integrity. For communication devices applied in the millimeter-wave band (>30GHz), such as 5G base station array antennas and vehicle-mounted millimeter-wave radar, they are highly sensitive to dielectric loss and temperature stability. Although traditional polymer-based materials (such as polytetrafluoroethylene and epoxy resin) have excellent processability and low dielectric loss, their coefficient of thermal expansion is much higher than that of semiconductor materials, making them prone to thermal mismatch and device failure.

[0004] Recent studies have shown that calcium aluminates are promising microwave dielectric ceramic materials with a dielectric constant of around 8, low thermal expansion, and excellent thermal properties. However, their sintering temperature of around 1400–1500 °C greatly limits their application in the field of electronic ceramic materials. Borate materials with low melting points are widely used in low-temperature and ultra-low-temperature sintering and also have low dielectric constants. Adding boric acid to the CaO-Al₂O₃ (CA) system to form the CaO-Al₂O₃-B₂O₃ (CAB) ternary system can reduce the sintering temperature to a certain extent and achieve a combination of properties. For example, Chinese invention patent (application number CN202011072559.7) discloses the preparation and synthesis of a calcium aluminate with the chemical formula CaAl₂O₃ by solid-state sintering. 2x The material is B2O7 (x=0.25~1); the main crystalline phase of this material is CaAl2B2O7, the sintering temperature is 930℃~1040℃, and it has a dielectric constant of 4~6 and a loss as low as 2.14×10⁻⁶. -4 With a frequency temperature coefficient of -20 to -30 ppm / ℃, it is a typical low-dielectric, low-loss ceramic material. Meanwhile, Chinese invention patents (application numbers CN202011075136.0 and 202210391924.3) disclose microcrystalline glass materials with CaAl2B2O7 as the main crystalline phase, meeting the process temperature requirements for low-temperature co-fired ceramics (LTCC); however, the coefficient of thermal expansion of the CaAl2B2O7 material system is 7.32 × 10⁻⁶. -6 The coefficient of thermal expansion (C / K) is still higher than that of monocrystalline silicon, posing a risk of thermal mismatch and hindering the application and promotion of this material. Summary of the Invention

[0005] To address the aforementioned problems and shortcomings, the present invention aims to provide a novel calcium aluminum borate microcrystalline glass material with a low coefficient of thermal expansion and its preparation method.

[0006] The raw material composition is CaCO3, Al2O3, and H3BO3, with the general chemical formula CaAl3BO7-xH3BO3, where 5wt.% ≤ x ≤ 15wt.%. After melting, water quenching, and ball milling, glass powder is obtained. The glass powder is granulated and sintered at 850–950℃ to obtain samples with dielectric constants between 7.41 and 9.14. The molar ratio of Ca:Al:B is 1:3:1, with an additional 10wt.% H3BO3 added. Samples sintered at 925℃ achieve a Q×f value of up to 28561 GHz (@15.725 GHz) and a coefficient of thermal expansion of 3.08 × 10⁻⁶. -6 / K.

[0007] The preparation method of the above-mentioned microwave dielectric ceramic is as follows:

[0008] Step 1: Weigh out three high-purity raw materials, CaCO3, Al2O3, and H3BO3, according to the molar ratio of Ca:Al:B = 1:3:1. Since H3BO3 has a low melting point and is easily lost through volatilization during sintering, it is necessary to weigh out an additional 5 to 15 wt.%.

[0009] Step 2: Load the prepared powder into a nylon ball mill jar and ball mill with deionized water for 4-5 hours. The mass ratio of powder, zirconium balls and deionized water is about 1:5:2 to 1:5:3. Dry the ball-milled slurry in an oven at 110°C for 10 hours.

[0010] Step 3: After sieving through an 80-mesh sieve, place the glass melt into a crucible and heat it to 1250℃~1350℃ at a heating rate of 3℃ / min, and hold it at that temperature for 1 hour to obtain the glass melt.

[0011] Step 4: Remove the glass melt from Step 3 at high temperature and pour it into deionized water for rapid cooling to obtain glass slag. The glass slag is ball-milled for 1-2 hours, dried in an oven at 110°C for 10 hours, then granulated using a 10wt.% PVA solution as a binder, and pressed into shape at 15 MPa.

[0012] Step 5: After molding, the sample is first heated to 650℃ at a heating rate of 3℃ / min and held at that temperature for 2 hours to remove the adhesive. Then, the temperature is raised to 850-950℃ and sintered in air atmosphere for 4 hours.

[0013] Based on the above methods, calcium aluminum boron microcrystalline glass materials were obtained, with CaAl3BO7 as the main crystalline phase and a sintering temperature of 850℃~950℃. The production process is simple, and the material has the characteristics of low dielectric constant, low dielectric loss and low coefficient of thermal expansion, which can be applied to electronic packaging substrate materials. Attached Figure Description

[0014] Figure 1 This corresponds to the XRD pattern after sintering in Example 9;

[0015] Figure 2 This is a comparison chart of the thermal expansion coefficient test results of the corresponding Example 9 and the CaAl2B2O7 system;

[0016] Figure 3 These are surface SEM test results corresponding to Examples 6, 7, 8, 9, and 10. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0018] The material of this invention is mainly composed of CaAl3BO7, Al2O3 and Ca2B2O5, and is obtained through high-temperature melting, water quenching, molding and sintering processes.

[0019] The raw materials for preparing this calcium aluminum borate material are CaCO3 (99.9%), Al2O3 (99.9%), and H3BO3 (99.9%). Depending on the amount of boric acid added and the sintering temperature, the present invention provides the following embodiments, and the specific preparation steps are as follows:

[0020] Examples 1-5: CaCO3, Al2O3, and 5% excess H3BO3 were weighed according to the molar ratio of Ca:Al:B = 1:3:1; the raw materials were mixed and ball-milled for 4-5 hours (powder:zirconium balls:water = 1:5:2-3), dried at 110℃ for 10 hours; after passing through an 80-mesh sieve, the mixture was melted in a crucible at 3℃ / min to 1300℃ for 1 hour; the water-quenched glass slag was ball-milled again for 1-2 hours, dried, granulated with 10wt.% PVA binder, and pressed into shape at 15MPa; finally, the mixture was first heated to 650℃ at 3℃ / min to remove the binder for 2 hours, and then sintered in air at 850, 875, 900, 925, and 950℃ for 4 hours respectively.

[0021] Examples 6-10: The difference from Examples 1-5 is that 10% of H3BO3 is added. The other preparation steps are basically the same as those in Examples 1-5. The sintering temperatures corresponding to Examples 6, 7, 8, 9, and 10 are 850, 875, 900, 925, and 950℃, respectively.

[0022] Examples 11-15: The difference from Examples 1-5 is that the amount of H3BO3 added is 15%. The other preparation steps are basically the same as those in Examples 1-5. The sintering temperatures corresponding to Examples 11, 12, 13, 14 and 15 are 850, 875, 900, 925 and 950℃, respectively.

[0023] The microwave dielectric properties of the above fifteen embodiments were tested using a vector network analyzer, and the results are shown in Table 1.

[0024]

[0025] As can be seen from the examples in Table 1, the dielectric constant fluctuates between 7.41 and 9.14 as the amount of boric acid added and the sintering temperature change. The dielectric constant values ​​of all examples are in the low dielectric range. The example with an additional 10% H3BO3 has the highest Q×f value of 28561 GHz (@15.725 GHz).

[0026] Temperature stability, coefficient of thermal expansion and bending strength were tested on Examples 6-10, which had better average dielectric properties. The results are shown in Table 2.

[0027]

[0028] The temperature coefficients of the resonant frequencies of Examples 6-10 range from -13 to -25.63, exhibiting better temperature stability compared to the CaAl₂B₂O₇ system. The coefficients of thermal expansion range from 3.08 to 5.43 × 10⁻⁶. -6 The range of / K is approximately the same as the coefficient of thermal expansion of silicon semiconductor materials. The optimal bending strength of the sample is 140 MPa, which meets the application requirements. The microcrystalline glass material corresponding to Example 9 has the characteristics of low dielectric constant, low dielectric loss, and low coefficient of thermal expansion, and has good application prospects in packaging substrate materials.

Claims

1. A calcium aluminum borate microcrystalline glass material with a low coefficient of thermal expansion, characterized in that: The raw materials consist of CaCO3, Al2O3, and H3BO3, with the general chemical formula CaAl3BO7-xH3BO3, where 5wt.%≤x≤15wt.%. After batching the raw materials according to the general chemical formula, the mixture is melted, water-quenched, and sintered to obtain a microcrystalline glass material. The melting temperature is 1250–1350℃, the sintering temperature is 850–925℃, the main crystalline phase is CaAl3BO7, the dielectric constant is 7.41–9.14, the Q×f value is 6915–28561 GHz, and the coefficient of thermal expansion is 3.08–5.43×10⁻⁶. -6 K -1 Its flexural strength is 118–140 MPa.

2. The method for preparing the low thermal expansion coefficient calcium aluminum borate microcrystalline glass material according to claim 1, characterized in that, Includes the following steps: Step 1: Weigh the raw materials according to the molar ratio of Ca:Al:B = 1:3:1: CaCO3, Al2O3 and H3BO3, of which an additional 5-15 wt.% of H3BO3 needs to be weighed to compensate for sintering loss; Step 2: Transfer the weighed powder to a nylon ball mill jar. The mass ratio of powder, zirconium balls and water should be controlled at 1:5:2 to 1:5:

3. After ball milling for 4 to 5 hours, dry for 10 hours. Step 3: Sieve the dried powder through a sieve, put it into a crucible, heat it to 1250℃~1350℃ at a heating rate of 3℃ / min, and hold it at that temperature for 1 hour to complete the preparation of glass melt; Step 4: Remove the glass melt at high temperature and quench it with water to obtain glass slag, then ball mill it again for 1-2 hours, and then dry it at 110°C for 10 hours; use a 10wt.% PVA solution as a binder for granulation, and press it into shape under 15MPa pressure; Step 5: Heat the molded sample to 650℃ at 3℃ / min and hold for 2 hours to remove the adhesive. Then continue to heat to 850~950℃ for sintering and hold for 4 hours to obtain a microcrystalline glass material with a low coefficient of thermal expansion.

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