阅读说明：本技术 一种高可靠性氮化硅覆铜陶瓷基板的铜瓷界面结构及其制备方法 (Copper-ceramic interface structure of high-reliability silicon nitride copper-clad ceramic substrate and preparation method thereof ) 是由 王斌 贺贤汉 郭建岳 张恩荣 马敬伟 孙泉 于 2020-03-03 设计创作，主要内容包括：本发明公开了一种高可靠性氮化硅覆铜陶瓷基板的铜瓷界面结构,自上而下分别为铜,连接层,反应层,氮化硅陶瓷,反应层,连接层和铜；所述反应层是活性金属元素与氮化硅反应形成的活性金属的氮化物,用于实现焊料与氮化硅陶瓷和铜的浸润及连接；所述连接层为连接铜与氮化硅陶瓷的应力缓冲层,所述应力缓冲层为铜与活性金属元素的铜合金层；通过对焊接界面的优化设计及使用不含Ag焊片,可以有效提高焊接层的均匀性,降低铜-瓷界面之间的残余应力,从而提高铜瓷界面的结合力,同时减少环境污染的风险。(The invention discloses a copper-ceramic interface structure of a high-reliability silicon nitride copper-coated ceramic substrate, which comprises copper, a connecting layer, a reaction layer, silicon nitride ceramic, the reaction layer, the connecting layer and the copper from top to bottom; the reaction layer is an active metal nitride formed by the reaction of an active metal element and silicon nitride and is used for realizing the infiltration and connection of the solder, the silicon nitride ceramic and the copper; the connecting layer is a stress buffer layer for connecting copper and silicon nitride ceramics, and the stress buffer layer is a copper alloy layer of copper and active metal elements; through the optimized design of the welding interface and the use of the welding piece without Ag, the uniformity of the welding layer can be effectively improved, and the residual stress between the copper and the ceramic interface is reduced, so that the binding force of the copper and ceramic interface is improved, and the risk of environmental pollution is reduced.)

1. The utility model provides a high reliability silicon nitride covers copper ceramic interface structure of copper ceramic base plate which characterized in that: copper, a connecting layer, a reaction layer, silicon nitride ceramics, a reaction layer, a connecting layer and copper are respectively arranged from top to bottom;

the reaction layer is an active metal nitride formed by the reaction of an active metal element and silicon nitride and is used for realizing the infiltration and connection of the solder, the silicon nitride ceramic and the copper; the connecting layer is a stress buffer layer for connecting copper and silicon nitride ceramics, and the stress buffer layer is a copper alloy layer containing copper and active metal elements.

2. The copper-ceramic interface structure of the high-reliability silicon nitride-coated copper ceramic substrate according to claim 1, wherein: the active metal element is one or the combination of more than two of Ti, Zr, Hf, Cr, V, Si and Al.

3. The copper-ceramic interface structure of the high-reliability silicon nitride-coated copper ceramic substrate according to claim 1, wherein: the total content of active metal elements in the copper alloy layer is between 3 and 40 weight percent, the content of copper elements is between 50 and 90 weight percent, and the content of nitrogen elements is between 2 and 10 weight percent, wherein nitrogen is nitrogen elements formed in the reaction process.

4. The copper-ceramic interface structure of the high-reliability silicon nitride-coated copper ceramic substrate according to claim 1, wherein: the nitride thickness of the reaction layer is 0.05-3 μm.

5. The copper-ceramic interface structure of the high-reliability silicon nitride-coated copper ceramic substrate according to claim 1, wherein: the thickness of the connecting layer is 2-50 μm.

6. The copper-ceramic interface structure of the high-reliability silicon nitride-coated copper ceramic substrate according to claim 1, wherein: the coefficient of thermal expansion of the tie layer is 6-12 ppm/DEG C.

7. A method for preparing the copper-ceramic interface structure of the high-reliability silicon nitride-coated copper ceramic substrate according to any one of claims 1 to 6, wherein the method comprises the following steps: the method comprises the following specific steps:

step one, selecting a prefabricated soldering lug; the soldering lug is a copper alloy containing active metal elements, and the copper alloy is an Ag-free alloy; the Ag-free copper alloy is characterized in that the copper alloy does not use silver as a main alloy element, and the content of Ag is less than 0.5%;

placing the soldering lug selected in the step one between copper and silicon nitride ceramic, clamping the soldering lug into a copper-soldering lug-silicon nitride ceramic-soldering lug-copper laminated structure, placing the laminated structure in a tool clamp, and applying uniform pressure on the copper surface of the laminated structure;

and step three, placing the laminated structure in the step two in a vacuum brazing furnace and brazing the laminated structure into the silicon nitride copper-clad ceramic substrate.

8. The method of claim 7, wherein: the total content of active metal elements in the soldering lug is between 3 and 40 weight percent, and the rest elements are copper.

9. The method of claim 7, wherein: the thickness of the soldering lug is 10-50 microns.

10. The method of claim 7, wherein: and in the third step, the brazing in the vacuum brazing furnace is brazing in an atmospheric pressure sintering furnace under the protection of argon atmosphere.

Technical Field

The invention belongs to the field of power semiconductor manufacturing, and particularly relates to a copper-ceramic interface design method of a high-reliability silicon nitride copper-clad ceramic substrate, which is particularly suitable for manufacturing copper-clad ceramic substrates of semiconductor refrigerators, power semiconductors and the like.

Background

The silicon nitride copper-clad ceramic substrate is a copper-ceramic composite material formed by silicon nitride ceramic and copper through an active brazing process, and is a new basic material for a high-power electronic circuit structure technology and an interconnection technology. The reliability of the copper-clad ceramic substrate is closely related to the performance of the ceramic material. Usually, 96% alumina ceramic, aluminum nitride ceramic or zirconia toughened alumina ceramic is mostly adopted as the ceramic material, but the bending strength and fracture toughness of the ceramic are low, so that the reliability of the copper-clad ceramic substrate is influenced. The silicon nitride ceramic has excellent mechanical property and high heat conductivity coefficient. The copper-clad ceramic substrate made of the silicon nitride ceramic has excellent reliability, and the service life of the power electronic module can be prolonged by more than 10 times.

The key technology for producing the silicon nitride copper-clad ceramic substrate is to obtain a copper-ceramic connection with high reliability. However, since the difference between the thermal expansion coefficients of silicon nitride ceramic and copper is large, a large residual stress is generated during the bonding process, and excellent bonding performance is not easily obtained. A common method for achieving copper-ceramic connections with silicon nitride copper clad ceramic substrates is to use active metal brazing, where AgCuTi is a common active metal brazing paste. The AgCuTi has wide application and good brazing performance, but the AgCuTi active metal brazing soldering paste applied to the brazing process of the copper-clad ceramic substrate can bring some problems:

1. even welding seams are not easy to obtain by using AgCuTi active metal brazing soldering paste, and the AgCuTi solder is usually coated on the surface of silicon nitride in a slurry mode and is clamped with a copper sheet into a sandwich structure for vacuum brazing. Due to the influence of factors such as the coating thickness of the solder, the flow of the solder after melting, the diffusion of silver in the solder into copper, the crystallization of the solder during solidification, and the like, the copper-ceramic interface brazed by using the AgCuTi slurry has poor uniformity, as shown in FIG. 1. Solder with poor uniformity can affect the subsequent etching process and affect the dimensional accuracy and reliability of the product.

Ag in the AgCuTi solder is used as heavy metal, and the risk of environmental pollution is brought in the subsequent etching process of the copper-clad ceramic substrate.

3. The silver-containing brazing layer can affect the accuracy of circuit etching, and the silver-containing solder can cause incomplete etching and affect the insulating property of the circuit board.

4. The silver has a high electromigration coefficient, and the electromigration of the silver in the AgCuTi solder can influence the reliability of the product under a severe use environment.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides the copper-ceramic interface structure of the high-reliability silicon nitride-coated copper ceramic substrate and the preparation method thereof, and through the optimized design of the welding interface and the use of the welding piece without Ag, the uniformity of the welding layer can be effectively improved, and the residual stress between the copper-ceramic interface is reduced, so that the bonding force of the copper-ceramic interface is improved, and the risk of environmental pollution is reduced.

The technical scheme of the invention is as follows: a copper-ceramic interface structure of a high-reliability silicon nitride copper-clad ceramic substrate comprises copper, a connecting layer, a reaction layer, silicon nitride ceramic, a reaction layer, a connecting layer and copper from top to bottom;

the reaction layer is an active metal nitride formed by the reaction of an active metal element and silicon nitride and is used for realizing the infiltration and connection of the solder, the silicon nitride ceramic and the copper; the connecting layer is a stress buffer layer for connecting copper and silicon nitride ceramics, and the stress buffer layer is a copper alloy layer of copper and active metal elements.

Furthermore, the active metal element is one or the combination of more than two of Ti, Zr, Hf, Cr, V, Si and Al.

Furthermore, the total content of active metal elements in the copper alloy layer is between 3 and 40 weight percent, the content of copper elements is between 50 and 90 weight percent, and the content of nitrogen elements is between 2 and 10 weight percent, wherein nitrogen is nitrogen elements formed in the reaction process.

Further, the nitride thickness of the reaction layer is 0.05-3 μm.

Further, the thickness of the connecting layer is 2-50 μm.

Further, the thermal expansion coefficient of the connecting layer is 6-12 ppm/DEG C.

The invention also provides a method for preparing the copper-ceramic interface structure of the high-reliability silicon nitride-coated copper ceramic substrate, which comprises the following specific steps:

step one, selecting a prefabricated soldering lug; the soldering lug is a copper alloy containing active metal elements, and the copper alloy is an Ag-free alloy; the Ag-free copper alloy is characterized in that the copper alloy does not use silver as a main alloy element, and the content of Ag is less than 0.5%;

placing the soldering lug selected in the step one between copper and silicon nitride ceramic, clamping the soldering lug into a copper-soldering lug-silicon nitride ceramic-soldering lug-copper laminated structure, placing the laminated structure in a tool clamp, and applying uniform pressure on the copper surface of the laminated structure;

and step three, placing the laminated structure in the step two in a vacuum brazing furnace and brazing the laminated structure into the silicon nitride copper-clad ceramic substrate.

Furthermore, the total content of active metal elements in the soldering lug is between 3 and 40 weight percent, and the rest elements are copper.

Further, the thickness of the soldering lug is 10-50 microns.

Further, the brazing in the vacuum brazing furnace in the third step is brazing in an atmosphere of argon in an atmospheric sintering furnace.

The invention has the beneficial effects that:

1. the solder printing process is replaced by the preformed soldering lug pasting process, so that a soldered layer is uniform after soldering, and stress concentration is not easy to form. The main component of the soldering lug is copper alloy containing active metal elements of Ti, Zr, Hf, Cr, V, Si, Al, etc., wherein the active metal elements may be one or several of the above elements, the total content of the active metal elements in the solder is 10-99.9 wt%, and the rest elements are copper.

2. And using the Ag-free brazing soldering lug for connecting the silicon nitride ceramic substrate with copper to manufacture the copper-clad ceramic substrate. Wherein, the fact that no Ag is present means that the soldering lug alloy does not use silver as a main alloy element, and the content of Ag is less than 0.5 percent. The brazing layer of the copper-clad ceramic substrate manufactured by using the silver-free active soldering lug does not contain silver, and the environment pollution caused by heavy metal can be effectively avoided in the etching and processing process.

3. A reaction layer and a connection layer are formed on the copper-ceramic connection interface to a specific thickness. The reaction layer is the nitride of active metal formed by the reaction of active metal elements and silicon nitride, and has the function of realizing the infiltration and connection of solder, silicon nitride ceramic and copper, and effectively reducing the thermal stress generated by the connection of the silicon nitride and the copper. When the thickness of the reaction layer is less than 0.05 μm, the silicon nitride surface is not easy to be soaked by the solder; when the thickness of the reaction layer is more than 4 μm, the reliability of the product may be affected. The copper and the silicon nitride form the following structure under the action of the solder: a nitride of the active metal element is formed adjacent to the silicon nitride ceramic, the layer of the nitride of the active metal having a thickness of 0.05-3 μm. The nitride is a nitride of an active metal element such as Ti, Zr, Hf, Cr, V, Si, Al, etc., and the nitride may be one or more nitrides. A connecting layer exists between the reaction layer and the copper, the connecting layer is used for connecting the copper and the silicon nitride ceramic and is a stress buffer layer which can buffer the stress of the thermal mismatch of the ceramic and the copper. Wherein, the main component of the connecting layer is copper alloy of copper and active elements, such as Ti-Cu alloy, Zr-Cu alloy, Hf-Cu alloy, or copper alloy containing one or more elements of Ti, Zr, Hf, Cr, V, Si, Al, etc. The active metal content in the alloy layer is 3-95 wt%. The thickness of this layer is designed to be 2-50 μm.

4. The coefficient of thermal expansion of the bonding layer is between that of the silicon nitride ceramic and that of copper. The thermal expansion coefficient of the connecting layer is positioned between the copper and the ceramic, so that the thermal stress generated by the connection between the copper and the ceramic can be effectively buffered, and the reliability of the copper-clad ceramic substrate is improved. The coefficient of thermal expansion of the tie layer is 6-12 ppm/DEG C.

Drawings

FIG. 1 shows the poor uniformity of the interface of copper porcelain brazed using AgCuTi slurry in the comparative example.

FIG. 2 is an interface structure for a copper-silicon nitride ceramic connection of a silicon nitride copper clad ceramic substrate.

FIG. 3 shows the interface structure of the copper-silicon nitride ceramic connection of the silicon nitride-coated copper ceramic substrate prepared in example 1.

FIG. 4 shows the interface structure of the copper-silicon nitride ceramic connection of the silicon nitride-coated copper ceramic substrate prepared in example 2.

FIG. 5 shows the interface structure of the copper-silicon nitride ceramic connection of the silicon nitride-coated copper ceramic substrate prepared in example 3.

Detailed Description

The invention is further described below with reference to the accompanying drawings.

Comparative examples

The method comprises the steps of coating AgCuTi active brazing solder on the surface of a silicon nitride ceramic substrate in a printing mode, wherein the thickness of an active brazing solder layer is about 20 microns, clamping copper and silicon nitride ceramic into a laminated structure of copper-active solder-silicon nitride ceramic-active solder-copper, placing the laminated structure in a tool fixture, heating to 830 ℃ at a speed of 10 ℃/min, sintering, wherein the whole sintering time is 10min, the sintering process is carried out under a vacuum condition, and the vacuum degree is 5 × 10^-3And Pa, cooling to room temperature after sintering, and taking out the sample. FIG. 1 shows the poor uniformity of the interface of copper porcelain brazed using AgCuTi slurry in the comparative example.