Agcuti-based composite filler metal and brazing method for connecting aln ceramic and cu

Abstract

The application discloses AgCuTi-based composite brazing filler metal and a brazing method for connecting AlN ceramics and Cu, and the AgCuTi-based composite brazing filler metal comprises, in percentage by mass, 1-4% of rare earth oxide and the balance of AgCuTi active brazing filler metal; the CTE of the rare earth oxide is 5*10 ‑6 K ‑1 ~12*10 ‑6 K ‑1 The method for brazing and connecting AlN ceramics and Cu by the AgCuTi-based composite brazing filler metal comprises the following steps: assembling a to-be-brazed assembly into a sandwich structure according to Cu / AgCuTi-based composite brazing filler metal / AlN ceramics; and brazing and connecting the to-be-brazed assembly under vacuum conditions; the brazing temperature is 850-900 DEG C, and the holding time is 10-30 min. The AgCuTi-based composite brazing filler metal has the rare earth oxide with the CTE of 5*10 ‑6 K ‑1 ~12*10 ‑6 K ‑1 as the reinforcing particles, can effectively improve the joint strength of the AlN ceramic and Cu brazed joint, and obtains a high-strength brazed joint.

Description

Technical Field

[0001] This invention belongs to the field of brazing technology, and particularly relates to an AgCuTi-based composite brazing filler metal and a brazing method for connecting AlN ceramics and Cu. Background Technology

[0002] AlN ceramics have a thermal conductivity seven times that of Al2O3 ceramics, and are non-toxic, harmless, and have good thermal stability, making them an indispensable material in fields such as heat dissipation in high-power integrated circuit substrate packaging. Metallic Cu possesses excellent thermal conductivity. With the frequent occurrence of poor heat dissipation problems in high-power electronic packaging devices, researchers in this field have attempted to attach a Cu layer to an AlN ceramic substrate. This Cu layer can then transfer the heat generated by the chip in the electronic packaging device to solve the packaging failure problem of power devices.

[0003] Currently, brazing filler metals used for joining AlN ceramics and pure Cu are mainly AgCuTi and AgCuInTi systems. Adding the active metal element Ti to the filler metal improves the wettability of the liquid filler metal on the ceramic surface, thereby promoting the connection between the ceramic and the metal. However, due to the significant differences in the physicochemical properties of metal and ceramic materials, the residual stress during ceramic-metal brazing is high. This additional residual stress adversely affects the connection strength of the brazed joint, causing crack initiation or even complete cracking of the ceramic under relatively small external loads.

[0004] Therefore, there is an urgent need to develop a new type of brazing filler metal for relieving residual stress at the joint and exhibiting excellent high-temperature performance in brazing AlN ceramics and Cu. Summary of the Invention

[0005] Based on the above-mentioned technical problems, the purpose of this invention is to provide an AgCuTi-based composite solder and a brazing method for connecting AlN ceramics and Cu, with a CTE of 5×10 -6 K -1 ~12×10 -6 K -1 Rare earth oxides, used as reinforcing particles, can effectively improve the joint strength of AlN ceramic and Cu brazed joints, resulting in high-strength brazed joints.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] An AgCuTi-based composite solder comprises, by mass percentage: 1-4% rare earth oxides, with the balance being AgCuTi active solder; the rare earth oxides have a CTE (coefficient of thermal expansion) of 5 × 10⁻⁶. -6 K -1 ~12×10 -6 K -1 .

[0008] Preferably, the alloy comprises, by mass percentage: 3% rare earth oxides, with the balance being AgCuTi active solder.

[0009] Preferably, the rare earth oxide is selected from one or two of ZrO2 and Y2O3.

[0010] Preferably, the mass fraction of Ti in the AgCuTi active solder is ≤4.5%, and more preferably in the range of 1.5% to 4.5%, for example, the mass fraction of Ti in the AgCuTi active solder is 1.5%, 1.8%, 2%, 3%, 4.5%, etc. The mass percentage of Ag in both Ag and Cu is 70% to 75%.

[0011] Preferably, the AgCuTi-based composite solder is obtained by ball milling and mixing AgCuTi active solder powder and rare earth oxide powder as raw materials.

[0012] The present invention also provides a brazing method for connecting AlN ceramics and Cu using the aforementioned AgCuTi-based composite brazing filler metal, comprising the following steps: the AgCuTi-based composite brazing filler metal is bonded to the surface of the AlN ceramic to be brazed and the surface of the Cu base material to be brazed using adhesive, thereby obtaining a sandwich structure assembly to be brazed consisting of Cu base material / AgCuTi-based composite brazing filler metal / AlN ceramic; the assembly to be brazed is then brazed under vacuum conditions at a brazing temperature of 850-900℃ and a brazing holding time of 10-30 min.

[0013] Preferably, the brazing temperature is 850°C and the holding time is 10 minutes.

[0014] Preferably, during brazing, the temperature is raised to the brazing temperature using a programmed heating method, then held at the brazing temperature, and finally cooled down to room temperature using a programmed cooling method.

[0015] Preferably, the programmed heating process involves raising the temperature from room temperature to the brazing temperature at a heating rate of 5~15℃ / min, and the programmed cooling process involves lowering the temperature to 250~350℃ at a cooling rate of 3~8℃ / min, followed by natural cooling to room temperature with the furnace.

[0016] Preferably, the vacuum degree of the vacuum condition is ≤5×10⁻⁶. -3 Pa, the assembled components to be brazed are kept in close contact with each other by a molybdenum pressure block, and a pressure of 0.05-0.1 MPa is applied.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1. This invention provides an AgCuTi-based composite solder, which, compared to existing AgCuTi-based active solders, adds only a certain amount of [specific component] and has a CTE of 5 × 10 [units]. -6 K -1 ~12×10 -6 K -1 Rare earth oxides. Using the AgCuTi-based composite brazing filler metal for brazing AlN ceramics to Cu can produce high-strength brazed joints, improving the current problems of high residual stress and low connection strength in AlN ceramic copper-clad joints.

[0019] 2. By further limiting the rare earth oxide content in the AgCuTi-based composite brazing filler metal, this invention achieves brazed joints with a shear strength as high as 274.7 MPa. This shear strength is close to that of the base material AlN ceramic and far exceeds the level of existing technologies, achieving unexpected technical results.

[0020] 3. This invention also provides a novel strengthening mechanism for AgCuTi-based composite solders:

[0021] (1) The CTE of rare earth oxides is between that of AgCuTi active solder and AlN ceramics. Furthermore, rare earth oxides fill the solder gap in the form of solid particles, which can have a positive effect on reducing the overall thermal expansion coefficient of the solder.

[0022] (2) During the brazing process, the AgCuTi active brazing filler melts at the brazing temperature, while the stable rare earth oxides neither react with the AgCuTi active brazing filler nor decompose. On the one hand, this helps to ensure the content of active Ti elements participating in the interfacial reaction in the brazing joint structure. The Ti in the AgCuTi active brazing filler reacts with the AlN ceramic to generate a TiN reaction layer with a thickness of about 1 μm, thereby creating a reliable connection between the base materials. On the other hand, the rare earth oxides, as reinforcing particles, further improve the joint strength.

[0023] (3) The weld obtained by brazing mainly contains AgCu eutectic phase (Ag(s,s), Cu(s,s)), CuTi, rare earth oxides and TiN phase. The uniform dispersion of rare earth oxides in the brazing seam helps to refine the AgCu eutectic phase in the brazing filler metal. The refined AgCu eutectic matrix is ​​beneficial to improving the mechanical properties of the brazed joint of AlN ceramic and Cu. Attached Figure Description

[0024] Figure 1 This is a high-magnification SEM image of the brazed joint obtained in Embodiment 3 of the present invention;

[0025] Figure 2SEM images of brazed joints obtained in Examples 1-4 and Comparative Example 1 of the present invention are shown, wherein (a)-(d) correspond to Examples 1-4 respectively; and (e) corresponds to Comparative Example 1.

[0026] Figure 3 This is a SEM image of the brazed joint obtained in Comparative Example 2 of the present invention. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0028] The AgCuTi-based composite solders described in the following embodiments of the present invention are all obtained by ball milling and mixing. Specifically, AgCuTi active solder powder and rare earth oxide powder are weighed according to a certain ratio; the two raw materials are placed in a planetary ball mill and ball-milled for 1 hour to ensure uniform mixing of the powders, then dried, and the AgCuTi-based composite solder is collected. The obtained AgCuTi-based composite solder is a solder powder with a particle size of 5-10 μm. Specifically, the AgCuTi active solder actually uses (AgCu)98Ti2, and the AgCu is Ag72Cu28. That is, the mass percentage of Ti in the AgCuTi active solder is 2%, and the mass percentage of Ag in both Ag and Cu is 72% and Cu is 28%.

[0029] Example 1

[0030] An AgCuTi-based composite solder, by mass percentage, comprises: 1% Y₂O₃, with the balance being AgCuTi active solder; the rare earth oxide Y₂O₃ has a CTE of (8-10) × 10⁻⁶. -6 K -1 .

[0031] The method for brazing AlN ceramic and Cu using AgCuTi-based composite brazing filler metal includes the following steps: AgCuTi-based composite brazing filler metal is bonded to the surface of the AlN ceramic to be brazed and the surface of the Cu base material to be brazed using adhesive, resulting in a sandwich structure assembly of Cu base material / AgCuTi-based composite brazing filler metal / AlN ceramic; the assembly to be brazed is then brazed under vacuum conditions to obtain a brazed joint of AlN ceramic and Cu; the brazing temperature is 850℃ and the holding time is 10min.

[0032] The welding conditions in Example 1 include: (1) controlling the vacuum degree at 2×10 -3Pa, the assembled components to be brazed are kept in close contact with each other by a molybdenum pressure block, and the pressure is 0.05MPa; (2) the temperature is raised to the brazing temperature by a programmed heating method, specifically: the temperature is raised from room temperature to 300℃ at a heating rate of 10℃ / min and held for 10min; then the temperature is raised to the brazing temperature of 850℃ at a rate of 10℃ / min and held for 10min; finally the temperature is lowered to 300℃ at a rate of 6℃ / min and then naturally cooled to room temperature with the furnace; (3) before brazing, the AlN ceramic and Cu surfaces to be brazed are polished step by step with sandpaper until they are free of marks, then ultrasonically cleaned in acetone solution and then taken out, ultrasonically cleaned in alcohol solution, and finally dried to obtain the surface-treated base material; the base material Cu in this embodiment is pure copper with a content of 99.95-99.99%.

[0033] Example 2

[0034] An AgCuTi-based composite solder, by mass percentage, comprises: 2% Y₂O₃, with the balance being AgCuTi active solder; the rare earth oxide Y₂O₃ has a CTE of (8-10) × 10⁻⁶. -6 K -1 .

[0035] In Example 2, the method of brazing AlN ceramic and Cu with AgCuTi-based composite solder is the same as that in Example 1, except that the content of Y2O3 in the AgCuTi-based composite solder is different.

[0036] Example 3

[0037] An AgCuTi-based composite solder, by mass percentage, comprises: 3% Y₂O₃, with the balance being AgCuTi active solder; the rare earth oxide Y₂O₃ has a CTE of (8-10) × 10⁻⁶. -6 K -1 .

[0038] In Example 3, the method of brazing AlN ceramic and Cu with AgCuTi-based composite brazing filler metal is the same as that in Example 1, except that the content of Y2O3 in AgCuTi-based composite brazing filler metal is different.

[0039] Example 4

[0040] An AgCuTi-based composite solder, by mass percentage, comprises: 4% Y₂O₃, with the balance being AgCuTi active solder; the rare earth oxide Y₂O₃ has a CTE of (8-10) × 10⁻⁶. -6 K -1 .

[0041] In Example 4, the method of brazing AlN ceramic and Cu with AgCuTi-based composite brazing filler metal is the same as in Example 1, except that the content of Y2O3 in the AgCuTi-based composite brazing filler metal is different.

[0042] Example 5

[0043] An AgCuTi-based composite solder, by mass percentage, comprises: 3% ZrO2, with the balance being AgCuTi active solder; the rare earth oxide ZrO2 has a CTE of 10.5 × 10⁻⁶. -6 K -1 .

[0044] The method for brazing AlN ceramic and Cu using AgCuTi-based composite brazing filler metal includes the following steps: AgCuTi-based composite brazing filler metal is bonded to the surface of the AlN ceramic to be brazed and the surface of the Cu base material to be brazed using adhesive, resulting in a sandwich structure assembly of Cu base material / AgCuTi-based composite brazing filler metal / AlN ceramic; the assembly to be brazed is then brazed under vacuum conditions to obtain a brazed joint of AlN ceramic and Cu; the brazing temperature is 850℃ and the holding time is 10min.

[0045] The welding conditions in Example 5 include: (1) controlling the vacuum degree at 3×10 -3 Pa, the assembled components to be brazed are kept in close contact with each other by a molybdenum pressure block, and the pressure is 0.05 MPa; (2) the temperature is raised to the brazing temperature by a programmed heating method, and the specific method is the same as in Example 1; (3) before brazing, the AlN ceramic and Cu surfaces to be brazed are polished step by step with sandpaper until they are free of marks, and then ultrasonically cleaned in acetone solution, and then taken out and ultrasonically cleaned in alcohol solution, and finally dried to obtain the surface-treated base material; the base material Cu in this example is pure copper with a content of 99.95-99.99%.

[0046] Comparative Example 1

[0047] An AgCuTi-based composite solder, by mass percentage, comprises: 5% Y₂O₃, with the balance being AgCuTi active solder; the rare earth oxide Y₂O₃ has a CTE of (8-10) × 10⁻⁶. -6 K -1 .

[0048] The method for brazing AlN ceramics and Cu with the AgCuTi-based composite brazing filler metal is the same as in Example 1, except that the content of Y2O3 in the AgCuTi-based composite brazing filler metal is different.

[0049] Comparative Example 2

[0050] A method for brazing AlN ceramics to Cu using AgCuTi active solder is disclosed. The method and control parameters are the same as in Example 1, except that pure AgCuTi active solder powder is used instead of the AgCuTi-based composite solder powder in Example 1. Specifically, the AgCuTi active solder used is (AgCu)98Ti2, and AgCu is Ag72Cu28.

[0051] Performance testing:

[0052] 1. The brazed joints of AlN ceramics and Cu obtained in Examples 1-4 and Comparative Examples 1-2 were tested for shear strength on a universal testing machine. The results are shown in Table 1 below.

[0053]

[0054] As can be seen from the table above, (1) the shear strength of the brazed joints prepared by the present invention is better than that of Comparative Example 2; (2) as the content of rare earth oxides increases, the shear strength of the brazed joints first increases and then decreases. Among them, when the rare earth oxide is Y2O3 and the content is 3%, the shear strength of the brazed joints is as high as 274.7 MPa, which is much higher than that of other embodiments and the prior art.

[0055] 2. The brazed joints obtained in the examples and comparative examples were examined by scanning electron microscopy. The low-magnification and high-magnification SEM images of Examples 1-4 and Comparative Example 1 are shown below. Figure 2 As shown in (a)-(e); the low-magnification and high-magnification SEM images of the brazed joints obtained in Comparative Example 2 are shown in Figure 2. Figure 3 As shown.

[0056] It can be seen that the weld interface prepared by this invention does not exhibit phenomena such as pores or cracks, and the microstructure is uniform. Combined with EDS and XRD detection, it was determined that the joint includes AgCu eutectic phase (Ag(s,s), Cu(s,s)), CuTi, Y2O3 and TiN phases.

[0057] Based on the above data and analysis of the microstructure, it can be inferred that: (1) When the content of rare earth oxides is too low, it is not enough to reduce the CTE of the entire brazing filler layer, so the effect of relieving residual stress is not obvious, and the shear strength is only slightly improved; (2) When the content of rare earth oxides exceeds a certain value, although it can reduce the CTE of the entire brazing filler layer, it also makes the wettability of the brazing filler worse, and the bonding degree between the brazing filler and the base material decreases, which in turn leads to a decrease in shear strength.

[0058] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A brazing method for joining AlN ceramics and Cu, characterized in that, Applying AgCuTi-based composite brazing filler metal to at least one of the AlN ceramic surface and the Cu base material surface to be brazed, and then brazing, includes the following steps: the AgCuTi-based composite brazing filler metal is bonded firmly between the AlN ceramic surface and the Cu base material surface to be brazed with adhesive, resulting in a sandwich structure assembly of Cu base material / AgCuTi-based composite brazing filler metal / AlN ceramic; the assembly to be brazed is then brazed under vacuum conditions at a brazing temperature of 850-900℃ and a brazing holding time of 10-30 min. During the brazing connection, the temperature is raised to the brazing temperature using a programmed heating method, then held at the brazing temperature, and finally cooled to room temperature using a programmed cooling method. The programmed heating process raises the temperature from room temperature to the brazing temperature at a heating rate of 5-15℃ / min, and the programmed cooling process lowers the temperature to 250-350℃ at a cooling rate of 3-8℃ / min, and then allows the furnace to cool naturally to room temperature. The AgCuTi-based composite solder comprises, by mass percentage: 3% rare earth oxides, with the balance being AgCuTi active solder; the rare earth oxides are selected from Y₂O₃, and the CTE of the rare earth oxides is (8-10) × 10⁻⁶. -6 K -1 The mass fraction of Ti in AgCuTi active solder is ≤4.5%.

2. The brazing method for connecting AlN ceramic and Cu as described in claim 1, characterized in that, The mass fraction of Ti in AgCuTi active solder is in the range of 1.5% to 4.5%; the mass percentage of Ag in both Ag and Cu is 70% to 75%.

3. The brazing method for connecting AlN ceramic and Cu as described in claim 1, characterized in that, The AgCuTi-based composite solder is obtained by ball milling and mixing AgCuTi active solder powder and rare earth oxide powder.

4. The brazing method for connecting AlN ceramic and Cu as described in claim 1, characterized in that, The vacuum level of the vacuum condition is ≤5×10⁻⁶. -3 Pa, the assembled components to be brazed are kept in close contact with each other by a molybdenum pressure block, and a pressure of 0.05-0.1 MPa is applied.

Images