A copper-aluminum or aluminum-aluminum interconnection structure and method

Abstract

The present invention discloses a copper-aluminum or aluminum-aluminum interconnection structure and method, comprising the following steps: plating a first nickel metal layer on the surface of an aluminum heat sink layer, printing a copper solder paste on the surface of the first nickel metal layer and then preheating to obtain a sintered copper layer, aligning and pre-bonding a substrate on the surface of the sintered copper layer for sintering interconnection, and the substrate is a copper substrate or an aluminum substrate with a second nickel metal layer plated on the surface. The present invention uses a copper solder paste with high thermal conductivity as an interconnection material, which can achieve rapid heat transfer; the stress distribution can be adjusted by patterned printing of the copper solder paste and the porous structure of the sintered copper itself, avoiding the problem of interconnection defects such as warping and deformation during large-area sintering interconnection; nickel plating the surface of the aluminum heat sink and the surface of the aluminum-clad substrate solves the problem of interconnection defects caused by metal interconnection interface reaction and thermal expansion coefficient mismatch; the interconnection structure has high strength and good heat dissipation, and the interconnection method is simple and efficient; at the same time, the material cost is low, and it has good cost-effectiveness.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor manufacturing, and in particular to a copper-aluminum or aluminum-aluminum interconnection structure and method. Background Art

[0002] With the continuous rise of 5G technology, Internet of Things technology, biochip technology, etc., the modern electronics industry has also ushered in rapid development, and the demand for the performance and speed of microelectronic devices is getting higher and higher. Wide bandgap semiconductor materials represented by SiC and GaN have the characteristics of high breakdown voltage, high saturation electron velocity, high thermal conductivity, high electron density, high mobility, and high power tolerance. They are very suitable for making power modules for high frequency, high voltage, high temperature and other applications, and help to improve the efficiency and power density of power electronic systems. At the same time, electronic packaging is also constantly developing towards miniaturization, high performance and high reliability. However, the rapid increase in chip integration will inevitably lead to an increase in its heat generation rate. If the large amount of heat generated by the device during use cannot be dissipated in time, its life and stability will be affected. Therefore, the development of efficient and reliable heat dissipation packaging technology has become a key issue that needs to be urgently solved in the current electronics industry.

[0003] Introducing a heat sink into the packaging structure can quickly remove the heat from the chip carrier and improve the chip's operating stability and efficiency. Copper material has become one of the first choices for electronic packaging heat sink materials due to its excellent thermal conductivity (thermal conductivity is about 400W / (m·K)) and good machinability. However, the density of copper is relatively large (about 8.96g / cm 3 ), copper heat sinks tend to have a high weight. This may become one of the limiting factors in the pursuit of lightweight electronic devices. For example, in the field of new energy vehicles, the weight of electronic equipment is a key factor, especially when pursuing higher fuel efficiency and driving range. Common heat sink alternative materials include aluminum (density is about 2.7g / cm 3 ), although its thermal conductivity is slightly lower, it is light in weight and can meet the heat dissipation needs of electronic devices, while significantly reducing the overall weight, and has good application prospects.

[0004] In order to ensure that the heat on the chip carrier can be quickly introduced into the heat sink material, it is usually necessary to fill the interface between the power chip carrier (such as copper-clad ceramic substrate DBC / DPC and aluminum-clad ceramic substrate DBA) and the heat sink (such as copper heat sink and aluminum heat sink) with thermal interface material to effectively discharge the air between the gaps and accelerate heat conduction by increasing the contact area. Thermal grease, as a thermal interface material for heat dissipation of high-power electronic devices, can directly reduce the air gap between the contact surfaces and have excellent thermal conductivity. However, the thermal conductivity of silicone oil is low, and its thermal conductivity is usually not higher than 10W / (m·K), so it is difficult to prepare thermal grease with high thermal conductivity. Therefore, for scenarios with high thermal conductivity requirements, it is urgent to develop new high thermal conductivity thermal interface interconnect structures and processes.

[0005] Silver solder paste sintering technology is an important connection technology in power semiconductor packaging. Compared with the traditional thermal conductive silicone grease connection method, it has superior thermal conductivity, high temperature resistance and long-term durability. Chen et al. used silver solder paste sintering technology to achieve large-area (30×30mm) connection between DBA and aluminum heat sink. 2 ) interconnection. However, due to the lack of a strong metallurgical bond, after power cycling, interface separation occurs at the interface between the DBA and the sintered silver layer, resulting in reduced reliability.

[0006] In order to meet the high reliability electrical and mechanical performance requirements of power devices, low temperature and large area high reliability interconnection of aluminum-aluminum homogeneous and copper-aluminum heterogeneous metals is still a challenge. 2 ) During the thermal interface interconnection process, the problem of warping caused by uneven thermal stress distribution is very serious. This not only destroys the integrity and stability of the connection structure, but when the warping deformation is serious, it may even lead to connection failure or performance degradation of the entire system.

[0007] Patent CN114918572A provides a transient liquid phase connection method of aluminum-aluminum, which uses Ga or Ga-containing alloys as solder for transient liquid phase connection between single crystal or few crystal pure Al or Al-containing alloy substrates. However, Ga and its alloys are relatively expensive as solders, especially in large-scale production applications, which will increase manufacturing costs. In addition, the solid solution formed by the mutual diffusion of Al and Ga during the welding process is relatively brittle, which reduces the reliability of large-area interconnect joints.

[0008] Patent CN114434039A provides a solder and welding method for low-temperature interconnection of copper and aluminum dissimilar materials, using a pure Sn strip or Sn alloy strip with a thickness of less than 0.5 mm as the intermediate welding substrate, and using a powder molding method to press a uniform and dense zinc layer with a thickness of 0.05-0.5 mm on one or both sides of the intermediate welding substrate. Although this method alleviates the thermal stress problem to a certain extent, the formation of intermetallic compounds that is difficult to avoid during copper-aluminum welding still poses a challenge to the mechanical properties of the welded joint.

[0009] Therefore, developing a large-area interconnect structure and process that can effectively improve aluminum-aluminum homogeneous and copper-aluminum heterogeneous metals remains a key issue that needs to be solved urgently. Summary of the invention

[0010] The technical problem to be solved by the present invention is to provide a copper-aluminum or aluminum-aluminum interconnection structure and method, which adopts copper solder paste with high thermal conductivity as the interconnection material, can realize rapid heat transfer, and has the advantage of low cost; the stress distribution can be adjusted by patterned printing of copper solder paste and the porous structure of sintered copper itself, thereby avoiding the problem of interconnection defects such as warping and deformation during large-area sintering interconnection; and the problem of interconnection defects caused by metal interconnection interface reaction and thermal expansion coefficient mismatch is solved by nickel plating on the surface of aluminum heat sink and aluminum-clad substrate.

[0011] In order to solve the above technical problems, the present invention provides a copper-aluminum or aluminum-aluminum interconnection method, comprising the following steps:

[0012] S1, plating a first nickel metal layer on the surface of the aluminum heat sink layer;

[0013] S2, printing a layer of copper solder paste on the surface of the first nickel metal layer, and then preheating it under a protective atmosphere to obtain a sintered copper layer on the surface of the first nickel metal layer;

[0014] S3, aligning and pre-bonding the substrate on the surface of the sintered copper layer, and then sintering and interconnecting under a protective atmosphere;

[0015] Wherein, the substrate is a copper substrate or an aluminum substrate with a second nickel metal layer plated on the surface, and the second nickel metal layer is bonded to the sintered copper layer.

[0016] The present invention adopts copper solder paste as interconnection material. The copper solder paste has high thermal conductivity and can quickly transfer the heat of electronic devices to the aluminum heat sink layer and dissipate it through the heat sink, thereby effectively reducing the operating temperature of the electronic devices. The copper solder paste is patterned and printed to form a patterned pore structure in the sintered copper layer. Combined with the porous structure of the sintered copper itself, the stress distribution of large-area interconnection can be effectively adjusted, and the problem of interconnection defects can be improved. A nickel layer is plated on the surface of the aluminum heat sink, and when the substrate is an aluminum-clad substrate, a nickel layer is plated on the surface of the aluminum substrate, thereby solving the problems of interface reaction and thermal expansion coefficient mismatch of metal interconnection, and realizing effective interconnection between the copper-clad substrate (DBC / DPC) and the aluminum heat sink, and between the aluminum-clad substrate (DBA) and the aluminum heat sink. The interconnection structure has sufficient mechanical strength and good heat dissipation performance, the interconnection method is simple, and automated production can be realized with high efficiency. Meanwhile, the copper solder paste and the nickel-plated layer are low in cost and have good cost-effectiveness.

[0017] Furthermore, in S2, the preheating treatment is performed at a temperature of 110-180°C and for a time of 10-60 minutes.

[0018] Furthermore, in S3, the temperature of the sintering interconnection is 160-230° C., the pressure is 10-30 MPa, and the time is 10-30 min.

[0019] Furthermore, in S2, the copper solder paste is patterned printed by a steel mesh to prepare a sintered copper layer with a patterned porous structure, which is convenient for adjusting stress distribution and avoiding interconnection defects.

[0020] Furthermore, in S1, the thickness of the first nickel metal layer is 2-10 μm.

[0021] Furthermore, in S3, the thickness of the second nickel metal layer is 0.3-5 μm.

[0022] Furthermore, the first nickel metal layer is obtained by electroplating, and the second nickel metal layer is obtained by chemical plating.

[0023] Furthermore, the protective atmosphere is nitrogen or argon.

[0024] The second aspect of the present invention provides a copper-aluminum or aluminum-aluminum interconnect structure prepared by the method described in the first aspect.

[0025] Furthermore, it comprises an aluminum heat sink layer, a first nickel metal layer, a sintered copper layer and a substrate layer which are stacked in sequence, wherein the substrate layer is a copper substrate or an aluminum substrate with a second nickel metal layer plated on the surface, and the second nickel metal layer is bonded to the sintered copper layer.

[0026] Beneficial effects of the present invention:

[0027] The present invention adopts copper solder paste as the interconnection material. The copper solder paste has high thermal conductivity and can quickly transfer the heat of the electronic device to the aluminum heat sink layer and dissipate it through the heat sink, effectively reducing the operating temperature of the electronic device.

[0028] The present invention forms a patterned pore structure in the sintered copper layer by patterned printing of copper solder paste, and combined with the porous structure of the sintered copper itself, can effectively adjust the stress distribution of large-area interconnection and improve the problem of interconnection defects.

[0029] The present invention plates a nickel layer on the surface of an aluminum heat sink, and when the substrate is an aluminum-clad substrate, plates a nickel layer on the surface of an aluminum substrate, thereby solving the problems of interface reaction of metal interconnection and mismatch of thermal expansion coefficients, and realizing effective interconnection between a copper-clad substrate (DBC / DPC) and an aluminum heat sink, and between an aluminum-clad substrate (DBA) and an aluminum heat sink.

[0030] The copper-aluminum and aluminum-aluminum interconnection structures of the present invention have sufficient mechanical strength and good heat dissipation performance, and the interconnection method is simple, and automated production can be realized with high efficiency; meanwhile, the copper solder paste and the nickel plating layer have low costs and good cost-effectiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic diagram of the copper-aluminum interconnection structure of the present invention;

[0032] Figure 2 is a schematic diagram of the aluminum-aluminum interconnection structure of the present invention;

[0033] Figure 3 is a schematic diagram of the interconnect structure packaging of the present invention;

[0034] Explanation of the numbers in the figure: 1. Aluminum heat sink layer, 2. First nickel metal layer, 3. Sintered copper layer, 4. Copper substrate layer, 5. Second nickel metal layer, 6. Aluminum substrate, 7. Patterned hole structure, 8. Chip. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0036] like Figure 1-2 As shown, an embodiment of the present invention provides a copper-aluminum or aluminum-aluminum interconnection structure including an aluminum heat sink layer 1, a first nickel metal layer 2, a sintered copper layer 3 and a substrate layer 4 which are sequentially stacked, wherein the substrate layer is a copper substrate 4 or an aluminum substrate 6 with a second nickel metal layer 5 plated on the surface, and the second nickel metal layer 5 is bonded to the sintered copper layer 3.

[0037] Example 1

[0038] This embodiment provides a copper-aluminum interconnection method, comprising the following steps:

[0039] (1) A 5 μm nickel layer is uniformly deposited on the surface of the aluminum heat sink by electroplating.

[0040] (2) Add PEG300 solvent to copper powder, wherein the mass ratio of copper powder to solvent is 89:11, and stir thoroughly to obtain copper solder paste.

[0041] (3) Print the copper solder paste on the nickel-plated aluminum heat sink by screen printing. The printing pattern is as follows: Figure 3 As shown, a patterned hole structure 7 is formed in the sintered copper layer, and then a drying pretreatment is performed in a nitrogen atmosphere at a heating environment of 180° C. for 10 minutes.

[0042] (4) The copper-clad side of the copper-clad substrate (DBC) is attached to the preheated copper solder paste (where the substrate area is 50 mm×60 mm), and then placed in a nitrogen atmosphere, sintered for 30 minutes at a heating environment of 220°C and a pressure of 15 MPa to form an interconnection structure, which can realize the packaging of chip 8, such as Figure 3 shown.

[0043] Example 2

[0044] The difference between this embodiment and embodiment 1 is that: in step (1), the thickness of the nickel plating layer on the surface of the heat sink is 2 μm; in step (3), a drying pretreatment is performed for 60 minutes in a heating environment of 110° C.; the other steps remain unchanged.

[0045] Example 3

[0046] The difference between this embodiment and embodiment 1 is that: in step (1), the thickness of the nickel plating layer on the surface of the aluminum heat sink is 8 μm; in step (3), a drying pretreatment is performed for 20 minutes in a heating environment of 150° C.; the other steps remain unchanged.

[0047] Example 4

[0048] The difference between this embodiment and embodiment 1 is that the thickness of the nickel plating layer on the surface of the aluminum heat sink is 10 μm, and the other steps remain unchanged.

[0049] Example 5

[0050] The difference between this embodiment and embodiment 1 is that the sintering temperature in step (4) is 160° C., the pressure is 30 MPa, and the time is 30 min, while the other steps remain unchanged.

[0051] Example 6

[0052] The difference between this embodiment and embodiment 1 is that the sintering temperature in step (4) is 200° C., the pressure is 20 MPa, and the time is 20 min, while the other steps remain unchanged.

[0053] Example 7

[0054] The difference between this embodiment and embodiment 1 is that the sintering temperature in step (4) is 230° C., the pressure is 10 MPa, and the time is 10 min, while the other steps remain unchanged.

[0055] Example 8

[0056] This embodiment provides an aluminum-aluminum interconnection method, comprising the following steps:

[0057] (1) A 5 μm nickel layer is uniformly deposited on the surface of the aluminum heat sink by electroplating, and a 3 μm nickel layer is plated on the aluminum side of the DBA by chemical plating.

[0058] (2) Add PEG300 solvent to copper powder, wherein the mass ratio of copper powder to solvent is 89:11, and stir thoroughly to obtain copper solder paste.

[0059] (3) Print the copper solder paste on the nickel-plated aluminum heat sink by screen printing. The printing pattern is as follows: Figure 3 As shown, a drying pretreatment was then performed in a nitrogen atmosphere at 160° C. for 15 min.

[0060] (4) The nickel layer side of the nickel-plated DBA substrate was attached to the preheated copper solder paste (where the substrate area was 40 mm×50 mm), and then placed in a nitrogen atmosphere and sintered for 30 minutes at a heating environment of 220°C and a pressure of 15 MPa.

[0061] Example 9

[0062] The difference between this embodiment and embodiment 8 is that the thickness of the nickel-plated layer on the surface of the aluminum-clad substrate is 0.3 μm, and the other steps remain unchanged.

[0063] Example 10

[0064] The difference between this embodiment and embodiment 8 is that the thickness of the nickel-plated layer on the surface of the aluminum-clad substrate is 1.5 μm, and the other steps remain unchanged.

[0065] Embodiment 11

[0066] The difference between this embodiment and embodiment 8 is that the thickness of the nickel-plated layer on the surface of the aluminum-clad substrate is 5 μm, and the other steps remain unchanged.

[0067] Comparative Example 1

[0068] The difference between this comparative example and Example 1 is that the step of plating a nickel layer on the surface of the aluminum heat sink is omitted, and the other steps remain unchanged.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 8 is that the step of plating the nickel layer on the surface of the DBA substrate is omitted, and the other steps remain unchanged.

[0071] Comparative Example 3

[0072] The difference between this comparative example and Example 1 is that the copper solder paste is replaced by silver solder paste, and the other steps remain unchanged.

[0073] Comparative Example 4

[0074] The difference between this comparative example and Example 1 is that the sintering interconnection process is performed at normal pressure, and the other steps remain unchanged.

[0075] Comparative Example 5

[0076] The difference between this comparative example and Example 1 is that the temperature for sintering interconnection is 280° C., and the other steps remain unchanged.

[0077] Test Case

[0078] First, the large-area interconnect structures prepared in the embodiments and comparative examples were cut into 3×3 mm 2 The shear strength of the interconnected joints was tested at room temperature using a Sigma push-pull tester from Xyztec Company at a test speed of 1000 μm / s. The test results are shown in Table 1.

[0079] Group Shear strength(MPa) Example 1 87.16 Example 2 82.48 Example 3 91.37 Example 4 87.52 Example 5 68.49 Example 6 72.19 Example 7 84.58 Example 8 90.22 Example 9 88.54 Example 10 87.18 Embodiment 11 89.42 Comparative Example 1 Interconnection failed Comparative Example 2 Interconnection failed Comparative Example 3 25.37 Comparative Example 4 Interconnection failed Comparative Example 5 50.19

[0080] It can be seen from Table 1 that the aluminum heat sink package interconnection structures prepared by Examples 1-11 of the method of the present invention form very reliable connections and can meet the use requirements. Among them, the shear strength of the copper-aluminum interconnection structure of Example 3 is as high as 91.37 MPa, and the shear strength of the aluminum-aluminum interconnection structure of Example 8 is as high as 90.22 MPa.

[0081] In Comparative Examples 1 and 2, the lack of nickel plating makes it impossible to achieve sintering interconnection between copper solder paste and aluminum heat sink, or copper solder paste and aluminum substrate, because there is a significant difference in the CTE of copper and aluminum, and copper and aluminum will also produce interface reactions to form some brittle phases of intermetallic compounds, which eventually lead to connection failure. In Comparative Example 3, the shear strength of the interconnection structure is only 25.37MPa, and the shear strength of the silver solder paste and nickel connection is low. Since the mutual diffusion rate between silver and nickel is not as fast as the mutual diffusion rate between copper and nickel, the mutual diffusion rate of the elements during sintering is relatively slow, resulting in Kirkendall voids, which significantly reduces the strength and reliability of the welded joint. In Comparative Example 4, it is difficult to achieve large-area packaging interconnection by pressureless sintering. Pressureless sintering reduces the density of the copper solder paste after sintering, and cannot ensure good contact with the substrate and the heat sink. In Comparative Example 5, the shear strength of the interconnection structure is only 50.19 MPa. This is because the sintering temperature is too high, which will also reduce the mechanical properties of the joint. At high temperatures, each material will expand to different degrees according to its own CTE. When the temperature drops to room temperature, the shrinkage degree of each layer of material is also different, which will cause stress inside the package. If the temperature is too high, this stress accumulation to a certain extent will cause warping and affect the interconnection strength.

[0082] In summary, the present invention adopts copper solder paste as the interconnection material. The copper solder paste has high thermal conductivity and can quickly transfer the heat of the electronic device to the aluminum heat sink layer and dissipate it through the heat sink, thereby effectively reducing the operating temperature of the electronic device; by patterning the copper solder paste, a patterned pore structure is formed in the sintered copper layer, and combined with the porous structure of the sintered copper itself, the stress distribution of large-area interconnection can be effectively adjusted, and the problem of interconnection defects can be improved; a nickel layer is plated on the surface of the aluminum heat sink, and when the substrate is an aluminum-clad substrate, a nickel layer is plated on the surface of the aluminum substrate, thereby solving the problems of interface reaction and thermal expansion coefficient mismatch of metal interconnection, and realizing effective interconnection between the copper-clad substrate (DBC / DPC) and the aluminum heat sink, and between the aluminum-clad substrate (DBA) and the aluminum heat sink; the copper-aluminum and aluminum-aluminum interconnection structures have sufficient mechanical strength and good heat dissipation performance, the interconnection method is simple, and automated production can be realized with high efficiency; at the same time, the copper solder paste and the nickel-plated layer are low in cost and have good cost-effectiveness.

[0083] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A copper-aluminum or aluminum-aluminum interconnection method, characterized in that: The steps include: S1, plating a first nickel metal layer on the surface of the aluminum heat sink layer; S2, printing a layer of copper solder paste on the surface of the first nickel metal layer, and then preheating it under a protective atmosphere to obtain a sintered copper layer on the surface of the first nickel metal layer; S3, aligning and pre-bonding the substrate on the surface of the sintered copper layer, and then sintering and interconnecting under a protective atmosphere; Wherein, the substrate is a copper substrate or an aluminum substrate with a second nickel metal layer plated on the surface, and the second nickel metal layer is bonded to the sintered copper layer.

2. The copper-aluminum or aluminum-aluminum interconnection method according to claim 1, characterized in that: In S2, the preheating treatment is performed at a temperature of 110-180°C and for a time of 10-60 minutes.

3. The copper-aluminum or aluminum-aluminum interconnection method according to claim 1, characterized in that: In S3, the interconnection sintering is performed at a temperature of 160-230°C, a pressure of 10-30 MPa, and a time of 10-30 min.

4. The copper-aluminum or aluminum-aluminum interconnection method according to claim 1, characterized in that: In S2, the copper solder paste is pattern-printed through a steel mesh.

5. The copper-aluminum or aluminum-aluminum interconnection method according to claim 1, characterized in that: In S1, the thickness of the first nickel metal layer is 2-10 μm.

6. The copper-aluminum or aluminum-aluminum interconnection method according to claim 1, characterized in that: In S3, the thickness of the second nickel metal layer is 0.3-5 μm.

7. The copper-aluminum or aluminum-aluminum interconnection method according to claim 1, characterized in that: The first nickel metal layer is formed by electroplating, and the second nickel metal layer is formed by chemical plating.

8. The copper-aluminum or aluminum-aluminum interconnection method according to claim 1, characterized in that: The protective atmosphere is nitrogen or argon.

9. A copper-aluminum or aluminum-aluminum interconnect structure prepared by the method according to any one of claims 1 to 8.

10. The copper-aluminum or aluminum-aluminum interconnect structure according to claim 9, characterized in that: It comprises an aluminum heat sink layer, a first nickel metal layer, a sintered copper layer and a substrate layer which are sequentially stacked. The substrate layer is a copper substrate or an aluminum substrate with a second nickel metal layer plated on the surface. The second nickel metal layer is bonded to the sintered copper layer.

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