A clip material of sandwich structure and power module

Abstract

The application relates to the technical field of electrical element connection, in particular to a sandwich structure clip material and a power module. The sandwich structure clip material comprises a bending section and two welding sections. The welding sections and the bending section each comprise a low-thermal-expansion-coefficient metal layer and a high-conductivity metal layer. At least one bending node is arranged on the bending section, the thickness of the low-thermal-expansion-coefficient metal layer is symmetrically thinned at the bending node, and the thickness of the high-conductivity metal layer is symmetrically increased. The sandwich structure clip material provided by the application can be more easily bent as a whole by symmetrically thinning the thickness of the low-thermal-expansion-coefficient metal layer corresponding to the bending node in the bending section and symmetrically thickening the thickness of the high-conductivity metal layer, stress concentration generated at the bending node of the clip material can be reduced, and the probability of failure behaviors such as delamination and cracking of the clip material as a whole during the manufacturing process can be reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrical element connection, and in particular to a sandwich structure clip material and a power module. BACKGROUND

[0002] In the design and application of power modules, the parasitic inductance generated by the chip interconnection conductor is a key factor restricting the performance improvement of the module. The existence of parasitic inductance can significantly increase voltage overshoot and excitation oscillation, not only intensifying the electrical stress borne by the chip, but also greatly increasing power loss. This influence is particularly prominent on silicon semiconductor chips, especially silicon carbide (SiC) chips working at high frequency, which severely limits the performance of power modules in high-frequency, high-power scenarios. Therefore, for high-frequency power chips with large power and large current, using low-inductance packaging technology to optimize parasitic inductance has become a core technical direction to improve the performance of power modules.

[0003] Traditional power module chip interconnection technology generally uses copper and aluminum bonding wires. Since the permeability of copper and aluminum materials is close to the permeability of vacuum, simply replacing the material cannot reduce the parasitic inductance, and only the current-carrying capacity can be improved by changing the material resistance characteristics. In order to effectively reduce the parasitic inductance, the industry has gradually turned to optimization from the material structure and layout design level, giving rise to new interconnection technologies such as copper tape, aluminum tape, copper-coated aluminum tape, copper (aluminum or silver) sandwich tape, and clip. Taking Cu clip as an example, Cu clip material bonding technology has been widely used in power module packaging due to its larger conductive and heat dissipation area, lower parasitic inductance value, and excellent heat dissipation performance.

[0004] However, Cu clip material has exposed obvious reliability short board in actual application. Due to the significant difference in thermal expansion coefficient between copper and chip, Cu clip will bear high thermal stress under the frequent temperature cycle conditions of power module. With the continuous rise of chip heat flow density, Cu clip material has been difficult to meet the high reliability requirements. Therefore, at present, without changing the basic clip overall structure, a sandwich structure material of copper / molybdenum / copper (Cu / Mo / Cu, CMC) is used to replace the current pure copper material. In this structure, molybdenum as the middle core material, its thermal expansion coefficient is more matched with the chip, effectively alleviating the thermal stress problem, and has higher reliability, and its temperature cycle resistance times is significantly improved.

[0005] But in the actual use process, it is found that when the clip material is bent and connected, the core is usually made of pure molybdenum, kovar alloy or other metal materials with poor plasticity, high overall strength and poor processability, stress concentration is easily caused at the bending part, and failure behaviors such as delamination cracking are easily caused during the manufacturing process, especially when the bending radius is too small, these manufacturing defects will continuously deteriorate during the subsequent operation of the power module, become potential failure hazards, and seriously threaten the long-term stable operation of the power module. SUMMARY

[0006] The present application provides a sandwich structure clip material and a power module to solve the problem that the existing clip material is not easy to process, stress concentration is easily caused at the bending part, and failure behaviors such as delamination cracking are easily caused during the manufacturing process.

[0007] The present application provides a sandwich structure clip material, which adopts the following technical scheme: a sandwich structure clip material, comprising a bending section and two welding sections; the bending section and the two welding sections are all rectangular structures, the two welding sections are respectively located at two ends of the bending section in the length direction or the width direction, and are integrally formed with the bending section; the welding section and the bending section each comprise N metal layers, N is greater than or equal to 3, and N is an odd number; the N metal layers comprise a low-thermal-expansion-coefficient metal layer, and a high-conductivity metal layer, the low-thermal-expansion-coefficient metal layer is located between and in contact with two adjacent high-conductivity metal layers; at least one bending node is arranged on the bending section, the thickness of the low-thermal-expansion-coefficient metal layer at the bending node is symmetrically reduced, and the thickness of the high-conductivity metal layer at the bending node is symmetrically increased.

[0008] Further, the material of the high-conductivity metal layer is copper or aluminum or silver; the material of the low-thermal-expansion-coefficient metal layer is tungsten or molybdenum or kovar alloy or tungsten copper or molybdenum copper.

[0009] Further, in the N metal layers of the welding section, the thickness of the high-conductivity metal layer is uniformly distributed, the thickness of the low-thermal-expansion-coefficient metal layer is uniformly distributed, and the surfaces of the low-thermal-expansion-coefficient metal layer and the high-conductivity metal layer in contact with each other are both planes.

[0010] Further, the thickness ratio of the high-conductivity metal layer to the low-thermal-expansion-coefficient metal layer is 1:(1-5).

[0011] Further, in the N metal layers of the bending section, the two end faces of the low-thermal-expansion-coefficient metal layer along the length or width direction thereof are both symmetrically arranged wave surfaces; the end face of the high-conductivity metal layer along the length or width direction thereof towards the side of the low-thermal-expansion-coefficient metal layer adjacent thereto is a wave surface, and the low-thermal-expansion-coefficient metal layer can be in contact with the high-conductivity metal layer adjacent thereto; the bending node has a plurality of bending nodes and is located at the wave trough of the low-thermal-expansion-coefficient metal layer.

[0012] Further, in the N layers of metal layers of the bending section, the low-thermal-expansion-coefficient metal layer is a wave surface symmetrically arranged along both the length direction and the width direction of the two end faces; the high-conductivity metal layer is a wave surface along the length direction and the width direction towards the end face of the side of the low-thermal-expansion-coefficient metal layer arranged adjacent thereto, and the low-thermal-expansion-coefficient metal layer can be in close contact with the high-conductivity metal layer arranged adjacent thereto; the bending nodes are multiple and located at the wave troughs of the low-thermal-expansion-coefficient metal layer.

[0013] Further, when N=3, in the three layers of metal layers of the bending section, the high-conductivity metal layer is provided with multiple grooves on the end face of the side away from the low-thermal-expansion-coefficient metal layer arranged adjacent thereto.

[0014] Further, the overlapping area of the wave surface along the length direction and the wave trough along the width direction of the low-thermal-expansion-coefficient metal layer is referred to as a first area; the grooves correspond to the first areas one by one, and the grooves and the corresponding first areas are arranged side by side in the thickness direction of the bending section.

[0015] Further, the first area of the low-thermal-expansion-coefficient metal layer penetrates in the thickness direction thereof.

[0016] The application further provides a power module comprising the sandwich structure clip material, and further comprising a chip, a ceramic substrate circuit layer and a lead frame, the sandwich structure clip material being welded on the chip, the ceramic substrate circuit layer or the lead frame.

[0017] The application has the following beneficial effects: the sandwich structure clip material of the application can be bent more easily as a whole by thinning the thickness of the low-thermal-expansion-coefficient metal layer corresponding to the bending nodes in the bending section and thickening the thickness of the high-conductivity metal layer, and the thinning of the low-thermal-expansion-coefficient metal layer in the bending nodes is symmetrically arranged, and the thickening of the high-conductivity metal layer is symmetrically arranged synchronously, which can reduce the stress concentration of the clip material at the bending nodes, and the stress of the clip material when it is heated and expanded or cooled and shrunk is approximately symmetric, so the clip material is less likely to warp, and the probability of failure behaviors such as delamination and cracking of the clip material as a whole during the manufacturing process is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only show some embodiments of the application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0019] Figure 1Figure 2 is a cross-sectional view of the overall structure of an embodiment of a sandwich-structured clip material of the present application;

[0020] Figure 2 Figure 3 is a schematic view of the overall structure after bending of an embodiment of a sandwich-structured clip material of the present application;

[0021] Figure 3 Figure 4 is a cross-sectional view of the overall structure of another embodiment of a sandwich-structured clip material of the present application;

[0022] Figure 4 Figure 5 is a schematic view of the overall structure of another embodiment of a sandwich-structured clip material of the present application;

[0023] Figure 5 Figure 6 is a schematic view of the first region and the groove of another embodiment of a sandwich-structured clip material of the present application;

[0024] Figure 6 Figure 7 is a schematic view of the first region and the patch of another embodiment of a sandwich-structured clip material of the present application.

[0025] In the figure: 100, bending section; 101, low-thermal-expansion-coefficient metal layer; 102, high-conductivity metal layer; 110, welding section; 120, bending joint; 130, compensation joint; 140, groove; 150, first region; 160, second region; 170, patch. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be apparently and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0027] The present application provides an embodiment of a sandwich-structured clip material, as shown in Figures 1 to 6 .

[0028] The sandwich-structured clip material comprises a bending section 100 and two welding sections 110. The bending section 100 and the two welding sections 110 are all rectangular structures, the two welding sections 110 are respectively located at two ends of the bending section 100 in the length direction or the width direction, and are integrally formed with the bending section 100. The welding section 110 and the bending section 100 each comprise N metal layers, N≥3, and N is an odd number. The N metal layers comprise a low-thermal-expansion-coefficient metal layer 101 and A high-conductivity metal layer 102 and a low-thermal-expansion-coefficient metal layer 101 are located between two adjacent high-conductivity metal layers 102 and are bonded to each other. At least one bending node 120 is provided on the bending section 100. At the bending node 120, the thickness of the low-thermal-expansion-coefficient metal layer 101 decreases symmetrically, while the thickness of the high-conductivity metal layer 102 increases symmetrically.

[0029] For example, when N=3, the three metal layers include two highly conductive metal layers 102 and one metal layer with a low coefficient of thermal expansion 101, and the metal layer with a low coefficient of thermal expansion 101 is located between the two highly conductive metal layers 102, forming a sandwich structure.

[0030] The highly conductive metal layer 102 is made of metals such as copper, aluminum, or silver. Copper has good conductivity and is relatively inexpensive, making it a preferred material.

[0031] The low thermal expansion coefficient metal layer 101 is made of metals or alloys such as tungsten, molybdenum, Kovar alloy, tungsten copper, or molybdenum copper, with a linear thermal expansion coefficient of 4 ppm / K to 10 ppm / K in the temperature range of 25℃ to 200℃. While these materials have lower electrical conductivity than copper, copper typically has a higher thermal expansion coefficient than tungsten, molybdenum, Kovar alloy, tungsten copper, or molybdenum copper. In other words, when copper is used as the material for the high electrical conductivity metal layer 102 and molybdenum is used as the material for the low thermal expansion coefficient metal layer 101, copper exhibits both high electrical conductivity and a high thermal expansion coefficient, while molybdenum exhibits low electrical conductivity and a low thermal expansion coefficient.

[0032] Furthermore, in the N-layer metal layer of the welding section 110, the thickness of the high-conductivity metal layer 102 is uniformly distributed, the thickness of the low-thermal-expansion-coefficient metal layer 101 is uniformly distributed, and the surfaces where the low-thermal-expansion-coefficient metal layer 101 and the high-conductivity metal layer 102 are in contact are both planar. The two symmetrically arranged high-conductivity metal layers 102 have the same thickness and composition ratio, and the thickness ratio of the high-conductivity metal layer 102 to the low-thermal-expansion-coefficient metal layer 101 is 1:(1~5).

[0033] See Figure 1 As shown, when N=3, in the three metal layers, the middle region is a low thermal expansion coefficient metal layer 101, and the two sides are high conductivity metal layers 102. Wd is the thinning length of the low thermal expansion coefficient metal layer 101, Td is the maximum thinning thickness of the low thermal expansion coefficient metal layer 101, Tm is the total thickness of the three metal layers, and Ti is the thickness of the low thermal expansion coefficient metal layer 101; see also Figure 2 As shown, θ represents the bending angle of bending node 120 (90°≤θ<180°). After subsequent bending and forming, while maintaining good strength and reliability, when... hour, , ;when Time, , .

[0034] In this embodiment, the thickness of the low-thermal-expansion-coefficient metal layer 101 corresponding to the bending node 120 in the bending section 100 is thinned, and the thickness of the high-conductivity metal layer 102 is thickened, so that the clip material is easier to bend as a whole. Specifically, when copper, aluminum or silver is used as the high-conductivity metal layer 102, its plasticity is better than that of molybdenum, Kovar alloy or other metal materials with poor plasticity used as the low-thermal-expansion-coefficient metal layer 101. Therefore, thinning the low-thermal-expansion-coefficient metal layer 101 and thickening the high-conductivity metal layer 102 can make the clip material easier to bend as a whole.

[0035] In addition, the low-thermal-expansion-coefficient metal layer 101 in the bending node 120 is symmetrically thinned, and the high-conductivity metal layer 102 is symmetrically thickened, which can reduce the stress concentration of the clip material at the bending node 120, so that the stress on the clip material when it is heated and expanded or cooled and shrunk is approximately symmetrical, and the clip material is less likely to warp, thereby reducing the probability of failure behaviors such as delamination and cracking of the clip material as a whole during the manufacturing process.

[0036] In another possible embodiment, in the N-layer metal layer of the bending section 100, the two end faces of the low-thermal-expansion-coefficient metal layer 101 along its length or width direction are symmetrically arranged as wave surfaces. The high-conductivity metal layer 102 has a wave surface on the side facing the end face of the low-thermal-expansion-coefficient metal layer 101 adjacent thereto along its length or width direction, and the low-thermal-expansion-coefficient metal layer 101 can be in close contact with the high-conductivity metal layer 102 adjacent thereto. The bending node 120 is multiple and located at the wave trough of the low-thermal-expansion-coefficient metal layer 101.

[0037] Referring to Figure 3 and Figure 4 When the two end faces of the low-thermal-expansion-coefficient metal layer 101 along its length or width direction are symmetrically arranged as wave surfaces, the bending node 120 is located at the wave trough of the low-thermal-expansion-coefficient metal layer 101.

[0038] The embodiment sets the wavy end face on the low thermal expansion coefficient metal layer 101 and the high-conductivity metal layer 102, and then enables arbitrary bending in the length or width direction of the low thermal expansion coefficient metal layer 101, and the continuous curved surface of the wavy face is transitioned, which can avoid stress concentration at a certain point. For any bending node 120, the overall thermal expansion coefficient at this point will relatively increase due to the thinning of the low thermal expansion coefficient metal layer 101 and the thickening of the high-conductivity metal layer 102. For the convenience of description, the peak of the low thermal expansion coefficient metal layer 101 is called a compensation node 130. For any compensation node 130, the overall thermal expansion coefficient at this point will relatively decrease due to the thickening of the low thermal expansion coefficient metal layer 101 and the thinning of the high-conductivity metal layer 102. Through the complementation of the bending node 120 and the compensation node 130, compared with the symmetrical thinning of the low thermal expansion coefficient metal layer 101, the overall thermal expansion coefficient of the clip material is more uniform. The interface of the thinning area can be transitioned by a continuous curved surface such as a circular arc or an elliptical arc to avoid stress concentration at a certain point. The setting mode of the N layers of metal layers of the welding section 110 is unchanged to avoid the difference between the thermal expansion coefficients at different positions being too large when welding, which causes the welding point to creep and appear welding gaps.

[0039] In another possible embodiment, in the N layers of metal layers of the bending section 100, the two end faces of the low thermal expansion coefficient metal layer 101 in the length direction and the width direction are both symmetrically set as wavy faces. The end face of the high-conductivity metal layer 102 in the length direction and the width direction towards the side of the low thermal expansion coefficient metal layer 101 adjacent to the high-conductivity metal layer 102 is a wavy face, and the low thermal expansion coefficient metal layer 101 can be mutually attached to the high-conductivity metal layer 102 adjacent to the low thermal expansion coefficient metal layer 101. The bending node 120 is multiple and located at the wave trough of the low thermal expansion coefficient metal layer 101.

[0040] Further, when N=3, in the three layers of metal layers of the bending section 100, the high-conductivity metal layer 102 is provided with a plurality of grooves 140 on the end face away from the low thermal expansion coefficient metal layer 101 adjacent to the high-conductivity metal layer 102.

[0041] Alternatively, in the three layers of metal layers of the bending section 100, the overlapping area of the wavy face in the length direction and the wave trough of the wavy face in the width direction of the low thermal expansion coefficient metal layer 101 is called a first area 150. The groove 140 corresponds to the first area 150 one by one, and the groove 140 and the corresponding first area 150 are arranged side by side in the thickness direction of the bending section 100.

[0042] Referring to Figure 5As shown, the embodiment makes the two end faces of the low-thermal-expansion-coefficient metal layer 101 in the bending section 100 along the length direction and the width direction be symmetrical wave surfaces, and is adapted with the high-conductivity metal layer 102, so that the clip material can be arbitrarily bent along the length direction or the width direction, especially for the square clip material, without extra distinguishing direction, which is more convenient for operation.

[0043] When the clip material is composed of three metal layers, the recess 140 is arranged on the high-conductivity metal layer 102, which can improve the heat dissipation of the clip material as a whole, and when the recess 140 is arranged in the first area 150, the arrangement of the recess 140 can also reduce the thermal expansion coefficient of the bending section 100 as a whole, further improve the uniformity of the thermal expansion coefficient of the clip material as a whole, so that the thermal expansion coefficients of different parts of the clip material tend to be consistent. Therefore, even if the N metal layers of the bending section 100 and the welding section 110 are arranged as a uniform structure, that is, the low-thermal-expansion-coefficient metal layer 101 in the bending section 100 and the welding section 110 is arranged as a symmetrical wave surface along the length direction and the width direction, and is adapted with the high-conductivity metal layer 102, the difference of the expansion coefficient of the whole is relatively reduced, and the probability of creep of the welding point is reduced.

[0044] In another possible embodiment, when N=3, the first area 150 of the low-thermal-expansion-coefficient metal layer 101 in the three metal layers of the bending section 100 is through in the thickness direction.

[0045] Further, the overlapping area of the wave peaks of the wave surfaces of the high-conductivity metal layer 102 along the length direction and the width direction is referred to as the second area 160. The second area 160 is provided with the sticking block 170, and the sticking blocks 170 on the two high-conductivity metal layers 102 are stuck to each other.

[0046] Referring to Figure 6 As shown, the embodiment makes the first area 150 of the low-thermal-expansion-coefficient metal layer 101 be through in the thickness direction, so that the low-thermal-expansion-coefficient metal layer 101 forms a grid structure, which further enhances the heat dissipation of the clip material as a whole. The sticking block 170 is arranged on the second area 160, and the sticking blocks 170 on the two high-conductivity metal layers 102 are stuck to each other, which can improve the conductivity and is more convenient for bending operation.

[0047] The application also provides an embodiment of a power module, which comprises the sandwich structure clip material described above, and further comprises a chip, a ceramic substrate circuit layer and a lead frame, and the sandwich structure clip material is welded on the chip, the ceramic substrate circuit layer or the lead frame by tin-based solder or sintered silver.

[0048] The above merely provides the preferred embodiment of the present application, and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A sandwich-structured clip material, characterized by: The bending section and the two welding sections are all rectangular structures, the two welding sections are respectively located at two ends of the bending section in the length direction or the width direction, and are integrally formed with the bending section; the welding section and the bending section both comprise N metal layers, N≥3, and N is an odd number; the N metal layers comprise an Lth metal layer with low thermal expansion coefficient, and an HCE metal layer with high electric conductivity, the Lth metal layer is located between two adjacently arranged HCE metal layers and is in mutual adhesion with the two HCE metal layers; at least one bending node is arranged on the bending section, the thickness of the Lth metal layer at the bending node is symmetrically thinned, and the thickness of the HCE metal layer is symmetrically increased.

2. A sandwich structured clip material according to claim 1, characterized in that: The material of the high-conductivity metal layer is copper or aluminum or silver; the material of the low-thermal-expansion metal layer is tungsten or molybdenum or Kovar or tungsten copper or molybdenum copper.

3. A sandwich structure clip material according to claim 1, characterized in that: In the N-layer metal layers of the welding section, the thickness of the high-conductivity metal layer is uniformly distributed, the thickness of the low-thermal-expansion metal layer is uniformly distributed, and the surfaces of the low-thermal-expansion metal layer and the high-conductivity metal layer that are in contact with each other are planes.

4. A sandwich structure clip material according to claim 3, characterized in that: The thickness ratio of the high-conductivity metal layer to the low-thermal-expansion metal layer is 1:(1-5).

5. A sandwich structure clip material according to claim 1, characterized in that: In the N-layer metal layers of the bending section, the two end surfaces of the low-thermal-expansion metal layer along the length or width direction are symmetrically arranged as wave surfaces; the end surface of the high-conductivity metal layer along the length or width direction towards the side of the low-thermal-expansion metal layer arranged adjacent thereto is a wave surface, and the low-thermal-expansion metal layer can be in contact with the high-conductivity metal layer arranged adjacent thereto; the bending nodes are multiple and are located at the wave troughs of the low-thermal-expansion metal layer.

6. A sandwich structure clip material according to claim 1, characterized in that: In the N-layer metal layers of the bending section, the two end surfaces of the low-thermal-expansion metal layer along the length or width direction are symmetrically arranged as wave surfaces; the end surface of the high-conductivity metal layer along the length or width direction towards the side of the low-thermal-expansion metal layer arranged adjacent thereto is a wave surface, and the low-thermal-expansion metal layer can be in contact with the high-conductivity metal layer arranged adjacent thereto; the bending nodes are multiple and are located at the wave troughs of the low-thermal-expansion metal layer.

7. A sandwich structure clip material according to claim 5 or 6, characterised in that: When N=3, in the three-layer metal layers of the bending section, a plurality of grooves are formed on the end surface of the high-conductivity metal layer away from the side of the low-thermal-expansion metal layer arranged adjacent thereto.

8. A sandwich structure clip material according to claim 7, characterized in that: The overlapping area of the wave surfaces of the low-thermal-expansion metal layer along the length direction and the wave troughs of the wave surfaces along the width direction is referred to as a first area; the grooves correspond to the first areas one by one, and the grooves and the corresponding first areas are arranged side by side in the thickness direction of the bending section.

9. A sandwich structure clip material according to claim 8, characterized in that: The first area of the low-thermal-expansion metal layer penetrates in the thickness direction.

10. A power module comprising a sandwich structure of a clip material according to any one of claims 1 to 9, characterized in that: It also includes a chip, a ceramic substrate circuit layer and a lead frame, and the clip material of the sandwich structure is welded on the chip, the ceramic substrate circuit layer or the lead frame. The material of the high-conductivity metal layer is copper or aluminum or silver; the material of the low-thermal-expansion metal layer is tungsten or molybdenum or Kovar or tungsten copper or molybdenum copper.

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