Discrete device copper sintering and crimping device and preparation method

Abstract

The invention relates to the technical field of power device manufacturing, in particular to a discrete device copper sintering and crimping device and a preparation method. The device comprises a base for crimping a device, a crimping mechanism is assembled at the top of the base, and the crimping mechanism comprises an accommodating cavity and a fixing device. Through the characteristics of low-temperature sintering and high-temperature service of nano-copper, the TO247-3L packaging solder layer is kept stable in structure in a high-power-density and high-frequency working environment, and thermal-induced interface failure is avoided. For copper sintering pressure adjustment of a small-area discrete device, the contact surface area of a chip and a pressing block should be set to be 2-3 times of the area of the chip, and the problems of insufficient sintering strength and chip damage can be avoided. A fixing device at a corresponding position is arranged according to a device, so that a chip of the device is in good contact with a pressing block to finish sintering. The limitation of copper sintering height difference of discrete devices is broken through, and a slidable pressing block is arranged, so that the sintering process is completed.

Description

Technical Field

[0001] This invention relates to the field of power device manufacturing technology, and in particular to a copper sintering and pressing device and preparation method for discrete devices. Background Technology

[0002] With the rapid development of photovoltaic energy storage, high-voltage power transmission and distribution, new energy vehicles, aerospace and 5G communications, power electronic devices based on third-generation semiconductors have become an indispensable key component of modern industrial systems. Third-generation semiconductor materials, mainly including SiC, GaN, ZnO, AlN and diamond, possess excellent properties such as wide bandgap, high breakdown electric field and high electron saturation mobility.

[0003] Traditional chip mounting materials (such as high-temperature lead-free solder) generally suffer from low remelting temperatures, insufficient thermal conductivity, and poor long-term reliability at high temperatures. To address these challenges, industry research has proposed low-temperature sintering technology using nano-silver (Ag), which can, to some extent, meet the stringent requirements of third-generation semiconductor power devices for packaging materials. The principle lies in utilizing the unique size effect of nano-silver particles, allowing them to be sintered in air at temperatures far below the melting point of bulk silver (e.g., approximately 200°C). Furthermore, the theoretical service temperature of the sintered connector is close to the melting point of bulk silver, thus exhibiting significant technological advantages. However, low-temperature sintering technology using nano-silver also has obvious limitations: on the one hand, silver is expensive, leading to high costs; on the other hand, it has a strong tendency for electrochemical migration, which can easily cause packaging structure failure due to excessive diffusion of silver atoms during long-term service. In contrast, nano-copper (Cu) sintering technology has attracted considerable attention from researchers in recent years due to its low raw material cost, excellent electrical and thermal conductivity, and strong resistance to electromigration. However, this technology also faces serious challenges: the nano-copper particles are extremely easy to oxidize and have a strong tendency to agglomerate, resulting in poor stability of the current nano-copper paste, harsh sintering connection process conditions, and the mechanical strength of the sintered joint still needs to be further improved.

[0004] In the field of power device manufacturing, the crimping process is a core technology for achieving reliable thermodynamic and electrical connections between chips and external electrodes. Its quality directly determines the power density, electrical performance, and long-term service reliability of the devices. Especially in high-voltage, high-power devices such as IGBTs and SiC MOSFETs, the quality of crimping is a key factor affecting the operational stability of strategic industrial equipment such as new energy vehicles and smart grids. Currently, the mainstream crimping devices in the industry mainly revolve around two technical routes: hard crimping and flexible crimping. However, both have significant technical limitations: Hard crimping devices achieve connection by directly applying mechanical pressure through rigid electrodes. Although it has advantages such as small parasitic parameters, double-sided heat dissipation, and failure short-circuit characteristics, the pressure is not adjustable, and it cannot absorb the deformation caused by the difference in thermal expansion coefficients between the chip and electrode materials, resulting in significant uneven pressure distribution in multi-chip modules. Flexible crimping devices buffer thermal deformation through spring structures. Although this improves pressure uniformity, the presence of springs increases parasitic parameters, can only achieve single-sided heat dissipation, and loses long-term failure short-circuit capability. Its explosion-proof performance and sealing reliability are insufficient, making it difficult to meet the stringent failure protection requirements of scenarios such as flexible DC transmission.

[0005] Existing solutions:

[0006] CN119230427A proposes a power module sintering method and a power module. This invention only addresses the power module sintering method but does not involve the sintering and packaging method for single-transistor devices.

[0007] CN112735978A proposes a crimping device and a pressure sintering equipment, which avoids the problems of high cost and high site requirements of crimping devices in related technologies, thereby improving the convenience of using the crimping device and saving the manufacturing and maintenance costs of the crimping device.

[0008] CN120727625A proposes a power device crimping device, in which the control module issues control commands to the pressure control unit and the displacement control unit based on temperature parameters to achieve precise control.

[0009] CN118287988A proposes a crimping assembly method and configuration for IGBT power devices, which solves the problem of difficult assembly of the valve section of crimped IGBTs.

[0010] Current disadvantages of solder paste and traditional crimping devices:

[0011] 1. Traditional tin-based solders have low remelting temperatures. Under high junction temperatures (>200℃), the solder layer is prone to softening and failure, leading to premature interface damage.

[0012] 2. The thermal conductivity of ordinary solder paste is only tens of degrees. The high heat flux density accumulated inside the TO247-3L package cannot be quickly conducted, resulting in increased chip junction temperature and performance degradation.

[0013] 3. Under high temperature and high current density, metal atoms in solder paste are prone to migrate along the electric field, which can cause voids, broken lines or short circuits in the solder layer of TO247-3L package, reducing device life.

[0014] 4. The thermal expansion coefficient of the solder paste (19-25ppm / ℃) differs greatly from that of the copper layer on the back of the TO247-3L packaged chip (16.5ppm / ℃) and the ceramic substrate. This difference generates alternating stress during thermal cycling, which can cause the solder layer to crack.

[0015] 5. In terms of crimping force control, it is difficult to accurately control the crimping force. If the crimping force is too small, the chip shear strength cannot be achieved; if the crimping force is too large, the chip will be directly damaged and cracked.

[0016] 6. In terms of pressing position control, the device position cannot be located, resulting in inaccurate pressing chip position and easy pressing offset, which in turn affects the overall performance of power devices. To address this, we propose a copper sintering pressing device and preparation method for discrete devices. Summary of the Invention

[0017] The purpose of this invention is to provide a copper sintering and pressing device and a preparation method for discrete devices, so as to solve the problems mentioned in the background art.

[0018] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0019] A copper sintering and pressing device for discrete devices includes a base for pressing the devices. A pressing mechanism is mounted on the top of the base. The pressing mechanism includes a receiving cavity and a fixing device. The receiving cavity is opened on the top of the base. Positioning holes are opened at the four corners of the top of the base. A fixing device is slidably connected to the inner side of the plurality of positioning holes.

[0020] Preferably, the pressing mechanism further includes pressing blocks, and the top of the fixing device is provided with a plurality of mating interfaces, and pressing blocks are slidably connected to the inner side of each mating interface.

[0021] Preferably, the device consists of a copper base plate, a chip, and electrodes.

[0022] Preferably, the top of the device is provided with a solder layer.

[0023] Preferably, the crimping device includes an upper copper plate and a lower copper plate, and the top and bottom of the device are respectively provided with an upper copper plate and a lower copper plate.

[0024] A method for copper sintering and pressing of discrete components, applicable to a copper sintering and pressing device for discrete components, includes the following steps:

[0025] S1: Print the prepared copper paste onto the copper substrate using a 100um thick stencil;

[0026] S2: PI tape is applied to a copper substrate for copper paste printing, and then a chip is attached to form a chip assembly. The chip area is 3.4mm × 2.6mm.

[0027] S3: Place a layer of Teflon and a layer of graphite between the chip and the pressing block. Then, place the fixing device and the device together into the hot press furnace. First, fill with nitrogen gas. Then, apply vertical pressure to the upper and lower molds at a pressure of 20MPa for 12 minutes. Then, heat the furnace at a heating rate of 3℃ / min to a temperature of 280℃. After reaching the temperature, hold the temperature for 10 minutes to complete the sintering.

[0028] S4: Finally, the sintered chip is subjected to a shear strength test.

[0029] Preferably, in step S2, the area of ​​the end of the pressure block that contacts the chip assembly is d, the area of ​​the chip distribution area in the chip assembly is s, and the value of d ranges from 1.5s to d to 3s.

[0030] It is clear without a doubt that the technical solution described above in this application can solve the technical problem that this application aims to address.

[0031] Meanwhile, through the above technical solutions, the present invention has at least the following beneficial effects:

[0032] 1. High Temperature Resistance: Breaking through the temperature limitations of traditional solder paste encapsulation, the copper bonding layer formed after nano-copper sintering has a melting point close to 1083℃, which is close to that of pure copper, and can withstand high-temperature environments above 300℃. This avoids the risk of softening and melting of solder paste joints under high-temperature conditions, fundamentally solving the high-temperature failure problem of traditional encapsulation.

[0033] 2. Improved thermal conductivity: The thermal conductivity of traditional solder paste is approximately 50-70. The thermal conductivity of the nano-copper sintered layer can reach 200-300 W / m². It is 3-5 times that of solder paste. Lower thermal resistance allows for faster heat dissipation during chip operation, effectively reducing chip junction temperature and allowing devices to operate at higher power densities or extend their lifespan at the same power.

[0034] 3. Long-term reliability and stability: ① Thermal fatigue failure: The coefficient of thermal expansion (CTE) of solder paste differs significantly from that of chips and ceramic substrates, and repeated thermal expansion and contraction can easily lead to solder joint cracking; the CTE of nano copper is closer to that of metal substrates, resulting in better thermal matching and more than 10 times the resistance to thermal cycling; ② Electromigration failure: Under high temperature and high current, metal atoms in solder paste are prone to migration, leading to solder joint voids, increased resistance, or even open circuits; the electromigration rate of copper is much lower than that of tin, which can maintain the stability of the connection over a long period of time, especially suitable for high current power devices.

[0035] 4. Compliant with environmental protection and policies: As a lead-free and non-toxic metal material, nano-copper fully complies with global environmental protection policy requirements. At the same time, the cost of raw materials is relatively controllable, giving it policy and economic advantages for industrialization and promotion. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a three-dimensional structural diagram of the crimping device of the present invention;

[0038] Figure 2 This is a side view of the crimping device of the present invention;

[0039] Figure 3 This is a schematic diagram of the overall device structure according to Embodiment 1 of the present invention;

[0040] Figure 4 This is a side view of a single device according to Embodiment 1 of the present invention;

[0041] Figure 5 This is a schematic diagram of the front structure of the device according to Embodiment 3 of the present invention;

[0042] Figure 6 This is a schematic diagram of the device and the upper copper plate in Embodiment 3 of the present invention;

[0043] Figure 7 This is a side view of the device according to Embodiment 3 of the present invention;

[0044] Figure 8 This is a schematic diagram of the structure of the PI adhesive tape of the present invention;

[0045] Figure 9 This is a schematic diagram of pressure and time changes in Embodiment 1 of the present invention;

[0046] Figure 10This is a schematic diagram of the preparation process of the present invention;

[0047] Figure 11 This is a schematic diagram of pressure and time changes in Embodiment 3 of the present invention.

[0048] The attached diagram lists the components represented by each number as follows:

[0049] In the diagram: 1. Base; 2. Receiving cavity; 3. Component; 4. Fixing device; 5. Pressure block; 6. Copper base plate; 7. Chip; 8. Electrode; 9. Solder layer; 10. Upper copper plate; 11. Lower copper plate. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0051] Example 1

[0052] Reference Figure 1-4 8-9, a copper sintering and pressing device for discrete components, including a base 1 for pressing a component 3, a pressing mechanism is mounted on the top of the base 1, the pressing mechanism includes a receiving cavity 2 and a fixing device 4, the receiving cavity 2 is opened on the top of the base 1, the receiving cavity 2 is specifically used to place the product component for positioning; positioning holes are opened at the four corners of the top of the base 1, and a fixing device 4 is slidably connected to the inner side of the multiple positioning holes, the fixing device 4 is used to fix the position of the product and ensure that the plane is horizontal and not tilted.

[0053] The pressing mechanism also includes pressing blocks 5. Multiple mating interfaces are evenly distributed on the top of the fixing device 4. Pressing blocks 5 are slidably connected to the inner side of each mating interface. The pressing blocks 5 can move up and down according to the thickness of the product, and can press the chip assembly onto the copper base plate 6.

[0054] Device 3 consists of a copper base plate 6, a chip 7, and electrodes 8. A solder layer 9 is provided on the top of device 3. The driving assembly (referring to the cavity of the pressure sintering equipment, which includes: an upper die head (model A07-1, capable of pressing at a height of 14.5-18mm), hydraulically drives the upper die head to contact the pressing block of the pressing device, continuously applying pressure; and a lower die base for heating against the bottom of the pressing device to meet the temperature requirements during hot-pressing sintering) can push the pressing block 5 to slide, causing it to contact the chip assembly to be hot-pressed and sintered. The driving assembly continues to push the pressing block 5, continuously applying pressure to it, thus meeting the pressing requirements of the chip assembly during hot-pressing sintering. Furthermore, the driving assembly can adjust the pressure applied by the pressing block 5, meaning the pressure of the pressing block 5 is adjustable, which better meets the pressing requirements of the chip assembly during hot-pressing sintering.

[0055] Example 2

[0056] like Figure 10 As shown, a method for copper sintering and pressing of discrete devices, applicable to a copper sintering and pressing device for discrete devices, includes the following steps:

[0057] The prepared copper paste is printed onto a copper substrate using a designed stencil (100µm thick). Due to the height difference between the device leads and the copper substrate (e.g., ...), ... Figure 4 The printed stencil was difficult to make perfectly smooth on the copper substrate, causing the copper paste to overflow around the holes and compromise the overall thickness. Therefore, PI tape (with laser-cut holes of appropriate size) was used instead of the stencil for copper paste printing. This ensured both the overall thickness of the copper paste and a smooth surface. Then, the chip (3.4×2.6mm) was attached. The area of ​​the end of the pressing block in contact with the chip assembly was d, and the area of ​​the chip distribution area within the chip assembly was s, with d ranging from 1.5s ≤ d ≤ 3s. A layer of Teflon and a layer of graphite were placed between the chip and the pressing head (to reduce vertical pressure on the chip, prevent damage, and ensure a smooth chip surface). Finally, the pressing device and components were placed in a hot press furnace. Nitrogen was first introduced, followed by vertical pressure of 20MPa for 12 minutes. Heating was then carried out at a rate of 3℃ / min to 280℃, and held at that temperature for 10 minutes to complete the sintering process. Finally, the sintered chip was subjected to a shear strength test, and the test results are as follows: Figure 9 As shown in the table below, the sintered devices will possess excellent thermal and electrical conductivity and reliable mechanical strength, meeting the requirements of high-end microelectronic packaging:

[0058] Example 3

[0059] Further optimizations to Example 1, specifically, such as... Figure 5-7 and Figure 11 As shown, the crimping device includes an upper copper plate 10 and a lower copper plate 11. The upper copper plate 10 and the lower copper plate 11 are respectively disposed on the top and bottom of the device 3. The crimping device consists of three parts: the upper copper plate 10, the device 3, and the lower copper plate 11. The upper copper plate 10 and the pressure block 5 have the same function, allowing contact with the chip assembly for sintering; the lower copper plate 11 is placed under the pins of the device 3 to ensure that the entire device is flat and not tilted. Compared with the crimping device in Embodiment 1, the structure is simple and the cost is very low, greatly improving the convenience of using the crimping device and saving the manufacturing and maintenance costs of the crimping device.

[0060] Its preparation process is as follows:

[0061] The prepared copper paste (100µm thick) was printed onto the copper base plate 6 using PI tape. The copper base plate 6 (2mm) has a height of h and a height difference of H, where H ranges from 1h to d and from 1.5h. An upper copper plate 10 was used to compensate for the height difference between the pins of device 3 and the copper base plate 6. The upper copper plate 10 was also fixed with PI tape to prevent it from shifting during sintering. A lower copper plate 11 was placed under the pins of device 3 to ensure the overall stability of device 3. Finally, the pressing device and the entire device 3 were placed together in a hot press furnace. Nitrogen gas was first introduced, followed by vertical pressure of 20 MPa for 12 minutes. Heating was then performed at a rate of 3°C / min to 280°C, and the temperature was maintained for 10 minutes after reaching the target temperature, thus completing the sintering process. Currently, copper sintering technology is widely used for power modules, but there are few copper sintering technologies for discrete devices. Copper sintering for discrete devices has certain requirements in terms of process and tooling. The key point of this invention is the two parts: the upper copper plate 10 and the lower copper plate 11. The upper copper plate 10 contacts the chip assembly by applying pressure, while the lower copper plate 11 keeps the overall device 3 stable. This not only saves a lot of costs but also provides convenience for sintering technology and meets the requirements of microelectronic packaging.

[0062] In summary:

[0063] This invention addresses the following technical problems: Current solder paste and traditional bonding devices have drawbacks: traditional tin-based solders have low remelting temperatures, and under high junction temperatures (>200℃), the solder layer is prone to softening and failure, leading to premature interface damage. Ordinary solder paste has a thermal conductivity of only tens of... The high heat flux density accumulated inside the TO247-3L package cannot be quickly conducted, causing the chip junction temperature to rise and performance to degrade. Metal atoms in the solder paste easily migrate along the electric field under high temperature and high current density, leading to voids, breaks, or short circuits in the TO247-3L package solder layer, reducing device lifespan. The thermal expansion coefficient of the solder paste (19-25ppm / ℃) differs significantly from the copper layer on the back of the TO247-3L package chip (16.5ppm / ℃) and the ceramic substrate, generating alternating stress during thermal cycling and causing solder layer cracking. Regarding crimping force control, it is difficult to accurately control the crimping force; too little force results in insufficient chip shear strength, while too much force directly damages the chip, causing cracks. In terms of crimping position control, the inability to accurately position the device leads to inaccurate chip crimping, easily causing crimping misalignment, which in turn affects the overall performance of the power device. By adopting the technical solutions of the above embodiments and through the above settings, this application can certainly solve the above technical problems and achieve the following technical effects:

[0064] 1. High Temperature Resistance: Breaking through the temperature limitations of traditional solder paste encapsulation, the copper bonding layer formed after nano-copper sintering has a melting point close to 1083℃, which is close to that of pure copper, and can withstand high-temperature environments above 300℃. This avoids the risk of softening and melting of solder paste joints under high-temperature conditions, fundamentally solving the high-temperature failure problem of traditional encapsulation.

[0065] 2. Improved thermal conductivity: The thermal conductivity of traditional solder paste is approximately 50-70. The thermal conductivity of the nano-copper sintered layer can reach 200-300. It is 3-5 times that of solder paste. Lower thermal resistance allows for faster heat dissipation during chip operation, effectively reducing chip junction temperature and allowing devices to operate at higher power densities or extend their lifespan at the same power.

[0066] 3. Long-term reliability and stability: ① Thermal fatigue failure: The coefficient of thermal expansion (CTE) of solder paste differs significantly from that of chips and ceramic substrates, and repeated thermal expansion and contraction can easily lead to solder joint cracking; the CTE of nano copper is closer to that of metal substrates, resulting in better thermal matching and more than 10 times the resistance to thermal cycling; ② Electromigration failure: Under high temperature and high current, metal atoms in solder paste are prone to migration, leading to solder joint voids, increased resistance, or even open circuits; the electromigration rate of copper is much lower than that of tin, which can maintain the stability of the connection over a long period of time, especially suitable for high current power devices.

[0067] 4. Compliant with environmental protection and policies: As a lead-free and non-toxic metal material, nano-copper fully complies with global environmental protection policy requirements. At the same time, the cost of raw materials is relatively controllable, giving it policy and economic advantages for industrialization and promotion.

[0068] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0069] Obviously, the embodiments described above are merely some embodiments of the present invention, not all embodiments. The accompanying drawings show preferred embodiments of the present invention, but do not limit the patent scope of the present invention. The present invention can be implemented in many different forms; rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or make equivalent substitutions for some of the technical features. Any equivalent structures made using the content of this specification and drawings, directly or indirectly applied to other related technical fields, are similarly within the patent protection scope of this invention.

Claims

1. A copper sintering and pressing device for discrete components, characterized in that, It includes a base (1) for pressing the device (3), the top of the base (1) is equipped with a pressing mechanism, the pressing mechanism includes a receiving cavity (2) and a fixing device (4), the top of the base (1) is provided with a receiving cavity (2), and the four corners of the top of the base (1) are provided with positioning holes, and a fixing device (4) is slidably connected to the inner side of the multiple positioning holes.

2. The discrete device copper sintering and pressing device according to claim 1, characterized in that, The pressing mechanism also includes a pressing block (5). The top of the fixing device (4) is provided with multiple mating interfaces, and the inner side of each mating interface is slidably connected with a pressing block (5).

3. The discrete device copper sintering and pressing device according to claim 2, characterized in that, The device (3) consists of a copper base plate (6), a chip (7) and an electrode (8).

4. The discrete device copper sintering and pressing device according to claim 3, characterized in that, The top of the device (3) is provided with a solder layer (9).

5. The discrete device copper sintering and pressing device according to claim 1, characterized in that, The crimping device includes an upper copper plate (10) and a lower copper plate (11), and the top and bottom of the device (3) are respectively provided with an upper copper plate (10) and a lower copper plate (11).

6. A method for copper sintering and pressing of discrete components, applicable to the copper sintering and pressing device for discrete components as described in any one of claims 1-5, characterized in that, Includes the following steps: S1: Print the prepared copper paste onto the copper substrate using a 100um thick stencil; S2: PI tape is applied to the copper base plate (6) for copper paste printing, and then the chip (7) is attached to form a chip assembly. The chip (7) has an area of ​​3.4mm × 2.6mm. S3: Place a layer of Teflon and a layer of graphite between the chip (7) and the pressing block (5), then put the fixing device (4) and the device (3) into the hot press furnace together. First, fill with nitrogen gas, then apply vertical pressure to the upper and lower molds at a pressure of 20MPa for 12 minutes. Then heat the furnace at a heating rate of 3℃ / min and a temperature of 280℃. After reaching the temperature, hold the temperature for 10 minutes to complete the sintering. S4: Finally, the sintered chip (7) is subjected to shear strength test.

7. The method for copper sintering and pressing of discrete devices according to claim 6, characterized in that, In step S2, the area of ​​the end of the pressure block (5) that contacts the chip assembly is d, and the area of ​​the distribution area of ​​the chip (7) in the chip assembly is s. The value of d is 1.5s≤d≤3s.

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