Sintered silver pad with low modulus and high thermal conductivity and manufacturing device and method thereof

Abstract

The application belongs to the technical field of power electronic packaging, and provides a sintered silver pad with low modulus and high thermal conductivity, and a manufacturing device and method thereof. The technical scheme is as follows: (1) a mold is used to print and dry the nano silver solder paste layer by layer, a layer of nano silver solder paste is printed first, dried at 110-120 DEG C for 10-20 min, then the second layer of nano silver solder paste with the same shape and area is printed and dried in the same way above the dried solder paste, the thickness of each layer of solder paste is 0.2-0.6 mm, and the operation is repeated to reach the required thickness; (2) the nano silver solder paste dried layer by layer is pretreated, and kept at 200-220 DEG C for 10-30 min; (3) the pretreated solder paste is heated to 250-260 DEG C and sintered for 20-40 min to form the sintered silver pad with low modulus, high thermal conductivity and porous structure. The sintered silver pad is used to replace the metal column pad in the double-sided module, so that the thermal mechanical stress and junction temperature of the chip can be reduced, and surface metallization treatment is not needed. The application is applied to the power electronic packaging occasion, and can improve the module reliability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronic packaging, and particularly relates to a sintered silver pad block with low modulus and high thermal conductivity and a manufacturing device and method thereof. BACKGROUND

[0002] With the rapid development of new energy automobile, photovoltaic power generation, wind power and other new energy industries, power electronic devices, as important power electronic devices in energy conversion systems, are attracting more and more attention. Traditional silicon-based power modules have gradually failed to meet the development needs of high power density, high junction temperature and low loss. New third-generation semiconductor materials such as silicon carbide (SiC) and gallium nitride (GaN) have the advantages of high withstand voltage, high thermal conductivity and low power consumption compared with traditional silicon materials, and are increasingly widely used in new energy industries. The use of SiC modules instead of silicon-based modules can greatly improve the module working frequency and power density. However, the increase in power density and the rise in chip working temperature have put higher requirements on the reliability of SiC module packaging. Since the Young's modulus of SiC material is about three times that of silicon material, greater thermal mechanical cyclic stress will be generated in the service of the module. Under the current lead bonding packaging method mainly used in commercial production, the reliability of SiC module is relatively low. In recent years, double-sided packaging structure has attracted more and more attention because it can improve the reliability of SiC module. This packaging structure uses metal pillars to realize the electrical interconnection between the chip and the substrate. However, the mismatch of the thermal expansion coefficients of various materials in the module will cause greater thermal mechanical cyclic stress on the chip, thereby leading to module aging failure. Moreover, the surface of the metal pillar needs additional metallization treatment to realize welding connection.

[0003] In the prior art, the double-sided packaging structure usually uses copper or molybdenum as the metal column. However, the thermal expansion coefficient of copper (16.5 ppm / ℃) is quite different from the thermal expansion coefficient of the SiC chip (3-5 ppm / ℃), and the Young's modulus of copper (128 GPa) is large, so that the chip is prone to generate large thermal mechanical stress during the use of the power module, thereby accelerating the aging failure speed of the module. The thermal expansion coefficient of molybdenum (4.9 ppm / ℃) is similar to the thermal expansion coefficient of the SiC chip, and the use of molybdenum instead of copper as the metal column can reduce the stress of the chip and improve the reliability. However, the thermal conductivity of molybdenum (142 W / (m·℃)) is much smaller than that of copper (385 W / (m·℃)), which is not conducive to the heat dissipation of the chip, resulting in the rise of the junction temperature of the chip during the operation of the module. Some technicians try to improve the above problems by designing and processing metal columns with complex shape and structure, but the processing of special-shaped metal columns is difficult, which on the one hand increases the difficulty of process operation, and on the other hand increases the production cost. In addition, the use of copper or molybdenum as the metal column usually requires metalization treatment such as gold plating and silver plating on the surface of the metal column, which increases the process steps, and if the surface plating quality is poor, it will also seriously affect the reliability of the module. The prior art cannot realize the reduction of the stress of the chip while preventing the junction temperature from rising too high, therefore, a new technical method is needed to solve the above problems and further improve the reliability of the double-sided packaging module and the production efficiency. SUMMARY

[0004] The present application provides a sintered silver pad with low modulus and high thermal conductivity, and a manufacturing device and method thereof, aiming to provide a new type of metal column pad technical solution for double-sided packaging structure power electronic devices, to realize the reduction of the thermal mechanical stress and the junction temperature of the chip, and without the need for surface metalization treatment.

[0005] To achieve the above-mentioned purposes, the technical solution of the present application is as follows:

[0006] A sintered silver pad with low modulus and high thermal conductivity, and a manufacturing device and method thereof, the specific technical solution is as follows:

[0007] (1) using a mold layer printing dry nano-silver solder paste, the mold consists of a base, positioning pins and multilayer steel mesh, the positioning pins are located in the four corners of the base, the steel mesh is located vertically above the base, the base is provided with a recess with the same shape and size as the required pad, and the steel mesh is provided with a through hole with the same shape and size at the same position corresponding to the recess. First, print a layer of nano-silver solder paste in the recess of the base, the thickness of the solder paste is 0.2-0.6mm, then place the base above the heating device, dry at 110-120℃ for 10-20min. Then take the base off the heating device, place the steel mesh above the base according to the required number of layers, and print and dry the second layer of nano-silver solder paste with the same shape and area above the dried solder paste using the same printing thickness and drying method. After drying, do not remove the steel mesh, place the steel mesh to print and dry the third layer of solder paste, repeat the operation, and finally reach the required thickness.

[0008] (2) pretreatment, remove the uppermost layer of the mold printed and dried in step (1), expose the silver solder paste to a height of 0.2-0.6mm, then place the mold as a whole above the heating device, heat to 200-220℃ at a heating rate of 5-10℃ / min and keep for 10-30min, so that the silver solder paste obtains a certain strength.

[0009] (3) sintering, place a pressure block above the mold and silver solder paste after pretreatment in step (2), apply a pressure of 0-2MPa with a pressure device, then quickly heat to 250-260℃, sinter for 20-40min, after sintering, cool to room temperature in the furnace, remove the mold to obtain the sintered silver pad after forming.

[0010] The base thickness in step (1) is 3-5mm, the recess depth is 0.2-0.6mm, and the steel mesh thickness is 0.2-0.6mm.

[0011] The sintered silver pad in step (3) is a porous structure, the Young's modulus is 5-10GPa, the thermal conductivity is 200-240W / (m·℃), the sintering porosity is 10%-30%, and the thickness is 1-3mm.

[0012] The nano-silver solder paste is used to complete the sintering of the double-sided structure packaging connection, the chip is connected on the lower copper substrate, the sintered silver pad is connected on the upper surface of the chip, and the upper copper substrate is connected with the other side of the sintered silver pad.

[0013] Nano silver solder paste low temperature sintering connection technology has been gradually applied, and the thickness of the connection layer is usually 50-100 mu m. The thickness of the double-sided module metal column is generally 1.5-2.5 mm, and the organic matter in the solder paste cannot be uniformly volatilized by directly sintering once, and defects such as cavities and cracks are easily formed in the sintered silver pad, which seriously affects the performance of the module. The present application adopts the method of layered printing and drying, which can make the organic matter in the solder paste fully volatilize, and avoid the formation of defects such as cavities and cracks in the sintered silver pad. The thickness of each layer of solder paste is controlled to be 0.2-0.6 mm, and the drying temperature is 110-120 DEG C, which can ensure that the low-temperature organic matter can be effectively volatilized. If the thickness is too large, the volatilization of the organic matter will be blocked, and if the thickness is too small, the number of solder paste layers will be too many, and the production efficiency will be low. After layered printing and drying, the solder paste is heated at a temperature of 200-220 DEG C for pretreatment, so that part of the high-temperature organic matter is volatilized, and the solder paste obtains a certain strength, preventing the problem of sintered silver pad deformation and damage caused by pressure in the subsequent sintering process.

[0014] In the prior art, the double-sided module mainly uses copper or molybdenum metal columns. Copper has good thermal conductivity, but the thermal expansion coefficient of copper is quite different from that of SiC chips, and the chips are prone to generate large thermal mechanical stress during the use of the module, thereby causing the module to age and fail quickly. The thermal expansion coefficient of molybdenum is similar to that of SiC chips, but the thermal conductivity of molybdenum is much smaller than that of copper, and the chip junction temperature rises too high during the operation of the module. The present application uses sintered silver pads to replace metal columns, and since the Young's modulus of sintered silver is much smaller than that of copper and molybdenum, the chip stress can be greatly reduced, thereby improving the reliability of the module. At the same time, sintered silver has high thermal conductivity and will not cause the chip junction temperature to rise too high, avoiding the damage of the chip due to overheating. When copper or molybdenum and other metal materials are sintered and connected using nano silver solder paste, a surface metallization treatment is required to form a gold or silver plating layer on the surface to realize diffusion connection during the sintering process. The additional metallization treatment increases the process steps, and the joint connection strength of the poor plating layer is poor, and cracks are easily generated at the interface between the metal and the plating layer, which seriously affects the reliability of the module. The present application uses sintered silver pads to connect with nano silver solder paste, which does not require surface metallization treatment, and can form an interface diffusion connection. Moreover, the sintered silver pad is a porous structure, and when the sintered silver pad and the nano silver solder paste are sintered and connected, more silver atoms in the solder paste can diffuse through the sintered silver pores, thereby improving the joint connection strength. In addition, the sintered silver pad has low hardness and a porous structure, and is easy to deform to adapt to various geometric changes generated in the packaging and assembly process of the double-sided module.

[0015] Compared with the prior art, the present application has the following characteristics and advantages:

[0016] The present application provides a sintered silver pad with low modulus and high thermal conductivity, and a manufacturing device and method thereof, which can reduce the thermal mechanical stress and junction temperature of a chip without surface metallization treatment. When the sintered silver pad is used to replace the metal column in a double-sided module, the sintered silver has a lower Young's modulus than copper and molybdenum, which can greatly reduce the stress of the chip and improve the reliability; at the same time, the thermal conductivity of the sintered silver is better than that of molybdenum, which will not cause the junction temperature of the chip to rise too much; and the sintered silver pad does not need surface metallization treatment and can realize sintering connection of nano-silver solder paste. In addition, the sintered silver has low hardness and porous structure, and can play a stress buffering role when the outside of the module is extruded, preventing the chip from being damaged by excessive extrusion force. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a mold structure schematic diagram of the present application;

[0018] Figure 2 is a layered printing and drying process schematic diagram of the present application;

[0019] Figure 3 is a pretreatment process schematic diagram of the present application;

[0020] Figure 4 is a sintering forming process schematic diagram of the present application;

[0021] Figure 5 is a sintered silver pad physical diagram of the present application;

[0022] Figure 6 is a double-sided packaging structure schematic diagram of the present application using a sintered silver pad;

[0023] Figure 7 is a sintering temperature curve diagram of the present application;

[0024] In the figure: 1, base, 2, positioning pin, 3, steel mesh, 4, groove, 5, through hole, 6, steel mesh positioning hole, 7, nano-silver solder paste, 8, heating device, 9, pressing block, 10, pressing device, 11, sintered silver pad, 12, lower copper clad plate, 13, sintered silver connecting layer, 14, chip, 15, upper copper clad plate. DETAILED DESCRIPTION

[0025] A sintered silver pad with low modulus and high thermal conductivity, and a manufacturing device and method thereof, the specific steps are as follows:

[0026] Step 1. Layered printing and drying of the nano-silver solder paste using a mold, which is composed of a base, positioning pins located at the four corners of the base, and a multilayer steel mesh located vertically above the base. A recess with the same shape and size as the desired pad is formed on the base, and a through hole with the same shape and size as the recess is formed on the steel mesh. First, a layer of nano-silver solder paste is printed in the recess of the base with a thickness of 0.2-0.6 mm. Then, the base is placed above a heating device and dried at a temperature of 110-120℃ for 10-20 min. After that, the base is removed from the heating device, and the steel mesh is placed above the base according to the desired number of layers. The same printing thickness and drying method are used to print and dry the second layer of nano-silver solder paste on the vertically dried solder paste, with the same shape and area. After drying, the steel mesh is not removed, and the third layer of solder paste is printed and dried by repeating the above steps. Finally, the desired thickness is achieved.

[0027] Step 2. Pretreatment. The uppermost layer of the steel mesh of the mold printed and dried in step 1 is removed, exposing the silver solder paste to a height of 0.2-0.6 mm. Then, the mold is placed as a whole above a heating device, heated to 200-220℃ at a rate of 5-10℃ / min, and held for 10-30 min to obtain a certain strength of the silver solder paste.

[0028] Step 3. Sintering and forming. A pressing block is placed above the mold and silver solder paste after pretreatment in step 2, and a pressure of 0-2 MPa is applied using a pressure device. Then, the temperature is quickly raised to 250-260℃, and sintering is performed for 20-40 min. After sintering, the mold is removed and the sintered silver pad is obtained.

[0029] The nano-silver solder paste is used to complete the sintering of the double-sided structure packaging connection. The chip is connected to the lower copper substrate, the sintered silver pad is connected to the upper surface of the chip, and the upper copper substrate is connected to the other side of the sintered silver pad.

[0030] The technical solutions of the present application will now be further described in conjunction with the accompanying drawings.

[0031] The present application provides a sintered silver pad with low modulus and high thermal conductivity, as well as a manufacturing device and method thereof, which includes the following specific steps:

[0032] (1) Layered printing and drying of the nano-silver solder paste using a mold, as shown in Figure 1As shown, the mold is composed of a base 1, positioning pins 2 and multiple layers of steel mesh 3. The base 1 is 3-5 mm thick, the positioning pins 2 are located at the four corners of the base 1 for positioning and alignment of the base 1 and the steel mesh 3, and the steel mesh 3 is vertically above the base 1 and is 0.2-0.6 mm thick. A groove 4 with the same shape and size as the required cushion block is formed on the base 1, the groove 4 is 0.2-0.6 mm deep, and a through hole 5 with the same shape and size as the groove 4 is formed at the same position on the steel mesh 3, and a steel mesh positioning hole 6 is formed at the same position corresponding to the positioning pin 2. The layered printing and drying process is as shown in Figure 2 As shown, first, a layer of nano-silver solder paste 7 is printed in the base groove 4, and the solder paste is 0.2-0.6 mm thick. If the thickness of the solder paste is too large, the volatilization of organic matter will be hindered, and if the thickness of the solder paste is too small, the number of layers of the solder paste will be too large, resulting in low production efficiency. Then, the base 1 is placed above the heating device 8, and dried at a temperature of 110-120℃ for 10-20 min to ensure that the low-temperature organic matter can be effectively and fully volatilized. After that, the base 1 is removed from the heating device 8, and the steel mesh 3 is placed above the base 1 according to the required number of layers. The same printing thickness and drying method is used to print and dry a second layer of nano-silver solder paste 7 with the same shape and area vertically above the dried solder paste. After drying, the steel mesh 3 is not removed, and the third layer of solder paste is printed and dried by placing the steel mesh 3 again. This operation is repeated until the desired thickness is achieved.

[0033] (2) The pretreatment process is as shown in Figure 3 The uppermost layer of steel mesh 3 of the mold after the layered printing and drying in step (1) is removed, and the nano-silver solder paste 7 is exposed to a height of 0.2-0.6 mm to facilitate the subsequent application of pressure to the solder paste. Then, the mold is placed as a whole above the heating device 8, heated to 200-220℃ at a heating rate of 5-10℃ / min, and held for 10-30 min to partially decompose and volatilize the high-temperature organic matter in the solder paste. Under these conditions, part of the silver particles in the nano-silver solder paste 7 form a necked structure, and the solder paste obtains a certain strength to prevent deformation and damage of the sintered silver cushion block caused by pressure during the subsequent sintering and forming process.

[0034] (3) The sintering and forming process is as shown in Figure 4 After the pretreatment in step (2), the mold and the nano-silver solder paste 7 are placed above the pressing block 9, and a pressure of 0-2 MPa is applied by the pressure device 10, and then quickly heated to 250-260℃ and sintered for 20-40 min. During this process, the nano-silver solder paste is sintered and densified to form a porous structure. After sintering, the mold is cooled to room temperature in the furnace, and the sintered silver cushion block 11 after forming is obtained. The sintered silver cushion block 11 after forming is a porous structure with a sintering porosity of 10%-30%, a relatively low Young's modulus (5-10 GPa), and a relatively high thermal conductivity (200-240 W / (m·℃)). The sintered silver cushion block is as shown in Figure 5 .

[0035] Figure 6 The double-sided packaging structure using sintered silver pads 11 is shown, the chip 14 is connected on the lower copper substrate 12, the sintered silver pads 11 are connected on the upper surface of the chip 14, the upper copper substrate 15 is connected with the other side of the sintered silver pads 11, and each layer of material is connected through the sintered silver connecting layer 13. Figure 7 The sintering temperature curve of the sintered silver pad is shown.

[0036] The specific implementation is as follows:

[0037] Example 1:

[0038] The process method for low-temperature large-area uniform sintering of nano-silver solder paste in this example is as follows:

[0039] (1) Layered printing and drying of nano-silver solder paste using a mold, the mold is composed of a base, positioning pins and multiple layers of steel mesh, the positioning pins are located at the four corners of the base, the steel mesh is vertically above the base, the base is provided with a recess with the same shape and size as the required pad, and the steel mesh is provided with a through hole with the same shape and size at the same position corresponding to the recess. First, print a layer of nano-silver solder paste in the recess of the base, with a thickness of 0.2 mm, then place the base above the heating device, and dry at 110°C for 10 min. Then take the base off the heating device, place the steel mesh above the base according to the required number of layers, and print and dry the second layer of nano-silver solder paste with the same shape and area vertically above the dried solder paste using the same printing thickness and drying method. After drying, do not remove the steel mesh, place the steel mesh to print and dry the third layer of solder paste, and repeat the operation until the desired thickness is reached.

[0040] (2) Pretreatment, remove the uppermost layer of steel mesh of the mold printed and dried in step (1) to expose the silver solder paste to a height of 0.2 mm, then place the mold as a whole above the heating device, heat to 200°C at a rate of 5°C / min and keep for 10 min.

[0041] (3) Sintering and forming, without applying pressure, then quickly heating to 250°C and sintering for 20 min, after sintering, cooling to room temperature in the furnace, and taking out the mold to obtain the sintered silver pad after forming.

[0042] Example 2:

[0043] The process method for low-temperature large-area uniform sintering of nano-silver solder paste in this example is as follows:

[0044] (1) Using a mold to print and dry the nano-silver solder paste layer by layer, the mold is composed of a base, positioning pins and multiple layers of steel mesh, the positioning pins are located at the four corners of the base, the steel mesh is located vertically above the base, the base has a recess with the same shape and size as the required pad, and the steel mesh has a through hole with the same shape and size at the same position corresponding to the recess. First, print a layer of nano-silver solder paste in the recess of the base with a thickness of 0.2 mm, then place the base above the heating device, and dry it at 120°C for 20 min. Then remove the base from the heating device, place the steel mesh above the base according to the required number of layers, and use the same printing thickness and drying method to print and dry the second layer of nano-silver solder paste with the same shape and area vertically above the dried solder paste. After drying, do not remove the steel mesh, place the steel mesh to print and dry the third layer of solder paste, and repeat the operation until the required thickness is reached.

[0045] (2) Pretreatment, remove the uppermost layer of steel mesh from the mold printed and dried in step (1), expose the silver solder paste to a height of 0.2 mm, then place the entire mold above the heating device, heat to 220°C at a rate of 10°C / min and keep for 30 min.

[0046] (3) Sintering and forming, no pressure is applied, then quickly heat to 260°C and sinter for 40 min, after sintering, cool to room temperature in the furnace, remove the mold to obtain the sintered silver pad after forming.

[0047] Example 3:

[0048] The process for low-temperature and large-area uniform sintering of nano-silver solder paste in this example is as follows:

[0049] (1) Using a mold to print and dry the nano-silver solder paste layer by layer, the mold is composed of a base, positioning pins and multiple layers of steel mesh, the positioning pins are located at the four corners of the base, the steel mesh is located vertically above the base, the base has a recess with the same shape and size as the required pad, and the steel mesh has a through hole with the same shape and size at the same position corresponding to the recess. First, print a layer of nano-silver solder paste in the recess of the base with a thickness of 0.2 mm, then place the base above the heating device, and dry it at 120°C for 20 min. Then remove the base from the heating device, place the steel mesh above the base according to the required number of layers, and use the same printing thickness and drying method to print and dry the second layer of nano-silver solder paste with the same shape and area vertically above the dried solder paste. After drying, do not remove the steel mesh, place the steel mesh to print and dry the third layer of solder paste, and repeat the operation until the required thickness is reached.

[0050] (2) Pretreatment, the uppermost layer of the mold after step (1) is printed and dried, the silver solder paste is exposed to a height of 0.4 mm, and then the mold is placed on the heating device, heated to 200°C at a rate of 5°C / min and kept for 10 min.

[0051] (3) Sintering, place a pressure block above the mold and silver solder paste after step 2 pretreatment, press with a pressure device at a pressure of 1 MPa, then quickly heat to 250°C and sinter for 20 min, after sintering, cool to room temperature with the furnace, and then remove the mold to obtain the sintered silver pad after molding.

[0052] Example 4:

[0053] The process for low-temperature large-area uniform sintering of nano-silver solder paste in this example is as follows:

[0054] (1) Layered printing and drying of nano-silver solder paste using a mold, the mold is composed of a base, positioning pins and multiple layers of steel mesh, the positioning pins are located at the four corners of the base, the steel mesh is vertically above the base, the base has a recess with the same shape and size as the desired pad, and the steel mesh has a through hole with the same shape and size as the recess. First, print a layer of nano-silver solder paste in the recess of the base, the thickness of the solder paste is 0.4 mm, then place the base on the heating device, dry at 120°C for 20 min. Then remove the base from the heating device, place the steel mesh above the base according to the required number of layers, and use the same printing thickness and drying method to print and dry the second layer of nano-silver solder paste vertically above the dried solder paste. After drying, do not remove the steel mesh, place the steel mesh to print and dry the third layer of solder paste, repeat the operation, and finally reach the desired thickness.

[0055] (2) Pretreatment, the uppermost layer of the mold after step (1) is printed and dried, the silver solder paste is exposed to a height of 0.4 mm, and then the mold is placed on the heating device, heated to 200°C at a rate of 5°C / min and kept for 10 min.

[0056] (3) Sintering, place a pressure block above the mold and silver solder paste after step 2 pretreatment, press with a pressure device at a pressure of 1 MPa, then quickly heat to 250°C and sinter for 20 min, after sintering, cool to room temperature with the furnace, and then remove the mold to obtain the sintered silver pad after molding.

[0057] Example 5:

[0058] The process for low-temperature large-area uniform sintering of nano-silver solder paste in this example is as follows:

[0059] (1) Using a mold to print and dry the nano-silver solder paste layer by layer, the mold is composed of a base, positioning pins and multiple layers of steel mesh, the positioning pins are located at the four corners of the base, the steel mesh is located vertically above the base, the base has a recess with the same shape and size as the required pad, and the steel mesh has a through hole with the same shape and size at the same position corresponding to the recess. First, print a layer of nano-silver solder paste in the recess of the base with a thickness of 0.6 mm, then place the base above the heating device, and dry it at 110°C for 10 min. Then remove the base from the heating device, place the steel mesh above the base according to the required number of layers, and use the same printing thickness and drying method to print and dry the second layer of nano-silver solder paste with the same shape and area vertically above the dried solder paste. After drying, do not remove the steel mesh, place the steel mesh to print and dry the third layer of solder paste, and repeat the operation until the required thickness is reached.

[0060] (2) Pretreatment, remove the uppermost layer of steel mesh from the mold printed and dried in step (1), expose the silver solder paste to a height of 0.6 mm, then place the entire mold above the heating device, heat to 200°C at a rate of 5°C / min and hold for 10 min.

[0061] (3) Sintering, place a pressure block above the mold and silver solder paste after pretreatment in step 2, apply a pressure of 2 MPa with a pressure device, then quickly heat to 250°C and sinter for 20 min. After sintering, cool to room temperature in the furnace, remove the mold to obtain the sintered silver pad after forming.

[0062] Example 6:

[0063] The process for low-temperature and large-area uniform sintering of nano-silver solder paste in this example is as follows:

[0064] (1) Using a mold to print and dry the nano-silver solder paste layer by layer, the mold is composed of a base, positioning pins and multiple layers of steel mesh, the positioning pins are located at the four corners of the base, the steel mesh is located vertically above the base, the base has a recess with the same shape and size as the required pad, and the steel mesh has a through hole with the same shape and size at the same position corresponding to the recess. First, print a layer of nano-silver solder paste in the recess of the base with a thickness of 0.6 mm, then place the base above the heating device, and dry it at 110°C for 10 min. Then remove the base from the heating device, place the steel mesh above the base according to the required number of layers, and use the same printing thickness and drying method to print and dry the second layer of nano-silver solder paste with the same shape and area vertically above the dried solder paste. After drying, do not remove the steel mesh, place the steel mesh to print and dry the third layer of solder paste, and repeat the operation until the required thickness is reached.

[0065] (2) Pretreatment, the uppermost layer of the mold printed and dried in step (1) is taken off, the silver solder paste is exposed to a height of 0.6 mm, and then the whole mold is placed above the heating device, heated to 220℃ at a heating rate of 10℃ / min and kept for 30 min.

[0066] (3) Sintering forming, placing a pressing block above the mold and silver solder paste pretreated in step 2, using a pressure device to press a pressure of 2 MPa, then quickly heating to 260℃ and sintering for 40 min, after sintering, cooling to room temperature in the furnace, and taking out the mold to get the sintered silver pad block after forming.

Claims

1. A method for making a low modulus, high thermal conductivity sintered silver slug, comprising: Specifically comprising the following steps: Step 1. Layered printing and drying of silver nano solder paste using a mold, the mold is composed of a base, positioning pins and multiple layers of steel mesh, the positioning pins are located at the four corners of the base, the steel mesh is vertically above the base, the base is provided with a recess with the same shape and size as the required pad, the steel mesh is provided with a through hole with the same shape and size at the same position corresponding to the recess, first, print a layer of silver nano solder paste in the recess of the base, the thickness of the solder paste is 0.2-0.6 mm, then place the base above the heating device, dry at a temperature of 110-120℃ for 10-20 min, then take the base off the heating device, place the steel mesh above the base according to the required number of layers, print and dry the second layer of silver nano solder paste with the same shape and area above the dried solder paste using the same printing thickness and drying method, without taking off the steel mesh after drying, place the steel mesh to print and dry the third layer of solder paste, repeat the operation, and finally reach the required thickness; Step 2. Pretreatment, remove the uppermost layer of steel mesh from the mold printed and dried in step 1, expose the silver solder paste to a height of 0.2-0.6 mm, then place the entire mold above the heating device, heat to 200-220℃ at a heating rate of 5-10℃ / min and maintain for 10-30 min, so that the silver solder paste obtains a certain strength; Step 3. Sintering, place a pressing block above the mold and silver solder paste after pretreatment in step 2, apply a pressure of 0-2 MPa using a pressure device, then quickly heat to 250-260℃, sinter for 20-40 min, after sintering, cool to room temperature in the furnace, take out the mold to obtain the sintered silver pad after forming.

2. The method of claim 1 ; characterized in that, The base thickness in step 1 is 3-5 mm, the recess depth is 0.2-0.6 mm, and the steel mesh thickness is 0.2-0.6 mm.

3. The method of claim 1 ; wherein, The sintered silver pad in step 3 is a porous structure with a Young's modulus of 5-10 GPa, a thermal conductivity of 200-240 W / (m·℃), a sintering porosity of 10%-30%, and a thickness of 1.0-3.0 mm.

4. The method of claim 1 ; wherein, The double-sided structure packaging connection is completed using the sintered silver nano solder paste, the chip is connected to the lower copper substrate, the sintered silver pad is connected to the upper surface of the chip, and the upper copper substrate is connected to the other side of the sintered silver pad.

Images