Prefabricated silver soldering lug for interconnection of power module chips and manufacturing method of prefabricated silver soldering lug

Abstract

The invention provides a prefabricated silver soldering lug for interconnection of chips of a power module and a manufacturing method of the prefabricated silver soldering lug. The prefabricated silver soldering lug comprises a thin silver piece, silver paste layers coated on the upper surface and the lower surface of the thin silver piece, and a chip fixed on the thin silver piece through the silver paste layers. Through unique structure and process design, the prefabricated silver soldering lug shows remarkable advantages in the aspects of electrical performance, thermal management performance, process adaptability, product consistency and the like, powerful guarantee is provided for high-performance and high-reliability operation of a power module, and the prefabricated silver soldering lug has wide application prospects and huge economic value.

Description

Technical Field

[0001] This invention relates to a prefabricated silver solder pad for interconnecting power module chips and its manufacturing method. Background Technology

[0002] In the power modules of electronic devices, chip interconnect and system sintering technologies are crucial for ensuring the performance and reliability of the power modules.

[0003] Traditional soldering materials and technologies are increasingly revealing numerous problems when facing the demands of modern power modules with high power density and high operating temperatures. For example, traditional tin-based solders typically have a thermal conductivity of around 60 W / (mK), which is insufficient to meet the rapid heat dissipation requirements of power modules. Under high power operation, this can lead to excessively high chip temperatures, thereby affecting chip performance and lifespan. Moreover, tin-based solders have a relatively low melting point, making them prone to softening or even melting at high temperatures. This reduces the connection strength of the solder joints and impacts the reliability of the power module.

[0004] In chip interconnection, while traditional wire bonding technology can achieve electrical connections between chips and substrates to a certain extent, it occupies a significant amount of space and limits the integration density of power modules as they become increasingly miniaturized and highly integrated. Furthermore, wire bonding has limited mechanical strength; when power modules are subjected to vibration, impact, or other external forces, the wires are prone to breakage, leading to electrical connection failure. Additionally, some existing sintering technologies may experience agglomeration of sintering materials during the sintering process, resulting in uneven sintering and affecting connection quality. Moreover, excessively high sintering temperatures for some materials can cause thermal damage to chips and other electronic components, reducing component performance and reliability. For example, while some nano-silver materials have good electrical and thermal conductivity, the nanoparticles are prone to agglomeration and there are large batch-to-batch differences, making the sintering process difficult to control and resulting in poor product consistency and stability. Furthermore, traditional welding and sintering processes have high requirements for the coplanarity of the connecting surfaces. For example, the lap joint technology for sintered silver requires a coplanarity tolerance of only 20µm at the lap joint, which is a major challenge for complex bending and forming technologies, increasing the difficulty and cost of the process.

[0005] With the rapid development of new energy vehicles, 5G communications, photovoltaic energy storage, and other fields, the performance requirements for power modules are becoming increasingly stringent, such as higher power density, better heat dissipation, stronger reliability, and wider operating temperature ranges. Traditional welding and sintering technologies and materials are no longer sufficient to meet these increasingly demanding requirements. Therefore, there is an urgent need for high-performance materials and technologies for power module chip interconnection and system sintering to solve the aforementioned problems in existing technologies. Summary of the Invention

[0006] This invention provides a prefabricated silver solder pad for interconnecting power module chips and its manufacturing method, which can effectively solve the above-mentioned problems.

[0007] This invention is implemented as follows:

[0008] A prefabricated silver solder pad for interconnecting power module chips includes a thin silver sheet, a silver paste layer coated on the upper and lower surfaces of the thin silver sheet, and a chip fixed on the thin silver sheet by the silver paste layer.

[0009] A method for fabricating a pre-fabricated silver solder pad for interconnecting power module chips includes the following steps:

[0010] S1. Prepare thin silver sheets and silver paste, wherein the thin silver sheets are obtained through surface treatment;

[0011] S2, silver paste coating;

[0012] S3. Drying treatment.

[0013] The beneficial effects of this invention are:

[0014] (1) The combination of thin silver sheet and silver paste provides excellent thermal conductivity. On the one hand, the high purity of the thin silver sheet ensures its good thermal conductivity; on the other hand, the high silver powder content in the silver paste and the dense structure formed after sintering allow heat to be quickly transferred from the chip to the substrate and then dissipated through the heat dissipation system. Tests show that the thermal conductivity of the pre-fabricated silver solder sheet of this invention is 1-2 times higher than that of traditional tin-based solder, effectively reducing the chip's operating temperature. In high-power operation of new energy vehicle power modules, the chip temperature can be reduced by 15-20°C, which is crucial for improving chip performance and lifespan. Lower operating temperature reduces electron migration within the chip, preventing performance degradation and failure due to excessive temperature, and extending chip lifespan. Simultaneously, the silver paste is uniformly coated on the upper and lower surfaces of the thin silver sheet and adheres fully to the chip and substrate during sintering, ensuring uniform heat transfer at the interface. This effectively avoids the generation of localized hot spots and ensures the overall temperature uniformity of the power module. For example, in the server power modules of some large data centers, uniform heat dissipation can prevent equipment performance degradation and failures caused by local overheating, improve the stability and reliability of server operation, and reduce maintenance costs caused by uneven heat dissipation.

[0015] (2) Reliable Connection Strength: Special treatment of the silver sheet surface enhances the adhesion between the silver paste and the silver sheet. Furthermore, the metallurgical bond formed during sintering further improves the connection strength. In simulated tests under harsh environmental conditions such as vibration and impact, the connection points of this invention can withstand greater external forces without detachment or damage. For example, in power module applications in the aerospace field, this prefabricated silver solder sheet ensures a reliable connection between the chip and the substrate under intense vibration during high-speed flight, guaranteeing the normal operation of avionics equipment.

[0016] (3) Tolerant Process Conditions: Compared to traditional sintering processes, the low-temperature sintering process of this invention has more tolerant temperature requirements. The lower sintering temperature not only reduces the risk of thermal damage to chips and other electronic components but also lowers the requirements for sintering equipment, saving energy consumption. Simultaneously, the requirements for the coplanarity of the connecting surfaces are relatively relaxed, with tolerances allowed to be relaxed to approximately 50µm, reducing process difficulty and improving production efficiency and yield. This makes it easier to ensure product quality in actual production, reducing increased production costs and product scrap rates caused by excessively difficult processes.

[0017] (4) Precise Material Formulation and Preparation Process: During the preparation of silver paste, the precise control of the proportions and mixing processes of various components such as silver powder and organic carrier, as well as the strict screening of raw materials for thin silver sheets and the standardization of surface treatment processes, ensures the performance consistency of each batch of products. The fluctuation range of various performance indicators (such as resistance, thermal conductivity, connection strength, etc.) is controlled within a very small range, ensuring the stability of product quality during large-scale production. This is of great significance for industries that use power modules on a large scale, such as photovoltaic power plants and electric vehicle manufacturing, as it can reduce system compatibility issues and after-sales maintenance costs caused by differences in product performance. Attached Figure Description

[0018] Figure 1 This is a cross-sectional view of a prefabricated silver solder sheet for interconnecting power module chips and its manufacturing method, according to the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0020] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0021] Reference Figure 1 As shown, a prefabricated silver solder pad for interconnecting power module chips includes a thin silver sheet, a silver paste layer coated on the upper and lower surfaces of the thin silver sheet, and a chip fixed on the thin silver sheet by the silver paste layer.

[0022] The silver sheet has a purity ≥99.95% and a thickness of 50μm-100μm. In one embodiment, to ensure the thermal conductivity, resistivity, and strength of the silver sheet, the purity is approximately 99.99%. This ensures excellent electrical conductivity (resistivity reduced by 30%-50%) and thermal conductivity (thermal conductivity 220 W / (m·K)). Furthermore, it prevents impurity agglomeration during high-temperature sintering. If the purity is <99.95%, the increased impurity content leads to increased resistivity (measurements show that the resistance of a 99.9% pure silver sheet increases by approximately 15%); decreased thermal conductivity (thermal conductivity reduced to below approximately 200 W / (m·K)); and the potential formation of brittle phases by impurity elements during sintering, reducing bond strength (shear strength reduced by 20-30%).

[0023] In the above embodiments, in the most preferred embodiment, the purity of the silver sheet is set to 99.99%. Experimental data shows (see the table below):

[0024]

[0025] Test conditions:

[0026] Sample dimensions: 10mm (length) × 5mm (width) × 80μm (thickness);

[0027] Environment: 25℃±1℃, 50%±5% RH;

[0028] Method: Four-point probe method (according to ASTM F84 standard);

[0029] Data source: Average value of 3 parallel experiments.

[0030] As shown in the chart above, when the purity of the silver sheet decreases from 99.99% to 99.9%, the resistance increases by 15% (0.015Ω → 0.01725Ω), corresponding to an increase of approximately 18% in the conduction loss of the power module.

[0031] In the above embodiments, to balance mechanical strength and cost and to be applicable to most power modules, the thickness of the silver sheet is approximately 80 μm. Specifically, if the thickness of the silver sheet is <50 μm, the mechanical strength of the silver sheet is insufficient (the fracture probability of the 50 μm sample in the bending test is <1%, while that of the 30 μm sample reaches 15%), and the current carrying capacity is limited (at a current of 100A, the temperature rise of the 30 μm silver sheet is 8°C higher than that of the 50 μm sheet); if the thickness of the silver sheet is >100 μm, it will increase the material cost (the cost of the silver sheet will increase by more than 40%), and may also affect the miniaturization of the power module (increased thickness leads to increased module size).

[0032] Specifically, the thickness of the thin silver sheet needs to be selected according to different power requirements, so this case does not impose too many restrictions. In the actual production process, the appropriate thickness needs to be selected according to the actual requirements.

[0033] The silver paste layer is composed of alloy silver powder and an organic carrier, wherein the organic carrier has a mass fraction of 5%-7%; wherein the alloy silver powder is composed of silver powder, copper powder and palladium powder, wherein the mass fraction of silver powder is 90%-95%, the mass fraction of copper powder is 3%-6%, the mass fraction of palladium powder is 1%-3%, and the total mass fraction of silver powder, copper powder and palladium powder is 100%. In the silver paste formulation, silver (Ag) dominates electrical and thermal conductivity, copper (Cu) enhances mechanical strength and inhibits silver migration, and palladium (Pd) improves high-temperature oxidation resistance (stable at 280℃). The optimal ratio (Ag 93% - Cu 5% - Pd 2%) was verified by differential scanning calorimetry (DSC) and thermal conductivity testing to be the best in terms of overall performance. The silver paste layer thickness of 25μm-35μm avoids uneven coverage caused by being too thin (<25μm is prone to incomplete sintering) and prevents increased porosity caused by being too thick (>35μm). It forms a thickness ratio of 1:0.3 to 0.7 with the thin silver sheet, ensuring the interface strength (optimal shear strength) after sintering.

[0034] The surface of the thin silver sheet was treated with acid pickling in dilute nitric acid solution and ultrasonic cleaning. Specifically, the surface treatment (8% nitric acid pickling + 40kHz ultrasonic cleaning) was confirmed by SEM to control the surface roughness to ≤0.1μm, significantly improving the adhesion of silver paste (50% higher than the untreated sample), while the formation of metallurgical bonding (grain size 1-5μm) was verified by SEM and aging test (resistance change <5% after 5000 hours), demonstrating its long-term stability.

[0035] In the above embodiments, the high-purity silver sheet and optimized silver paste formula reduce the resistance by 30%-50% and achieve a thermal conductivity of 220W / (m·K), far exceeding that of traditional tin-based solder (60W / (m·K)), significantly reducing power loss. The uniform silver paste layer and thin silver sheet work together to dissipate heat, reducing the chip operating temperature by 15-20℃ and avoiding local overheating. Furthermore, acid pickling and ultrasonic cleaning ensure strong adhesion of the silver paste, and the sintering temperature (250-280℃) is lower than that of traditional processes, reducing thermal damage. The coplanarity requirement is relaxed to 50μm (compared to 20μm in the traditional process), reducing production difficulty. Moreover, the metallurgical bonding interface remains stable under vibration and high-temperature environments (resistance change after aging <5%), and its lifespan far exceeds that of traditional welding technologies.

[0036] A method for fabricating a pre-fabricated silver solder pad for interconnecting power module chips includes the following steps:

[0037] S1. Prepare thin silver sheets and silver paste, wherein the thin silver sheets are obtained through surface treatment;

[0038] S2, silver paste coating;

[0039] S3. Drying treatment.

[0040] In step S1, the thin silver sheet is acid-washed with 8% dilute nitric acid solution for 4 minutes and ultrasonically cleaned with 0.5%-1.5% sodium dodecylbenzenesulfonate solution at 40 kHz for 15 minutes. The silver paste preparation process in step S1 is as follows: silver powder, copper powder, and palladium powder are mixed and alloyed; after melting, the mixture is cooled and then powdered to form alloy silver powder. The alloy silver powder undergoes surface treatment and is finally mixed with an organic carrier at a mass ratio of 5%-7%, as detailed below.

[0041] The purity of the silver sheet directly affects its electrical and thermal conductivity. Therefore, high-quality silver with a purity of 99.95% or higher must be used to make the silver sheet. The thickness of the silver sheet needs to take into account factors such as the power level of the power module, space constraints, and heat dissipation requirements. For small and medium power modules, while pursuing good electrical performance and heat dissipation, cost and space occupation are taken into account, and a silver sheet with a thickness of 50μm is often selected. For high power modules, due to higher requirements for heat dissipation and current carrying capacity, a silver sheet with a thickness of 100μm may be selected.

[0042] When selecting thin silver sheets, their surface quality must be strictly controlled. Optical microscopes and scanning electron microscopes (SEM) should be used for inspection to ensure a smooth, flat surface free of visible scratches, pits, and impurities. Even extremely small surface defects can cause problems during subsequent silver paste coating and sintering processes, such as poor localized adhesion of the silver paste, leading to decreased bonding performance.

[0043] During storage and processing, a thin silver oxide film inevitably forms on the surface of the silver sheet, which severely affects the adhesion between the silver paste and the silver sheet. Therefore, the silver sheet is first placed in a specially designed pickling tank containing a precisely prepared 8% dilute nitric acid solution. The solution is then soaked for 4 minutes at room temperature. The chemical reaction between the dilute nitric acid and the silver oxide dissolves and removes the oxide layer. During the soaking process, the solution is slowly stirred using a magnetic stirrer at a speed of 50-100 rpm to ensure that the solution is in full contact with the surface of the silver sheet and that the oxide layer is dissolved uniformly.

[0044] After pickling, quickly remove the thin silver sheet and rinse it in running deionized water. Rinse for at least 5 minutes to ensure that any residual dilute nitric acid solution on the surface of the silver sheet is completely removed, preventing residual acid from corroding subsequent processes. After rinsing, check the pH value of the rinsing water to confirm the cleaning effect. Only when the pH value reaches the neutral range of 6.5-7.5 can the next step be carried out. Place the pickled and rinsed thin silver sheet into an ultrasonic cleaning tank containing a surfactant solution. The surfactant used is sodium dodecylbenzenesulfonate, with a concentration of 0.5-1.5%. The ultrasonic cleaning tank is equipped with an ultrasonic generator with precisely adjustable frequency. The ultrasonic frequency is set to 40kHz, and the ultrasonic power is 100-200W. Under ultrasonic action, cleaning lasts for 15 minutes. The high-frequency vibrations generated by the ultrasound create countless tiny cavitation bubbles in the solution. When these bubbles break on the surface of the thin silver sheet, they generate a powerful impact force, effectively removing residual impurity particles and allowing surfactant molecules to be more evenly adsorbed onto the silver sheet surface. This reduces surface tension and enhances the wettability and activity of the silver sheet surface, creating favorable conditions for subsequent silver paste coating. After ultrasonic cleaning, the thin silver sheet is removed from the cleaning tank and rinsed again with deionized water to remove residual surfactant solution. Then, the thin silver sheet is placed in an oven at 90℃ and dried for 1.5 hours. The air circulation system in the oven ensures uniform temperature distribution, allowing the thin silver sheet to dry thoroughly for later use.

[0045] The specific steps of step S1 are as follows: Silver, as the basic component, plays a dominant role in this solder sheet due to its excellent electrical and thermal conductivity, with a mass fraction set at 90-95%. Copper is added in appropriate amounts; copper not only enhances the alloy's strength but also positively contributes to improving electrical and thermal conductivity, with a mass fraction controlled at 3-6%. A small amount of palladium is added; palladium has good oxidation resistance and high-temperature stability, with a mass fraction of 1-3%. For example, the silver content is precisely set at 93%, the copper content at 5%, and the palladium content at 2%. Under this formula, the... Thermal conductivity testing showed that the thermal conductivity of the solder pads reached 220 W / (m·K). Differential scanning calorimetry (DSC) measurements indicated a melting point as high as 280℃, fully meeting the heat dissipation and high-temperature stability requirements of the power module during high-power operation. High-purity silver, copper, and palladium raw materials were selected and placed in a precise ratio into a vacuum melting furnace. This furnace is equipped with an advanced temperature control system and vacuum monitoring device, ensuring thorough fusion of the raw materials at a high temperature of 1500-1600℃. During the melting process, a vacuum pump maintained the vacuum level inside the furnace at 10... -3 -10 - 4 The process effectively prevents metal oxidation at high temperatures. Simultaneously, an electromagnetic stirring device agitates the molten metal within the furnace, ensuring uniform distribution of elements. The melting time is strictly controlled to 1-2 hours; too short a time may result in insufficient element fusion, while too long a time may cause metal burn-off. After rapid water cooling, the molten alloy undergoes a gas atomization powdering process. High-pressure gas is used through specially designed atomizing nozzles to break the molten alloy into fine droplets. These droplets rapidly cool and solidify during flight, forming powder. Specifically, the pressure of the atomizing gas (nitrogen is used to avoid introducing impurities) is controlled at 3-5 MPa, and the flow rate of the atomizing medium is precisely adjusted using a mass flow controller. This method yields silver alloy powder with an average particle size of 10-30 μm. Particle size control is crucial for the performance of subsequent solder sheets; excessively small particle sizes may lead to powder agglomeration, while excessively large particle sizes will affect the forming and sintering effect of the solder sheets.

[0046] In step S1, to avoid easy agglomeration of silver alloy powder, this embodiment further employs a chemically modified surface treatment method; the powder is placed in a solution containing a specific surfactant, which is prepared in a specially designed reaction vessel equipped with an ultrasonic generator and a stirring device. Under ultrasonic action, the mixture is stirred for 30-60 minutes at an ultrasonic frequency of 20-40 kHz, so that the surfactant molecules can be uniformly adsorbed on the powder surface. Taking silane coupling agent as an example, it can form a chemically bonded protective film on the powder surface, which not only improves the dispersibility of the powder but also enhances its compatibility with subsequent added components. The treated powder is filtered through a precision filter device, then washed multiple times with deionized water to remove excess surfactant, and finally dried in a vacuum drying oven at 50-80°C for 12-24 hours for later use.

[0047] Furthermore, the organic carrier in the silver paste layer is an important component of the silver paste. It is composed of multiple ingredients working synergistically. Among them, terpineol, as the main solvent, effectively dissolves other components such as thickeners and dispersants due to its good solubility and volatility, and adjusts the viscosity during the silver paste coating process. Terpineol accounts for approximately 60-70% of the organic carrier by mass. The addition of ethyl cellulose, a thickener, aims to increase the viscosity of the silver paste and prevent it from flowing due to gravity during coating. Its mass percentage is 15-25%. Fatty acid compounds (such as oleic acid), a dispersant, can significantly reduce the surface tension between silver powders, allowing them to be uniformly dispersed in the organic carrier and avoiding agglomeration. Its mass percentage is 5-10%. In addition, a small amount of leveling agent (such as silicone leveling agent), accounting for about 1-3% by weight, can be added to improve the surface smoothness after the silver paste is applied, ensuring that the silver paste forms a uniform coating on the surface of the thin silver sheet. Finally, the accurately weighed silver powder and each component of the organic carrier are added sequentially to a planetary mixer equipped with a high-precision speed control system and temperature monitoring device. During the mixing process, the mixture is first stirred at a low speed of 100-150 r / min for 15-30 minutes to ensure that the components are initially mixed evenly and to prevent the silver powder from agglomerating due to high-speed stirring. Subsequently, the speed is increased to 250-350 r / min and stirring is continued for 1-2 hours to ensure that the silver powder and organic carrier are fully mixed. During the stirring process, the temperature is controlled at 25-35℃ using a temperature monitoring device to avoid the volatilization of organic carrier components or oxidation of silver powder due to heat generated by stirring friction, which would affect the performance of the silver paste. After stirring, a fine and uniform silver paste with good thixotropic properties is obtained.

[0048] In step S2, the silver paste is applied by screen printing, spraying, or scraping. After coating, multiple points are randomly selected for multiple sets of measurements. If the difference between the average values ​​of the multiple sets of measurements is greater than 5µm, recoating is performed, as detailed below:

[0049] Among them, screen printing: If screen printing is used, the screen must be carefully selected according to the characteristics of the silver paste and the precision requirements of the product. For the silver paste system of this invention, when a silver paste layer with a thickness of 25-35μm needs to be coated, a 300-mesh stainless steel screen is a more ideal choice. Before printing, the screen printing machine is fully debugged and the squeegee angle of the printing machine is adjusted so that it forms an angle of 60-70° with the screen surface. This angle can ensure that when the squeegee scrapes the silver paste, it has enough pressure to make the silver paste pass through the screen holes, while avoiding excessive pressure that would cause the silver paste to be over-compressed and deformed. The squeegee speed is set at 15-25mm / s and the pressure is controlled at 0.15-0.25MPa. At the same time, the positioning system of the printing machine ensures that the position of the thin silver sheet on the printing table is accurately fixed, ensuring that the positional accuracy of each printing is within ±0.1mm.

[0050] Spraying: If spraying is selected, a special precision spray gun must be used. The nozzle diameter of the spray gun is selected according to the particle size and viscosity of the silver paste, generally 0.5-1.0mm. Connect the spray gun to the adjustable compressed air source and the silver paste delivery system. Before spraying, dilute the silver paste appropriately to make its viscosity meet the spraying requirements (generally the viscosity is controlled at 10-20Pa·s). Adjust the compressed air pressure to 0.3-0.5MPa. Keep the distance between the spray gun and the surface of the thin silver sheet at 150-200mm to ensure that the silver paste can be evenly sprayed on the surface of the thin silver sheet. At the same time, the movement path and speed of the spray gun are controlled by programming to ensure the uniformity and coverage of the silver paste coating.

[0051] Scraping: Scraping is suitable for applications with relatively low coating precision requirements and small production scale. A suitable scraper is selected, typically made of stainless steel or PTFE. Its thickness and hardness are chosen based on the thickness and rheological properties of the silver paste. Before scraping, the silver paste is evenly applied to one end of a thin silver sheet. Then, the scraper is moved from the starting end to the other end at a uniform speed and pressure, with the speed controlled at 5-10 mm / s. The pressure is adjusted according to the required silver paste thickness, generally controlled by feel and experience to ensure uniform silver paste coating thickness.

[0052] After coating, immediately use a non-contact laser thickness gauge to measure the thickness of the silver paste layer at multiple points. Measure at least five points at different locations on the thin silver sheet (e.g., the four corners and the center), and record the thickness data for each point. Calculate the average thickness and compare it with the preset target thickness. If the average thickness deviation exceeds ±5μm, analyze the cause based on the direction and magnitude of the deviation. If it's a coating parameter issue, such as scraper speed, pressure, or spray gun flow rate, adjust the parameters promptly and recoat. If it's a viscosity or flowability issue with the silver paste itself, adjust the silver paste appropriately (e.g., add solvent or thickener) and recoat. Simultaneously, observe the smoothness and uniformity of the silver paste surface using an optical microscope to check for defects such as missed coatings, accumulation, and bubbles. For tiny bubbles, use low-temperature baking (40-50℃, 5-10 minutes) to allow them to escape. For missed coatings and accumulation areas, treat them manually or recoat.

[0053] During the above coating process, regardless of the coating method used, the coating status of the silver paste must be closely monitored. For screen printing, observe the flow of the silver paste on the screen and its passage through the screen openings in real time. If the silver paste is found to clog the screen openings, the machine must be stopped immediately for cleaning. For spraying, pay attention to the shape and uniformity of the spray. If the spray is uneven or skewed, adjust the spray gun parameters in time. For squeegee coating, constantly check the consistency of the amount of silver paste extruded under the squeegee and the coating thickness.

[0054] In step S3, the coated silver sheet is placed in a forced-ventilation drying oven at 70℃-80℃ for 20-30 minutes. During the drying process, the hot air inside the drying oven circulates at a flow rate of 0.5-1.0 m / s, as follows:

[0055] The thin silver sheets coated with silver paste are placed in a drying oven with forced ventilation for drying. The drying oven is equipped with multiple shelves to ensure sufficient space between the silver sheets and smooth air circulation. The drying temperature is set to 70℃ and the drying time is 20 minutes. During the drying process, the hot air in the drying oven circulates at a flow rate of 0.5-1.0m / s, allowing the solvent in the silver paste to evaporate quickly and evenly, improving the initial adhesion of the silver paste layer, and avoiding problems such as cracking or peeling of the silver paste due to local overheating. After drying, the thin silver sheets are removed and allowed to cool to room temperature before proceeding to the next step.

[0056] The prefabricated silver solder sheet (a composite structure consisting of a thin silver sheet and a double-sided silver paste layer) in this invention is used in conjunction with a specially designed low-temperature sintering process when applied to chip interconnects. This process can achieve high-quality sintering connections at relatively low temperatures (30-50°C lower than traditional sintering temperatures), reducing the risk of thermal damage to chips and other electronic components, as well as lowering process difficulty and cost. Furthermore, the prefabricated silver solder sheet has relatively relaxed requirements for the coplanarity of the connection surfaces, with tolerances allowed to be relaxed to approximately 50µm, significantly reducing the process challenges of complex bending and forming techniques, and improving production efficiency and yield. Secondly, in terms of the microstructure design of the solder sheet, a special preparation process forms uniformly distributed nanoscale pores within the silver solder sheet. This porous structure not only increases the contact area between the solder sheet and the chip and substrate surfaces, making the weld stronger, but also effectively alleviates stress concentration problems caused by differences in thermal expansion coefficients during sintering, further improving connection reliability. Simultaneously, the porous structure facilitates the discharge of flux and gases during sintering, reducing welding defects and improving welding quality.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A prefabricated silver solder pad for interconnecting power module chips, characterized in that, It includes a thin silver sheet, a silver paste layer coated on the upper and lower surfaces of the thin silver sheet, and a chip fixed on the thin silver sheet by the silver paste layer.

2. The prefabricated silver solder sheet for interconnecting power module chips according to claim 1, characterized in that, The silver sheet has a purity of ≥99.95% and a thickness of 50μm-100μm.

3. The prefabricated silver solder sheet for interconnecting power module chips according to claim 1, characterized in that, The silver paste layer is composed of alloy silver powder and an organic carrier, wherein the organic carrier has a mass fraction of 5%-7%; wherein the alloy silver powder is composed of silver powder, copper powder and palladium powder, wherein the mass fraction of silver powder is 90%-95%, the mass fraction of copper powder is 3%-6%, the mass fraction of palladium powder is 1%-3%, and the total mass fraction of silver powder, copper powder and palladium powder is 100%.

4. The prefabricated silver solder sheet for interconnecting power module chips according to claim 1, characterized in that, The thickness of the silver paste layer is 25μm-35μm.

5. The prefabricated silver solder sheet for interconnecting power module chips according to claim 1, characterized in that, The surface of the thin silver sheet is treated with acid washing with dilute nitric acid solution and ultrasonic cleaning.

6. A method for fabricating a pre-fabricated silver solder pad for interconnecting power module chips, characterized in that: The method for manufacturing a prefabricated silver solder pad for power module chip interconnect as described in any one of claims 1-5 includes the following steps: S1. Prepare thin silver sheets and silver paste, wherein the thin silver sheets are obtained through surface treatment; S2, silver paste coating; S3. Drying treatment.

7. The method for fabricating a pre-fabricated silver solder pad for interconnecting power module chips according to claim 6, characterized in that, In step S1, the thin silver sheet is acid-washed with 8% dilute nitric acid solution for 4 minutes and ultrasonically cleaned with 0.5%-1.5% sodium dodecylbenzenesulfonate solution at 40 kHz for 15 minutes.

8. The method for fabricating a pre-fabricated silver solder pad for interconnecting power module chips according to claim 6, characterized in that, In step S1, the silver paste preparation process is as follows: silver powder, copper powder and palladium powder are mixed and alloyed, cooled after melting, and then powdered to form alloy silver powder. The alloy silver powder is then surface-treated and finally mixed with an organic carrier with a mass ratio of 5%-7%.

9. The method for fabricating a pre-fabricated silver solder pad for interconnecting power module chips according to claim 6, characterized in that, In step S2, the silver paste is applied by screen printing, spraying, or scraping. After the coating is completed, multiple points are randomly selected for multiple sets of measurements. If the difference between the average values ​​of the multiple sets of measurement data is greater than 5 μm, the paste is recoated.

10. The method for fabricating a pre-fabricated silver solder pad for interconnecting power module chips according to claim 6, characterized in that, In step S3, the coated thin silver sheet is placed in a forced ventilation drying oven at 70℃-80℃ for 20-30 minutes. During the drying process, the hot air in the drying oven circulates at a flow rate of 0.5-1.0m / s.

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