A high-reliability ultra-low void rate chip epoxy mounting vacuum high-temperature curing method

Abstract

The application discloses a high-reliability ultra-low void ratio chip epoxy mounting vacuum high-temperature curing method and belongs to the technical field of microelectronic packaging and microassembly. The method comprises the following steps: sequentially performing alcohol immersion, nitrogen baking and plasma cleaning on a substrate and pads on the surface of the substrate to obtain a pretreated substrate and pretreated pads; obtaining pretreated conductive glue; uniformly spraying the pretreated conductive glue on the center position of the pretreated pads under a set dispensing air pressure to form a conductive glue layer; mounting a to-be-mounted chip on the conductive glue layer to obtain a semi-finished product; and after the semi-finished product is alternately replaced through multiple rounds of vacuumizing and nitrogen charging, sequentially performing three-stage nitrogen atmosphere temperature rising, constant-temperature curing and temperature falling, and the preparation is completed. The method is used to solve the technical problems of high void ratio, unstable bonding quality and difficulty in simultaneously considering high reliability and ultra-low void ratio in the chip bonding process in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of microelectronic packaging and microassembly technology, specifically relating to a high-reliability, ultra-low void ratio chip epoxy mounting vacuum high-temperature curing method. Background Technology

[0002] With the continuous development of microelectronics technology, the integration and power density of chips are constantly increasing, leading to a significant increase in the internal heat flux density of chips. To ensure the normal function and reliability of chips, it is essential to provide them with a good heat dissipation path. In the field of microelectronic packaging, die bonding is a critical step, directly affecting the chip's heat dissipation and electrical performance. Currently, conductive silver paste bonding technology is widely used in chip assembly due to its excellent thermal conductivity, high bonding strength, and ease of assembly.

[0003] However, existing chip mounting and bonding technologies still face many unresolved issues. First, traditional chip bonding processes generally have a high void ratio, typically between 5% and 10%, and the bonding quality is unstable. For highly integrated, high-power products such as miniaturized power amplifiers, the internal heat flux density of the chip is high, and an excessively high void ratio severely impacts heat dissipation, leading to low heat transfer efficiency, increased thermal resistance, and even causing semiconductor device failure due to thermal fatigue. Second, during the bonding process, air bubbles are generated during the curing of the conductive silver paste. These bubbles cause uneven bonding, further increasing the void ratio. Simultaneously, air can easily be trapped during the transfer of the conductive silver paste from the storage syringe to the dispensing syringe, directly affecting dispensing quality and bonding accuracy. Furthermore, existing low-void ratio technologies, such as vacuum reflow soldering, often suffer from complex processes, high costs, and the need for extremely high pressure / temperature, limiting their application in large-scale production. Moreover, current chip bonding methods struggle to simultaneously achieve high reliability and ultra-low void ratios, especially at high temperatures, where the performance and stability of the bonding materials still need improvement, failing to meet the long-term usage requirements of high-power chips.

[0004] Therefore, developing a chip bonding method that can achieve high reliability and ultra-low void ratio is of great significance for improving the heat dissipation and electrical performance of chips. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a high-reliability, ultra-low void ratio chip epoxy mounting vacuum high-temperature curing method to solve the technical problems of high void ratio, unstable bonding quality, and difficulty in simultaneously achieving high reliability and ultra-low void ratio in the chip bonding process of the prior art.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a high-reliability, ultra-low void ratio chip epoxy mounting vacuum high-temperature curing method, comprising the following steps: The substrate and its surface pads were sequentially subjected to alcohol immersion, nitrogen baking and plasma cleaning to obtain the pretreated substrate and pretreated pads. The conductive adhesive is transferred from the storage syringe to the dispensing syringe, and after being allowed to stand vertically to warm up and the overflow adhesive is removed, the pretreated conductive adhesive is obtained. Match the appropriate dispensing needle to the size of the chip to be mounted, and spray the pre-treated conductive adhesive evenly at the center of the pre-treated pad under the set dispensing pressure to form a conductive adhesive layer; mount the chip to be mounted on the conductive adhesive layer to obtain a semi-finished product. After multiple rounds of alternating vacuuming and nitrogen purging of the semi-finished product, the product is then subjected to three stages of nitrogen atmosphere heating, constant temperature curing, and cooling to complete the preparation.

[0007] In one embodiment, the alcohol soaking time is 20-30 minutes, and the temperature is 40-50°C; The nitrogen baking is carried out in an anaerobic oven at a temperature of 80-100℃ for 50-70 minutes. The plasma cleaning uses an oxygen / nitrogen mixture, with a power of 40-80W and a time of 4-8 minutes, in which oxygen accounts for 10%-30%.

[0008] In one embodiment, the storage temperature of the storage syringe is -40°C, the transfer time is less than 2 minutes, and the vertical resting and warming is carried out at room temperature for 1 hour.

[0009] In one embodiment, matching the appropriate dispensing needle according to the size of the chip to be mounted specifically involves: Use 0.5mm, 0.7mm or 0.9mm dispensing needles. For chips smaller than 1mm in size, the diameter of the dispensing needle should be 0.15-0.25mm smaller than the size of the chip to be mounted.

[0010] In one embodiment, the set dispensing air pressure is 0.06-0.08 MPa; the spraying amount of the pretreated conductive adhesive is 0.3-0.5 mg / mm. 2 .

[0011] In one embodiment, the process of alternating vacuuming and nitrogen purging is as follows: The semi-finished product is pre-treated in the vacuum baking equipment in the following order: vacuuming, nitrogen filling, vacuuming, nitrogen filling, and vacuuming. Each vacuuming process takes between 2 minutes and 30 seconds and 3 minutes and 30 seconds, and each nitrogen filling process takes 2 minutes and 30 seconds.

[0012] In one embodiment, the three-stage nitrogen atmosphere heating process is as follows: In the first stage, the temperature is raised from room temperature to 30-40°C below the glass transition temperature of the conductive adhesive, and the heating time is 7-10 minutes, during which nitrogen is used for protection throughout the process. In the second stage, solvent removal is carried out at 30-40°C below the glass transition temperature of the conductive adhesive. In the third stage, the temperature is increased from 30-40°C below the glass transition temperature of the conductive adhesive to the glass transition temperature of the conductive adhesive, with a heating time of 5-10 minutes, and nitrogen gas is used for protection throughout the process.

[0013] In one embodiment, the solvent discharge process consists of at least two alternating vacuuming and nitrogen purging operations; each vacuuming operation lasts between 2 minutes and 30 seconds and 3 minutes and 30 seconds, and each nitrogen purging operation lasts 2 minutes and 30 seconds.

[0014] In one embodiment, the isothermal curing temperature is 120°C, and the time is 1 hour. When the isothermal curing process is halfway through, a vacuuming and nitrogen purging process is performed once. The vacuuming time is between 2 minutes and 30 seconds and 3 minutes and 30 seconds, and the nitrogen purging time is 2 minutes and 30 seconds. In another embodiment, the cooling process involves lowering the temperature from the isothermal curing temperature to 40°C, and the cooling time is 6-8 minutes.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention addresses the industry-wide problems of high void ratios, difficulty in removing air bubbles during curing, poor bonding quality stability, insufficient mass production adaptability of existing low-voidity processes, and difficulty in balancing ultra-low void ratios with long-term reliability under high-temperature conditions in existing chip epoxy mounting processes. It provides a highly reliable, ultra-low void ratio chip epoxy mounting vacuum high-temperature curing method. First, a combination of alcohol immersion, nitrogen baking, and oxygen-nitrogen mixed plasma cleaning pre-treatment is performed on the substrate and pads. This process removes organic oil, adsorbed moisture, and micro-oxide layers from the surfaces of the pads and substrate, increasing the surface energy of the pads and improving the interfacial wettability of the conductive adhesive. This fundamentally avoids voids and uneven bonding caused by poor interfacial bonding. Simultaneously, to address the issue of air entrapment during conductive adhesive transfer, a pre-treatment process involving low-temperature, short-time transfer, vertical resting at room temperature for rewarming, and venting and removing excess adhesive is employed to fully remove air mixed in with the adhesive. Combined with precise matching of chip size and dispensing needle, and a low-pressure, quantitative, and uniform dispensing process, the conductive adhesive is ensured to spread evenly, preventing air entrapment during chip mounting. Addressing the core challenge of solvents and small volatile molecules from cross-linking reactions failing to escape during the curing process of conductive adhesives, resulting in solidification voids trapped within the adhesive layer, this invention first performs a three-stage vacuum-nitrogen purging process on the assembled semi-finished product to expel residual air from the cavity and adhesive layer. Then, a staged, stepped temperature-curing scheme is employed. The system is first gently heated to 30-40°C below the glass transition temperature of the conductive adhesive, allowing the solvent within the adhesive to evaporate gently and uniformly. Simultaneously, within this temperature range, at least two alternating vacuum-nitrogen purging operations are performed. Before the adhesive layer crosslinks and cures, solvent volatiles are completely removed, and then the temperature is gradually increased to the glass transition temperature of the conductive adhesive to complete the curing transition. This avoids premature curing of the adhesive layer surface and sealing of gas. During the constant temperature curing process, vacuuming and nitrogen filling are alternately performed when the curing time is more than halfway through to remove small molecule gases generated by the crosslinking reaction. After curing, the internal stress of the system is eliminated by controlled and gradual cooling, preventing stress-induced interface microcracks and microvoids. This achieves complete removal of bubbles and volatiles throughout the curing cycle and significantly reduces the void rate after curing. Meanwhile, this invention achieves ultra-low void ratio control throughout the entire process, effectively reduces the thermal resistance of the adhesive layer, and solves the problem of heat dissipation failure of high-power chips. By using nitrogen-oxygen-free protection throughout the substrate baking and curing process, it avoids the problems of pad oxidation and conductive adhesive aging and degradation under high-temperature conditions, ensuring the long-term stability of the conductive and thermal conductivity and bonding strength of the adhesive layer. Combined with the stress relief design of stepped heating and controllable cooling, it significantly improves the thermal fatigue resistance of the package and solves the contradiction between ultra-low void ratio and long-term reliability that existing processes cannot achieve. It can fully meet the packaging requirements of highly integrated and high-power chips. Attached Figure Description

[0016] Figure 1 This is an image showing the appearance of the attenuator chip after bonding in Embodiment 1 of the present invention; Figure 2 This is an X-ray image of the attenuator chip after bonding in Embodiment 1 of the present invention; Figure 3 This is a diagram showing the shear force test results of the attenuator chip in Embodiment 1 of the present invention. Detailed Implementation

[0017] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0018] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0019] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0020] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0021] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0022] This invention provides a high-reliability, ultra-low void ratio chip epoxy mounting vacuum high-temperature curing method, comprising the following steps: Step 1: Pre-treatment of the substrate and its surface pads; Step 2: Transfer and warming of the one-component epoxy conductive adhesive; Step 3: Adjust dispensing parameters and conduct dispensing tests; Step 4: Vacuum high-temperature curing; Step 5: Test the bonding and curing effect.

[0023] Step 1 specifically involves sequentially subjecting the substrate and its surface pads to alcohol immersion, nitrogen baking, and plasma cleaning to obtain a pretreated substrate and pretreated pads, including the following steps: Step 101: Soak in alcohol for 20-30 minutes at a temperature of 40-50°C. Step 102: Use cotton swabs to wipe away surface dirt and alcohol residue; Step 103: Place in an anaerobic oven for nitrogen baking at a temperature of 80-100℃ for 50-70 minutes; Step 104: Use oxygen / nitrogen mixed plasma cleaning at a power of 40-80W for 4-8 minutes, with oxygen accounting for 10%-30%.

[0024] Step 2 specifically involves transferring the conductive adhesive from the storage syringe to the dispensing syringe, allowing it to stand vertically to warm up, and then venting and removing excess adhesive to obtain the pretreated conductive adhesive. This includes the following steps: Step 201: Take the storage syringe of the single-component epoxy conductive adhesive out of the -40℃ ultra-low temperature freezer and transfer it to the dispensing syringe within 2 minutes. During the transfer process, prevent air from being trapped in the conductive adhesive. Step 202: Place the dispensing syringe vertically with the tip facing down and let it stand at room temperature for 1 hour to allow it to warm up. Step 203: Gently touch the end of the syringe to block it, causing the conductive adhesive to slightly overflow; Step 204: Use an anti-static lint-free cloth to wipe away any excess conductive adhesive from the tip.

[0025] In step 3, specifically, a suitable dispensing needle is matched according to the size of the chip to be mounted, and the pre-treated conductive adhesive is evenly sprayed onto the center position of the pre-treated pad under a set dispensing pressure to form a conductive adhesive layer; the chip to be mounted is then mounted onto the conductive adhesive layer to obtain a semi-finished product, including the following steps: Step 301: Select 0.5, 0.7, or 0.9 mm probes according to the chip size. For chips smaller than 1 mm, the probe diameter should be 0.15-0.25 mm smaller than the chip size. Step 302: Control the dispensing air pressure at 0.06-0.08 MPa; Step 303: Evenly spray the pretreated conductive adhesive (silver paste) onto the pads. The pretreated conductive adhesive (silver paste) should be sprayed onto the center of the pads, with a spraying amount of 0.3-0.5 mg / mm. 2 ; Step 304: Use a soft nozzle to pick up the chip and perform high-precision, non-destructive mounting using a rotatable nozzle head.

[0026] Step 4 specifically involves alternating between vacuuming and nitrogen purging of the semi-finished product, followed by a three-stage process of nitrogen atmosphere heating, constant temperature curing, and cooling, including the following steps: Step 401: Place the substrate into a vacuum baking equipment for pretreatment and vacuuming. The vacuuming time is 2 minutes and 30 seconds to 3 minutes and 30 seconds. Step 402: Nitrogen filling time is 2 minutes and 30 seconds; Step 403: The vacuuming time is 2 minutes and 30 seconds to 3 minutes and 30 seconds; Step 404: Nitrogen filling time is 2 minutes and 30 seconds; Step 405: The vacuuming time is 2 minutes and 30 seconds to 3 minutes and 30 seconds; Step 406, Heating stage: Increase the temperature from room temperature to 30-40°C below the glass transition temperature of the conductive adhesive, for 7-10 minutes, during which nitrogen gas is introduced. Step 407: Under conditions 30-40°C below the glass transition temperature of the conductive adhesive: evacuate for 2 minutes 30 seconds to 3 minutes 30 seconds, purge with nitrogen for 2 minutes 30 seconds, evacuate for 2 minutes 30 seconds to 3 minutes 30 seconds, purge with nitrogen for 2 minutes 30 seconds, and remove solvent volatiles. Step 408: Heat to the glass transition temperature of the conductive adhesive: time 5-10 minutes, nitrogen gas is used during the process; Step 409, Curing stage: Curing is carried out according to the conductive silver paste product specifications (120℃ / 1 hour). At 30 minutes of curing, vacuuming is performed for 2 minutes 30 seconds to 3 minutes 30 seconds, followed by nitrogen purging for 2 minutes 30 seconds to remove volatile substances and bubbles. Step 410, Cooling stage: Cool down to 40℃ for 6-8 minutes.

[0027] This invention employs a substrate pretreatment method combining alcohol immersion, high-temperature baking, and plasma cleaning, avoiding substrate damage that may be caused by traditional ultrasonic cleaning. Simultaneously, a special transfer and vertical static reheating process for the single-component conductive adhesive (conductive silver paste) eliminates air trapped during the transfer process, ensuring no gas residue during dispensing. In the dispensing stage, precise needle selection and dispensing pressure control ensure an appropriate amount of adhesive, preventing insufficient dispensing from affecting strength and excessive dispensing from causing uneven bonding, effectively solving the problem of uneven bonding caused by air bubbles in traditional dispensing processes. During the subsequent vacuum high-temperature curing process, multiple alternating vacuuming and nitrogen purging operations efficiently remove air bubbles generated by solvent evaporation, achieving an ultra-low void ratio of less than 3%, significantly improving heat dissipation and electrical performance. Furthermore, the chip pick-up and placement utilize a combination of soft nozzles and rotatable nozzle heads, effectively preventing edge chipping and damage caused by hard contact such as metal nozzles or tweezers. The synergistic effect of these processes significantly improves the reliability and stability of chip bonding.

[0028] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0029] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0030] Example 1: A high-reliability, ultra-low void ratio epoxy mounting vacuum high-temperature curing method for attenuator chip mounting includes the following steps: Step 1, Substrate Pretreatment: Step 101: Use alcohol immersion treatment. Immerse the substrate and its surface pads in a 95% ethanol solution for 25 minutes, and maintain the immersion temperature at 45°C. Step 102: Use a clean cotton swab dipped in anhydrous ethanol to gently wipe away dirt and residual alcohol from the substrate surface and the pads on its surface. Step 103: Place the pretreated substrate into a vacuum oven and bake it in a nitrogen atmosphere at a temperature of 90°C for 60 minutes. Step 104: Use an oxygen / nitrogen mixed plasma cleaning device with a power of 60W and a cleaning time of 6 minutes, wherein the volume ratio of oxygen to nitrogen is 3:7.

[0031] Step 2: Transfer and warming of the one-component epoxy conductive adhesive: Step 201: Take the single-component epoxy conductive adhesive out of the -40℃ ultra-low temperature freezer and immediately transfer it into the dispensing syringe; Step 202: Place the dispensing syringe vertically on the workbench with the tip facing down, and let it stand at room temperature for 1 hour to allow it to warm up. Step 203: Gently press the end of the dispensing syringe to allow the conductive adhesive to slightly overflow from the syringe eye; Step 204: Use an anti-static lint-free cloth to gently wipe away any conductive adhesive that has overflowed from the tip of the dispensing syringe.

[0032] Step 3: Adjusting dispensing parameters and conducting dispensing tests: Step 301: Select the appropriate dispensing needle according to the chip size. For a 0.65mm × 0.65mm chip, select a 0.5mm needle. Step 302: Adjust the dispensing air pressure to 0.07 MPa; Step 303: Use a dispensing machine to evenly spray silver paste onto the center of the solder pads, controlling the spraying amount to 0.4 mg / mm². 2 ; Step 304: Use an anti-static polyurethane nozzle to pick up the chip, and use the rotatable nozzle head to accurately position and mount it on the pad.

[0033] Step 4: Vacuum high-temperature curing: Step 401: Place the substrate in a vacuum baking oven and evacuate for 2.5 minutes; Step 402: Pour nitrogen gas for 2.5 minutes; Step 403: Vacuum for 2.5 minutes; Step 404: Pour nitrogen gas for 2.5 minutes; Step 405: Vacuum for 2.5 minutes; Step 406, Heating stage: Heat to 85°C at a heating rate of 12°C / minute, with nitrogen continuously purging during the process; Step 407, 30-40°C below the glass transition temperature: Evacuate for 3 minutes, purge with nitrogen for 3 minutes, repeat this operation 3 times to remove solvent volatiles; Step 408: Heat to the glass transition temperature: Heat to 120°C over five minutes, continuously purging with nitrogen during the process; Step 409, Curing Stage: Curing is carried out according to the requirements of the conductive silver paste product specifications, usually by baking at 120℃ for 1 hour, followed by vacuuming for 3 minutes and purging with nitrogen for 2.5 minutes at 30 minutes to remove volatile substances and air bubbles. Step 410, Cooling stage: Cool down to 40℃ at a rate of 20℃ / minute.

[0034] Step 5: Testing the bonding and curing effect: Step 501: Detect the bonding void rate, and control the void rate within 2%; Step 402: Measure the bond shear strength. The shear strength is 1.97 kg, which is 7.5 times the force value required by GJB548C.

[0035] like Figure 1 The image shown is an image of the attenuator chip after bonding. The conductive adhesive is spread evenly around the chip and does not extend to the upper surface of the chip. There is no peeling, flaking or bulging, and no cracks.

[0036] like Figure 2The image shown is an X-ray image of the chip after bonding. After bonding and curing, the void rate of the chip is extremely low, controlled within 2%, which is far lower than the void rate of more than 5% for traditional curing in a nitrogen atmosphere alone.

[0037] like Figure 3 The figure shows the shear force test results after chip bonding. The chip shear strength reached 1.97Kg, which is 7.5 times the minimum force required by GJB548C.

[0038] Example 2: A high-reliability, ultra-low void ratio epoxy mounting vacuum high-temperature curing method for filter chip mounting includes the following steps: Step 1, Substrate Pretreatment: Step 101: Use alcohol immersion treatment. Immerse the substrate and its surface pads in a 95% ethanol solution for 30 minutes, and maintain the immersion temperature at 48°C. Step 102: Use a lint-free cloth dampened with anhydrous ethanol to gently wipe away dirt and residual alcohol from the substrate surface and the pads on its surface. Step 103: Place the pretreated substrate into an oven and bake it in a nitrogen atmosphere at a temperature of 95°C for 65 minutes. Step 104: Use an oxygen / nitrogen mixed plasma cleaning device with a power of 70W and a cleaning time of 7 minutes, wherein the volume ratio of oxygen to nitrogen is 2:8.

[0039] Step 2: Transfer and warming of the one-component epoxy conductive adhesive: Step 201: Take the single-component epoxy conductive adhesive out of the -40℃ ultra-low temperature freezer and immediately transfer it into the dispensing syringe; Step 202: Place the dispensing syringe vertically on the workbench with the tip facing down, and let it stand at room temperature for 1 hour to allow it to warm up. Step 203: Gently press the end of the dispensing syringe to allow the conductive adhesive to slightly overflow from the syringe eye; Step 204: Use an anti-static lint-free cloth to gently wipe away any conductive adhesive that has overflowed from the tip of the dispensing syringe.

[0040] Step 3: Adjusting dispensing parameters and conducting dispensing tests: Step 301: Select the appropriate dispensing needle according to the chip size. For example, for a 0.9mm × 0.9mm chip, select a 0.7mm needle. Step 302: Adjust the dispensing air pressure to 0.08 MPa; Step 303: Use a spray gun to evenly spray silver paste onto the center of the solder pads, controlling the spraying amount to 0.35 mg / mm². 2 ; Step 304: Use an anti-static polyurethane nozzle to pick up the chip, and use the rotatable nozzle head to accurately position and mount it on the pad.

[0041] Step 4: Vacuum high-temperature curing: Step 401: Place the substrate in a vacuum baking oven and evacuate for 3 minutes; Step 402: Pour nitrogen gas for 2.5 minutes; Step 403: Vacuum for 3 minutes; Step 404: Pour nitrogen gas for 2.5 minutes; Step 405: Vacuum for 3 minutes; Step 406, Heating Stage: Heat to 90°C in 8 minutes, continuously purging with nitrogen during the process; Step 407, 30-40°C below the glass transition temperature: Evacuate for 2.5 minutes, purge with nitrogen for 2.5 minutes, repeat this operation twice to remove solvent volatiles; Step 408, Heat to glass transition temperature: Heat to 120°C over 5 minutes, continuously purging with nitrogen during the process; Step 409, Curing Stage: Curing is carried out according to the requirements of the conductive silver paste product specifications, usually by baking at 120℃ for 1 hour, followed by vacuuming for 3 minutes and purging with nitrogen for 2.5 minutes at 30 minutes to remove volatile substances and air bubbles. Step 410, Cooling stage: Cool down to 40°C at a cooling rate of 25°C / minute.

[0042] Step 5: Testing the bonding and curing effect: Step 501: Detect the bonding void rate, and control the void rate within 2%; Step 402: Measure the bond shear strength, which should be 5.3 times the force value required by GJB548C.

[0043] This invention provides a highly reliable, ultra-low void ratio epoxy bonding vacuum high-temperature curing method for chips, belonging to the field of microelectronic packaging and micro-assembly technology. The method sequentially includes four steps: substrate pretreatment, transfer and reheating of single-component epoxy conductive adhesive, dispensing parameter adjustment and dispensing testing, and vacuum high-temperature curing. The substrate is treated using a combination of alcohol immersion, nitrogen baking, and plasma cleaning, combined with a bubble-free transfer and reheating process for the conductive adhesive. This is further enhanced by precise dispensing parameter control and non-destructive bonding using a soft, rotatable nozzle. Finally, the chip is bonded through multiple vacuum-assisted nitrogen-filled high-temperature curing processes. This invention eliminates the risk of substrate damage from ultrasonic cleaning, effectively solving the problems of air inclusions in the conductive adhesive, uneven dispensing, and residual curing bubbles. It achieves a soldering void ratio of less than 3%, while avoiding chip edge chipping damage, significantly improving the chip's heat dissipation performance, electrical performance, and die bonding reliability. It is suitable for the mass production of highly integrated, high-power chips.

[0044] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A high-reliability, ultra-low void ratio chip epoxy mounting vacuum high-temperature curing method, characterized in that, Includes the following steps: The substrate and its surface pads were sequentially subjected to alcohol immersion, nitrogen baking and plasma cleaning to obtain the pretreated substrate and pretreated pads. The conductive adhesive is transferred from the storage syringe to the dispensing syringe, and after being allowed to stand vertically to warm up and the overflow adhesive is removed, the pretreated conductive adhesive is obtained. Match the appropriate dispensing needle to the size of the chip to be mounted, and spray the pre-treated conductive adhesive evenly at the center of the pre-treated pad under the set dispensing pressure to form a conductive adhesive layer; mount the chip to be mounted on the conductive adhesive layer to obtain a semi-finished product. After multiple rounds of alternating vacuuming and nitrogen purging of the semi-finished product, the product is then subjected to three stages of nitrogen atmosphere heating, constant temperature curing, and cooling to complete the preparation.

2. The high-reliability, ultra-low void ratio chip epoxy mounting vacuum high-temperature curing method according to claim 1, characterized in that, The alcohol soaking time is 20-30 minutes, and the temperature is 40-50℃; The nitrogen baking is carried out in an anaerobic oven at a temperature of 80-100℃ for 50-70 minutes. The plasma cleaning uses an oxygen / nitrogen mixture, with a power of 40-80W and a time of 4-8 minutes, in which oxygen accounts for 10%-30%.

3. The method for high-reliability, ultra-low void ratio chip epoxy mounting vacuum high-temperature curing according to claim 1, characterized in that, The storage temperature of the storage syringe is -40℃, and the transfer time is less than 2 minutes; the vertical static warming is carried out at room temperature for 1 hour.

4. The method for high-reliability, ultra-low void ratio chip epoxy mounting vacuum high-temperature curing according to claim 1, characterized in that, The process of matching the appropriate dispensing needle according to the size of the chip to be mounted specifically involves: Use 0.5mm, 0.7mm or 0.9mm dispensing needles. For chips smaller than 1mm in size, the diameter of the dispensing needle should be 0.15-0.25mm smaller than the size of the chip to be mounted.

5. The method for high-reliability, ultra-low void ratio chip epoxy mounting vacuum high-temperature curing according to claim 1, characterized in that, The set dispensing air pressure is 0.06-0.08 MPa; the spraying amount of the pretreated conductive adhesive is 0.3-0.5 mg / mm. 2 .

6. The method for high-reliability, ultra-low void ratio chip epoxy mounting vacuum high-temperature curing according to claim 1, characterized in that, The process of alternating vacuuming and nitrogen purging is as follows: The semi-finished product is pre-treated in the vacuum baking equipment in the following order: vacuuming, nitrogen filling, vacuuming, nitrogen filling, and vacuuming. Each vacuuming process takes between 2 minutes and 30 seconds and 3 minutes and 30 seconds, and each nitrogen filling process takes 2 minutes and 30 seconds.

7. The method for high-reliability, ultra-low void ratio chip epoxy mounting vacuum high-temperature curing according to claim 1, characterized in that, The three-stage nitrogen atmosphere heating process is as follows: In the first stage, the temperature is raised from room temperature to 30-40°C below the glass transition temperature of the conductive adhesive, and the heating time is 7-10 minutes, during which nitrogen is used for protection throughout the process. In the second stage, solvent removal is carried out at 30-40°C below the glass transition temperature of the conductive adhesive. In the third stage, the temperature is increased from 30-40°C below the glass transition temperature of the conductive adhesive to the glass transition temperature of the conductive adhesive, with a heating time of 5-10 minutes, and nitrogen gas is used for protection throughout the process.

8. The high-reliability, ultra-low void ratio chip epoxy mounting vacuum high-temperature curing method according to claim 7, characterized in that, The solvent discharge process consists of at least two alternating vacuuming and nitrogen purging operations; each vacuuming operation lasts between 2 minutes and 30 seconds and 3 minutes and 30 seconds, and each nitrogen purging operation lasts 2 minutes and 30 seconds.

9. The method for high-reliability, ultra-low void ratio chip epoxy mounting vacuum high-temperature curing according to claim 1, characterized in that, The constant temperature curing temperature is 120℃ and the time is 1 hour. When the constant temperature curing process is halfway through, vacuuming and nitrogen filling are performed once. The vacuuming time is between 2 minutes and 30 seconds and 3 minutes and 30 seconds, and the nitrogen filling time is 2 minutes and 30 seconds.

10. The method for high-reliability, ultra-low void ratio chip epoxy mounting vacuum high-temperature curing according to claim 1, characterized in that, The cooling process involves reducing the temperature from the constant-temperature curing temperature to 40°C over a period of 6-8 minutes.

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