Packaging process for preventing packaging layering of power device

Abstract

The invention belongs to the technical field of plastic electronic packaging, and particularly relates to a packaging process for preventing packaging layering of a power device. Comprising the following steps: welding a chip on a lead frame; carrying out plasma cleaning on the lead frame welded with the chip; uniformly mixing a silane coupling agent and a diluent to obtain a glue solution; debugging the height of a glue spraying head, a glue spraying path and a glue spraying speed, so that the silane coupling agent is uniformly sputtered on the surface of the chip; carrying out plasma cleaning on the lead frame after spraying is completed again; carrying out plastic package curing on the chip by using a plastic package material to obtain a plastic package piece; in the plastic package curing process, glue solution molecules and a plastic package material are subjected to chemical reaction to form firm chemical bonds. The problems that in the prior art, after a large chip power device is packaged, due to the fact that the bonding strength of a plastic packaging material and the surface of the chip is insufficient, the layering defect is prone to occurring, the reliability of the device is reduced, and the service life is shortened are solved.

Description

Technical Field

[0001] This invention belongs to the field of plastic electronic packaging technology, and specifically relates to a packaging process to prevent delamination of power device packaging. Background Technology

[0002] In the field of plastic electronic packaging, delamination (also known as separation) refers to the separation between different materials at the interface within a plastic-encapsulated device due to various factors. Delamination between the molding compound and the chip surface is the most common and also the most risky. Delamination itself constitutes a device defect, but it may not immediately cause externally visible problems. Its main harm lies in severely reducing the device's reliability and significantly shortening its lifespan. Because plastic packaging is inherently a non-hermetic structure, delamination allows moisture to penetrate. When heated, the internal moisture rapidly vaporizes, generating enormous vapor pressure, which in turn forces open the weakly bonded interfaces.

[0003] Delamination of molded devices can trap moisture, leading to electrochemical corrosion; it can also create insulating air gaps, hindering heat dissipation and causing thermal failure; and it can weaken mechanical strength, making the package more susceptible to damage from external forces.

[0004] To prevent delamination in molded devices, strict management is required in multiple stages, including material selection, process control, and frame design. Common measures include selecting materials with matching coefficients of thermal expansion to reduce thermal stress, controlling encapsulation process parameters such as mold preheating, injection pressure, speed, and time, and improving the curing process after molding.

[0005] However, for power devices with larger chips, the above-mentioned conventional measures are still insufficient to effectively solve the layering problem, so a targeted process improvement solution is urgently needed. Summary of the Invention

[0006] The purpose of this invention is to provide a silane coupling agent spraying process to prevent delamination of power device packages. This solves the problem in the prior art where large chip power devices are prone to delamination defects due to insufficient bonding strength between the molding compound and the chip surface, which leads to reduced device reliability and shortened service life.

[0007] This invention is achieved through the following technical solution: This invention discloses a packaging process to prevent delamination of power device packages, comprising the following steps: S1. Solder the chip onto the lead frame; The lead frame of the soldered chip is then subjected to plasma cleaning. S2. Mix the silane coupling agent and diluent evenly to obtain the adhesive solution, and let it stand for later use; S3. Adjust the height of the spray nozzle, the spray path and the spray speed to ensure that the silane coupling agent is evenly sputtered onto the chip surface; S4. Perform plasma cleaning on the coated lead frame again. S5. The chip is encapsulated and cured with molding compound to obtain a molded part; during the molding and curing process, the adhesive molecules and molding compound react chemically to form strong chemical bonds.

[0008] Furthermore, in S1, the chip is soldered onto the lead frame using solder.

[0009] Furthermore, in S2, the shelf life of the adhesive solution at room temperature is one day.

[0010] Furthermore, in S2, the silane coupling agent is γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethylsilane, or γ-methacryloyloxypropyltrimethoxysilane.

[0011] Furthermore, in S2, the diluent is anhydrous ethanol, isopropanol, or acetone.

[0012] Furthermore, in S2, the volume ratio of the silane coupling agent to the diluent is 1:9.

[0013] Furthermore, in S3, the adhesive spraying path is as follows: the adhesive spraying head sprays along a unidirectional, non-closed straight or curved path in a preset direction, with the end of the path pointing towards the process flow direction.

[0014] Furthermore, in S3, the spraying height is controlled at 20-30mm; the spraying speed is set at 50-70mm / s.

[0015] Furthermore, in S5, the molding and curing conditions are curing at 170-180°C.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: The purpose of this invention is to provide a silane coupling agent spraying process to prevent delamination of power device packages. To address the issue of delamination that easily occurs after packaging large-chip power devices, an improvement method is designed. This method involves spraying a silane coupling agent, which, due to its simultaneous presence of organic and inorganic functional groups, forms covalent bonds with the inorganic groups on the chip surface and the organic groups in the molding compound after a dehydration reaction. This significantly improves the adhesion between the chip and the molding compound, fundamentally suppressing delamination defects. Furthermore, this invention optimizes key aspects such as plasma cleaning, adhesive mixing ratios, spraying parameters, and curing conditions to further ensure adhesion reliability and improve the long-term stability and lifespan of the power devices. In addition, this process is simple, with controllable parameters, and is easily compatible with existing packaging production lines, demonstrating promising prospects for industrial application.

[0017] Furthermore, the ratio of the adhesive solution directly affects the film quality of the coupling agent on the chip surface. If the proportion of silane coupling agent is too high, the viscosity of the adhesive solution will be too large, and accumulation and unevenness will easily occur after spraying. If the proportion is too low, a continuous coupling agent film layer cannot be formed, and it is difficult to guarantee the bonding effect. Therefore, the volume ratio must be strictly controlled at 1:9.

[0018] Furthermore, spraying the adhesive too high will cause the adhesive to disperse and the film thickness to be uneven; spraying it too low will easily cause it to collide with the chip and damage it. Therefore, it needs to be controlled within the range of 20-30mm. Spraying the adhesive too fast will result in a film layer that is too thin, while spraying it too slowly will result in a film layer that is too thick. It needs to be adjusted within the range of 50-70mm / s according to the adhesive concentration and the required spraying thickness.

[0019] Furthermore, the curing temperature and time must be strictly controlled. If the temperature is too low or the time is too short, the reaction will be insufficient and the bonding strength will be inadequate. If the temperature is too high or the time is too long, the performance of the molding compound may be degraded. Therefore, the curing temperature should be controlled at 170-180℃. Attached Figure Description

[0020] Figure 1 Schematic diagram for setting the glue spraying height; Figure 2 This is a schematic diagram of the glue spraying path; where diagram a shows the first type of glue spraying path; and diagram b shows the second type of glue spraying path. Figure 3 The structure is a layered structure after ultra-scanning without adhesive spraying; Figure 4 The result of ultrascanning after adhesive spraying shows no delamination; Figure 5 The image shows the surface of the chip under a microscope after the adhesive has been sprayed.

[0021] Among them, 1. glue spray head, 2. chip. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0023] The detailed description of the embodiments of the present invention provided in the following figures is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the figures and embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0024] The process steps, parameter selection, and technical effects of the present invention will be described in detail below with reference to specific embodiments.

[0025] This embodiment takes the packaging process of a certain type of large-size power chip (size is 10mm×10mm) as an example to verify the anti-delamination effect of the spraying process of the present invention.

[0026] Example 1 A packaging process to prevent delamination of power device packages, comprising the following steps: S1, Chip Welding and Initial Plasma Cleaning 1.1 Chip Soldering: AgPbSn solder (lead-tin-silver) is used to precisely solder large-size power chips to the center of the lead frame. During soldering, the size of the solder pad is controlled so that its outer contour is larger than the chip's circumference, and the chip's circumference / solder's circumference is 85%. After placement, the lead frame is placed in a soldering oven at a temperature 50°C higher than the solder pad's melting point for 180 seconds to ensure a firm, non-detached solder joint and to control voids. The selected solder pad has good thermal and electrical conductivity, meeting the heat dissipation and electrical connection requirements of power devices. 1.2 First Plasma Cleaning: The lead frame with the soldered chip is placed into a plasma cleaning device for surface cleaning.

[0027] The cleaning parameters were set as follows: a mixture of argon and oxygen (argon-oxygen mixture (95%Ar+5%O2)) was used, the gas flow rate was 25 mL / min, the cleaning power was 300W, and the cleaning time was 25S.

[0028] The purpose of plasma cleaning is to remove oil, dust, and other impurities from the chip surface and lead frame surface, while activating active groups such as hydroxyl (-OH) groups on the chip surface to improve the bonding ability of the subsequent silane coupling agent to the chip surface. If the cleaning is not thorough, impurities will hinder the bonding reaction between the coupling agent and the chip surface, reducing the adhesion strength. Therefore, it is necessary to strictly control the stability of the cleaning parameters.

[0029] S2. Preparation and settling of adhesive solution 2.1 Material Selection: A mixture of γ-aminopropyltriethoxysilane and anhydrous ethanol was selected as the silane coupling agent. The organic functional group (amino) of this silane coupling agent can react chemically with the molding compound (epoxy resin), and the inorganic functional group (ethoxy) can undergo a dehydration condensation reaction with the hydroxyl groups on the chip surface, thereby forming a strong chemical bridge bond between the chip and the molding compound. Anhydrous ethanol is selected as a special diluent, which has good volatility and solubility. It can uniformly dilute the silane coupling agent and leave no residue after evaporation, so it will not have an adverse effect on the chip performance.

[0030] 2.2 Adhesive Preparation and Mixing: Accurately measure 10 mL of γ-aminopropyltriethoxysilane and 90 mL of anhydrous ethanol according to a 1:9 volume ratio of silane coupling agent to diluent. Pour the mixture into a storage tube and let it stand for 1 hour to ensure thorough mixing and a uniform, transparent adhesive solution. Note that the prepared adhesive solution has a shelf life of one day at room temperature. After this period, the silane coupling agent may undergo a self-polymerization reaction, leading to adhesive failure. Therefore, it must be applied within the shelf life.

[0031] S3. Spraying parameter adjustment and silane coupling agent spraying 3.1 Preparation of the glue spraying device: A high-precision automatic glue spraying machine is selected, which includes a glue spraying head 1 and a control system. First, the glue spraying device is thoroughly cleaned. The glue spraying head, pipelines, and platform are wiped with anhydrous ethanol to remove residual impurities and old glue, preventing contamination of the newly prepared glue. After cleaning, the prepared glue is poured into the glue storage tank of the glue spraying machine, ensuring the tank is well-sealed to prevent glue evaporation.

[0032] 3.2 Debugging: Adjust the positioning device of the glue spray head 1 according to the size of the lead frame, so that the glue spray head 1 can be positioned as follows. Figure 2 The adhesive spraying path shown is accurately sprayed, and it is ensured that the lead frame 2 fits tightly against the platform after placement and will not slip, thus avoiding spraying position deviation caused by displacement of the lead frame during the spraying process.

[0033] 3.3 Spraying Parameter Adjustment: Adjust the height of the spray nozzle 1, the spraying path, and the spraying speed through the control system of the spraying machine. Specifically, the spraying height should be controlled at 25mm (the distance between the spray nozzle 1 and the chip surface, e.g., ...). Figure 1 As shown), the glue spraying speed is set to 50mm / s, and the glue spraying path adopts a zigzag path (e.g., Figure 2 As shown in Figure a), the adhesive spray head sprays adhesive along a unidirectional, non-closed straight path in a preset direction, with the end of the path pointing in the process flow direction. This path design ensures that the adhesive evenly covers the surface of chip 2, while avoiding adhesive accumulation at the end of the path during spraying. The specific path length and spacing are set according to the chip size; in this embodiment, the path spacing is 20mm, covering the entire chip surface. Furthermore, the spraying pressure is adjusted to 0.2MPa to ensure that the adhesive is sputtered onto the chip surface in a uniform mist form.

[0034] S4, Secondary Plasma Cleaning The coated lead frame was then placed back into the plasma cleaning equipment for a second cleaning. Cleaning parameters were set as follows: gas flow rate 10 mL / min, cleaning power 350W, and cleaning time 10 seconds.

[0035] The purpose of secondary plasma cleaning is to remove impurities that may be generated during the pre-drying process, and at the same time further activate the surface activity of the silane coupling agent film, improve its reactivity with the molding compound, and ensure the firmness of subsequent bonding.

[0036] S5, Molding and Curing After the leadframe has undergone secondary plasma cleaning, it is quickly transferred to a molding die. An epoxy resin molding compound is then used, and molding and curing are performed under preset molding process parameters. It is important to note that the coated leadframe must be molded and cured within 8 hours to prevent the silane coupling agent film from being exposed to air for extended periods, which could lead to contamination or oxidation and affect the adhesion.

[0037] During the molding and curing process, the organic functional groups of the silane coupling agent molecules react chemically with the epoxy resin groups of the molding compound to form strong chemical bonds. At the same time, the inorganic functional groups of the silane coupling agent molecules form covalent bonds with the hydroxyl groups on the chip surface, thereby building a stable chemical bridge bond between the chip and the molding compound, significantly improving the bonding strength between the two.

[0038] Example 2 The process steps in this embodiment are basically the same as those in Embodiment 1, with the only difference being the following parameters: In S1, the initial cleaning parameters are set as follows: gas flow rate is 35 mL / min; cleaning power is 350 W; cleaning time is 20 s. In S2, the silane coupling agent is γ-glycidyloxypropyltrimethylsilane, and the volume ratio of the silane coupling agent to the diluent (isopropanol) is 1:9. In S3, the glue spraying height is controlled at 25mm, and the glue spraying speed is set to 60mm / s; the glue spraying path can also be as follows: Figure 2 The straight path shown in diagram b; In S4, the secondary cleaning parameters are set as follows: gas flow rate is 35 mL / min, cleaning power is 200 W, and cleaning time is 20 s. In S5, the molding and curing conditions are 170°C for 15 seconds.

[0039] Example 3 The process steps in this embodiment are basically the same as those in Embodiment 1, with the only difference being the following parameters: In S1, the initial cleaning parameters are set as follows: gas flow rate is 30 mL / min; cleaning power is 400 W; cleaning time is 25 s. In S2, the silane coupling agent is γ-methacryloxypropyltrimethoxysilane, and the volume ratio of the silane coupling agent to the diluent (acetone) is 1:9. In S3, the glue spraying height is controlled at 30mm, and the glue spraying speed is set to 70mm / s; In S4, the secondary cleaning parameters are set as follows: gas flow rate is 20 mL / min, cleaning power is 300W, and cleaning time is 5S. In S5, the molding and curing conditions are 180°C for 10 seconds.

[0040] Comparative experiment A control group was set up. The process steps of the control group were the same as those in Example 1, except that the silane coupling agent spraying and related treatment steps in S2-S4 were omitted. The lead frame after welding and first plasma cleaning was directly encapsulated and cured.

[0041] Performance testing and results analysis: The power devices prepared in Examples 1-3 and the control group were subjected to reliability tests, including temperature cycling tests and ultrasonic scanning (Ultra-scan) tests.

[0042] The test results are as follows: 1. Control Group: Large-chip power devices without adhesive coating underwent temperature cycling testing, and their layered structure was obtained through ultrasonic scanning (e.g., Figure 3 As shown in the figure, a significant separation gap appears between the molding compound and the chip surface, which severely affects the reliability, electrical performance, and thermal performance of the device, making it unable to meet the usage requirements.

[0043] 2. Examples 1-3: After temperature cycling testing, the ultrasonic scanning results of the power devices after adhesive spraying showed no delamination (e.g., Figure 4 As shown in the image, the chip and molding compound are tightly bonded at the interface. The surface effect of the chip after adhesive spraying is observed under a microscope (e.g., ...). Figure 5 As shown in the figure, a continuous and uniform silane coupling agent film was formed on the chip surface, without any defects such as accumulation or voids.

[0044] In summary, this invention effectively solves the problem of delamination in the packaging of large-size power devices by spraying a silane coupling agent onto the chip surface and optimizing the parameters of each process step, significantly improving the reliability and lifespan of the devices. This process has advantages such as controllable parameters, good compatibility, and broad prospects for industrial application, and can be widely used in the plastic electronic packaging production of various power devices.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A packaging process for preventing delamination of a power device package, comprising: The method comprises the following steps: S1, welding a chip on a lead frame; S2, mixing silane coupling agent and diluent uniformly to obtain glue solution, and standing for use; S3, adjusting the height, path and speed of the glue spraying head to make the silane coupling agent uniformly sputter on the surface of the chip; S4, performing plasma cleaning on the lead frame again after spraying; S5, plastic sealing and curing the chip to obtain a plastic sealing part; during the plastic sealing and curing process, the glue solution molecules and the plastic sealing material chemically react to form a firm chemical bond. In S1, the chip is welded on the lead frame by solder.

2. The packaging process for preventing delamination of a power device package of claim 1, wherein, In S2, the shelf life of the glue solution at room temperature is one day.

3. The packaging process for preventing delamination of a power device package of claim 1, wherein, In S2, the silane coupling agent is γ-aminopropyl triethoxysilane, γ-glycidyl ether propyl trimethyl silane or γ-methacryloyl propyl trimethoxysilane.

4. The packaging process for preventing delamination of a power device package of claim 1, wherein, In S2, the diluent is anhydrous ethanol, isopropyl alcohol or acetone.

5. The packaging process for preventing delamination of a power device package of claim 1, wherein, In S2, the volume ratio of the silane coupling agent to the diluent is 1:

9.

6. The packaging process for preventing delamination of a power device package of claim 1, wherein, In S3, the glue spraying path is that the glue spraying head sprays in a one-way, non-closed straight line or curve path in a preset direction, and the path end points to the process flow direction.

7. The packaging process for preventing delamination of a power device package of claim 1, wherein, In S3, the glue spraying height is controlled at 20-30 mm, and the glue spraying speed is set at 50-70 mm / s.

8. The packaging process for preventing delamination of a power device package of claim 1, wherein, In S5, the plastic sealing and curing condition is curing at 170-180 DEG C.

9. The packaging process for preventing delamination of a power device package of claim 1, wherein, ​

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