Plastic encapsulation method and electronic device

Abstract

The application belongs to the field of semiconductor packaging, and particularly relates to a plastic sealing method and an electronic device. The plastic sealing method pre-charges a protective gas into an internal cavity of a packaging substrate before plastic sealing and seals the internal cavity, so that the difference between the pressure of the internal gas after expansion in a subsequent high-temperature plastic sealing environment and the external injection pressure is less than the critical pressure resistance strength of the packaging substrate, destructive pressure difference is eliminated from the root, the packaging substrate is effectively prevented from being pressed to collapse or cracked in the plastic sealing process, the internal and external pressure of the fragile packaging substrate (such as a ceramic base pipe) is always kept in dynamic balance in the whole plastic sealing thermal cycle process, the problem of pressure cracking of the packaging substrate caused by excessive pressure difference is fundamentally avoided, and the production yield and reliability of the electronic device are improved.

Description

Technical Field

[0001] This application relates to the field of semiconductor packaging technology, and more particularly to a molding process and electronic device. Background Technology

[0002] Power semiconductor devices (such as insulated-gate bipolar transistors and silicon carbide modules) face significant heat dissipation challenges in high-power-density applications. Encapsulation using ceramic substrates with internal cooling channels effectively reduces the overall thermal resistance of the devices, becoming an important solution. During the manufacturing process of such devices, critical areas such as the chip and bonding wires typically require epoxy resin transfer molding encapsulation to provide mechanical protection and electrical insulation.

[0003] However, existing molding processes have certain drawbacks when applied to electronic devices containing hollow cavities (such as cooling channels in ceramic substrates). In traditional transfer molding processes, molten epoxy molding compound (approximately 175°C) is injected into the mold cavity under high pressure (8MPa to 12MPa). This injection pressure acts directly on the outer surface of the ceramic substrate, easily exceeding the compressive strength limit of the ceramic material. This can lead to the ceramic substrate collapsing or cracking during the molding process, resulting in device scrap and severely impacting production yield and reliability. Summary of the Invention

[0004] This application provides a molding method and electronic device, aiming to solve the technical problem that brittle components containing cavities are damaged by injection pressure during the packaging process.

[0005] To achieve the above objectives, this application provides a molding encapsulation method applied to electronic devices, the electronic devices including an encapsulation substrate having an internal cavity, the molding encapsulation method comprising the following steps: Before encapsulation, a protective gas is filled into the internal cavity of the encapsulation substrate and sealed to form a closed gas cavity. The inflated and sealed electronic device is placed into the cavity of the molding die and then encapsulated.

[0006] Furthermore, the pressure P1 of the protective gas in the sealed cavity is determined according to the following formula: P1=P2*(T1 / T2), where P2 is the peak external pressure borne by the encapsulation substrate when the molding compound is injected into the cavity, T1 is the ambient temperature when the protective gas is filled, and T2 is the process temperature of the molding mold when the molding compound is injected.

[0007] Furthermore, the plastic encapsulation includes the following steps: Preheat the molding die; Inject molding compound into the cavity until it covers the bottom of the cavity; Vacuum the cavity until the molding compound completely fills the cavity.

[0008] Furthermore, after the step of evacuating the cavity until the molding compound completely fills the cavity, the process also includes pressure holding and curing, cooling and shaping, and demolding steps. The pressure holding and curing is carried out at 170°C to 180°C for 90 to 120 seconds.

[0009] Furthermore, prior to the step of filling the internal cavity of the packaging substrate with a protective gas and sealing it, the method further includes the step of completing the chip bonding and internal interconnection of the electronic device; and / or Prior to the step of placing the gas-sealed electronic device into the cavity of the molding die, the step of plasma cleaning the electronic device is also included.

[0010] Furthermore, the protective gas includes nitrogen or an inert gas.

[0011] This application also provides a molding encapsulation method applied to power devices comprising a ceramic substrate tube having a hollow flow channel, the molding encapsulation method comprising the following steps: Based on the peak external pressure P2 of the molding injection and the molding temperature T2, the room temperature pre-charge pressure P1 is calculated according to the formula P1=P2*(T1 / T2), where T1 is the room temperature. At room temperature, a protective gas at a pressure of P1 is introduced into the hollow flow channel of the ceramic base tube, and both ends of the hollow flow channel are sealed. The gas-filled and sealed power device is placed into the cavity of the plastic encapsulation mold and the mold is closed. Preheat the molding die to the molding temperature T2; Inject molding compound into the cavity until it covers the bottom of the cavity; The cavity is evacuated until the molding compound completely fills the cavity.

[0012] Furthermore, after the step of evacuating the cavity until the molding compound completely fills the cavity, the process also includes pressure holding and curing, cooling and shaping, and demolding steps. The pressure holding and curing is carried out at 170°C to 180°C for 90 to 120 seconds.

[0013] This application also provides an electronic device manufactured using the encapsulation method described above.

[0014] Furthermore, the encapsulation substrate is made of a brittle non-metallic material; and / or The electronic device is a power semiconductor device, a sensor, or a MEMS device; and / or The internal cavity forms a hollow flow channel.

[0015] The beneficial effects of the encapsulation method and electronic device provided in this application are as follows: This molding process involves pre-filling and sealing the internal cavity of the encapsulation substrate with protective gas before molding. This ensures that the pressure difference between the internal gas after expansion and the external injection pressure is less than the critical compressive strength of the encapsulation substrate during the subsequent high-temperature molding process. This eliminates destructive pressure differentials at the source, effectively preventing the encapsulation substrate from collapsing or cracking under pressure during molding. As a result, the internal and external pressures of the brittle encapsulation substrate (such as a ceramic tube) remain dynamically balanced throughout the entire molding thermal cycle, fundamentally avoiding the problem of the encapsulation substrate cracking due to excessive pressure differentials. This improves the production yield and reliability of electronic devices. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] in: Figure 1 This is a flow chart of the molding process for existing general-purpose power devices; Figure 2 This is a schematic diagram of the plastic packaging of existing general-purpose power devices; Figure 3 This is a schematic diagram of an electronic device shown in one embodiment of this application. Figure 1 ; Figure 4 This is a schematic diagram of an electronic device shown in one embodiment of this application. Figure 2 ; Figure 5 This is a cross-sectional view of an electronic device shown in an embodiment of this application; Figure 6 This is an exploded view of an electronic device shown in one embodiment of this application; Figure 7 This is a process flow diagram illustrating a molding method according to an embodiment of this application; Figure 8 This is a flowchart illustrating the molding process in an embodiment of this application; Figure 9 This is an overall process flow diagram of the encapsulation method shown in one embodiment of this application; Figure 10 This is a schematic diagram illustrating the encapsulation process of an electronic device according to an embodiment of this application; Figure 11 This is a schematic diagram illustrating the heat preservation and pressure curing process of an electronic device according to an embodiment of this application.

[0018] Explanation of key component symbols: 1. Molding mold; 2. Cavity; 100. Electronic component; 10. Packaging substrate; 11. Internal cavity; 101. Liquid inlet; 102. Liquid outlet; 20. Copper metal layer; 21. Solder lead; 30. Solder layer; 40. Chip; 41. Bonding wire; 50. Molded enclosure; 1000, mold; 2000, mold cavity; 3000, power device. Detailed Implementation

[0019] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many other different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0020] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0021] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0023] In existing technologies, such as Figure 1 and Figure 2As shown, in the molding process of power device 3000, after the material is loaded and the mold is closed, injection pressure is applied in the barrel. The temperature of mold 1000 is kept constant. The molten epoxy molding compound is rapidly filled into mold cavity 2000 through runner and gate under the action of pressure transmission. It is cured under heat and pressure. The mold plate of mold 1000 is opened under the action of return spring (not shown in the figure), and the ejector rod (not shown in the figure) ejects power device 3000 and runner solidified material together.

[0024] The main process conditions for typical transfer molding (injection molding) are as follows: Because traditional power devices are all solid structures, the probability of structural breakage due to injection pressure and holding pressure acting on the package structure during the molding process is extremely small. However, for devices containing... Hollow flow channel For low thermal resistance power devices based on ceramic substrates, when the outer surface of the ceramic substrate is integrally / partially encapsulated, the injection pressure and holding pressure act on the outer surface of the ceramic substrate, resulting in a pressure difference between the inside and outside of the ceramic substrate. P=P 外 -P 内 Exceeding the critical external pressure resistance of ceramic tubes can easily lead to cracking of the ceramic base tube.

[0025] To address the aforementioned problems, embodiments of this application provide a method for encapsulating an electronic device. The electronic device includes an encapsulation substrate with an internal cavity, wherein the material of the encapsulation substrate is primarily a brittle non-metallic material, such as ceramic, glass, or silicon. For example, as... Figures 3-6 As shown, the electronic device 100 can be a power semiconductor device, comprising a ceramic substrate, an inlet nozzle 101, an outlet nozzle 102, a chip 40, a solder layer 30, bonding wires 41, solder leads 21, and a molding compound 50. The ceramic substrate is a packaging substrate 10 with an internal cavity 11, and its surface is partially plated with copper to form a copper metal layer 20. The solder leads 21 are disposed on the copper metal layer 20. The inlet nozzle 101 and the outlet nozzle 102 can be made of aluminum alloy (such as AlSi10Mg) and are brazed to both ends of the ceramic substrate. Hollow flow channel Together, they form a cooling and heat dissipation channel. Chip 40 is connected to copper metal layer 20 via solder layer 30, and interconnection between chips 40 and between chips 40 and solder pins 21 is achieved via bonding wires 41. Molding package 50 is used to encapsulate and protect copper metal layer 20, chip 40, solder layer 30, and bonding wires 41. The ceramic substrate serves as both the skeleton carrier and heat dissipation channel for the power device, providing stable support for chip 40, bonding wires 41, and solder terminals; it also provides a flow path for coolant, effectively reducing package thermal resistance and external heat dissipation resistance.

[0026] It is understood that the electronic device 100 to which this encapsulation method is applicable can also be a sensor or MEMS (Micro-Electro-Mechanical System) device, as long as it includes a packaging substrate 10 with an internal cavity 11.

[0027] like Figure 7 As shown, the molding method includes the following steps: Before encapsulation, a protective gas is filled into the internal cavity of the encapsulation substrate and sealed to form a closed gas chamber. The pre-inflated and sealed electronic device is placed into the cavity of the molding die and then encapsulated.

[0028] The protective gas can be nitrogen, an inert gas, or a mixture thereof. These gases are chemically stable and will not react chemically with the cavity walls (such as ceramics or metals) at high temperatures, eliminating the potential risks of abnormal pressure changes, corrosive byproducts, or pollution of the internal environment due to gas reactions.

[0029] In this embodiment, the encapsulation method pre-fills the internal cavity of the encapsulation substrate with protective gas and seals it before encapsulation. This ensures that the pressure difference between the internal gas after expansion and the external injection pressure is less than the critical compressive strength of the encapsulation substrate under subsequent high-temperature encapsulation conditions. This eliminates the destructive pressure difference at its source and effectively prevents the encapsulation substrate from collapsing or cracking under pressure during the encapsulation process. As a result, the internal and external pressures of the brittle encapsulation substrate (such as a ceramic base tube) can always maintain a dynamic balance during the entire encapsulation thermal cycle. This fundamentally avoids the problem of the encapsulation substrate cracking due to excessive pressure difference and improves the production yield and reliability of electronic devices.

[0030] Furthermore, this encapsulation method does not require modification of existing encapsulation molds; it can be achieved simply by optimizing process steps and parameters. It cleverly utilizes the internal cavity of the encapsulation substrate itself as a pressure buffer chamber, solving an industry problem at extremely low cost.

[0031] The sealing method for the internal cavity on the encapsulation substrate can be a variety of temporary sealing forms such as mechanical plugs or curable colloids, and no limitation is made here.

[0032] Furthermore, the pressure P1 of the protective gas in the sealed cavity is determined according to the following formula: P1=P2*(T1 / T2), where P2 is the peak external pressure borne by the encapsulation substrate when the molding compound is injected into the cavity, T1 is the ambient temperature when the protective gas is filled, and T2 is the process temperature of the molding mold when the molding compound is injected.

[0033] The process temperature T2 is 170℃ to 180℃.

[0034] The pre-charge pressure P1 can also be fine-tuned based on a more accurate real gas state equation or in combination with the actual strength curve of the hollow encapsulation substrate, as long as the maximum pressure difference does not exceed the critical value.

[0035] In one specific embodiment, such as Figure 8 As shown, plastic encapsulation includes the following steps: Preheat the molding die; Inject molding compound into the cavity until it covers the bottom of the cavity; Vacuum the cavity until the molding compound completely fills it.

[0036] It should be noted that in the prior art, in order to reduce air bubbles in the molding compound and reduce the probability of internal pore defects, the cavity of the molding compound is usually evacuated after mold closing and before injection molding. This operation will further increase the probability of the packaging substrate with internal cavity bursting.

[0037] In this embodiment, the step sequence of "injecting the mold first, then drawing a vacuum" is proposed, which avoids the risk of the encapsulation substrate bursting due to the relative vacuum inside the cavity caused by drawing a vacuum inside the encapsulation mold before encapsulation.

[0038] In one embodiment, combined with Figures 9 to 11 As shown, taking a power device containing a ceramic substrate with a hollow flow channel as an example, the molding method is described in detail. The molding method of this embodiment includes the following steps: Pre-charge pressure calculation at room temperature: Based on the molding process parameters, determine the peak pressure P2 that the outer wall of the ceramic base tube will bear during molding (e.g., obtained through a mold pressure sensor or estimated based on process settings). Set the molding mold 1 temperature to T2 (e.g., 175°C) and the room temperature to T1 (e.g., 25°C) during molding. Calculate the gas pressure P1 that needs to be injected into the ceramic base tube flow channel at room temperature according to the ideal gas law: P1 = P2 * (T1 / T2). This calculation ensures that the pressure of the gas inside the flow channel after expansion is basically balanced with the external injection pressure at the high temperature of molding.

[0039] Pre-filling and sealing: After completing the chip soldering, bonding and other front-end processes, high-purity nitrogen (or inert gas) is slowly filled into the internal flow channel of the ceramic substrate through the inlet nozzle 101 or outlet nozzle 102 until the pressure reaches P1. Then, the inlet nozzle 101 and outlet nozzle 102 are immediately temporarily sealed (for example, by using a weldable sealing cap or a special fixture) to form a closed gas chamber in the flow channel.

[0040] Pre-molding cleaning: A plasma cleaner is used to clean the surface of the power devices that have been pre-inflated and sealed to remove organic matter and microparticles, thereby improving the interfacial adhesion between the molding compound and the ceramic and metal surfaces.

[0041] Mold closing and positioning: Place the pre-inflated and sealed power device into the cavity 2 of the plastic sealing mold 1, and close the upper and lower molds.

[0042] Mold preheating: The mold 1 after molding is completed is heated to uniformly raise its temperature to the molding temperature T2 (e.g., 175℃). During this process, the pressure of the gas sealed inside the ceramic base tube gradually increases due to heating, and it increases synchronously with the pressure of the external environment (cavity 2), eliminating the risk of pressure difference.

[0043] Injection molding die: Start the molding machine and inject molten epoxy molding compound (EMC) into the cavity 2 of the molding die 1 at a certain injection pressure, so that it basically covers the chip, bonding wires and solder pins 21 area on the surface of the ceramic base tube. During this process, the pressure on the outside of the ceramic base tube gradually increases; Mold vacuuming: After the epoxy molding compound has essentially completely covered the chip, bonding wires, and solder pins 21 area on the surface of the ceramic substrate (i.e., covering the bottom of cavity 2), the mold vacuuming system is activated. The main purpose of vacuuming at this time is to remove residual gas from cavity 2, preventing air bubbles or voids from forming inside the molding compound. Since the ceramic substrate is already under the pressure of the injected molding compound and the internal gas pressure has increased due to heat, the vacuuming operation will not cause a harmful pressure difference between the inside and outside, thus avoiding the risk of the ceramic substrate bursting. This sequence is completely different from the traditional process (vacuuming before injection molding).

[0044] Pressure holding and curing: Under the conditions of maintaining the temperature of the molding die 1 (170°C to 180°C, preferably 175°C) and a certain pressure holding pressure (approximately 80% of the injection pressure), the molding compound is fully cross-linked and cured for a duration of approximately 90 to 120 seconds. During this period, the pressure inside and outside the ceramic base tube remains balanced.

[0045] It should be noted that within this temperature range, the curing kinetics of the selected epoxy molding compound are optimal. The lower limit of 170℃ ensures that the curing reaction is fully initiated, avoiding low crosslinking degree, poor mechanical strength, and insufficient heat resistance due to insufficient temperature; the upper limit of 180℃ prevents thermal degradation or excessive shrinkage of the material that may be caused by excessive temperature. Combined with a holding pressure time of 90 to 120 seconds, a necessary time window is provided for the full crosslinking of the polymer chains, enabling the molded body to achieve excellent mechanical strength, electrical insulation properties, and long-term environmental reliability. The holding pressure time of 90 to 120 seconds represents a reasonable balance between production efficiency and ensuring sufficient curing. Too short a holding pressure time may lead to incomplete curing, affecting product reliability; too long a holding pressure time will reduce production cycle time and increase costs.

[0046] Cooling and shaping: Stop heating and allow the molding mold 1 and electronic components to cool slowly. As the temperature drops, the gas pressure inside the ceramic base tube drops synchronously, always keeping it close to the external environmental pressure to avoid stress caused by sudden pressure difference.

[0047] Demolding and post-curing: After demolding, remove the encapsulated electronic device and place it in an oven for post-curing at a specified temperature. This allows the encapsulating material to cross-link more thoroughly, releases internal stress, and improves reliability.

[0048] Understandably, this encapsulation method is also applicable to applications involving the overall encapsulation of the outer surface of ceramic-based tubes (such as...). Figure 4 As shown in the figure, this is to further improve the reliability of the device in a humid and hot environment.

[0049] Furthermore, embodiments of this application also provide an electronic device manufactured using the encapsulation method described in the above embodiments.

[0050] Because the encapsulation method described in the above embodiments is adopted, it effectively prevents brittle encapsulation substrates (such as ceramic base tubes) from collapsing and cracking under pressure during the encapsulation process, enabling stable mass production and improving the production yield and reliability of electronic devices.

[0051] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0052] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A molding encapsulation method applied to an electronic device, said electronic device comprising an encapsulation substrate having an internal cavity, characterized in that, The sealing method includes the following steps: Before encapsulation, a protective gas is filled into the internal cavity of the encapsulation substrate and sealed to form a closed gas cavity. The inflated and sealed electronic device is placed into the cavity of the molding die and then encapsulated.

2. The sealing method according to claim 1, characterized in that, The pressure P1 of the protective gas in the sealed cavity is determined according to the following formula: P1=P2*(T1 / T2), where P2 is the peak external pressure borne by the encapsulation substrate when the molding compound is injected into the cavity, T1 is the ambient temperature when the protective gas is filled, and T2 is the process temperature of the molding mold when the molding compound is injected.

3. The encapsulation method according to claim 1 or 2, characterized in that, The plastic encapsulation includes the following steps: Preheat the molding die; Inject molding compound into the cavity until it covers the bottom of the cavity; Vacuum the cavity until the molding compound completely fills the cavity.

4. The molding method according to claim 3, characterized in that, After the step of evacuating the cavity until the molding compound completely fills the cavity, the process also includes pressure holding and curing, cooling and shaping, and demolding. The pressure holding and curing is carried out at 170°C to 180°C for 90 to 120 seconds.

5. The molding method according to claim 1, characterized in that, Prior to the step of filling the internal cavity of the package substrate with a protective gas and sealing it, the method further includes the step of completing the chip bonding and internal interconnection of the electronic device; and / or Prior to the step of placing the gas-sealed electronic device into the cavity of the molding die, the step of plasma cleaning the electronic device is also included.

6. The molding method according to claim 1, characterized in that, The protective gas includes nitrogen or an inert gas.

7. A molding process for power devices comprising a ceramic substrate tube with a hollow flow channel, characterized in that, The sealing method includes the following steps: Based on the peak external pressure P2 of the molding injection and the molding temperature T2, the room temperature pre-charge pressure P1 is calculated according to the formula P1=P2*(T1 / T2), where T1 is the room temperature. At room temperature, a protective gas at a pressure of P1 is introduced into the hollow flow channel of the ceramic base tube, and both ends of the hollow flow channel are sealed. The gas-filled and sealed power device is placed into the cavity of the plastic encapsulation mold and the mold is closed. Preheat the molding die to the molding temperature T2; Inject molding compound into the cavity until it covers the bottom of the cavity; Vacuum the cavity until the molding compound completely fills the cavity.

8. The molding method according to claim 7, characterized in that, After the step of evacuating the cavity until the molding compound completely fills the cavity, the process also includes pressure holding and curing, cooling and shaping, and demolding. The pressure holding and curing is carried out at 170°C to 180°C for 90 to 120 seconds.

9. An electronic device, characterized in that, It is manufactured using the molding method described in any one of claims 1 to 8.

10. The electronic device according to claim 9, characterized in that, The encapsulation substrate is made of a brittle non-metallic material; and / or The electronic device is a power semiconductor device, a sensor, or a MEMS device; and / or The internal cavity forms a hollow flow channel.

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