A low defect mold structure for intelligent power module plastic encapsulation and related method

Abstract

The application provides a low-defect mold structure for intelligent power module plastic packaging and a related method, and belongs to the technical field of semiconductor packaging. The mold structure comprises a mold cavity, at least two symmetrically arranged sprue gates on the same side of the cavity, and a gourd-shaped overflow groove arranged at the corner of the cavity and corresponding to the position of the high support column of the module, the overflow groove having a narrow entrance and an enlarged internal cavity. The optimization method determines the priority of the bonding wire function, combines finite element simulation, and selects the sprue gate position that minimizes the bonding wire offset of the core function pin. The application adopts a double-sprue gate layout, which can reduce the plastic packaging material filling speed, change the included angle between the flow direction and the bonding wire, and significantly reduce the bonding wire offset. The gourd-shaped overflow groove can actively guide the gas discharge and effectively reduce the trapped gas volume. Compared with the prior art, the application can reduce the average offset of the key bonding wire by more than 56%, and the trapped gas volume can be reduced by up to 20.45%.

Description

Technical Field

[0001] This application relates to the field of semiconductor packaging technology, and in particular to a low-defect mold structure and related methods for molding smart power modules. Background Technology

[0002] Intelligent Power Modules (IPMs) are power semiconductor modules that highly integrate power switching devices (such as IGBTs and MOSFETs), drive circuits, protection circuits, and control logic into a single unit. They are widely used in industrial frequency converters, new energy vehicles, and smart home appliances. Their packaging and manufacturing process mainly includes three key processes: chip mounting, wire bonding, and molding. The molding process involves injecting molten epoxy molding compound into a mold cavity, ensuring it fully fills the tiny gaps between the chip, bonding wires, and the substrate. After curing, it forms an integrated shell, providing mechanical support, electrical insulation, and environmental protection. The quality of the molding process directly determines whether the electrical performance obtained from the preceding processes can remain stable over the long term.

[0003] However, the complex pin frame structure of intelligent power modules and the stepped height differences on the chip surface cause severe pressure fluctuations and uneven flow rates of the molding compound during filling. This hydrodynamic load easily leads to bond wire misalignment, a phenomenon known as "wire bleed." Wire bleed not only causes short circuits between wires but can also lead to bond point fracture under stress, seriously threatening the module's electrical performance and long-term reliability. Furthermore, certain models, such as the IM3756-SST intelligent power module, have high support pillars at their four corners. These pillars can easily create dead cavities that are difficult to vent during injection molding, resulting in trapped air defects and, in severe cases, even a risk of short-shot injection.

[0004] Currently, commonly used mold solutions in the production of similar power modules include: 1) Single-side single-gate layout, where a fan-shaped or rectangular gate is set at one end of the mold cavity along its length, and the molding compound flows into the cavity from a single direction. This solution is simple to design and has low mold processing costs, but it results in excessive pressure gradients between the near and far gate ends, uneven stress on the bond lines, and excessive gold wire offset. 2) Conventional rectangular overflow channels, where simple rectangular overflow channels are symmetrically set at the ends of the mold cavity away from the gate, using pressure differences to force gas into the overflow channels. However, the fixed and simple geometry of the rectangular overflow channel makes it difficult to adapt to the complex and irregular fluid filling front inside the intelligent power module, and it cannot effectively balance the fluid pressure distribution at the end of the cavity, so the problem of poor venting still exists.

[0005] Therefore, how to improve the flow field distribution in the mold cavity, reduce punching defects, and effectively eliminate trapped air through precise mold structure design has become a technical challenge that urgently needs to be solved in the field of intelligent power module packaging. Summary of the Invention

[0006] The main objective of this application is to propose a low-defect mold structure, a low-defect molding optimization method, and a molding method for smart power modules, in order to solve the problems of severe bonding wire punching defects caused by a single gate on one side and air entrapment caused by poor venting of conventional overflow grooves in the prior art.

[0007] To achieve the above objectives, one aspect of this application proposes a low-defect mold structure for molding a smart power module. The smart power module has a chip and bonding wires integrated on its substrate, and high support pillars are provided at the corners of the module. The mold structure includes: The mold cavity is shaped to match the shape of the intelligent power module; At least two gates are symmetrically arranged on the same side of the mold cavity to allow molding compound to be injected into the cavity simultaneously from at least two directions; A gourd-shaped overflow channel is provided at the corner of the mold cavity and corresponds to the position of the high support column. The overflow channel has a narrow inlet and an enlarged internal cavity connected to it.

[0008] In some embodiments, the number of gates is two, and the line connecting the centers of the two gates tends to be parallel to the axial direction of the bonding line, so as to reduce the vertical component of the molding compound flow direction on the bonding line.

[0009] In some embodiments, the two inlets are located at a predetermined distance from the edge of the smart power module, such that when the molding compound flow front reaches the bonding wire region corresponding to the core functional pin, the offset of the bonding wire is minimized preferentially compared to the bonding wire corresponding to the non-core functional pin.

[0010] In some embodiments, the core function pin is a logic power supply pin (VCC), and the predetermined distance is 15%-25% of the total length of the smart power module in that direction.

[0011] In some embodiments, the total length of the gourd-shaped overflow trough is 3.0mm-4.0mm, the width of the narrow inlet is 1.2mm-1.8mm, the maximum width of the enlarged internal cavity is 2.8mm-3.2mm, and the narrow inlet and the enlarged internal cavity are transitioned by rounded corners.

[0012] In some embodiments, the thickness of the gourd-shaped overflow channel matches the thickness of the smart power module encapsulation, and the length of the narrow inlet accounts for 1 / 7 to 1 / 5 of the total length.

[0013] In some embodiments, the narrow inlet of the gourd-shaped overflow channel is configured to throttle the incoming molding compound to balance the pressure at the corner of the cavity; the enlarged internal cavity is configured to provide gas expansion and retention space to actively guide and collect the gas pushed forward by the molding compound.

[0014] To achieve the above objectives, another aspect of this application proposes an optimization method based on the aforementioned low-defect mold structure, comprising the following steps: Step S1: Determine the functional priority of the bonding wires in the intelligent power module, define the bonding wires corresponding to the core function pins as the first priority, and define the bonding wires corresponding to the non-core function pins as the second priority; Step S2: Establish a three-dimensional finite element model of the intelligent power module and the mold structure, and set at least two simulation schemes with different gate positions; Step S3: Simulate and calculate the maximum offset of the first priority bonding line and the second priority bonding line under each scheme. Step S4: Compare the simulation results of each group of schemes, and select the scheme that minimizes the offset of the first priority bond line as the optimal gate position scheme, even if the scheme causes the offset of the second priority bond line to increase.

[0015] In some embodiments, step S4 is followed by: Step S5: Based on the determination of the optimal gate location scheme, further optimize the shape of the overflow groove set at the corresponding position of the high support column, and compare the air trapping volume of the gourd-shaped overflow groove and the conventional rectangular overflow groove under the same cavity pressure conditions. Step S6: Select the geometric parameters of the overflow trough that maximize the reduction in trapped gas volume as the final design.

[0016] To achieve the above objectives, another aspect of this application proposes a molding method for a smart power module. The method employs the low-defect mold structure described above, or the optimal mold parameters obtained by the method described above, to simultaneously inject molten epoxy molding compound into the mold cavity from at least two inlets. The flow front of the molding compound discharges gas into the enlarged internal cavity of the gourd-shaped overflow groove at the flow front of the overflow groove, and after curing, a molded body is formed.

[0017] Compared with the prior art, this application has the following beneficial effects: 1) Significant reduction in bonding wire defects: The dual-gate symmetrical layout reduces the local filling speed by approximately 50% within the same filling time. Simultaneously, it aligns the flow direction of the molding compound with the bond wire axis, reducing the fluid force perpendicular to the bond wire. Simulation data shows that the dual-gate scheme reduces the average offset of the 27 critical bond wires by 56.2%, the standard deviation by 34.2%, and the global maximum offset from 1.512% to 0.874%, successfully keeping it within safe limits.

[0018] 2) Enhanced Molding Consistency and Reliability: By employing a central gate positioning scheme based on functional priority, the bond wire offset of the core power pin VCC was further reduced by 13.6%, effectively mitigating the risk of overall functional failure due to logic power supply failure. Simultaneously, the flow field distribution became smoother, and the velocity gradient in each region decreased, enhancing the consistency of the molding process.

[0019] 3) Effectively solves the problem of trapped air in complex structures: Addressing the dead cavity formed by high support pillars, the gourd-shaped overflow channel designed in this application features a "narrow inlet - large cavity" characteristic. The narrow inlet creates a throttling effect, preventing excessive molten material from rapidly entering and causing pressure loss in the cavity; the enlarged internal cavity provides ample space for gas expansion and retention; and the rounded corners reduce stress concentration and enhance mold strength. Experiments show that its trapped air volume is reduced by up to 20.45% compared to traditional rectangular overflow channels, significantly improving short-shot phenomena and localized stress concentration, thus increasing product yield. Attached Figure Description

[0020] Figure 1 This is a diagram showing the distribution of bond lines of different diameters in the smart power module in the embodiments of this application; Figure 2 This is a schematic diagram showing the connection and naming of the bonding wires around the driver chip in the embodiments of this application; Figure 3 This is a finite element model diagram of the IM3756-SST type intelligent power module in the embodiments of this application; Figure 4 These are flow wavefront time contour maps for different numbers of gates in the embodiments of this application; Figure 5 This is an offset contour plot of the bond lines under different numbers of gates in the embodiments of this application; Figure 6 This is a comparison chart of the offset of each bond line under different numbers of gates in the embodiments of this application; Figure 7 This is a schematic diagram comparing the drag angle of the molding compound on the bond line under different numbers of gates in the embodiments of this application; Figure 8 This is an offset contour map of each bond line at different gate positions in the embodiments of this application; Figure 9This is a comparison diagram of the offset of each bond line at different gate positions in the embodiments of this application; Figure 10 This is a schematic diagram showing the dimensional parameters of the gourd-shaped overflow trough in the embodiments of this application; Figure 11 This is a comparison diagram of the trapped air volume under different overflow trough structures in the embodiments of this application; Figure 12 This is a flowchart illustrating the steps of the low-defect molding optimization method in the embodiments of this application. Detailed Implementation

[0021] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. The step numbers in the following embodiments are set only for ease of explanation, and there is no limitation on the order between the steps. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0022] In the description of this application, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, 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.

[0023] In the description of this application, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0024] In the description of this application, unless otherwise expressly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0025] Before providing a detailed description of the embodiments of this application, some of the nouns and terms involved in the embodiments of this application will be explained first. The nouns and terms involved in the embodiments of this application are subject to the following interpretations.

[0026] 1) Wire rigging: During the molding process, the molten molding compound causes dragging and displacement of the internal bonding metal wires.

[0027] 2) Trapped air: Gas inside the mold cavity is surrounded by molding compound and cannot escape, forming voids or bubbles; 3) Short shot: The molding compound does not completely fill the mold cavity, resulting in defects in the product's shape; 4) Gold wire offset: The ratio of the maximum displacement of the bond wire perpendicular to the flow direction to the projected length of the bond wire.

[0028] Currently, the world is undergoing an industrial revolution characterized by digitalization, intelligentization, and green low-carbon development. Semiconductor devices, as the cornerstone of modern industrial future development, are increasingly highlighting their strategic importance. Simultaneously, with the booming development of new energy vehicles, industrial automation, and consumer electronics, the market demand for power semiconductor devices is also showing rapid growth. These application areas place high demands on the efficiency, density, and reliability of power conversion. With the evolution of semiconductor technology, power devices continue to develop towards higher integration and smaller size, evolving from the initial thyristors to today's intelligent power modules that integrate inverter functions, drive circuits, and fault protection. Intelligent power modules can efficiently and reliably drive loads such as motors, compressors, and inverters, achieving precise conversion between DC and AC power, frequency regulation, and power control. This enables key goals such as motor speed regulation, energy saving, and system intelligence in fields such as industrial frequency converters, new energy vehicles, and smart home appliances. At the same time, high integration design significantly simplifies the overall design process while improving system power density and reliability.

[0029] The packaging and manufacturing process of a high-performance smart power module is an extremely precise systems engineering project, which mainly includes the following key process steps: 1) Chip mounting: This process mainly involves precisely and securely mounting various semiconductor components onto designated pads on an aluminum-based copper-clad laminate.

[0030] 2) Wire bonding: After the chip is mounted, this process is required to establish an electrical connection between the chip and the substrate pads.

[0031] 3) Molding: This process involves placing the completed lead frame into a preheated mold cavity and using an injection molding machine to inject molten epoxy molding compound into the cavity under high pressure, so that it fully fills every tiny gap between the chip, bonding wires and the substrate. Then, it is heated and cured to form an integrated hard shell, achieving multiple functions such as mechanical support, electrical insulation and environmental protection.

[0032] Whether the processing quality of the intelligent power module obtained in the preceding processes can be effectively preserved, and whether its excellent electrical performance can be maintained stably in various application environments over a long period of time, ultimately depends to a large extent on the quality of the final molding process.

[0033] Due to the complex pin frame structure and stepped height on the chip surface of intelligent power modules, the molding compound experiences severe pressure fluctuations and uneven flow rates during filling. This hydrodynamic load easily leads to bond wire misalignment, a phenomenon known as "wire bleed." Wire bleed not only causes short circuits between wires but can also lead to bond point fracture under stress, seriously threatening the module's electrical performance and long-term reliability. Therefore, how to improve the flow field distribution within the mold cavity through precise mold structure design has become a key technical challenge in the field of intelligent power module packaging.

[0034] Compared to other types of modules, the IM3756-SST intelligent power module features high support pillars at its four corners. These corners are typically the areas with the longest flow paths and the latest filling times in the mold cavity. Without these high support pillars, even as the end points, the corners can still release air through the mold parting line. However, with the addition of these pillars, dead cavities that are difficult to vent are easily created during injection molding, ultimately leading to air entrapment defects and, in severe cases, the risk of short shots.

[0035] Currently, the most commonly used technical solutions in the production of similar power modules mainly include the following two: 1) Single-side single-gate layout: Plastic sealing molds usually have a fan-shaped or rectangular gate at one end of the mold cavity along its length. The plastic sealant flows into the cavity from a single direction. This design is simple, has low mold processing costs, and facilitates the cleaning of mold runner waste.

[0036] 2) Conventional rectangular overflow groove: A simple rectangular overflow groove is symmetrically set at the end of the mold cavity away from the gate. Utilizing the pressure difference inside and outside the cavity, the gas at the end of the filling is forced into the overflow groove, reducing the risk of trapped air.

[0037] In summary, the existing technical solutions have the following drawbacks: 1) Severe flow field imbalance: Unilateral feeding leads to excessive pressure gradients between the near and far gate ends within the mold cavity. The intense impact of the molding compound during the initial filling stage and the pressure surge at the end of filling cause uneven stress on the bond lines at different locations, resulting in excessive gold wire offset of the bond lines; 2) Incomplete elimination of trapped air: Due to its fixed and simple geometry, the existing rectangular overflow groove is difficult to adapt to the complex and irregular fluid filling front inside the intelligent power module. As a result, it cannot effectively balance the fluid pressure distribution at the end of the cavity according to the change of fluid flow rate during the molding process, and it is very easy to form trapped air areas with poor exhaust at the dead corners where the flow channels converge.

[0038] To address the shortcomings of the existing technology, this application provides a low-defect mold structure and its optimization method for molding smart power modules, solving the problems of severe bond line punching defects caused by a single gate on one side and air entrapment caused by poor venting in conventional overflow channels. Specific objectives include: 1) Achieve cavity flow field balance: By controlling the position and number of gates, change the flow trajectory of the molding compound in the cavity, reduce the instantaneous impact force at the beginning of filling, make the velocity gradient in each area of ​​the cavity more gradual, and weaken the fluid drag force that causes the rimping phenomenon from the source. 2) Achieve precise control of wire bonding defects: One of the purposes of this application is to control the maximum offset of the critical bonding wire inside the intelligent power module within a safe threshold of 1.0% to eliminate the risk of short circuit between wires, ensure the electrical connection stability of the wire bonding under high current conditions, and thus improve the yield of the module. 3) Improve exhaust problem through geometric structure optimization: In view of the complex internal structure of intelligent power module, this application provides a gourd-shaped overflow groove, which actively guides the gas at the fluid front to the exhaust port by utilizing its specific geometric contraction and expansion characteristics. The goal is to significantly reduce the volume of the gas trapped area in the cavity and improve the risk of local stress concentration and encapsulation delamination caused by gas trapping.

[0039] This embodiment uses a certain company's IM3756-SST intelligent power module as an example for illustration. Figure 1 As shown, the bonding wires inside this module are available in three diameters: 400 µm, 125 µm, and 38 µm, each performing a specific function in the circuit structure. The 400 µm thick aluminum wire, for example... Figure 1 The area circled in red is commonly used in main power circuits, covering key areas such as inverters, PFC, and rectifier bridges. Its core design principle is to ensure excellent high current-carrying capacity and heat dissipation performance, thereby effectively reducing conduction losses and meeting the reliability requirements of the main circuit for high current transmission. 125 µm medium-diameter aluminum wire, such as... Figure 1 The area circled in green primarily consists of components in the inverter and PFC sections. It connects the driver chip and the power device IGBT, transmitting high-frequency switching control signals. Its electrical performance must balance low parasitic inductance and sufficient current carrying capacity to ensure gate drive response speed and stability. The 38 µm fine aluminum wire, like... Figure 1 The area circled in blue typically contains densely packed wires around the driver chip, responsible for signal interaction with external control pins. It receives external pulse commands and transmits internal control signals to each IGBT gate, enabling precise control of the power device's switching state. Its fine wire diameter supports high-density interconnection, but it is more sensitive to mechanical stress during packaging. Because medium-diameter and thick aluminum wires possess high mechanical strength and deformation resistance under normal wire bonding conditions, the probability of wire breakage under conventional injection molding is relatively low. Therefore, the fine aluminum wire portion is the primary evaluation target for wire breakage defects. The connection and naming of the bonding wires around the driver chip are as follows: Figure 2 As shown.

[0040] The low-defect mold structure for encapsulating smart power modules provided in this embodiment includes: a mold cavity, two gates, and four gourd-shaped overflow channels.

[0041] (1) Symmetrical layout with double gates like Figure 3 As shown, a finite element model of the IM3756-SST intelligent power module was established using Moldex 3D simulation software.

[0042] The mold gate, as a crucial channel for molding compound to enter the mold cavity, directly determines the initial flow state of the molding compound through its characteristic parameters, thus significantly influencing the drag force on the bond lines and the formation of bonding defects. The flow wavefront time diagrams for different numbers of gates are shown below. Figure 4 As shown, when using a single-gate injection molding scheme, after the molding compound is injected into the cavity from a single gate, its flow front extends into the cavity in an approximately hemispherical shape. When the number of gates is increased to two and arranged symmetrically, the molding compound is injected simultaneously from both gates, forming two independent flow fronts that converge and fuse in the central region of the cavity. The offset distribution cloud diagrams of various bond lines under different gate numbers are shown below. Figure 5 As shown, to further quantify the impact of different gating schemes on bonding defects, the maximum offset data of a total of 27 bonding wires around the driver chip under the two gating schemes were extracted. The results are as follows. Figure 6 As shown in the comparison, the maximum offset of the bond lines in the single-gate scheme is significantly higher than that in the double-gate scheme. Furthermore, among the 27 bond lines, 23 have a greater maximum offset than the corresponding value in the double-gate scheme. Based on the bond line offset data of the two schemes, further statistical calculations were performed. The results show that compared to the single-gate scheme, the average offset of the 27 bond lines in the double-gate scheme is reduced by 56.2%, and the standard deviation is reduced by 34.2%. This indicates that the double-gate design not only reduces the average breakage level of the bond lines by more than half, but also effectively reduces the dispersion between the offsets of each bond line, enhancing the consistency of the molding process. In addition, the global maximum bond line offset also decreased from 1.512% in the single-gate scheme to 0.874% in the double-gate scheme, further verifying the superiority of the double-gate layout in suppressing breakage defects.

[0043] The underlying mechanism by which the number of gates affects bonding wire defects can be attributed primarily to the differences in the magnitude and direction of the molding compound flow velocity under different gate layouts. In a single-gate injection molding scheme, the molding compound must fill the entire cavity from one side of a single gate. With a constant filling time, the volume of molding compound delivered by a single gate is twice that of each gate in a dual-gate scheme, resulting in a filling speed approximately twice that of the dual-gate scheme. This higher filling speed significantly enhances the drag effect of the molding compound on the bonding wire, leading to a substantial increase in wire offset. In contrast, the dual-gate scheme uses two symmetrically arranged gates to feed simultaneously. Within the same filling time, the flow velocity reaching the bonding wire region is correspondingly reduced, effectively weakening the drag effect on the bonding wire.

[0044] Furthermore, the flow direction of the molding compound varies significantly with different numbers of gates, thus affecting the angle between the flow direction of the molding compound and the bond line axis, specifically as follows: Figure 7 As shown in the diagram, in the single-gate design, the molding compound is injected from the center of the cavity. When its flow front reaches the bond line region, the flow direction of the molding compound is approximately perpendicular to the bond line. At this point, most of the drag force acts directly on the lateral side of the bond line, easily causing significant offset. In the dual-gate design, the molding compound advances along the axial direction of the bond line, and the angle between the flow direction and the bond line is smaller, thus reducing the effective component of the drag force perpendicular to the bond line and minimizing its effect on the bond line. In summary, the dual-gate design can effectively reduce the maximum offset of the bond line and improve the uniformity of the offset distribution of each bond line by optimizing the flow path and velocity distribution of the molding compound, thereby suppressing the occurrence of bonding line defects to a certain extent.

[0045] (2) Positioning of the middle gate based on functional priority Based on the established dual-gate scheme, this embodiment also designs three mold schemes with different gate positions. These three gate positions are defined as outer gate, middle gate, and inner gate, with distances from the module edge of 6 mm, 8 mm, and 10 mm respectively. The bond line offset distribution cloud diagrams corresponding to the gate position schemes are shown below. Figure 8 As shown in the figure, the distribution of bond line offsets reveals significant differences in the areas of large offsets under different gate location schemes. In the outer and middle gate schemes, the areas with large bond line offsets are mainly concentrated near bond line 27, while in the inner gate scheme, the areas with large offsets appear at bond lines 18 and 27. To further quantify the comparison, the maximum offset data of all 27 bond lines under the three gate locations were extracted, and the results are shown below. Figure 9As shown in the figure. Analysis shows that among the external gate schemes, the angle between the gate position and bond line 27 is the largest, and the drag effect of the molding compound melt on the bond line is the most significant, resulting in the highest maximum offset among the three schemes. Moreover, the offsets between different bond lines vary greatly, and the overall uniformity is poor, so it is excluded.

[0046] Comparing the simulation results of the center gate and inner gate schemes reveals different distribution characteristics in the offset of the critical bond wires. The offset of bond wire 27 is higher in the center gate scheme than in the inner gate scheme, while the offset of bond wire 18 is lower. Bond wire 18 corresponds to the VCC pin, and bond wire 27 corresponds to the VB1 pin. VCC is the basic logic power supply for the driver chip, undertaking the core function of providing global power to the internal driver integrated circuit, control logic, and various protection circuits. The integrity of its electrical connection directly affects the system-level functionality of the entire module. Failure of the VCC bond wire will cause the driver chip to lose its logic control capability, leading to overall module malfunction or even systemic damage. VB1, as the local floating power supply for the U-phase high-voltage side driver circuit, is mainly limited to the switching action of a single phase. Therefore, from the perspective of global system reliability, the structural stability of the bond wire corresponding to the VCC pin should be given higher optimization priority. Compared to the inner gate design, the central gate design reduces the offset of bond wire 18 corresponding to the core power pin VCC by 13.6%. Although this design increases the offset of bond wire 27 corresponding to the secondary pin VB1 by 12.8%, the overall system reliability is better. Therefore, the central gate design (8mm from the module edge, approximately 20% of the total module length) was selected as the final design.

[0047] (3) Gourd-shaped overflow trough structure Based on the determined locations of the dual inlet gates and the central gate, and addressing the air trapping defects caused by the high support columns at the four corners, this embodiment optimizes the design with a special gourd-shaped overflow chute structure, replacing the conventional rectangular overflow chute of the prior art. The specific dimensions and configuration of the overflow chute in this embodiment are as follows: Figure 10As shown, the overall structure adopts a gourd-shaped design with rounded corners, with a total length of 3.5 mm. The inlet section is 0.5 mm long and 1.5 mm wide. The internal cavity radius is 1.5 mm, the corner radius is 0.5 mm, and the overflow groove thickness is 1 mm. The overflow grooves at the four high support pillars are 2 mm from the module edge. The narrow inlet section of the gourd-shaped design helps to throttle the molten material, preventing excessive molten material from rapidly flowing into the overflow groove and causing pressure loss in the cavity. The larger internal cavity effectively stores excess molten material and provides ample space for gas venting. The rounded corner design effectively reduces stress concentration, thereby enhancing the mold's structural strength and preventing fatigue cracking during long-term use. It also facilitates molten material flow and filling. The overflow groove thickness of 1 mm matches the thickness of the module's encapsulation, ensuring sufficient overflow capacity without compromising the overall structural strength of the mold. The distance between each overflow trough and the module edge ensures that overflow and gas are effectively discharged without affecting the dimensional accuracy and structural integrity of the module body. Simulation comparisons of the gas trapping volume of gourd-shaped overflow troughs and conventional rectangular overflow troughs (same length, same thickness) yield the following results: Figure 11 As shown.

[0048] Through the above structural design, this application can effectively adapt to the irregular filling front generated by the high support column structure, actively guide the gas in the trapped gas area to be discharged into the overflow trough. Compared with the traditional rectangular overflow trough, the volume of the trapped gas area is reduced by up to 20.45%, which significantly improves the problems of short shot and local stress concentration, and meets the high-quality plastic encapsulation requirements of the IM3756-SST type intelligent power module.

[0049] like Figure 12 As shown, this embodiment also provides a low-defect molding optimization method based on the above-described mold structure, including the following steps: Step S1: Determine the functional priority of the bonding wire.

[0050] For the IM3756-SST intelligent power module, analyze the functions of each pin. Define the bond wire corresponding to the VCC logic power supply pin as first priority (core function), and define the bond wires corresponding to local power supply or signal pins such as VB1 and VB2 as second priority (non-core function). Record the number, location, and corresponding pin function of each bond wire.

[0051] Step S2: Establish a finite element model and set up a simulation scheme.

[0052] A three-dimensional finite element model of the intelligent power module and mold structure was created using Moldex 3D software. At least three different gate location schemes were set, for example, 6 mm, 8 mm, and 10 mm from the module edge. The same injection molding process parameters (injection pressure, mold temperature, material temperature, filling time, etc.) were set.

[0053] Step S3: Simulate and calculate the bond line offset.

[0054] Run each simulation separately and extract the maximum offset of the first priority bond line (e.g., VCC bond line 18) and the second priority bond line (e.g., VB1 bond line 27). Record the data.

[0055] Step S4: Select the optimal gate location.

[0056] Compare the offset of the first-priority bond line in each group of schemes, and select the scheme that minimizes the offset as the optimal scheme. If the scheme results in an increase in the offset of the second-priority bond line, the scheme is still adopted.

[0057] In this embodiment, the inner gate (10 mm) causes the offset of bond line 18 to be 0.096%, and the middle gate (8 mm) causes the offset of bond line 18 to be 0.083% (a reduction of 13.6%). Although the offset of bond line 27 increases from 0.102% to 0.115%, the middle gate scheme is still selected.

[0058] Step S5: Optimize the shape of the overflow trough.

[0059] After determining the optimal gate location, rectangular and gourd-shaped overflow channels were installed in the corner areas corresponding to the high support columns. Keeping the total volume of the overflow channels similar, the volume of trapped air was simulated and calculated. The reduction in trapped air volume under the two shapes was compared.

[0060] Step S6: Determine the final mold parameters.

[0061] The geometric parameters of the overflow chute that maximize the reduction in trapped gas volume were selected as the final design. In this embodiment, the gourd-shaped overflow chute (total length 3.5 mm, inlet width 1.5 mm, inner radius 1.5 mm, and corner radius 0.5 mm) showed the best effect.

[0062] This embodiment also provides a method for encapsulating a smart power module using the above-described mold structure, the specific steps of which are as follows: Step 1: Place the semi-finished substrate with completed chip mounting and wire bonding into the preheated mold cavity and close the mold; Step 2: Heat the epoxy molding compound granules to a molten state (temperature approximately 175-185℃). Step 3: Using the injection molding machine piston, inject the molten molding compound into the cavity simultaneously from two symmetrically arranged central gates. The injection pressure is 40-80 MPa, and the filling time is 2-5 seconds. Step 4: The molding compound flow front advances within the cavity. When it reaches the high support pillar areas at the four corners, the gas is pushed by the front edge into the enlarged internal cavity of the gourd-shaped overflow channel. The narrow inlet throttles the molten material, preventing it from blocking the exhaust channel prematurely. Step 5: After the molding compound has completely filled the cavity, maintain the pressure (holding pressure 20-40 MPa, holding time 5-10 seconds) to fully compact the molding compound; Step 6: Cool and solidify (cooling time 30-60 seconds), open the mold, remove the sealed module, and cut off the gate and overflow waste.

[0063] The intelligent power module prepared using this method, after testing, showed that the maximum offset of the bonding line was controlled within 0.9%, with no trapped air voids or short shot defects, and the yield rate reached over 98.5%, which is a significant improvement over the existing single gate + rectangular overflow groove solution (yield rate of about 91%).

[0064] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," or "some embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0065] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

[0066] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A low-defect mold structure for molding and encapsulating intelligent power modules, characterized in that, The intelligent power module has chips and bonding wires integrated on its substrate, and high support pillars are provided at the corners of the module. The mold structure includes: The mold cavity is shaped to match the shape of the intelligent power module; At least two gates are symmetrically arranged on the same side of the mold cavity to allow molding compound to be injected into the cavity simultaneously from at least two directions; A gourd-shaped overflow channel is provided at the corner of the mold cavity and corresponds to the position of the high support column. The overflow channel has a narrow inlet and an enlarged internal cavity connected to it.

2. The low-defect mold structure according to claim 1, characterized in that, The number of gates is two, and the line connecting the centers of the two gates is parallel to the axis of the bonding line to reduce the vertical component of the molding compound flow direction on the bonding line.

3. The low-defect mold structure according to claim 2, characterized in that, The two inlets are located at a predetermined distance from the edge of the smart power module. This predetermined distance ensures that when the flow front of the molding compound reaches the bonding wire region corresponding to the core functional pin, the offset of the bonding wire is minimized compared to the bonding wire region corresponding to the non-core functional pin.

4. The low-defect mold structure according to claim 3, characterized in that, The core functional pin is the logic power supply pin (VCC), and the predetermined distance is 15%-25% of the total length of the intelligent power module in that direction.

5. The low-defect mold structure according to claim 1, characterized in that, The total length of the gourd-shaped overflow trough is 3.0mm-4.0mm, the width of the narrow inlet is 1.2mm-1.8mm, the maximum width of the enlarged internal cavity is 2.8mm-3.2mm, and the narrow inlet and the enlarged internal cavity are connected by a rounded corner.

6. The low-defect mold structure according to claim 5, characterized in that, The thickness of the gourd-shaped overflow trough matches the thickness of the intelligent power module encapsulation, and the length of the narrow inlet accounts for 1 / 7 to 1 / 5 of the total length.

7. The low-defect mold structure according to claim 1, characterized in that, The narrow inlet of the gourd-shaped overflow channel is configured to create a throttling effect on the incoming molding compound to balance the pressure at the corners of the cavity; the enlarged internal cavity is configured to provide gas expansion and retention space to actively guide and collect the gas pushed forward by the molding compound.

8. An optimization method for a low-defect mold structure based on any one of claims 1 to 7, characterized in that, Includes the following steps: Step S1: Determine the functional priority of the bonding wires in the intelligent power module, define the bonding wires corresponding to the core function pins as the first priority, and define the bonding wires corresponding to the non-core function pins as the second priority; Step S2: Establish a three-dimensional finite element model of the intelligent power module and the mold structure, and set at least two simulation schemes with different gate positions; Step S3: Simulate and calculate the maximum offset of the first priority bonding line and the second priority bonding line under each scheme. Step S4: Compare the simulation results of each group of schemes, and select the scheme that minimizes the offset of the first priority bond line as the optimal gate position scheme, even if the scheme causes the offset of the second priority bond line to increase.

9. The optimization method according to claim 8, characterized in that, Following step S4, the following is also included: Step S5: Based on the determination of the optimal gate location scheme, further optimize the shape of the overflow groove set at the corresponding position of the high support column, and compare the air trapping volume of the gourd-shaped overflow groove and the conventional rectangular overflow groove under the same cavity pressure conditions. Step S6: Select the geometric parameters of the overflow trough that maximize the reduction in trapped gas volume as the final design.

10. A method for encapsulating a smart power module, characterized in that, Using the low-defect mold structure of any one of claims 1 to 7, or the optimal mold parameters obtained by the method of claim 8 or 9, molten epoxy molding compound is simultaneously injected into the mold cavity from the at least two gates, so that the flow front of the molding compound discharges gas into the enlarged internal cavity of the gourd-shaped overflow groove at the overflow groove, and forms a molding compound after curing.

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