Self-adaptive press-fit anti-glue-overflow semiconductor packaging mold and packaging process thereof

Abstract

The mold comprises a lower mold cavity strip, an upper mold cavity strip and a base of the lower mold cavity strip, a floating type radiator pressing block is arranged in the upper mold cavity strip, an elastic reset mechanism is arranged between the pressing block and the base, and in the initial stage of mold opening and mold closing, the elastic reset mechanism is arranged between the pressing block and the base. The elastic force enables the lower end face of the pressing block to protrude out of the bottom face of the cavity, the pressing block is automatically compensated and tightly attached to the radiator on the frame, and the situation that molten resin permeates into the surface of the radiator to cause glue overflowing is prevented, and in the injection molding pressure maintaining stage, when the pressure of the resin in the cavity reaches a preset threshold value, the upward thrust overcomes the elastic force to drive the pressing block to compress the elastic mechanism to return upwards; therefore, the mechanical stress accumulated in the frame during mold closing is released. According to the invention, through the physical process of floating lamination and dynamic release, self-adaption to the incoming material tolerance of the frame is realized, the problem of glue overflow caused by height difference fluctuation is effectively solved, and the long-term reliability of a packaged product is improved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor packaging technology, specifically relating to a semiconductor packaging mold with adaptive pressing and anti-overflow adhesive and its packaging process. Background Technology

[0002] In conventional semiconductor packaging processes, especially for products such as IGBT modules where the heat sink needs to be exposed after packaging, a specific mold structure is typically used to achieve good isolation between the exposed heat sink surface and the resin. This structure includes a lower mold cavity strip and an upper mold cavity strip mounted on a base of the upper mold cavity strip. This process uses the upper mold cavity to press the frame with the heat sink into place, followed by resin encapsulation.

[0003] To ensure that the bottom of the upper mold cavity can fit tightly against the exposed surface of the heat sink after mold closing, thereby effectively preventing resin overflow, the key design is to make the height difference between the exposed surface of the heat sink and the terminal surface of the frame greater than the cavity depth.

[0004] However, due to the difficulty in controlling the precision during the manufacturing process, the height difference often fluctuates, and it is easy for the height difference to be less than the cavity depth.

[0005] When this happens, a gap will be created between the exposed surface of the heat sink and the bottom of the upper mold cavity, making it impossible to fit completely after the mold is closed. During resin encapsulation, the resin can easily seep into the exposed surface of the heat sink along the gap, causing surface glue overflow, which in turn leads to product scrap. Summary of the Invention

[0006] The purpose of this invention is to provide an adaptive compression anti-overflow semiconductor packaging mold and its packaging process to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a semiconductor packaging mold for adaptive pressing and anti-overflow adhesive, comprising a lower mold cavity strip, an upper mold cavity strip and an upper mold cavity strip base, wherein a floating heat sink pressure block is provided inside the upper mold cavity strip, and an elastic reset mechanism is provided between the heat sink pressure block and the upper mold cavity strip base;

[0008] The elastic reset mechanism is used to provide pre-tightening force in the early stages of mold opening and closing, so that the lower end face of the heat sink pressure block protrudes from the bottom surface of the upper mold cavity strip to compensate for the height difference of the heat sink.

[0009] The radiator pressure block is configured to overcome the elastic force of the elastic reset mechanism and retract backward during the injection molding and holding pressure stage when the resin pressure in the cavity reaches a preset threshold, so as to release the stress in the frame.

[0010] Preferably, the elastic element is one of a spring, a sheet spring, a magnetic mechanism, or a pneumatic / hydraulic cylinder.

[0011] Preferably, a sealing structure is provided between the heat sink pressure block and the inner wall of the upper mold cavity strip to prevent resin from seeping into the installation area of ​​the elastic reset mechanism, thus creating a physical barrier and effectively blocking the penetration of molten resin into the installation area of ​​the elastic element.

[0012] A packaging process for an adaptive compression bonding anti-overflow adhesive semiconductor packaging mold includes the following physical processes:

[0013] Floating bonding process: When the mold is closed, the pre-tightening force of the elastic reset mechanism drives the lower end face of the heat sink block to fit tightly against the heat sink surface of the frame. At this time, a gap is maintained between the bottom surface of the upper mold cavity strip 3 and the terminal surface of the frame.

[0014] Dynamic release process: During injection molding and pressure holding, when the upward thrust generated by the resin pressure established in the cavity is greater than the sum of the elastic force and friction force of the elastic reset mechanism, the radiator pressure block compresses the elastic reset mechanism and retracts upward until the preset gap between the radiator pressure block and the upper mold cavity strip base is eliminated. At this time, the frame returns to a stress-free state or a low-stress state.

[0015] Preferably, according to the packaging process described in claim 1, the preload F of the elastic reset mechanism pre-satisfies:

[0016] During the mold closing stage, the pre-force F is greater than the deformation force required for heat sink pressing to ensure a seal;

[0017] During the holding pressure stage, Fpre is less than the product of the maximum resin pressure Pmax and the force-bearing area S of the heat sink, i.e., Fpre < Pmax x S, to ensure that the pressure block can be pushed back by the resin pressure; to ensure that at the moment of mold closing, the pressure block has enough force to compact the surface of the heat sink, eliminate micro gaps, and achieve physical anti-overflow of glue; and to ensure that during the injection holding pressure stage, the fluid thrust generated by the resin must be greater than the spring resistance, forcing the pressure block into the "retracted release" state.

[0018] The technical effects and advantages of this invention are as follows:

[0019] 1. The preload of an elastic reset mechanism (such as a spring) forces the heat sink block to protrude from the bottom surface of the cavity. Regardless of the fluctuation of the heat sink height difference H1 in the incoming frame, the block can actively conform to the heat sink surface in the early stage of mold closing, automatically eliminating micro gaps. This achieves "zero-sensitivity" encapsulation to the tolerance of the incoming frame, completely eliminating resin penetration and surface overflow caused by insufficient height difference, and significantly improving the yield.

[0020] 2. The static pressure of the resin established during the injection molding and holding stage is used as the driving force. When the pressure reaches the preset threshold, the radiator pressure block is reversed and the spring is compressed back. While maintaining the seal, the frame is allowed to rebound synchronously with the pressure block, releasing all the mechanical stress that was originally accumulated inside the frame. This greatly improves the long-term working stability of high-reliability products such as IGBT modules.

[0021] 3. By designing a sealing structure between the pressure block and the cavity wall, or by optimizing the stiffness of the elastic element, the stability of the structure under high-pressure injection molding is ensured. This prevents the spring from jamming due to resin infiltration and ensures a wide range of process parameters. The invention can be applied without making significant adjustments to the parameters of existing injection molding machines. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the present invention (in the mold-open state);

[0023] Figure 2 This is a schematic diagram of the mold closing process (pre-compression state) according to an embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram of the mold in a fully closed state (stress storage state) according to an embodiment of the present invention.

[0025] Figure 4 This is a schematic diagram of the mold injection filling stage (pressure balance state) according to an embodiment of the present invention.

[0026] Figure 5 This is a schematic diagram of the mold holding pressure and stress release stage (retraction state) in an embodiment of the present invention.

[0027] In the diagram: Lower mold cavity strip-1, frame-2, upper mold cavity strip-3, upper mold cavity strip base-4, radiator pressure block-5, elastic reset mechanism-6, h1-preset gap, h2-mold closing gap, H1-radiator height difference, H2-cavity depth. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] like Figure 1 As shown in the figure, the semiconductor packaging mold for adaptive pressing and anti-overflow adhesive provided in this embodiment of the invention mainly includes a lower mold cavity strip 1, an upper mold cavity strip 3, an upper mold cavity strip base 4, a heat sink pressing block 5, and an elastic reset mechanism 6.

[0030] In the open mold state, the radiator pressure block 5 is installed in the cavity of the upper mold cavity strip 3, and its top is connected to the upper mold cavity strip base 4 by screws or a slot structure. The elastic reset mechanism 6 (in this embodiment, a helical spring) is sleeved on the connecting rod, or is independently set between the radiator pressure block 5 and the upper mold cavity strip base 4. Since the compression amount is reserved in the mold design, the elastic reset mechanism 6 is in a pre-compressed state. The elastic force generated by it pushes the radiator pressure block 5 downward, so that the bottom end face of the radiator pressure block 5 protrudes from the bottom surface of the cavity of the upper mold cavity strip 3, forming a preset gap h1.

[0031] The work process is as follows:

[0032] Step 1: Mold making and material loading ( Figure 1 )

[0033] The mold is in the open state. The frame 2 with the heat sink is placed at the designated position of the lower mold cavity strip 1. At this time, the heat sink block 5 is kept in the extended state under the action of the elastic reset mechanism 6.

[0034] Step 2: Mold closing and floating bonding ( Figure 2 )

[0035] The lower mold cavity strip 1 moves upward to close the mold. When the surface of the heat sink on the frame 2 contacts the bottom surface of the heat sink pressure block 5, the mold closing action continues. Because the rigidity of the elastic reset mechanism 6 is designed to be much greater than the force required for the frame 2 to undergo slight deformation, the heat sink pressure block 5 remains in a fixed relative position, while the frame 2 continues to rise with the lower mold cavity strip 1. At this time, a gap h2 is still maintained between the upper surface of the terminal of the frame 2 and the bottom surface of the cavity of the upper mold cavity strip 3, and the heat sink is in close contact with the pressure block.

[0036] Step 3: Complete mold clamping and stress storage ( Figure 3 )

[0037] The lower mold cavity strip 1 continues to rise until the upper and lower molds are completely closed. At this time, the radiator pressure block 5 remains stationary under the action of the compression elastic reset mechanism 6. The height difference between the terminal of the frame 2 and the radiator decreases, and the radiator part of the frame 2 is tightly pressed against the bottom surface of the radiator pressure block 5, eliminating the tolerance gap between the radiator height difference H1 and the cavity depth H2. At this time, the frame 2 stores elastic deformation stress, ensuring the sealing of the radiator surface.

[0038] Step 4: Injection filling and pressure balancing ( Figure 4 )

[0039] When the epoxy resin is injected, the resin pressure gradually increases during the cavity filling stage, but it has not yet reached the threshold that is sufficient to overcome the elastic force of the elastic reset mechanism 6. At this time, the radiator block 5 remains stationary, and the radiator of the frame 2 continues to be pressed to ensure that the resin does not seep into the radiator surface.

[0040] Step 5: Pressure holding and stress release ( Figure 5 )

[0041] When the cavity is fully filled and the pressure holding stage begins, the static pressure of the resin established in the cavity acts on the lower surface of the radiator. When the upward thrust generated by this pressure is greater than the sum of the elastic force of the elastic reset mechanism 6 and the friction force of the side wall of the radiator pressing block 5, the radiator pressing block 5 begins to move upward and backward.

[0042] As the radiator pressure block 5 retracts, the frame 2, which was originally forced to bend, gradually straightens under the action of elastic force, and the mechanical stress accumulated inside the frame is completely released. This process continues until the radiator pressure block 5 completely retracts to the surface of the upper mold cavity strip base 4 (the gap h1 is reduced to zero), or a dynamic balance between resin pressure and spring force is achieved.

[0043] Step 6: Curing and Mold Opening

[0044] The resin is cured and molded under pressure. Then, the mold is opened, the elastic reset mechanism 6 returns to its original shape, and pushes the radiator block 5 out again, ready for the next cycle.

[0045] Regardless of fluctuations in the height difference H1 of the heat sink in the frame material, a tight fit can be achieved through the preload of the spring, solving the problem of excess glue. Utilizing the fluid pressure in the later stages of injection molding as the driving force, the mechanical stress generated during mold closing is actively released, protecting the internal chips and bonding wires.

[0046] The applicant further declares that while the above embodiments illustrate the implementation method and apparatus structure of the present invention, the present invention is not limited to the above-described embodiments, meaning that the present invention must rely on the above methods and structures to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the selected implementation methods, additions to steps, and selections of specific methods all fall within the protection and disclosure scope of the present invention.

[0047] This invention is not limited to the above-described embodiments. All methods that employ similar structures and approaches to achieve the objectives of this invention are within the scope of protection of this invention.

Claims

1. A semiconductor packaging mold for adaptive pressing and anti-overflow adhesive, comprising a lower mold cavity strip (1), an upper mold cavity strip (3), and an upper mold cavity strip base (4), characterized in that: The upper mold cavity strip (3) is provided with a floating radiator pressure block (5), and an elastic reset mechanism (6) is provided between the radiator pressure block (5) and the upper mold cavity strip base (4). The elastic reset mechanism (6) is used to provide pre-tightening force in the early stages of mold opening and closing, so that the lower end face of the radiator pressure block (5) protrudes from the bottom surface of the cavity of the upper mold cavity strip (3) to compensate for the height difference of the radiator. The radiator pressure block (5) is configured to overcome the elastic force of the elastic reset mechanism (6) and retract backward during the injection molding pressure holding stage when the resin pressure in the cavity reaches a preset threshold, so as to release the stress in the frame.

2. The semiconductor packaging mold for adaptive pressing and anti-overflow adhesive according to claim 1, characterized in that: The elastic element (6) is one of a spring, a sheet spring, a magnetic mechanism, or a pneumatic / hydraulic cylinder.

3. The semiconductor packaging mold for adaptive pressing and anti-overflow adhesive according to claim 1, characterized in that: A sealing structure is provided between the heat sink pressure block (5) and the inner wall of the upper mold cavity strip (3) to prevent resin from seeping into the installation area of ​​the elastic reset mechanism (6).

4. A packaging process for a semiconductor packaging mold based on the adaptive pressing anti-overflow adhesive as described in any one of claims 1-3, characterized in that, Includes the following physical processes: Floating bonding process: When the mold is closed, the pre-tightening force of the elastic reset mechanism (6) drives the lower end face of the heat sink block (5) to fit tightly against the heat sink surface of the frame (2). At this time, there is a gap between the bottom surface of the cavity of the upper mold cavity strip (3) and the terminal surface of the frame (2). Dynamic release process: During injection molding and pressure holding, when the upward thrust generated by the resin pressure established in the cavity is greater than the sum of the elastic force and friction of the elastic reset mechanism (6), the radiator pressure block (5) compresses the elastic reset mechanism (6) and retracts upward until the preset gap between the radiator pressure block (5) and the upper mold cavity strip base (4) is eliminated. At this time, the frame (2) returns to a stress-free state or a low-stress state.

5. The packaging process of a semiconductor packaging mold with adaptive pressing and anti-overflow adhesive according to claim 4, characterized in that, The preload F of the elastic reset mechanism (6) is pre-satisfied: During the mold closing stage, the pre-force F is greater than the deformation force required for heat sink pressing to ensure a seal; During the pressure holding phase, Fpre is less than the product of the maximum resin pressure Pmax and the surface area S of the heat sink, i.e., Fpre 预＜ P max x S, to ensure that the compact can be pushed back by the resin pressure.

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