Directional solidification welding method based on igbt module signal terminal assembly

Abstract

This application relates to a directional solidification soldering method for IGBT module signal terminal assemblies. The method includes: inserting metal terminals into an insulating housing and abutting against substrate solder paste; heating and pumping liquid solder into an anchoring groove on the inner wall of the housing using open capillary slits of the terminals; establishing a vertical temperature gradient with a lower temperature at the top than at the bottom, controlling the solder in the anchoring groove to solidify preferentially, and using the liquid solder at the bottom to compensate for the solidification shrinkage at the top. This application has the advantages of effectively eliminating voids caused by solidification shrinkage inside the solder joint, achieving a dense, defect-free rigid interlock between the terminals and the housing, and significantly improving the mechanical strength and reliability of the module packaging.

Description

Technical Field

[0001] This application relates to the field of electronic components, and in particular to a method for directional solidification soldering of IGBT module signal terminal assemblies. Background Technology

[0002] Insulated-gate bipolar transistor (IGBT) modules, as core power devices in power electronic systems, are widely used in new energy vehicles, rail transportation, and industrial frequency conversion control. In the module's packaging structure, the signal terminals play a crucial role in transmitting gate drive signals and sensor feedback signals; the reliability of their connections directly affects the operational safety of the entire power module. Existing IGBT modules typically use a direct-copper-clad ceramic substrate as the carrier for the internal circuitry. One end of the signal terminal is vertically soldered to the surface pads of the substrate, while the other end extends through the insulating shell to connect electrically to external control circuitry.

[0003] In existing packaging processes, the connection between signal terminals and the substrate primarily relies on the bottom fillet weld formed by reflow soldering. Due to the limited thickness of the copper plating on the ceramic substrate surface and the inherent brittleness of ceramic materials, this single bottom weld structure has limitations in mechanical performance. Specifically, signal terminals typically exhibit a slender cantilever beam shape. When the module is subjected to external insertion / extraction forces during subsequent assembly, or to continuous mechanical vibrations during vehicle operation, the portion of the terminal extending beyond the housing generates a torque, which is directly transmitted to the bottom weld root.

[0004] However, in traditional insulating housing designs, to facilitate easy terminal insertion and compensate for manufacturing tolerances, the terminal mounting holes on the housing are typically designed with clearance fits or simple through-hole structures. This means that the inner wall of the housing cannot provide effective axial holding force or radial support for the terminals. Therefore, almost all external mechanical stress is concentrated on the solder joints on the substrate surface and the underlying copper plating. Under long-term thermal cycling and mechanical stress, this stress concentration can easily lead to fatigue cracks in the solder joints, or even peel the copper plating off from the ceramic substrate, thereby causing signal transmission interruption or module failure.

[0005] Furthermore, under conventional reflow soldering process control, the flow behavior of liquid solder on the substrate plane often lacks effective longitudinal guidance and constraint. The solder tends to spread laterally along the substrate plane under the influence of gravity and surface tension, rather than climbing along the terminal height direction to form a more robust coating structure. This not only limits the improvement of solder joint strength but also increases the risk of solder bridging and short circuits between adjacent pads. Current solutions often require additional dispensing reinforcement steps or complex pressing processes, which not only increase production costs but may also introduce new stress sources. Summary of the Invention

[0006] In order to achieve a high-strength connection between the terminal, the housing, and the substrate by utilizing the thermohydrodynamic characteristics of the welding process itself without adding additional auxiliary materials, this application provides a directional solidification welding method based on IGBT module signal terminal assembly.

[0007] In a first aspect, this application provides a directional solidification welding method for IGBT module signal terminal assemblies, which adopts the following technical solution: A directional solidification welding method for an IGBT module signal terminal assembly, the IGBT module signal terminal assembly including an insulating shell and metal terminals passing through the insulating shell; the insulating shell has terminal mounting holes, and the inner wall of the terminal mounting holes has anchoring grooves; the metal terminals include a welding part with an open capillary slit, a transition part with a transverse overflow channel, and a signal transmission part extending outside the insulating shell; the directional solidification welding method includes the following steps: S1. Insert the metal terminal into the terminal mounting hole, and place the bottom surface of the solder part against the solder paste layer on the substrate surface; S2. Heat the metal terminal and the substrate to raise the temperature above the solder liquidus temperature, and use capillary action to transport the liquid solder formed by melting the solder paste layer upward along the open capillary slit and fill the anchoring groove. S3. After the liquid solder in the anchoring groove is filled, a cooling medium is applied to the signal transmission section, while maintaining the heating temperature of the bottom of the substrate higher than the solidus temperature, so that the liquid solder in the anchoring groove solidifies before the liquid solder in the open capillary slit. S4. Stop heating the substrate and remove the cooling medium to cool the IGBT module signal terminal assembly to room temperature.

[0008] Optionally, step S2 includes the following sub-steps: S21. Heat the IGBT module signal terminal assembly at a heating rate of 1-3 degrees Celsius per second until the solder paste layer melts; S22. Maintain the temperature within the range of 20-40 degrees Celsius above the liquidus temperature for 30 to 60 seconds; simultaneously, apply mechanical vibration at a frequency of 20 kHz to 40 kHz to the metal terminal.

[0009] Optionally, step S21 includes the following sub-steps: S211. The IGBT module signal terminal assembly is placed in the heating chamber of the reflow soldering equipment. The heating chamber is equipped with a bottom heating platform for supporting the substrate and performing contact heat conduction, and a top heating device located above the insulating shell for performing non-contact heat radiation and non-contact heat convection. S212. While the heating chamber is under normal pressure or protective atmosphere, the bottom heating platform is activated to directly heat the substrate by heat conduction, so as to provide 60% to 80% of the heat energy required to melt the solder paste layer and establish a dominant heat flow path from bottom to top. S213. Simultaneously start the top heating device, use heat convection and heat radiation to heat together, reduce the temperature difference between the insulating shell and the metal terminal, and preheat the metal terminal to 85% to 95% of the liquidus temperature, so as to reduce the heat loss of the liquid solder when it enters the open capillary slit. S214. After the metal terminal reaches the preheating temperature, the heat convection function of the top heating device is stopped and the air pressure in the heating chamber is pumped to a low vacuum state of 500Pa to 1000Pa to remove the residual gas in the anchoring groove. S215. Using only the heat conduction of the bottom heating platform and the heat radiation of the top heating device, the temperature of the solder paste layer is raised above the liquidus temperature until the solder paste layer is completely melted into liquid solder.

[0010] Optionally, step S3 includes the following sub-steps: S31. Heat is continuously supplied to the substrate through the bottom heating platform to control the temperature at the inlet of the open capillary slit to be between the liquidus temperature and the highest heating temperature reached in S2; S32. A cooling medium is sprayed into the signal transmission unit through a nozzle, and the heat in the anchoring groove area is carried away by heat conduction, so that the temperature of the anchoring groove area drops below the solidus temperature at a preset rate; wherein, the cooling medium is a cooling gas; S33. Maintain the heating state in S31 and the cooling state in S32 until the solid-liquid phase change interface crosses the transverse overflow channel and descends to the open capillary slit region.

[0011] Optionally, step S32 includes the following sub-steps: S321. A nozzle is aimed at the side wall of the signal transmission unit, and the temperature of the cooling medium is set to 25 degrees Celsius to 50 degrees Celsius; wherein the cooling medium is a nitrogen gas flow. S322. Open the nozzle to spray nitrogen gas and adjust the flow rate of the cooling medium to maintain a temperature difference of 15 degrees Celsius to 30 degrees Celsius between the anchoring groove area and the open capillary slit area.

[0012] Optionally, in step S3, gas is introduced into the heating chamber to raise the ambient air pressure to a positive pressure state of 0.15MPa to 0.3MPa to act on the exposed liquid solder surface. The formation of micropores inside the liquid solder is suppressed by the isostatic pressure effect, and the negative pressure suction force generated by the solidification and shrinkage of the liquid solder in the anchoring groove and the pressure difference with the ambient positive pressure are used to promote the bottom liquid solder to compensate and fill the solidification and shrinkage zone.

[0013] Optionally, step S1 includes the following sub-steps: S11. Print the solder paste layer on the surface of the substrate, such that the coverage area of ​​the solder paste layer includes the projection area of ​​the bottom surface of the metal terminal and the open capillary slit; S12. Press the metal terminal axially into the terminal mounting hole and apply vertical pressure to embed the bottom surface of the metal terminal into the solder paste layer until the distance between the bottom surface of the metal terminal and the surface of the substrate is less than 0.05 mm.

[0014] In summary, this application includes at least one of the following beneficial technical effects: 1. This application establishes a vertical temperature gradient with a lower temperature at the top than at the bottom, forcibly controlling the solidification phase transformation interface of the solder to advance from the anchoring groove towards the open capillary slit. This directional solidification mechanism utilizes the solder that is still in a liquid state at the bottom as a feeding source, actively compensating for the volume shrinkage of the solder at the top during the phase transformation process. This effectively eliminates the vacuum shrinkage defects caused by premature freezing of the flow channel neck in traditional natural cooling processes, ensuring a dense, void-free, rigid interlocking structure between the metal terminal and the insulating shell, significantly improving the tensile strength and mechanical reliability of the terminal.

[0015] 2. This application employs a segmented heating strategy combining atmospheric pressure convection preheating and vacuum radiation melting, and introduces a positive pressure environment to assist in feeding during the solidification stage. The low vacuum environment effectively eliminates residual gas in blind hole structures such as anchor grooves, preventing gas resistance effects; while the subsequently applied positive pressure utilizes hydrostatic pressure to inhibit the nucleation and growth of micropores inside the liquid solder, and, combined with the negative pressure suction generated by solidification shrinkage, not only improves the density of the metallographic structure inside the solder joint, but also significantly reduces the risk of bridging short circuits between adjacent solder pads.

[0016] 3. This application utilizes dual-sided independent heat source control, combining contact heat conduction and non-contact heat convection / radiation, to solve the problem of uneven heating caused by differences in heat capacity and emissivity between the metal terminals and the insulating shell. By using heat convection to balance the temperature difference during the preheating stage and using concentrated heat radiation to supply energy during the melting stage, it ensures that the metal terminals receive sufficient wetting temperature to activate capillary pumping, while preventing the insulating shell from undergoing thermal deformation or carbonization due to prolonged exposure to high-temperature radiation. This achieves improved thermal compatibility and yield of heterogeneous material components in complex reflow soldering processes. Attached Figure Description

[0017] Figure 1 A schematic diagram of the structure of an IGBT module signal terminal assembly is shown in one embodiment of the present invention.

[0018] Figure 2 A flowchart illustrating a method for directional solidification welding of IGBT module signal terminal assemblies according to an embodiment of the present invention is shown.

[0019] Explanation of reference numerals in the attached figures: 1. Heat dissipation base plate; 2. Substrate; 3. Metal terminal; 31. Welding part; 32. Transition part; 33. Signal transmission part; 4. Open capillary slit; 5. Lateral overflow channel; 51. Stress relief hole; 6. Anchoring groove; 7. Insulating shell; 8. Terminal mounting hole; 81. Lower locking mating area; 82. Upper flexible protection accommodating area; 9. Elastic protective sleeve; 91. Corrugated structure. Detailed Implementation

[0020] The present application will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the application and are not intended to limit the scope of the application.

[0021] This application discloses a directional solidification welding method for IGBT module signal terminal assemblies, referring to... Figure 1 The IGBT module signal terminal assembly includes an insulating housing 7 and metal terminals 3 passing through the insulating housing 7. The insulating housing 7 is provided with terminal mounting holes 8, and the inner wall of the terminal mounting holes 8 is provided with anchoring grooves 6. The metal terminals 3 include a welding part 31 with an open capillary slit 4, a transition part 32 with a transverse overflow channel 5, and a signal transmission part 33 extending out of the insulating housing 7. The welding part 31 is used for welding to a substrate 2, and the substrate 2 is disposed on a heat dissipation base plate 1.

[0022] Specifically, the insulating shell 7 is made of high-temperature resistant insulating plastic, such as polyphenylene sulfide (PPS) or polybutylene terephthalate (PBT), to withstand the high-temperature environment of subsequent reflow soldering. The terminal mounting hole 8 penetrates the insulating shell 7 axially and is divided into a lower locking mating area 81 and an upper flexible protective receiving area 82. The lower locking mating area 81 and the upper flexible protective receiving area 82 form a countersunk hole shape that is wider at the top and narrower at the bottom. The diameter of the lower locking mating area 81 is adapted to the transition portion 32 of the metal terminal 3. An anchoring groove 6 is formed on the inner wall of the lower locking mating area 81, and its cross-sectional shape is preferably a dovetail shape or an inverted trapezoid with a snap-fit ​​function. The welding portion 31 of the metal terminal 3 is located at the bottom end. An open capillary slit 4 penetrates the bottom surface of the welding portion 31 and extends axially upwards, with a width set to 0.2 mm to 0.4 mm to ensure sufficient capillary adhesion. The transition section 32 is located in the middle of the metal terminal 3. The transverse overflow channel 5 is in fluid communication with the open capillary slit 4, and the outlets at both ends are located on the sidewalls of the metal terminal 3. At the intersection of the open capillary slit 4 and the transverse overflow channel 5, a stress relief hole 51 with a larger aperture is also provided, forming a cross-shaped or T-shaped fluid diversion structure. An elastic protective sleeve 9 is provided in the upper flexible protective receiving area 82, and its bottom directly abuts against the stepped surface in the terminal mounting hole 8. The top of the elastic protective sleeve 9 is fitted onto the root of the signal transmission section 33 of the metal terminal 3 and is slightly higher than the top surface of the insulating shell 7. The outer side wall of the elastic protective sleeve 9 is provided with a corrugated structure 91. The signal transmission section 33 extends upward from the transition section 32 and passes through the top surface of the insulating shell 7 for connection with external circuits.

[0023] Based on the structure of the IGBT module signal terminal assembly described above, this application further discloses a directional solidification welding method, referring to... Figure 2 This includes the following steps S1-S4.

[0024] S1. Insert the metal terminal 3 into the terminal mounting hole 8, and place the bottom surface of the solder part 31 against the solder paste layer on the surface of the substrate 2.

[0025] Specifically, step S1 includes the following sub-steps S11-S12.

[0026] S11. Print the solder paste layer on the surface of the substrate 2 such that the coverage area of ​​the solder paste layer includes the projection area of ​​the bottom surface of the metal terminal 3 and the open capillary slit 4.

[0027] S12. Press the metal terminal 3 axially into the terminal mounting hole 8, and apply vertical pressure to embed the bottom surface of the metal terminal 3 into the solder paste layer until the distance between the bottom surface of the metal terminal 3 and the surface of the substrate 2 is less than 0.05 mm.

[0028] The stepped surface inside the insulating housing 7 or the external mounting fixture provides a clear axial positioning reference. This, combined with a clearance fit or slight interference fit between the terminal mounting hole 8 and the transition portion 32 of the metal terminal 3, restricts the radial and axial degrees of freedom of the metal terminal 3. The axial pressing action precisely aligns the outlet of the transverse overflow channel 5 with the anchoring groove 6 on the inner wall of the insulating housing 7 in the height direction. This geometric alignment establishes a continuous fluid path from the inside of the metal terminal 3 to the inner wall of the insulating housing 7, defining the physical boundary for the subsequent directional delivery of liquid solder.

[0029] The solder paste layer is printed over a vertically projected area covering the bottom surface of the metal terminal 3 and the open capillary slit 4. This full-coverage printing strategy ensures that the bottom entrance of the open capillary slit 4 is completely submerged in the solder paste material after the metal terminal 3 is pressed in. Sufficient solder paste reserves provide a continuous liquid supply at the moment the solder melts, preventing supply interruptions at the slit entrance due to insufficient solder in certain areas, and ensuring continuous capillary pump suction power.

[0030] Vertical pressure drives the bottom surface of metal terminal 3 to pierce the flux film and oxide layer on the solder paste surface, physically embedding metal terminal 3 into the solder paste matrix. Embedded contact establishes a tight physical interface between the metal and solder paste before heating, reducing interface thermal resistance and promoting pre-activation and wetting of the metal surface by the flux.

[0031] The distance between the bottom surface of the metal terminal 3 and the surface of the substrate 2 is controlled to be less than 0.05 mm, thus creating a high flow resistance radial boundary at the hydrodynamic level. This tiny bottom gap utilizes fluid viscous resistance to inhibit the radial flow of liquid solder along the plane of the substrate 2, forcing the molten solder to preferentially climb axially along the open capillary slit 4 with lower flow resistance under the action of surface tension. This gap threshold, combined with the embedded contact, forms a liquid-sealed environment at the slit entrance, eliminating air pockets and preventing gas from being entrained into the flow channel to form air embolisms, ensuring that the capillary pumping effect is activated immediately upon the phase change.

[0032] S2. The metal terminal 3 and the substrate 2 are heated to a temperature above the solder liquidus temperature. The liquid solder formed by melting the solder paste layer is conveyed upward along the open capillary slit 4 and filled into the anchoring groove 6 by capillary action.

[0033] The heating process drives the overall temperature of the component to exceed the liquidus threshold of the solder, inducing a solid-liquid phase transition in the solder paste layer, transforming it into a low-viscosity liquid fluid. An open capillary slit 4, with a width set between 0.2 mm and 0.4 mm, utilizes the surface tension characteristics of the liquid solder to generate a significant capillary pressure difference at the gas-liquid interface of the slit. This capillary driving force overcomes the gravitational potential energy of the liquid solder and the viscous frictional resistance along the tube wall, establishing a vertically upward fluid transport dynamic balance. The liquid solder rises axially and flows through the transverse overflow channel 5 into the anchoring groove 6 on the inner wall of the insulating shell 7, filling the inverted cavity.

[0034] Optionally, step S2 includes the following sub-steps S21-S22.

[0035] S21. Heat the IGBT module signal terminal assembly at a heating rate of 1-3 degrees Celsius per second until the solder paste layer melts.

[0036] The 1-3 degree Celsius temperature rise range coordinates the thermal mismatch stress caused by the difference in thermal expansion coefficients between the ceramic substrate 2 and the insulating shell 7, preventing brittle fracture of the ceramic material or warping deformation of the plastic shell. The gentle temperature rise profile matches the active release window of the flux system in the solder paste, ensuring that the flux fully evaporates solvent and removes interface oxides before the solder melts, while avoiding solder paste splashing or damage to the liquid seal integrity at the slit entrance due to excessively rapid heating that could cause solvent boiling.

[0037] Specifically, step S21 includes the following sub-steps S211-S215.

[0038] S211. The IGBT module signal terminal assembly is placed in the heating chamber of the reflow soldering equipment. The heating chamber is equipped with a bottom heating platform for supporting the substrate 2 and performing contact heat conduction, and a top heating device located above the insulating shell 7 for performing non-contact heat radiation and non-contact heat convection.

[0039] S212. While the heating chamber is under normal pressure or a protective atmosphere, the bottom heating platform is activated to directly heat the substrate 2 through heat conduction, so as to provide 60% to 80% of the heat energy required to melt the solder paste layer and establish a dominant heat flow path from bottom to top.

[0040] S213. Simultaneously start the top heating device, use heat convection and heat radiation to heat together, reduce the temperature difference between the insulating shell 7 and the metal terminal 3, and preheat the metal terminal 3 to 85% to 95% of the liquidus temperature, so as to reduce the heat loss of the liquid solder when it enters the open capillary slit 4.

[0041] S214. After the metal terminal 3 reaches the preheating temperature, the heat convection function of the top heating device is stopped and the air pressure in the heating chamber is pumped to a low vacuum state of 500Pa to 1000Pa to remove the residual gas in the anchoring groove 6.

[0042] S215. Using only the heat conduction of the bottom heating platform and the heat radiation of the top heating device, the temperature of the solder paste layer is raised above the liquidus temperature until the solder paste layer is completely melted into liquid solder.

[0043] The heating chamber employs a dual-sided independent heat source configuration to address the thermal management requirements of heterogeneous material components. The bottom heating platform, serving as the main energy source, directly contacts the high-heat-capacity ceramic substrate 2, while the top heating device provides auxiliary temperature control for the low-heat-capacity metal terminals 3 and the heat-sensitive insulating outer shell 7.

[0044] The bottom heating platform provides 60% to 80% of the total heat energy, establishing a dominant heat flow vector from bottom to top. Heat is preferentially transferred to the solder paste layer on the surface of substrate 2, ensuring that the melting phase change begins at the bottom inlet of the open capillary slit 4. This heat flow path not only conforms to the bottom-up transport direction of the liquid solder, but also utilizes the thermal inertia of substrate 2 to maintain the stability of the root molten pool.

[0045] At atmospheric pressure, the top heating device utilizes thermal convection as a thermal equalization mechanism. The flow and exchange of the gaseous medium compensates for the uneven heat absorption caused by the difference in infrared emissivity between the insulating shell 7 and the metal terminals 3, preventing localized overheating and carbonization of the plastic shell. Preheating the metal terminals 3 to 85% to 95% of their liquidus temperature aims to establish a thermal buffer protection. This preheating temperature threshold ensures that the metal terminals 3 have sufficient enthalpy, and when the high-temperature liquid solder contacts the inner wall of the terminal, the minimal temperature difference prevents the solder front from condensing and becoming blocked due to instantaneous heat loss, ensuring the continuity of capillary flow.

[0046] Once the preheating temperature is reached, the system stops convection and switches to a low vacuum mode of 500Pa to 1000Pa. The low vacuum environment removes the stagnant gas in the anchoring groove 6 and the micro-slits before the solder melts on a large scale, eliminating the back pressure resistance of the blind hole structure and preventing air pockets from forming air emboli during the fluid filling process.

[0047] The maintenance of phase transition in a vacuum environment relies on the coupling effect of bottom conduction and top radiation. Bottom heat conduction continuously drives the solid-liquid transition of the solder paste layer, while top heat radiation penetrates the vacuum environment to maintain the body temperature of the metal terminal 3. The high energy density of radiative heating compensates for the decrease in heat flux caused by the lack of convection, ensuring that the solder can smoothly cross the liquidus line and maintain low viscosity rheological properties under vacuum conditions.

[0048] S22. Maintain the temperature within the range of 20-40 degrees Celsius above the liquidus temperature for 30 to 60 seconds; simultaneously, apply mechanical vibration at a frequency of 20 kHz to 40 kHz to the metal terminal 3.

[0049] This step maintains the temperature within a superheated range of 20 to 40 degrees Celsius above the liquidus line. This temperature setting stimulates the thermal motion of liquid metal molecules, disrupting the long-range ordered structure within the melt and reducing the dynamic viscosity of the liquid solder. The low viscosity reduces the internal friction between the fluid and the slit walls, allowing the limited capillary drive force to generate higher flow rates and head. A liquid phase holding time of 30 to 60 seconds ensures that the liquid solder completes the entire transport and lateral filling process from the bottom surface of substrate 2 to the top anchoring groove 6.

[0050] The acoustic pressure wave causes the formation, growth, and collapse of tiny cavities in the liquid. The micro-jet shock wave generated at the moment of collapse destroys the internal agglomeration structure and interfacial oxide film of the fluid. The acoustic flow effect generates a directional fluid driving force on a macroscopic scale, assisting capillary force in overcoming gravity. High-frequency vibration reduces the equivalent friction coefficient of the liquid-solid interface, forcing the fluid to penetrate deep into the dead zone of the anchoring groove 6, and stripping any remaining micro-bubbles from the blind end and discharging them in the reverse direction along the flow channel, ensuring that the interior of the locking structure reaches a near-completely dense filling state.

[0051] S3. After the liquid solder in the anchoring groove 6 is filled, a cooling medium is applied to the signal transmission section 33, while maintaining the heating temperature of the bottom of the substrate 2 above the solidus temperature, so that the liquid solder in the anchoring groove 6 solidifies before the liquid solder in the open capillary slit 4.

[0052] Directional solidification process avoids volume shrinkage defects caused by random cooling based on thermodynamic control. A reverse vertical temperature gradient is constructed with the top temperature lower than the bottom temperature, forcing the solid-liquid phase change interface to start from the anchoring groove 6 region away from the liquid source and advance unidirectionally towards the substrate 2, which serves as the feeding end.

[0053] Traditional overall cooling methods cause premature freezing of the neck of the open capillary slit 4 located below due to the faster heat dissipation rate of the metal terminal 3 compared to the substrate 2. The solidification blockage of the transport channel causes the liquid solder in the upper anchoring groove 6 to form an isolated molten pool, which cannot be replenished during subsequent phase transformation shrinkage, resulting in vacuum shrinkage cavities. The reverse temperature gradient ensures that the open capillary slit 4 remains in a connected liquid state during the solidification of the top. The phase transformation shrinkage of the top solder generates a local negative pressure, which, combined with capillary force, actively draws the liquid solder below upwards, filling the gaps left by volume shrinkage in real time and achieving densification.

[0054] Specifically, step S3 includes the following sub-steps S31-S33.

[0055] S31. Heat is continuously supplied to the substrate 2 through the bottom heating platform to control the temperature at the inlet of the open capillary slit 4 to be between the liquidus temperature and the highest heating temperature reached in S2.

[0056] The bottom heating platform continuously supplies heat to clamp the temperature at the entrance of the open capillary slit 4 between the liquidus temperature and the maximum heating temperature. This temperature setting maintains the liquid solder in the open capillary slit 4 in a low viscosity and high fluidity state, preventing the feeding source channel from freezing before the top solidification is completed, and ensuring the smooth flow of liquid.

[0057] S32. A cooling medium is sprayed into the signal transmission unit 33 through a nozzle, and the heat in the anchoring groove 6 region is carried away by heat conduction, so that the temperature of the anchoring groove 6 region drops below the solidus temperature at a preset rate; wherein, the cooling medium is a cooling gas.

[0058] The cooling gas undergoes convective heat exchange with the surface of the signal transmission unit 33, and the high thermal conductivity of the metal terminal 3 conducts the cold energy downwards to the anchoring groove 6 area inside the insulating housing 7. The heat in the anchoring groove 6 area is removed, and the temperature drops below the solidus temperature at a preset rate. Using gas as the cooling medium avoids the electrical insulation risks caused by liquid coolant residue and facilitates control of the cooling intensity through flow rate adjustment.

[0059] Specifically, step S32 includes the following sub-steps S321-S322.

[0060] S321. A nozzle is aimed at the side wall of the signal transmission unit 33, and the temperature of the cooling medium is set to 25 degrees Celsius to 50 degrees Celsius; wherein, the cooling medium is a nitrogen gas flow; S322. Open the nozzle to spray nitrogen gas and adjust the flow rate of the cooling medium to maintain a temperature difference of 15 degrees Celsius to 30 degrees Celsius between the anchoring groove 6 region and the open capillary slit 4 region.

[0061] The nozzle is aimed at the side wall of the signal transmission section 33 rather than the top, increasing the effective contact area between the cooling medium and the metal surface and extending the heat exchange path. The temperature of the cooling nitrogen gas flow is set at 25-50 degrees Celsius to balance cooling efficiency and thermal shock risk, avoiding excessive instantaneous temperature differences that could cause microcracks in the ceramic substrate 2. The nitrogen medium isolates oxygen, preventing oxidation and discoloration of the high-temperature metal terminal 3 surface. The temperature difference threshold in S322 drives the solid-liquid phase change interface to move smoothly downwards along the terminal axis, preventing shrinkage cavities caused by uncontrolled interface propagation speed due to excessive temperature difference, or directional solidification failure due to insufficient temperature difference.

[0062] Optionally, in step S3, gas is introduced into the heating chamber to raise the ambient air pressure to a positive pressure state of 0.15MPa to 0.3MPa to act on the exposed liquid solder surface. The formation of micropores inside the liquid solder is suppressed by the isostatic pressure effect, and the negative pressure suction generated by the solidification and shrinkage of the liquid solder in the anchoring groove 6 and the pressure difference with the ambient positive pressure are used to promote the bottom liquid solder to compensate and fill the solidification and shrinkage zone.

[0063] During the directional solidification stage, inert gas is introduced into the heating chamber to raise the pressure to 0.15 MPa to 0.3 MPa. The ambient positive pressure acts directly on the exposed surface of the liquid solder on the substrate 2 and the outlet surface of the transverse overflow channel 5, utilizing the isostatic pressure effect to increase the nucleation energy barrier of bubbles inside the liquid solder and suppress the formation of micropores. The combined ambient positive pressure and internal negative pressure create a total pressure difference, driving the liquid solder at the bottom to forcibly compensate and fill the solidification shrinkage zone at the top, eliminating porosity defects caused by insufficient natural feeding force, and improving the density and mechanical strength of the final solder joint.

[0064] S33. Maintain the heating state in S31 and the cooling state in S32 until the solid-liquid phase change interface crosses the transverse overflow channel 5 and descends to the open capillary slit 4 region.

[0065] This step maintains the heating and cooling state, controlling the solid-liquid phase change interface to advance from top to bottom. The phase change interface crosses the transverse overflow channel 5 and descends to the open capillary slit 4 region. The transverse overflow channel 5 acts as a geometric bottleneck node; premature truncation at this point would cause the anchoring groove 6 to disconnect from the feeding source. Controlling the interface's descent to the open capillary slit 4 region establishes the endpoint of the feeding process, ensuring that the entire mechanically interlocked structure has completed dense solidification under liquid supply. Time redundancy control prevents the phenomenon of false solidification where the surface solidifies while the internal liquid core remains, ensuring that the phase change is completely completed.

[0066] S4. Stop heating the substrate 2 and remove the cooling medium to cool the IGBT module signal terminal assembly to room temperature.

[0067] Bottom heating is stopped and the cooling medium is removed, allowing the system to return from a controlled non-equilibrium thermal field to a natural cooling equilibrium state. The overall cooling process releases residual thermal stress accumulated during welding due to the mismatch in thermal expansion coefficients. Ultimately, a dense metal interlocking structure is formed between the metal terminal 3 and the insulating shell 7. This structure converts the axial pull-out load on the terminal into compressive stress on the insulating shell 7, significantly improving the mechanical connection strength and vibration resistance of the assembly.

[0068] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0069] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for directional solidification welding of IGBT module signal terminal assemblies, characterized in that, The IGBT module signal terminal assembly includes an insulating housing (7) and a metal terminal (3) passing through the insulating housing (7); the insulating housing (7) is provided with a terminal mounting hole (8), and the inner wall of the terminal mounting hole (8) is provided with an anchoring groove (6); the metal terminal (3) includes a welding part (31) with an open capillary slit (4), a transition part (32) with a transverse overflow channel (5), and a signal transmission part (33) extending out of the insulating housing (7); the directional solidification welding method includes the following steps: S1. Insert the metal terminal (3) into the terminal mounting hole (8) and place the bottom surface of the solder part (31) against the solder paste layer on the surface of the substrate (2); S2. The metal terminal (3) and the substrate (2) are heated to raise the temperature above the solder liquidus temperature. The liquid solder formed by melting the solder paste layer is transported upward along the open capillary slit (4) and filled into the anchoring groove (6) by capillary action. S3. After the liquid solder in the anchoring groove (6) is filled, a cooling medium is applied to the signal transmission part (33), while maintaining the heating temperature of the bottom of the substrate (2) higher than the solidus temperature, so that the liquid solder in the anchoring groove (6) solidifies before the liquid solder in the open capillary slit (4). S4. Stop heating the substrate (2) and remove the cooling medium to cool the IGBT module signal terminal assembly to room temperature.

2. The directional solidification welding method for IGBT module signal terminal assemblies according to claim 1, characterized in that, Step S2 includes the following sub-steps: S21. Heat the IGBT module signal terminal assembly at a heating rate of 1-3 degrees Celsius per second until the solder paste layer melts; S22. Maintain the temperature in the range of 20-40 degrees Celsius above the liquidus temperature for 30 to 60 seconds; at the same time, apply mechanical vibration at a frequency of 20 kHz to 40 kHz to the metal terminal (3).

3. The directional solidification welding method for IGBT module signal terminal assemblies according to claim 2, characterized in that, Step S21 includes the following sub-steps: S211. The IGBT module signal terminal assembly is placed in the heating chamber of the reflow soldering equipment. The heating chamber is equipped with a bottom heating platform for supporting the substrate (2) and conducting contact heat conduction, and a top heating device located above the insulating shell (7) for conducting non-contact heat radiation and non-contact heat convection. S212. Under the condition that the heating cavity is maintained at normal pressure or protective atmosphere, the bottom heating platform is activated to directly heat the substrate (2) through heat conduction to provide 60% to 80% of the heat energy required to melt the solder paste layer and establish a dominant heat flow path from bottom to top. S213. Simultaneously start the top heating device, use heat convection and heat radiation to heat together, reduce the temperature difference between the insulating shell (7) and the metal terminal (3), and preheat the metal terminal (3) to 85% to 95% of the liquidus temperature, so as to reduce the heat loss of the liquid solder when it enters the open capillary slit (4) later. S214. After the metal terminal (3) reaches the preheating temperature, the heat convection function of the top heating device is stopped and the air pressure in the heating chamber is pumped to a low vacuum state of 500Pa to 1000Pa to remove the residual gas in the anchoring groove (6). S215. Using only the heat conduction of the bottom heating platform and the heat radiation of the top heating device, the temperature of the solder paste layer is raised above the liquidus temperature until the solder paste layer is completely melted into liquid solder.

4. The directional solidification welding method for IGBT module signal terminal assemblies according to claim 3, characterized in that, Step S3 includes the following sub-steps: S31. Heat is continuously supplied to the substrate (2) through the bottom heating platform to control the temperature at the inlet of the open capillary slit (4) to be between the liquidus temperature and the highest heating temperature reached in S2; S32. A cooling medium is sprayed into the signal transmission unit (33) through a nozzle, and the heat of the anchoring groove (6) region is carried away by heat conduction, so that the temperature of the anchoring groove (6) region drops below the solidus temperature at a preset rate; wherein, the cooling medium is a cooling gas; S33. Maintain the heating state in S31 and the cooling state in S32 until the solid-liquid phase change interface crosses the transverse overflow channel (5) and descends to the open capillary slit (4) region.

5. The directional solidification welding method for IGBT module signal terminal assemblies according to claim 4, characterized in that, Step S32 includes the following sub-steps: S321. A nozzle is aimed at the side wall of the signal transmission unit (33), and the temperature of the cooling medium is set to 25 degrees Celsius to 50 degrees Celsius; wherein the cooling medium is a nitrogen gas flow. S322. Open the nozzle to spray nitrogen gas and adjust the flow rate of the cooling medium to maintain a temperature difference of 15 degrees Celsius to 30 degrees Celsius between the anchoring groove (6) region and the open capillary slit (4) region.

6. The directional solidification welding method for IGBT module signal terminal assemblies according to claim 5, characterized in that, In step S3, gas is introduced into the heating chamber to raise the ambient air pressure to a positive pressure state of 0.15MPa to 0.3MPa to act on the exposed liquid solder surface. The formation of micropores inside the liquid solder is suppressed by the isostatic pressure effect. The negative pressure suction force generated by the solidification and shrinkage of the liquid solder in the anchoring groove (6) and the pressure difference with the ambient positive pressure are used to promote the bottom liquid solder to compensate and fill the solidification and shrinkage zone.

7. The directional solidification welding method for IGBT module signal terminal assemblies according to claim 1, characterized in that, Step S1 includes the following sub-steps: S11. Print the solder paste layer on the surface of the substrate (2) such that the coverage area of ​​the solder paste layer includes the projection area of ​​the bottom surface of the metal terminal (3) and the open capillary slit (4); S12. Press the metal terminal (3) into the terminal mounting hole (8) axially and apply vertical pressure to embed the bottom surface of the metal terminal (3) into the solder paste layer until the distance between the bottom surface of the metal terminal (3) and the surface of the substrate (2) is less than 0.05 mm.

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