Packaging method for power semiconductor device and packaged power semiconductor device

Abstract

The present invention relates to the field of packaging technology, and discloses a packaging method for a power semiconductor device and the packaged power semiconductor device. The method includes: immersing the packaging shell in a heat-conducting liquid in an immersion chamber, wherein the temperature of the heat-conducting liquid is greater than or equal to the junction temperature of the power semiconductor device, the thermal conductivity coefficient of the heat-conducting liquid is greater than a preset coefficient, the heat-conducting liquid is an insulating liquid, and there is a gap between the cathode and the gate of the power semiconductor device; putting packaging components into the packaging shell; inside the packaging shell, assembling the packaging components for the power semiconductor device in accordance with the packaging process sequence; and hermetically packaging the packaging shell. The present invention can improve the heat dissipation efficiency on the gate-cathode side, improve the heat dissipation balance between the anode and the cathode, increase the device junction temperature and enhance the turn-off ability, thereby improving the reliability and service life of the device. At the same time, it has the advantages of simple process, low cost and strong adaptability.

Description

Technical Field

[0001] The present invention relates to the field of packaging technology, and particularly to a packaging method for power semiconductor devices and the packaged power semiconductor devices. Background Art

[0002] Power semiconductor devices are the core components of modern power electronic systems and are widely used in fields such as electric energy regulation, control, and conversion. With the increasing attention to energy transmission and environmental protection, power semiconductor devices have become increasingly important in the power industry, which also poses higher requirements for their performance. Integrated Gate Commutated Thyristor (IGCT) is a new type of power semiconductor device that can achieve high-voltage and large-capacity energy conversion. It has the advantages of high voltage resistance, high current resistance, low loss, large capacity density, fast switching speed, simple structure, high safety, and high reliability, and can be widely used in fields such as high-voltage direct current transmission, new energy power generation, and rail transit.

[0003] Figure 1 is the longitudinal structure of the cell of the power semiconductor device. There is a gap between the cathode and the gate of the chip. The traditional thyristor packaging technology mainly adopts a press-packaging structure, and the gap is filled with air (as shown in Figure 1 or Figure 3a ). The thermal conductivity of air is small, and its heat conduction performance is poor. Vacuum completely isolates the heat transfer on this path. On the cathode side of the chip, when a large current is turned off, the heat generated by the gate can only conduct horizontally along the chip to the cathode mesa, and then is longitudinally exported to the molybdenum sheet for heat dissipation through the cathode mesa and the cathode electrode in contact with the molybdenum sheet. However, the area of the cathode electrode in contact with the molybdenum sheet is small, usually accounting for less than 40% of the anode electrode. Therefore, the heat dissipation efficiency is extremely low. The heat dissipation capabilities on both the cathode and anode sides are inconsistent. During long-term use, the cathode will first show problems such as aging and cracking. In addition, the heat dissipation on the cathode side seriously reduces the junction temperature and turn-off ability of the device, affecting the safety, reliability, and service life of the device. Summary of the Invention

[0004] The purpose of the present invention is to provide a packaging method for power semiconductor devices and the packaged power semiconductor devices, aiming to solve the problems such as uneven heat dissipation between the anode and cathode of the chip, low junction temperature of the device, and poor turn-off ability caused by the traditional packaging structure.

[0005] To achieve the above object, a first aspect of the present invention provides a packaging method for a power semiconductor device, the packaging method comprising: immersing a packaging case in a heat-conducting liquid in an immersion chamber, wherein the temperature of the heat-conducting liquid is greater than or equal to the junction temperature of the power semiconductor device, the thermal conductivity coefficient of the heat-conducting liquid is greater than a preset coefficient, the heat-conducting liquid is an insulating liquid, and there is a gap between the cathode and the gate of the power semiconductor device; placing packaging components into the packaging case; inside the packaging case, assembling the packaging components for the power semiconductor device in accordance with the packaging process sequence; and hermetically packaging the packaging case.

[0006] Preferably, after immersing the packaging case in the heat-conducting liquid in the immersion chamber, the packaging method further comprises: after the temperature of the packaging case rises to the temperature of the heat-conducting liquid, performing ultrasonic treatment to eliminate bubbles in the packaging case; and / or after placing the packaging components into the packaging case, the packaging method further comprises: after the temperature of the packaging components rises to the temperature of the heat-conducting liquid, performing ultrasonic treatment to eliminate bubbles in the packaging components.

[0007] Preferably, inside the packaging case, assembling the packaging components for the power semiconductor device in accordance with the packaging process sequence comprises: inside the packaging case, aligning the packaging components for the power semiconductor device in sequence in accordance with the packaging process sequence; and detecting the connection mode and the assembly sequence of the packaging components.

[0008] Preferably, the viscosity of the heat-conducting liquid is less than or equal to a preset viscosity and is non-corrosive.

[0009] Preferably, the coefficient of thermal expansion of the heat-conducting liquid is determined by , where is the compression coefficient of the heat-conducting liquid, is the temperature difference between the junction temperature of the power semiconductor device and the normal temperature, and is the pressure difference that the power semiconductor device can withstand.

[0010] Preferably, before immersing the packaging case in the heat-conducting liquid in the immersion chamber, the packaging method further comprises: cleaning and drying the packaging case, the power semiconductor device, and the packaging components.

[0011] Preferably, the packaging method further comprises: detecting the sealing performance and the performance of the power semiconductor device after hermetic packaging.

[0012] Preferably, the packaging case is provided with a diversion groove distributed longitudinally.

[0013] Through the above technical solution, the present invention creatively immerses the encapsulation housing in a highly thermally conductive insulating heat transfer fluid, so that the heat transfer fluid fills the gaps between the various encapsulation structures inside the housing, enhances the heat dissipation capacity on each path, improves the heat dissipation efficiency on the cathode side of the gate, and improves the heat dissipation balance between the anode and the cathode. The immersion liquid high thermal conductivity encapsulation technology can improve the device junction temperature and enhance the turn-off ability, improve the reliability and service life of the device. At the same time, it has the advantages of simple process, low cost, and strong adaptability.

[0014] In a second aspect of the present invention, there is provided a packaged power semiconductor device, which includes: a power semiconductor device, packaging components, an encapsulation housing, and a heat transfer fluid. Among them, the heat transfer fluid is filled between the power semiconductor device and the encapsulation housing, between the packaging components and the encapsulation housing, and between the cathode and the gate of the power semiconductor device. The thermal conductivity of the heat transfer fluid is greater than a preset value, the heat transfer fluid is an insulating liquid, and there is a gap between the cathode and the gate of the power semiconductor device.

[0015] Preferably, the viscosity of the heat transfer fluid is less than or equal to a preset viscosity and it is non-corrosive.

[0016] Preferably, the coefficient of thermal expansion of the heat transfer fluid is determined by where is the compressibility of the heat transfer fluid, is the temperature difference between the junction temperature of the power semiconductor device and the normal temperature, and is the pressure difference that the power semiconductor device can withstand.

[0017] Preferably, the encapsulation housing is provided with diversion grooves distributed longitudinally.

[0018] For the specific details and benefits of the packaged power semiconductor device provided by the embodiments of the present invention, reference can be made to the above description of the packaging method for power semiconductor devices, and details will not be repeated here.

[0019] Other features and advantages of the present invention will be described in detail in the subsequent specific implementation section. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings are used to provide a further understanding of the embodiments of the present invention, and constitute a part of the specification. Together with the following specific implementation, they are used to explain the embodiments of the present invention, but do not constitute a limitation to the embodiments of the present invention. In the drawings:

[0021] Figure 1 is a schematic diagram of the longitudinal structure of the cell of the power semiconductor device;

[0022] Figure 2It is a flowchart of a packaging method for a power semiconductor device provided by an embodiment of the present invention;

[0023] Figure 3a and Figure 3b are respectively schematic diagrams of the packaging structures of the power semiconductor device before and after filling with high thermal conductivity liquid provided by an embodiment of the present invention;

[0024] Figure 4a is a schematic diagram of an immersion packaging assembly based on a power semiconductor device provided by an embodiment of the present invention;

[0025] Figure 4b is a schematic diagram of an immersion packaging assembly based on a power semiconductor device provided by an embodiment of the present invention;

[0026] Figure 5 is a top view of the packaging shell of the power semiconductor device provided by an embodiment of the present invention; and

[0027] Figure 6 is a flowchart of the process steps of an immersion packaging based on a power semiconductor device provided by an embodiment of the present invention. Specific Embodiments

[0028] The following will describe in detail the specific embodiments of the present invention with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0029] Figure 2 is a flowchart of a packaging method for a power semiconductor device provided by an embodiment of the present invention. As Figure 2 shown, the packaging method includes: Step S201, immersing the packaging shell into the heat-conducting liquid in the immersion chamber, where the temperature of the heat-conducting liquid is greater than or equal to the junction temperature of the power semiconductor device, the thermal conductivity coefficient of the heat-conducting liquid is greater than a preset coefficient, the heat-conducting liquid is an insulating liquid, and there is a gap between the cathode and the gate of the power semiconductor device; Step S202, putting the packaging components into the packaging shell; Step S203, inside the packaging shell, assembling the packaging components for the power semiconductor device in accordance with the packaging process sequence; and Step S204, hermetically packaging the packaging shell.

[0030] A high-thermal-conductivity packaging technology for a liquid-immersed thyristor chip proposed in this embodiment has the following advantages compared with the traditional packaging technology:

[0031] (1)Improve the heat dissipation capacity of the device: The addition of the high thermal conductivity liquid improves the phenomenon of weak heat dissipation capacity on this path caused by the air filling between the gate and the cathode. Since the device is wrapped in the thermal conductivity liquid, it increases the heat dissipation path of the device to the surrounding environment, thereby enhancing the heat dissipation capacity of heat on each path, improving the heat dissipation efficiency on the gate-cathode side, and improving the heat dissipation balance between the anode and the cathode.

[0032] (2)Improve the reliability of the device: The addition of the high thermal conductivity liquid reduces the contact thermal resistance between the chip and the cathode molybdenum sheet. According to the calculation relationship of the junction temperature, the chip junction temperature decreases, thereby increasing the junction temperature threshold and improving the reliability and service life of the device. At the same time, it provides the possibility for further improving the turn-off voltage in the design.

[0033] (3)Improve the turn-off ability of the device: The heat that cannot be dissipated causes the chip to heat up. Previously, under the conditions of a normal operating temperature of 90 °C and traditional double-sided water cooling, it could only be turned off 3 times. After adding the thermal conductivity liquid, the maximum number of turn-offs can be increased to 5 times, significantly improving the turn-off ability of the device.

[0034] (4)Improve the heat dissipation performance and electrical performance: The high thermal conductivity packaging technology for liquid-immersed thyristor chips has the advantages of simple process, low cost, strong adaptability, etc. The insulation of the thermal conductivity liquid can eliminate the electrical stress breakdown caused by particles, burrs, etc. inside the device shell, and can effectively improve the heat dissipation performance and electrical performance of the thyristor.

[0035] The following will explain and illustrate each of the above steps separately.

[0036] Step S201: Immerse the packaging shell in the thermal conductivity liquid in the immersion chamber.

[0037] Among them, the temperature of the thermal conductivity liquid is greater than or equal to the junction temperature of the power semiconductor device, the thermal conductivity coefficient of the thermal conductivity liquid is greater than a preset coefficient, the thermal conductivity liquid is an insulating liquid, and there is a gap between the cathode and the gate of the power semiconductor device.

[0038] Specifically, the thermal conductivity coefficient of the thermal conductivity liquid should be greater than that of the traditional solid packaging material (the thermal conductivity coefficient range of the traditional solid packaging material is between 0.1 - 0.5 W / (m·K). For example, the preset coefficient can be 0.5 W / (m·K) to improve the heat dissipation performance; and, it should ensure the insulation between the chip and the shell to prevent leakage and short circuit, and it needs to have a high resistivity to ensure good insulation performance. For example, the resistivity should reach 10 8 Ω·m or more. For example, the thermal conductivity liquid includes highly insulating electronic fluorinated liquid, highly pure alcohol and other high thermal conductivity organic liquids, nanofluids, and other high thermal conductivity insulating liquids.

[0039] Among them, the packaging shell can be a ceramic shell; its seal can be made of stainless steel metal.

[0040] First, inject a heat-conducting liquid into the immersion chamber. To prevent thermal expansion and contraction of the heat-conducting liquid inside the package after encapsulation, heat the heat-conducting liquid to the designed temperature (such as the junction temperature designed for the chip) and then maintain a constant temperature. Then, immerse the package shell (such as a ceramic shell) into the heat-conducting liquid in the immersion chamber. Thereby, the stress generated by thermal expansion during actual use after encapsulation can be avoided.

[0041] In one embodiment, the heat-conducting liquid also meets other conditions. For example, the viscosity of the heat-conducting liquid is less than or equal to a preset viscosity and it is non-corrosive.

[0042] Low viscosity: It is convenient for filling and flowing, ensuring that the chip can be completely immersed in it. The viscosity is less than or equal to the preset viscosity (such as 10 m² / s). For example, the viscosity (or kinematic viscosity) is selected between 5 m² / s and 10 m² / s. In this embodiment, for the device, the high heat-conducting liquid has a lower requirement for fluidity but requires better heat conductivity.

[0043] Good chemical stability: It is not prone to chemical reactions during long-term use and will not corrode the chip and the shell. That is, non-corrosive: It does not have corrosiveness to all metal materials and other organic and inorganic materials.

[0044] In addition, generally, the coefficient of thermal expansion of the liquid at room temperature is relatively small, and this change can usually be ignored. However, the thyristor chip has high precision requirements and a corresponding stress tolerance range. Considering adding the high heat-conducting liquid in the present invention, the present invention predicts the safety of the device by considering the stress impact on the chip caused by the thermal expansion change of the high heat-conducting liquid during the working process.

[0045] Specifically, in a closed container, the thermal expansion of the liquid will cause an increase in pressure. According to the definition of the compressibility coefficient, we can obtain , where is the initial volume, is the change in pressure.

[0046] At the same time, according to the definition of the coefficient of thermal expansion of the liquid, the volume change of the liquid can also be expressed as .

[0047] Since the volume of the liquid is unique, according to the definition of the compressibility coefficient , so we can obtain

[0048] = .

[0049] Through the above equation, the calculation formula for the pressure of liquid thermal expansion can be obtained: .

[0050] In one embodiment, the coefficient of thermal expansion Determined by , where is the compressibility of the heat-conducting liquid, is the temperature difference between the junction temperature of the power semiconductor device and the normal temperature, and is the pressure difference that the power semiconductor device can withstand.

[0051] The pressure range that the chip can withstand is 5-10 MPa (i.e., = 5 MPa). After adding the high heat-conducting liquid, during the process of the device heating up from the normal temperature to the normal working temperature, the maximum temperature difference is 30°C, and the liquid is incompressible (for example, the compressibility is 1 / Pa). According to the prediction design basis of the liquid thermal expansion pressure , it can be obtained that when selecting the high heat-conducting type, the coefficient of thermal expansion α ≤ / °C.

[0052] Preferably, the coefficient of thermal expansion of the heat-conducting liquid is as small as possible to avoid the thermal expansion and contraction of the heat-conducting liquid in the closed shell due to temperature changes, which affects the device packaging stress.

[0053] Of course, in another embodiment, the heat-conducting liquid can meet the above various conditions. In addition, the boiling point of the heat-conducting liquid should be higher than the limit temperature of the chip during the on-off process (for example, the boiling point is 128°C) to avoid the heat-conducting liquid vaporizing inside the shell due to too high temperature and forming a high pressure, which affects the device packaging stress. The liquid density of the heat-conducting liquid can be selected as 880 kg / m 3 .

[0054] In step S201, the liquid level height of the heat-conducting liquid must completely immerse the shell to ensure that the inside of the shell is filled with the heat-conducting liquid.

[0055] In one embodiment, after immersing the packaging shell into the heat-conducting liquid in the immersion chamber (i.e., step S201), the packaging method further includes: after the temperature of the packaging shell rises to the temperature of the heat-conducting liquid, performing ultrasonic treatment to eliminate the bubbles in the packaging shell.

[0056] Specifically, the immersion chamber containing the heat-conducting liquid can have an ultrasonic function. Immerse the ceramic shell into the heat-conducting liquid in the immersion chamber, wait for the ceramic shell to rise to the temperature of the heat-conducting liquid, and perform ultrasonic treatment to eliminate the remaining bubbles in the shell.

[0057] Since the heating temperature of the heat-conducting liquid is the junction temperature designed for the chip, only by maintaining for a sufficient long time can it ensure that the ceramic shell immersed under the heat-conducting liquid rises to the temperature of the heat-conducting liquid; or, it is also very easy to obtain the temperature of the ceramic shell by using an infrared gun.

[0058] Optionally, the ultrasonic time is maintained at tens of seconds to several minutes; optionally, the ultrasonic frequency is maintained at 500 kHz to 2 MHz; optionally, the ultrasonic intensity is maintained at 180 kPa to 570 kPa.

[0059] Step S202: Place the packaged components into the packaging shell.

[0060] The packaged components may include: a gate insulator, a gate contact ring, a cathode molybdenum sheet, an anode molybdenum sheet, and an anode electrode. Among them, the gate insulator is polyimide; the gate contact ring is made of molybdenum; the anode electrode is a metal shell.

[0061] After placing the packaged components into the packaging shell (i.e., step S202), the packaging method further includes: after the temperature of the packaged components rises to the temperature of the heat-conducting liquid, perform ultrasonic treatment to eliminate the bubbles in the packaged components.

[0062] Specifically, place the packaged components into the packaging shell in the heat-conducting liquid in sequence. Similarly, after the components are heated to the temperature of the heat-conducting liquid, perform ultrasonic treatment successively to eliminate the remaining bubbles in the packaged components. Since the heating temperature of the heat-conducting liquid is the designed junction temperature of the chip, only by maintaining a sufficient long time can it be ensured that the packaged components immersed under the heat-conducting liquid are heated to the temperature of the heat-conducting liquid; or, it is also very easy to obtain the temperature of the packaged components by using an infrared gun.

[0063] Among them, the liquid level height of the heat-conducting liquid must completely immerse the packaged components, ensuring that the surface gaps of the packaged components and the spaces between the components are filled with the heat-conducting liquid and there are no bubbles.

[0064] Optionally, the ultrasonic time is maintained at tens of seconds to several minutes; optionally, the ultrasonic frequency is maintained at 500 kHz to 2 MHz; optionally, the ultrasonic intensity is maintained at 180 kPa to 570 kPa.

[0065] Of course, in another embodiment, after performing step S201 and step S202, ultrasonic treatment can be performed respectively in the above manner to eliminate the bubbles in the packaging shell and the packaged components.

[0066] Step S203: Assemble the packaged components for the power semiconductor device inside the packaging shell according to the packaging process sequence.

[0067] Assembling the packaged components for the power semiconductor device inside the packaging shell according to the packaging process sequence, that is, step S203 may include: inside the packaging shell, align the packaged components for the power semiconductor device in sequence according to the packaging process sequence; and detect the connection method and assembly sequence of the packaged components.

[0068] Specifically, in accordance with the packaging process sequence of the internal components of the device, the components are aligned in sequence (as Figure 4a shown), and it is detected whether the connection methods, assembly sequences, etc. of the components meet the packaging structure design.

[0069] Among them, all packaged components must be assembled and interconnected before packaging below the liquid level of the heat-conducting liquid immersion chamber.

[0070] Optionally, after the components are placed and interconnected according to the packaging design structure, ultrasonic treatment is required again to ensure that there are no residual bubbles; optionally, after the internal components of the device are assembled according to the packaging design structure, multi-angle rotation is required, and at the same time ultrasonic treatment is added to avoid residual bubbles in areas such as the gaps, micro-grooves, and micropores of each component, and to ensure that the heat-conducting liquid fills the surroundings of each component inside the packaging shell; optionally, the assembly and interconnection process between each packaged component should be kept as slow and stable as possible to avoid causing splashing of the heat-conducting liquid and the formation of bubbles inside the heat-conducting liquid.

[0071] Step S204, sealing the packaging shell.

[0072] Specifically, an appropriate packaging method and sealing material are used to seal the packaging shell after the previous step, so that the inside of the packaging shell can be fully filled with the heat-conducting liquid (such as Figure 3b the gap between the cathode and the gate of the chip shown is filled with the heat-conducting liquid). Among them, the packaging process must ensure that the heat-conducting liquid inside the shell cannot leak to prevent the formation of bubbles inside the shell. The packaging shell must have high sealing performance to avoid leakage of the heat-conducting liquid; the packaging process can be carried out below the liquid level of the heat-conducting liquid.

[0073] Optionally, the packaging method is crimping packaging, bonding packaging, or soldering packaging.

[0074] Before immersing the packaging shell into the heat-conducting liquid in the immersion chamber (i.e., step S201), the packaging method further includes: cleaning and drying the packaging shell, the power semiconductor device, and the packaged components.

[0075] Specifically, the packaging shell, the power semiconductor device, and the packaged components (such as electrode components, etc.) are cleaned to remove oil stains, impurities, etc. on the surface. Among them, when cleaning the chip, it is necessary to ensure that the surface of the chip is not affected by dissolution, corrosion, etc. of the cleaning liquid as much as possible. All the above-mentioned cleaned components should be dried after cleaning to keep them dry.

[0076] Optionally, the cleaning liquid includes deionized water, organic cleaning liquid, ethanol, acetone, hydrogen peroxide, etc.; optionally, to further ensure the cleaning effect, ultrasonic cleaning, heating cleaning, vibration cleaning, etc. can be selected.

[0077] After performing step S204, the encapsulation method further includes: detecting the sealing performance and the performance of the power semiconductor device after hermetic encapsulation.

[0078] Specifically, the encapsulated device is detected, and the detection scope includes the sealing performance of the package (whether there is leakage of the heat-conducting liquid) and the device performance, etc.

[0079] Optionally, the detection methods include visual observation, vibration detection, and detection of parameters such as thermal-electric-force.

[0080] First, according to the theoretical model of immersion encapsulation design, the stress impact of the thermal expansion change of the high heat-conducting liquid on the chip is checked to check the safety of the device; the reduction of the thermal resistance before and after replacing the high heat-conducting liquid is compared

[0081] (1) Liquid expansion coefficient check

[0082] Furthermore, the liquid expansion pressure and force of the power semiconductor device (such as an IGCT device) are calculated. The temperature difference between the extreme operating condition (120 °C) and the normal operating condition (90 °C) of the device is 30 °. At 90 °C, the liquid expansion pressure is 0 Pa. When the device operates at the extreme operating condition (120 °C), the liquid expansion pressure is 0.36 Pa.

[0083] The pressure that the Si chip side can withstand is 5 MPa - 10 MPa. Therefore, when the device operates at the extreme operating condition (120 °C), the pressure generated by the liquid on the chip side is much smaller than the withstand voltage of the chip.

[0084] (2) Reduction of thermal resistance

[0085] Taking the IGCT device as an example, the calculation method of the IGCT junction temperature is as follows: first, calculate its power at any time t , and then according to the relationship between the thermal resistance p ( t ) and the power t at any time , the junction temperature p ( t ) is obtained, specifically as follows:

[0086] .

[0087] According to the relevant parameters in the RB-IGCT device manual, the device thermal resistance relationship can be extracted as:

[0088] ,

[0089] In the formula, is the transient thermal resistance of the device; $R_{th,i}$ is the equivalent thermal resistance (in K / kW) of the $i$-th layer of dielectric (such as air or heat-conducting liquid) from the bottom to the top of the device, and $n$ is the total number of equivalent thermal resistances (as shown in Figure 3b where $n = 13$, which is the sum of the total volume thermal resistance formed by the dielectrics of each structural layer and the total contact thermal resistance formed by the dielectrics between adjacent structural layers); $\tau$ is the time constant (in s).

[0090] Mainly verify the absolute value of the reduction in the device thermal resistance and the relative value of the reduction in the overall device thermal resistance before and after adding the high heat-conducting liquid under the steady-state operating condition of the device during normal operation. Under the steady-state operating condition, the thermal resistance is independent of time $t$. The thermal resistance on the cathode and anode sides can simplify the above formula as:

[0091] ,

[0092] The device thermal resistance is obtained by parallel connection of the cathode and anode side thermal resistances. The overall device thermal resistance can be expressed as:

[0093] ,

[0094] where $R_{th,cathode}$ is the total thermal resistance on the cathode side, $R_{th,anode}$ is the total thermal resistance on the anode side.

[0095] Calculate the reduction ratio of the contact thermal resistance between Si and Mo:

[0096] When the gap is filled with air, assuming that the heat conduction path only conducts through the cathode comb bars and the air-filled part is a heat-insulating channel, the volume thermal resistance of this layer is used to replace the contact thermal resistance of this layer. Substituting the physical property parameters, it can be obtained as 0.000037 K·m 2 / W.

[0097] After the gap is filled with the high heat-conducting liquid, the volume thermal resistance after parallel connection of the heat conduction paths of the cathode comb bars and the high heat-conducting liquid is 0.0000317 K·m 2 / W.

[0098] Therefore, after the gap is filled with the high heat-conducting liquid, the absolute value reduction ratio of the contact thermal resistance between the Si chip and the Mo sheet is 14%.

[0099] Calculate the reduction ratio of the contact thermal resistance between Si and Mo to the reduction of the entire IGCT device thermal resistance after adding the high heat-conducting liquid.

[0100] When the gap is filled with air, according to the above assumption, the contact thermal resistance between Si and Mo is replaced by the volume thermal resistance of this layer. According to the above thermal resistance model, substituting the physical property parameters and empirical values, the calculated overall device thermal resistance is 0.75 K·m 2 / W.

[0101] After the gap is filled with the high thermal conductivity liquid, according to the above theoretical assumptions, the contact thermal resistance between Si_Mo is replaced by the bulk thermal resistance after parallel connection. According to the above thermal resistance model, substituting the physical property parameters and empirical values, the overall thermal resistance of the device can be calculated to be 1.17 K·m 2 / W.

[0102] Therefore, after the gap is filled with the high thermal conductivity liquid, the proportion of the reduction in the contact thermal resistance between Si_Mo to the reduction in the thermal resistance of the entire IGCT device is 56%.

[0103] In one embodiment, the encapsulation shell is provided with a diversion groove distributed longitudinally, as Figure 5 shown.

[0104] To ensure the smooth flow of the internal coolant, preferably, some longitudinal diversion grooves need to be provided on the shell, with the inner diameter unchanged. Figure 5 The structure of the diversion groove inside the shell of the power semiconductor device is schematically shown from a top view.

[0105] The encapsulation process of the power semiconductor device (such as an IGCT device) will be described below, as Figure 6 shown.

[0106] Step 1, clean the components.

[0107] Clean components such as the immersion chamber, the ceramic shell of the IGCT chip, the IGCT chip, and the electrodes to remove surface oil stains, impurities, etc.

[0108] During the production and transportation of the components, the surface may be contaminated with various impurities (such as dust, organic matter, metal particles, etc.). Clean components such as the immersion chamber, the ceramic shell of the IGCT chip, the selected IGCT chip, and the electrodes, and use ultrasonic cleaning to detach the impurities from the chip surface.

[0109] After cleaning, use nitrogen gas to dry it to ensure that the chip surface is dry and clean, and prepare for the subsequent encapsulation process.

[0110] Step 2, inject the high thermal conductivity liquid into the immersion chamber, and heat the thermal conductivity liquid to the designed temperature and then keep it constant.

[0111] The size specification of the immersion chamber should be larger than the encapsulation size of the device to facilitate the insertion, removal, and portable movement inside the chamber of each component to be encapsulated; the thermal conductivity liquid is selected from materials that meet the selection requirements described in 6.2; the heating temperature of the thermal conductivity liquid should be the designed junction temperature of the chip (80 °C).

[0112] Perform a hermeticity check to ensure good hermeticity. Use an inflation device to fill the immersion chamber with gas at 1.2 atmospheres, which can be an inert gas such as dry nitrogen. Close the intake valve, record the initial pressure. After 24 hours, if the pressure drop is within the allowable range (generally not exceeding 5%-10% of the specified pressure, depending on the requirements), it indicates good sealing performance.

[0113] Inject the high thermal conductivity liquid into the immersion chamber: Vacuum liquid injection can ensure that no air bubbles enter the immersion chamber, thus ensuring the good performance of the thermal conductivity liquid. Moreover, this method of liquid injection is relatively uniform, enabling the thermal conductivity liquid to better fill all corners of the immersion chamber. First, evacuate the inside of the immersion chamber to a vacuum state, and then use vacuum suction to suck the thermal conductivity liquid into the immersion chamber. This equipment mainly includes a vacuum pump and a liquid injection system. The vacuum pump first evacuates the immersion chamber, and then opens the liquid injection valve. The thermal conductivity liquid is sucked into the immersion chamber under the action of the pressure difference formed by the external atmospheric pressure and the vacuum inside the immersion chamber.

[0114] Liquid level control: It is necessary to control the liquid level of the high thermal conductivity liquid so that it can completely immerse the semiconductor device, but not too high or too low. Too high a liquid level may cause the liquid to overflow, while too low a liquid level cannot ensure that the device is completely immersed in the liquid, affecting the heat dissipation effect.

[0115] Then, heat the thermal conductivity liquid to 80°C and keep it at a constant temperature.

[0116] Step 3, immerse the ceramic package in the thermal conductivity liquid.

[0117] Immerse the cleaned and dried ceramic package into the thermal conductivity liquid in the immersion chamber, wait for the ceramic package to heat up to the temperature of the thermal conductivity liquid, and perform ultrasonic treatment to eliminate the remaining bubbles in the package.

[0118] Quality inspection of the ceramic package: Before immersion, it is necessary to check the appearance of the ceramic package again to ensure that there are no defects such as cracks and missing corners, so as not to affect the hermeticity of the package and the performance of the device. At the same time, it is necessary to confirm whether the dimensional accuracy of the ceramic package meets the requirements, which is crucial for its adaptability in the immersion chamber and subsequent cooperation with other packaging components.

[0119] Inspection of the thermal conductivity liquid: It is necessary to check the purity and quality of the thermal conductivity liquid to avoid containing impurities or moisture, so as not to affect the heat dissipation effect or cause corrosion to the device.

[0120] Debugging of the immersion chamber: It is necessary to debug the temperature control system, liquid level monitoring system, etc. of the immersion chamber to ensure that it can work normally and provide a stable immersion environment for the ceramic package.

[0121] Slow immersion: Slowly place the cleaned and dried ceramic shell into the heat-conducting liquid in the immersion chamber to avoid splashing of the heat-conducting liquid or generation of bubbles due to rapid placement. The presence of bubbles will affect the heat dissipation effect of the heat-conducting liquid because the thermal conductivity of bubbles is much lower than that of the heat-conducting liquid itself.

[0122] Immersion depth control: Precisely control the immersion depth of the ceramic shell to ensure that it is completely covered by the heat-conducting liquid and all parts are in full contact with the heat-conducting liquid to achieve the best heat dissipation effect. At the same time, attention should be paid to avoiding collision of the shell with the inner wall of the immersion chamber or other components to prevent damage to the shell.

[0123] Prevention of static electricity generation: During the operation, measures should be taken to prevent the generation of static electricity. Operators can wear anti-static bracelets, use anti-static tools, etc. Static electricity may cause damage to semiconductor devices and affect their performance and reliability.

[0124] Bubble discharge: After immersion is completed, if bubbles are found in the heat-conducting liquid, gently shake the immersion chamber to eliminate visible bubbles with the naked eye, and then use ultrasonic equipment to discharge them to ensure good thermal contact between the heat-conducting liquid and the ceramic shell.

[0125] Sealing inspection: Use pressure testing (described above) to inspect the sealing of the immersion chamber to ensure that after the ceramic shell is immersed, the sealing performance of the immersion chamber is still good and there is no leakage.

[0126] Temperature balance: Give enough time for the ceramic shell and the heat-conducting liquid to reach temperature balance, so that the heat-conducting liquid can fully play its heat dissipation role and stabilize the working temperature of the IGCT device.

[0127] Step 4, sequentially place the packaged components into the packaged ceramic shell in the heat-conducting liquid.

[0128] Sequentially place the other cleaned and dried packaged components into the packaged shell in the heat-conducting liquid (as Figure 4b shown), and similarly, after the components are heated to the temperature of the heat-conducting liquid, ultrasonically eliminate the remaining bubbles in the packaged components one by one.

[0129] Specifically, conduct quality inspection on other packaged components: Before immersion, it is necessary to re-check the appearance of each packaged component to ensure that there are no defects such as cracks and missing corners, so as not to affect the sealing performance of the package and the performance of the device. At the same time, it is necessary to confirm whether the dimensional accuracy of each packaged component meets the requirements, which is crucial for its adaptability in the immersion chamber and subsequent cooperation with other packaged components.

[0130] Then sequentially repeat the immersion steps such as inspection of the heat-conducting liquid, debugging of the immersion chamber, slow immersion, control of the immersion depth, prevention of static electricity generation, bubble discharge, sealing inspection, and temperature balance.

[0131] Then, the cathode molybdenum sheet, gate contact ring, gate insulator, etc. are placed in sequence (as Figure 4a shown). After proper alignment, align them according to the packaging design structure in sequence and eliminate air bubbles by ultrasonic wave.

[0132] Next, the IGCT chip is placed. There are micro-grooves inside the gate cathode of the chip. After placement, short-time ultrasonic wave is needed to eliminate air bubbles, and long-time ultrasonic wave is not allowed. At the same time, the temperature of the heat-conducting liquid should not be too high to avoid peeling of insulating materials such as red glue on the chip surface.

[0133] The anode molybdenum sheet and anode electrode (such as a metal case) are placed in sequence, and aligned, interconnected and sealed according to the packaging design structure.

[0134] The installation of each of the above components needs to be packaged inside the heat-conducting liquid.

[0135] The packaging pressure parameter is 80 kN, which can promote better tight assembly of components in the heat-conducting liquid environment. Appropriate pressure helps to compact each component, making the connection between them more stable. For example, it can make the gap between mutually fitting components smaller, enhancing the tightness of physical connection. For some components connected by crimping, fitting, etc., this pressure can ensure that the connection effect meets the packaging expectation. The pressure needs to be precisely controlled at 80 kN. If the pressure is too high, it may damage some relatively fragile components, such as causing internal structure deformation and pin breakage of precision components like chips, affecting their normal functions; while if the pressure is too low, a good assembly effect cannot be achieved, and there may be looseness between components, thus affecting the stability of the entire device and its subsequent performance.

[0136] Step 5: Align and inspect the components in sequence.

[0137] According to the packaging process sequence of the components inside the device ( Figure 4a the shown IGCT chip, cathode molybdenum sheet, anode molybdenum sheet, gate contact ring, gate insulator, metal case), align the components in sequence, and detect whether the connection methods, assembly sequences, etc. of the components meet the packaging structure design.

[0138] First, clarify whether the basic load-bearing structure components are accurately placed and fixed in the initial position as required to provide an accurate reference benchmark for the subsequent assembly of other components.

[0139] Next, for the core functional component like the IGCT chip, according to its connection relationship with the surrounding components and its spatial layout in the entire packaging structure, accurately align it to the corresponding position, and accurately dock it with the corresponding pins, circuits, etc. to ensure that the electrical connection, etc. meets the design plan.

[0140] After that, for the components with sealing or reinforcement functions, they should also be aligned to their respective positions in sequence. The sealing gasket should be completely and accurately clamped at the corresponding interfaces, etc.

[0141] Aligning the components in this way helps to ensure the integrity and accuracy of the entire packaging structure, enabling the components to work together in accordance with the design expectations, laying a good foundation for subsequent connection, detection, and the normal operation of the entire device, and avoiding problems such as electrical failures, poor heat dissipation, or structural instability due to misalignment of the components.

[0142] The assembly and interconnection process between the packaging components is preferably as slow and stable as possible, mainly to prevent the splashing of the heat-conducting liquid and the formation of bubbles inside the heat-conducting liquid. This belongs to a better operation suggestion.

[0143] After the components inside the device are assembled according to the packaging design structure, they are rotated at multiple angles. This operation has an important role.

[0144] By rotating at multiple angles, the position distribution of the components inside the packaging shell can be made more reasonable and uniform, ensuring that the fit between the components meets the design expectations and avoiding unreasonable local assembly.

[0145] Finally, combined with the additional ultrasonic operation, it can effectively promote the discharge of bubbles remaining in areas such as the gaps, micro-grooves, and micropores of the components, enabling the inside of the packaging shell to be fully filled with the heat-conducting liquid, ensuring that the heat-conducting liquid can better play its functions in heat dissipation, etc., improving the performance and stability of the entire device, and avoiding potential problems such as local overheating and affecting electrical performance that may be caused by the residual bubbles.

[0146] Step 6, seal the packaging shell.

[0147] Seal the packaging shell after the previous step with a suitable packaging method and sealing material. The packaging process must ensure that the heat-conducting liquid inside the shell does not leak to prevent the formation of bubbles inside the shell.

[0148] Optionally, the packaging shell must have high sealing performance to avoid leakage of the heat-conducting liquid; optionally, the packaging process can be carried out below the liquid level of the heat-conducting liquid; optionally, the packaging methods are crimping packaging, bonding packaging, and welding packaging.

[0149] After that, take out the IGCT shell from the heat-conducting liquid for drying. The drying methods include blowing dry, wiping dry, and spinning dry, etc.

[0150] Use a dedicated drying device. After properly placing the IGCT shell in it, start the device. By means of rapid rotation and utilizing the centrifugal force, let it rotate at high speed for a certain period of time. At the same time, manually perform appropriate rotational shaking actions. During the manual operation, pay attention to the strength and stability to avoid dropping and damaging the shell.

[0151] With the help of clean and soft wiping tools such as degreasing cotton balls and dust-free cloths, gently wipe the surface of the shell to remove the thermal conductive liquid. When wiping, pay attention to gentle actions and wipe different parts in a certain order to avoid scratching and other damages to the shell. For parts such as corners, more careful treatment is required.

[0152] Use the airflow generated by devices such as hair dryers to dry the thermal conductive liquid on the surface of the shell and in parts such as gaps and holes that may exist. The airflow can accelerate the evaporation of the liquid and take away the moisture. During the operation, usually keep a proper distance between the hair dryer and the shell and move the hair dryer evenly so that all parts of the shell can fully contact the airflow to ensure comprehensive drying.

[0153] Step 7: Detect the packaged IGCT device.

[0154] Conduct thermal, electrical and mechanical detections.

[0155] In terms of thermal detection: Semiconductor devices generate heat during operation, and whether the heat can be effectively dissipated directly affects the performance and service life of the devices. Thermal detection is to evaluate the heat dissipation ability of the devices and the internal thermal distribution to ensure that there is no phenomenon of local overheating leading to performance degradation or even damage. Measure the thermal resistance value from the heat source to the heat sink of the device. The smaller the thermal resistance, the smoother the heat conduction and the better the heat dissipation effect. Generally, temperature sensors are installed at the heat generation part and the heat dissipation part of the device, and combined with certain heating conditions and calculation formulas to obtain the thermal resistance value.

[0156] In terms of electrical detection: mainly to verify whether the electrical properties of the device meet the design requirements, including conductivity, insulation, and the accuracy of electrical parameters (such as resistance, capacitance, voltage, current, etc.), to ensure that the device can function properly in the circuit. First, use different function ranges of a multimeter, such as the resistance range to detect the resistance of the device and determine whether there are short - circuit or open - circuit problems; the voltage range and current range can be used to measure corresponding working voltage and current parameters, etc. The operation is simple and convenient, and it is often used for preliminary electrical performance troubleshooting. Then, using an oscilloscope can observe the waveform changes of signals such as voltage and current during the operation of the device. By analyzing characteristics such as the shape, frequency, and amplitude of the waveform, we can deeply understand the electrical characteristics of the device, such as whether there is signal distortion, interference, etc. It is very effective for detecting the electrical performance of some high - frequency and complex semiconductor devices. Finally, for a tester specialized in IGCT devices, it can accurately measure multiple electrical parameters of the device and compare them with standard parameters to accurately determine whether the electrical performance of the device is qualified.

[0157] In each of the above embodiments, the power semiconductor device includes: an IGCT device, an IGBT device, a MOSFET device, and a GTO device.

[0158] The IGCT chip in each embodiment of the present invention includes a GCT device (i.e., a whole - wafer structure), surface metal aluminum, PI glue, edge red glue, and silicon oxide.

[0159] In summary, the novel liquid - immersion thyristor chip high - thermal - conductivity packaging technology provided by the present invention mainly immerses the packaging shell in a high - thermal - conductivity insulating heat - conducting liquid, so that the heat - conducting liquid fills the gaps between the various packaging structures in the shell, enhances the heat - dissipation ability of heat in each path, improves the heat - dissipation efficiency on the gate - cathode side, and improves the heat - dissipation balance between the anode and cathode. The immersion - type liquid high - thermal - conductivity packaging technology can improve the device junction temperature and enhance the turn - off ability, improve the reliability and service life of the device. At the same time, it has advantages such as simple process, low cost, and strong adaptability.

[0160] An embodiment of the present invention provides a packaged power semiconductor device. The packaged power semiconductor device includes: a power semiconductor device, packaging components, a packaging shell, and a heat - conducting liquid. Among them, the heat - conducting liquid is filled between the power semiconductor device and the packaging shell, between the packaging components and the packaging shell, and between the cathode and the gate of the power semiconductor device. The thermal conductivity of the heat - conducting liquid is greater than a preset value, the heat - conducting liquid is an insulating liquid, and there is a gap between the cathode and the gate of the power semiconductor device.

[0161] In one embodiment, the viscosity of the heat - conducting liquid is less than or equal to a preset viscosity and it is non - corrosive.

[0162] In one embodiment, the coefficient of thermal expansion of the heat-conducting liquid is determined by , where is the compressibility of the heat-conducting liquid, is the temperature difference between the junction temperature of the power semiconductor device and the normal temperature, and is the pressure difference that the power semiconductor device can withstand.

[0163] In one embodiment, the encapsulation housing is provided with a diversion groove distributed longitudinally.

[0164] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0165] In addition, it should be noted that, in the above specific embodiments, the various specific technical features described can be combined in any suitable manner without conflict. To avoid unnecessary repetition, the present invention will not separately describe various possible combination manners.

[0166] Furthermore, any combination can be made between various different embodiments of the present invention as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A packaging method for a power semiconductor device, characterized in that: The packaging method comprises: Immersing the package tube shell into the heat-conducting liquid in the immersion chamber, wherein the temperature of the heat-conducting liquid is greater than or equal to the junction temperature of the power semiconductor device, the thermal conductivity of the heat-conducting liquid is greater than a preset coefficient, the heat-conducting liquid is an insulating liquid, and there is a gap between the cathode and the gate of the power semiconductor device; placing the packaged components into the package shell; Inside the packaging tube shell, assembling the packaging components for the power semiconductor device according to the packaging process sequence; and The packaging tube shell is sealed and packaged.

2. The packaging method according to claim 1, characterized in that: After immersing the package tube shell into the heat transfer liquid in the immersion chamber, the packaging method further includes: performing ultrasound to eliminate bubbles in the package tube shell after the temperature of the package tube shell rises to the temperature of the heat transfer liquid; and / or After placing the packaged component into the packaged tube shell, the packaging method further includes: after the temperature of the packaged component rises to the temperature of the thermal conductive liquid, performing ultrasound to eliminate bubbles in the packaged component.

3. The packaging method according to claim 1, characterized in that: Inside the packaging tube shell, the packaging components are assembled for the power semiconductor device according to the packaging process sequence, including: Inside the packaging tube shell, sequentially aligning the packaging components with respect to the power semiconductor device according to the packaging process sequence; and The connection mode and assembly sequence of the packaged components are detected.

4. The packaging method according to claim 1, characterized in that: The viscosity of the thermal conduction fluid is less than or equal to a preset viscosity and the thermal conduction fluid is non-corrosive.

5. The packaging method according to claim 1, characterized in that: The thermal expansion coefficient of the thermal fluid Depend on Determine, among which, is the compressibility coefficient of the thermal fluid, is the temperature difference between the junction temperature of the power semiconductor device and the normal temperature, and is the voltage difference that the power semiconductor device can withstand.

6. The packaging method according to claim 1, characterized in that: Before immersing the package tube shell into the heat transfer liquid in the immersion chamber, the packaging method further includes: The packaging tube shell, the power semiconductor device and the packaging parts are cleaned and dried.

7. The packaging method according to claim 1, characterized in that: The packaging method further comprises: Test the sealing and performance of power semiconductor devices after sealing and packaging.

8. The packaging method according to any one of claims 1 to 7, characterized in that: The packaging tube shell is provided with guide grooves distributed along the longitudinal direction.

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