Packaging structure for improving short-circuit tolerance of press-fit power semiconductor device and manufacturing method thereof
By adding high thermal conductivity and high thermal capacitance materials to the edge area of the chip active region of the crimp-type power semiconductor device, the problem of insufficient heat dissipation in the short-circuit transient is solved, and its short-circuit tolerance is significantly improved.
Patent Information
- Application Number
- CN202210826747.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-07-13
- Publication Date
- 2025-03-18
- Estimated Expiration
- 2042-07-13
AI Technical Summary
Crimp power semiconductor devices fail to effectively dissipate heat in short-circuit transients, resulting in thermal shock, which seriously affects their short-circuit withstandability.
High thermal conductivity and high thermal capacitance materials are added to the surface of the active region edge region of the power semiconductor chip to improve transient heat dissipation capacity and extend the time when the maximum junction temperature reaches the failure limit temperature.
By improving the transient heat dissipation capability at the edge of the chip's active region, the rise rate of the chip's maximum junction temperature during the short circuit is reduced, and the short circuit tolerance of crimp-type power semiconductor devices is significantly improved.
Smart Images
Figure CN115172299B_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of semiconductor packaging, and relates to a packaging structure for improving the short-circuit tolerance capability of a press-fit power semiconductor device and a manufacturing method thereof. Background Art
[0002] Compared with welded power semiconductor devices, press-fit power semiconductor devices have been widely used in high-voltage and high-power power electronic device applications such as high-voltage direct current transmission, rail transit, and pulse power due to their advantages of double-sided heat dissipation, failure short circuit, and easy series use. Press-fit power semiconductor devices need to have sufficient short-circuit tolerance to deal with short-circuit faults such as short circuit of the converter bridge arm, so that the device can withstand the short-circuit current for as long as possible without failure before the external protection circuit responds and acts. In engineering applications, although more press-fit modules can be connected in parallel to provide redundant capacity to reduce the short-circuit current borne by single-chip devices, this will result in higher operating and maintenance costs. Therefore, improving the short-circuit tolerance of single-chip press-fit power semiconductor devices is crucial to improving operational reliability and optimizing engineering costs.
[0003] During operation, press-fit power semiconductor devices require external pressure to form a stable electrical and thermal connection between the components of each layer. The chip terminal area cannot be in direct contact with the emitter molybdenum sheet, otherwise the device's withstand voltage will be destroyed, resulting in device failure. In order to keep the emitter molybdenum sheet at a safe distance from the chip terminal area, it is necessary to leave enough installation margin for the emitter molybdenum sheet, that is, the area of the emitter molybdenum sheet must be slightly smaller than the area of the chip active area. In the short-circuit transient, the edge area of the chip active area close to the terminal and not in contact with the emitter molybdenum sheet cannot effectively dissipate heat and thus produce a greater thermal shock, which is more likely to cause device failure and seriously affect its short-circuit tolerance. The existing packaging structure that improves the performance of press-fit devices does not consider the impact of the contact structure of the chip and the molybdenum sheet on the chip's transient heat dissipation capability, such as: the stacking structure of the traditional rigid press-fit IGBT single-chip sub-module, from top to bottom, is the collector electrode, collector molybdenum sheet, IGBT chip, emitter molybdenum sheet, silver gasket, boss and emitter electrode. The rigid press-fit IGBT single-chip sub-module applies a certain pressure through the clamp to form good contact between the components of each layer to achieve electrical and thermal connection. The front of the IGBT chip can be divided into the terminal area, the gate area and the active area. The terminal area is located at the edge of the chip and is used to reduce the electric field strength at the edge of the active area to prevent avalanche breakdown. In the package, the terminal area cannot be in direct contact with the emitter molybdenum sheet, otherwise it will destroy the withstand voltage of the device and cause the device to fail. The gate area is located in the corner of the active area and is used to control the on and off of the device, and is isolated from the active area. The cells of the IGBT chip are distributed in the active area, and a few microns of aluminum metal layer are deposited on its surface as an electrode connected to the outside. In order to keep a safe distance between the emitter molybdenum sheet and the terminal area of the IGBT chip during packaging, the rigid press-fit IGBT single-chip sub-module needs to leave enough installation margin for the emitter molybdenum sheet. The area of the emitter molybdenum sheet must be slightly smaller than the area of the active area of the IGBT chip. Therefore, the chip active area can be divided into an area in direct contact with the emitter molybdenum sheet and an edge area that is not in contact with the emitter molybdenum sheet.
[0004] Therefore, studying a packaging structure for improving the short-circuit tolerance of press-fit power semiconductor devices based on improving the transient heat dissipation capability at the edge of the chip active area is of great significance for improving the economy and reliability of press-fit packaged power semiconductor devices. Summary of the invention
[0005] In view of this, the purpose of the present invention is to provide a packaging structure and a manufacturing method for improving the short-circuit tolerance of press-fit power semiconductor devices, thereby improving the short-circuit tolerance of press-fit packaged power semiconductor devices, thereby achieving the purpose of improving the operating reliability of press-fit power semiconductor devices and optimizing engineering costs, and providing support for optimizing the packaging reliability of press-fit power semiconductor devices.
[0006] In order to achieve the above object, the present invention provides the following technical solutions:
[0007] Solution 1: A packaging structure for improving the short-circuit tolerance of a press-fit power semiconductor device, comprising stacked power semiconductor chips, collector molybdenum sheets, emitter molybdenum sheets, buffer layers such as silver gaskets, collector electrodes and bosses (or elastic elements); the power semiconductor chip has a terminal area, a gate area and an active area, the terminal area is located at the edge of the chip, and is used to reduce the electric field strength at the edge of the active area to prevent avalanche breakdown, and is not in direct contact with the emitter molybdenum sheet, otherwise the withstand voltage of the device will be destroyed, resulting in device failure; the gate area is used to control the on and off of the device; the active area is a cell distribution area, and a few microns of aluminum metal layer are deposited on its surface as an electrode connected to the outside, and the active area includes a central area that is in direct contact with the emitter molybdenum sheet, and an edge area that is not in direct contact with the emitter molybdenum sheet and is adjacent to the terminal area.
[0008] The specific optimization design plan is: adding high thermal conductivity and high heat capacity materials to the surface of the edge area of the active area of the power semiconductor chip to improve the transient heat dissipation capability of the edge of the chip active area, thereby enhancing the short-circuit tolerance of the press-fit power semiconductor device.
[0009] Among them, improving the transient heat dissipation capability of the edge of the chip active area is to use high thermal conductivity and high heat capacity materials added to the edge surface of the active area of the power semiconductor chip to absorb part of the transient heat generated by the chip during the short circuit process, so as to reduce the rise rate of the chip's maximum junction temperature.
[0010] The short-circuit tolerance of press-fit power semiconductor devices is improved by adding high thermal conductivity and high heat capacity materials to the edge surface of the active area of the power semiconductor chip to absorb part of the transient heat generated by the chip during the short-circuit process, so as to reduce the rise rate of the chip's maximum junction temperature and extend the time for the maximum junction temperature to reach the failure limit temperature, thereby improving the short-circuit tolerance of the device.
[0011] Furthermore, the high thermal conductivity and high heat capacity material includes a cured polymer metal conductive paste, a sintered metal conductive paste after sintering, or a metal layer obtained by electroplating.
[0012] Solution 2: A method for manufacturing a packaging structure for improving the short-circuit tolerance of a press-fit power semiconductor device, specifically comprising the following steps:
[0013] S1: Based on the principle of steel screen printing, a mask sticker of a specific shape and thickness is used to cover the terminal area and gate area on the surface of the power semiconductor chip, while exposing the active area, limiting the coating area on the chip surface to avoid high thermal conductivity and high thermal capacity materials being mistakenly coated on the terminal and gate areas;
[0014] S2: Place the emitter molybdenum sheet at a designated position on the surface of the power semiconductor chip, use a special fixture to fix the power semiconductor chip, the emitter molybdenum sheet and the collector molybdenum sheet into a whole and apply a certain pressure to prevent high thermal conductivity and high heat capacity materials from entering the contact gap between the power semiconductor chip and the emitter molybdenum sheet;
[0015] S3: evenly apply the high thermal conductivity and high heat capacity material to the edge of the active area of the power semiconductor chip that is not in direct contact with the emitter molybdenum sheet, wherein the thickness of the high thermal conductivity and high heat capacity material coating is the thickness of the mask sticker; after the application is completed, the mask sticker is immediately removed, and at this time, the high thermal conductivity and high heat capacity material evenly covers the edge of the active area of the power semiconductor chip;
[0016] S4: Use a heating table to heat the fixture containing the power semiconductor chip, the high thermal conductivity and high heat capacity material coating, the emitter molybdenum sheet and the collector molybdenum sheet, so that the heat can be evenly transferred to the high thermal conductivity and high heat capacity material coating on the power semiconductor chip through the fixture. After the high thermal conductivity and high heat capacity material is completely cured, the power semiconductor chip, the collector molybdenum sheet and the emitter molybdenum sheet are immediately removed.
[0017] Furthermore, the high thermal conductivity and high heat capacity material includes a cured polymer metal conductive paste, a sintered metal conductive paste after sintering, or a metal layer obtained by electroplating.
[0018] The beneficial effect of the present invention is that: the present invention takes into account the influence of the contact structure of the power semiconductor chip and the molybdenum sheet on the transient heat dissipation capability of the chip, and proposes a packaging optimization design that adds high thermal conductivity and high heat capacity materials to the edge surface of the active area of the power semiconductor chip, which can greatly improve the transient heat dissipation capability of the edge of the chip active area, thereby reducing the rate of increase of the maximum junction temperature of the chip during a short circuit, and by extending the time for the maximum junction temperature to reach the failure limit temperature, the short circuit tolerance capability of the power semiconductor device is improved.
[0019] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:
[0021] Figure 1 This is a schematic diagram of the structure of a press-fit IGBT device optimized according to an embodiment of the present invention;
[0022] Figure 2The figure is a comparison of the short-circuit withstand test results of the embodiment of the present invention and two conventional crimp-type IGBT devices.
[0023] Figure markings: 1-collector electrode; 2-collector molybdenum sheet; 3-IGBT chip; 4-emitter molybdenum sheet; 5-silver gasket; 6-boss and emitter electrode; 7-IGBT chip terminal area; 8-edge area of the IGBT chip active area that is not in direct contact with the emitter molybdenum sheet; 9-central area of the IGBT chip active area that is in direct contact with the emitter molybdenum sheet; 10-IGBT chip gate area; 11-conductive silver glue coating. DETAILED DESCRIPTION
[0024] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.
[0025] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.
[0026] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.
[0027] See also Figure 1-2 The optimized press-fit IGBT device structure designed in this embodiment is as follows: Figure 1As shown, from top to bottom are the collector electrode 1, the collector molybdenum sheet 2, the IGBT chip 3, the emitter molybdenum sheet 4, the silver gasket 5, the boss and the emitter electrode 6. Among them, the rigid press-fit type IGBT single-chip sub-module applies a certain pressure through the clamp to form good contact between the components of each layer to achieve electrical and thermal connection. The front of the IGBT chip can be divided into a terminal area, a gate area and an active area. The terminal area is located at the edge of the chip, which is used to reduce the electric field strength at the edge of the active area to prevent avalanche breakdown. In the package, the terminal area cannot be in direct contact with the emitter molybdenum sheet 4, otherwise it will destroy the withstand voltage of the device and cause the device to fail. The gate area is located in the corner of the active area, which is used to control the conduction and shutdown of the device, and is isolated from the active area.
[0028] When a short circuit occurs in the rigid press-fit IGBT single-chip sub-module, the edge area 8 of the active area of the IGBT chip in the traditional structure, which is close to the terminal area 7 of the IGBT chip and not in direct contact with the emitter molybdenum sheet, cannot effectively dissipate heat, thereby generating a greater thermal shock, which is more likely to cause device failure and seriously affect its short-circuit tolerance. Therefore, an embodiment of the present invention adds high thermal conductivity and high heat capacity materials to the surface of the edge area 8 of the active area of the IGBT chip, and improves the short-circuit tolerance of the rigid press-fit IGBT single-chip sub-module by improving the transient heat dissipation capability of the edge area 8 of the active area of the IGBT chip.
[0029] Conductive silver paste is a type of silver conductive paste. It uses organic polymers such as resin as a bonding phase and has the characteristics of low curing temperature, high bonding strength, and easy steel screen printing. After curing, it has high thermal conductivity and heat capacity. Therefore, in this embodiment, conductive silver paste is selected as the packaging optimization material for the edge area 8 of the IGBT chip active area. The processing steps are as follows:
[0030] S1: Based on the principle of steel screen printing, a mask sticker of a specific shape and thickness is used to cover the terminal area and gate area on the surface of the IGBT chip while exposing the active area, limiting the coating area on the chip surface to avoid the conductive silver paste from being accidentally coated on the terminal and gate areas.
[0031] S2: Place the emitter molybdenum sheet 4 at a designated position on the surface of the IGBT chip, use a special fixture to fix the IGBT chip 3, the emitter molybdenum sheet 4 and the collector molybdenum sheet 2 into a whole and apply a certain pressure to prevent the conductive silver glue from entering the contact gap between the IGBT chip 3 and the emitter molybdenum sheet 4.
[0032] S3: Apply the conductive silver paste evenly to the edge area 8 of the active area of the IGBT chip that is not in direct contact with the emitter molybdenum sheet, wherein the thickness of the conductive silver paste coating is the thickness of the mask sticker. After the application is completed, the mask sticker is immediately removed, and the conductive silver paste evenly covers the edge of the active area of the IGBT chip.
[0033] S4: Use a heating table to heat the fixture containing the IGBT chip 3, the conductive silver paste coating 11, the emitter molybdenum sheet 4 and the collector molybdenum sheet 2 and keep it at 180°C for 60 minutes. The heat can be evenly transferred to the conductive silver paste coating 11 on the IGBT chip through the fixture. After the conductive silver paste is completely cured, the IGBT chip 3 and the molybdenum sheet (including the emitter molybdenum sheet 4 and the collector molybdenum sheet 2) are immediately removed, and then the components are assembled into a sub-module, such as Figure 1 shown.
[0034] In order to verify the optimization effect of the present invention, the short circuit tolerance capabilities of the conventional rigid press-fit IGBT single-chip sub-module and the optimized rigid press-fit IGBT single-chip sub-module were compared and analyzed through a short circuit tolerance test. In this embodiment, a total of 6 groups of rigid press-fit IGBT single-chip sub-modules with similar dynamic and static characteristics were subjected to short circuit tolerance tests, where devices #1 to #3 were conventional rigid press-fit packages, and devices #4 to #6 were optimized rigid press-fit packages.
[0035] Set the initial pressure of the fixture to 1200N, set the voltage across the device collector and emitter to 400V, set the device conduction time to 1ms, and the short-circuit waveforms of crimp-type IGBT devices with different packaging forms are as follows: Figure 2 (a)~ Figure 2 (b) As shown. The short-circuit tolerance time of the conventional rigid press-fit IGBT single-chip sub-module is about 310us, and the critical short-circuit energy is 31.03J; after the device is optimized using the present invention, its short-circuit tolerance time can be increased to about 460us, and the critical short-circuit energy can be increased to 42.25J, an increase of about 36.2%. It can be seen that the package optimization design proposed by the present invention can improve the short-circuit tolerance capability of the rigid press-fit IGBT single-chip sub-module.
[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.
Claims
1. A packaging structure for improving the short-circuit tolerance of a press-fit power semiconductor device, comprising a power semiconductor chip, a collector molybdenum sheet, an emitter molybdenum sheet, a buffer layer, a collector electrode and a boss; characterized in that: The power semiconductor chip has a terminal area, a gate area and an active area, wherein the terminal area is located at the edge of the chip and is not in direct contact with the emitter molybdenum sheet; the active area includes a central area in direct contact with the emitter molybdenum sheet, and an edge area that is not in direct contact with the emitter molybdenum sheet and is adjacent to the terminal area; High thermal conductivity and high heat capacity materials are added to the edge area of the active area of the power semiconductor chip.
2. The packaging structure according to claim 1, characterized in that: The high thermal conductivity and high heat capacity material includes a cured polymer metal conductive paste, a sintered metal conductive paste, or a metal layer obtained by electroplating.
3. A method for manufacturing a packaging structure for improving the short-circuit tolerance of a press-fit power semiconductor device, characterized in that: The method specifically comprises the following steps: S1: Based on the principle of steel screen printing, a mask sticker of a specific shape and thickness is used to cover the terminal area and gate area on the surface of the power semiconductor chip, while exposing the active area, limiting the coating area on the chip surface to avoid high thermal conductivity and high thermal capacity materials being mistakenly coated on the terminal and gate areas; S2: Place the emitter molybdenum sheet at a designated position on the surface of the power semiconductor chip, use a special fixture to fix the power semiconductor chip, the emitter molybdenum sheet and the collector molybdenum sheet into a whole and apply a certain pressure to prevent high thermal conductivity and high heat capacity materials from entering the contact gap between the power semiconductor chip and the emitter molybdenum sheet; S3: evenly apply the high thermal conductivity and high heat capacity material to the edge of the active area of the power semiconductor chip that is not in direct contact with the emitter molybdenum sheet, wherein the thickness of the high thermal conductivity and high heat capacity material coating is the thickness of the mask sticker; after the application is completed, the mask sticker is immediately removed, and at this time, the high thermal conductivity and high heat capacity material evenly covers the edge of the active area of the power semiconductor chip; S4: Use a heating table to heat the fixture containing the power semiconductor chip, the high thermal conductivity and high heat capacity material coating, the emitter molybdenum sheet and the collector molybdenum sheet, so that the heat can be evenly transferred to the high thermal conductivity and high heat capacity material coating on the power semiconductor chip through the fixture. After the high thermal conductivity and high heat capacity material is completely cured, the power semiconductor chip, the collector molybdenum sheet and the emitter molybdenum sheet are immediately removed.
4. The method for manufacturing a packaging structure according to claim 3, characterized in that: The high thermal conductivity and high heat capacity material includes a cured polymer metal conductive paste, a sintered metal conductive paste, or a metal layer obtained by electroplating.