Highly reliable pinless power module and leadframe

Abstract

The application relates to a high-reliability pinless power module and a lead frame, and belongs to the technical field of semiconductors. The application comprises a substrate, a power chip, a pin and a plastic package; the pin comprises a connecting part and an external soldering pin; the connecting part is connected with the substrate and is completely covered inside the plastic package, at least part of the lower surface of the external soldering pin is exposed outside the plastic package, and the bottom surface of the external soldering pin does not exceed the bottom surface of the plastic package. When being attached, the bottom surface of the plastic package can reliably attach to a PCB to form effective support, and the external soldering pin can also fully contact soldering paste to complete high-quality metallurgical welding. The differential size matching design is customized for the pressure-bearing heat dissipation assembly scene of the application, is different from the general shape design of a conventional non-supporting structure device, and can consider structure pressure-bearing protection, welding process adaptation and batch assembly consistency, so that the problem of uneven thickness of heat-conducting glue and local device high-temperature early decay in the assembly of multiple devices is effectively solved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a high-reliability leadless power module and lead frame. Background Technology

[0002] With the rapid development of high-end power electronic equipment such as new energy vehicles, photovoltaic inverters, and industrial frequency converters towards higher power density, higher integration, longer lifespan, and higher reliability, top-heat-cooled power devices, with their core advantages of short heat dissipation paths, high heat dissipation efficiency, and small integrated size, have gradually replaced traditional bottom-heat-cooled devices and become core components of high-power power electronic equipment. The core heat dissipation structure of top-heat-cooled power devices involves attaching an external heat sink to the top of the device. This rigid contact between the heat sink and the device enables rapid heat dissipation. To ensure proper contact and heat dissipation performance, the industry commonly uses clamps and bolts to apply a constant clamping force between the PCB board and the heat sink, thereby eliminating heat dissipation gaps and reducing thermal resistance.

[0003] However, in the existing technical solutions, top-heat-dissipating power devices have exposed three major technical bottlenecks during mass assembly and long-term service, which seriously restrict the service life of the devices and the stability of the whole machine.

[0004] Firstly, the problem of weld stress failure caused by assembly clamping force. After the existing top-heat-dissipating power devices are assembled, the clamping force between the PCB board and the heat sink is directly and vertically transmitted to the solder joints connecting the device and the PCB board, causing the solder joints to be subjected to constant mechanical compressive stress over a long period of time. When the device operates under alternating high and low temperatures for a long time, the internal structure will undergo periodic thermal expansion and contraction deformation. Under the coupled effect of constant assembly stress and alternating temperature stress, the solder joints are prone to stress concentration and fatigue aging, eventually leading to failure problems such as solder joint cracking, detachment, and poor soldering. This significantly shortens the service life of the device and is a major hidden danger to the long-term stable operation of high-end power equipment.

[0005] Secondly, the height tolerance of multi-component assembly is difficult to control. In high-power power electronic devices, multiple power devices are typically connected in parallel or combined to meet power output requirements. Current power devices use conventional pin soldering for mounting, where the soldering height depends entirely on the solder joint thickness. Due to factors such as deviations in automated soldering processes, differences in solder wetting, and device manufacturing tolerances, the solder joint thickness of multiple devices cannot be kept completely consistent. This directly leads to uneven heights of the top heat dissipation surfaces of multiple devices, preventing a fully uniform fit with the heat sink. Excessive heat dissipation gaps in some devices cause a surge in thermal resistance, resulting in single-point overheating and power attenuation. In severe cases, this can lead to thermal breakdown. Furthermore, this height tolerance issue is difficult to completely eliminate through conventional soldering process optimization, resulting in extremely poor consistency in batch assembly.

[0006] To address the common pain points in the industry mentioned above, various improvement solutions have been proposed, but all of them have inherent technical flaws and cannot fundamentally balance device heat dissipation performance, solder joint reliability, and batch assembly accuracy. Specific flaws are as follows: Current mainstream solution 1: Thicken the solder layer and use high-toughness solder material to buffer stress. This solution attempts to offset the stress generated by assembly clamping force and thermal deformation by increasing the thickness and toughness of the solder layer. However, in practical applications, thickening the solder layer significantly increases the conduction impedance of the solder joint, reducing the electrical performance of the device. At the same time, the solder joint itself generates more heat, creating a vicious cycle of temperature rise and failure. Furthermore, the procurement and welding costs of high-toughness solder are high, and it can only achieve a small degree of stress buffering. It cannot solve the problem of height tolerance of multiple devices, and the defect of uneven heat dissipation and bonding of devices after batch assembly still exists. The overall improvement effect is extremely limited.

[0007] Existing mainstream solution two: Adding elastic thermally conductive pads to compensate for assembly errors and buffer stress. This solution adds an elastic thermally conductive pad between the heat sink and the heat dissipation surface of the device, using the elastic deformation of the pad to compensate for the height tolerance of multiple components, while also buffering the mechanical stress caused by assembly clamping force. However, the thermal conductivity of the elastic thermally conductive pad is much lower than that of the rigid metal bonding structure, which will significantly increase the overall thermal resistance of the device and greatly sacrifice the heat dissipation advantage of the core of the top heat sink. At the same time, the elastic pad is under high temperature and compression conditions for a long time, which makes it prone to aging, loosening and permanent deformation. In the later stage of service, the stress buffering and height compensation functions will completely fail, and the long-term reliability of the device will be greatly reduced, which cannot meet the long service life requirements of power equipment.

[0008] Existing mainstream solution three: Optimize PCB solder joint layout to distribute stress This solution aims to moderately disperse the concentrated stress at the solder joints by adjusting the arrangement of the solder points on the PCB board. However, this optimization method can only slightly improve the stress distribution and cannot fundamentally eliminate the alternating stress caused by the clamping force of the heat sink and the thermal deformation of the components. Furthermore, it completely fails to solve the core problems of uneven solder thickness and poor assembly height consistency among multiple components, resulting in extremely poor technical adaptability and optimization effect.

[0009] Existing mainstream solution four: US9219019B2 grooved lead soldering reinforcement structure This patent discloses a semiconductor packaging structure that creates grooves on both sides of the leads of a leadless device. By adding grooves, the solderable surface area of ​​the leads is increased, allowing the solder to fully wet the inner wall of the groove, thus increasing the bonding area between the solder joint and the lead, and slightly improving the connection strength and fatigue resistance of the solder joint. However, this structure has significant process and performance defects: the precision machining of the lead grooves is difficult and the yield rate is low, significantly increasing the manufacturing cost of the device; moreover, during the molding process of the lead grooves, the inner sidewall of the groove is very prone to residual molding compound, which is difficult to completely remove, directly hindering the wetting and adhesion of the solder. This results in the actual effective soldering area being far lower than the design value, failing to achieve the expected solder joint strengthening effect, and having limited reliability improvement, making it difficult to scale up mass production applications.

[0010] The fifth mainstream solution is the US10978378B2 sidewall exposed leadless package structure. This patent discloses an encapsulated leadless packaging structure. By exposing part of the chip carrier lead's sidewalls outside the molded enclosure, the solder can fully contact the lead sidewalls, increasing the soldering contact area and thus improving solder joint reliability. However, this solution has a fatal assembly precision defect: the bottom surface of the lead protrudes from the bottom surface of the enclosure. During device mounting and soldering, the bottom of the lead directly contacts the PCB mounting substrate for rigid positioning. This relies entirely on manual and process control of the solder filling amount, making it impossible to accurately control the solder joint thickness. The solder joint thickness deviation of a single device is large, and the height consistency of multiple devices in parallel assembly is extremely poor. It is completely unsuitable for assembly scenarios with top heat dissipation of multiple devices and cannot solve the core problem of height tolerance in this field.

[0011] In summary, current technologies, whether conventional structural improvements, process optimizations, or existing patented pin enhancements and package optimizations, can only address specific defects and cannot simultaneously solve multiple core technical problems such as solder joint stress fatigue cracking caused by top clamping force, large height tolerance in multi-device assembly, lack of stress buffering in pinless structures, and poor mass production consistency. Furthermore, they generally suffer from secondary defects such as sacrificed heat dissipation performance, poor electrical performance, high processing costs, and insufficient reliability. Currently, the industry lacks a top-heat-dissipated pinless power device structure that balances excellent heat dissipation performance, high solder joint fatigue resistance reliability, high-precision assembly consistency, low cost, and suitability for demanding automotive and industrial operating conditions. Therefore, developing a new power device that can completely solve the aforementioned industry technical bottlenecks has significant engineering application value and market demand. Summary of the Invention

[0012] To address the above problems, this invention provides a highly reliable leadless power module that optimizes the device packaging and pin structure without increasing the overall package size or sacrificing heat dissipation and electrical performance. This effectively solves the industry pain points of traditional leadless power devices, such as easy stress fatigue cracking of solder joints and poor consistency of assembly height among multiple devices, and significantly improves the connection reliability and service stability of the device solder joints and PCB mounting substrate.

[0013] Meanwhile, this invention provides a lead frame that, through structural optimization, transmits the molding pressure to the substrate, avoiding excess adhesive on the back of the substrate after molding, thus improving molding yield and saving costs. In addition, by setting the internal solder pads of the frame at different heights, it avoids poor soldering of the internal solder pads during the manufacturing process, thereby improving product yield and reliability.

[0014] The technical solution of this invention is: A high-reliability pinless power module, comprising: A semiconductor chip assembly, including a substrate and a power chip connected to the substrate; Multiple pins, including a plurality of first-side pins and a plurality of second-side pins; the first-side pins and the second-side pins are respectively electrically connected to the semiconductor chip assembly; A molding compound that encapsulates the power chip, at least a portion of the substrate, and at least a portion of the pins; Each pin includes a connected connector and an external solder pad; the connector is located within the molding compound and extends outward from the molding compound, and the external solder pad has at least its lower surface exposed outside the molding compound, and the bottom surface of the external solder pad does not extend beyond the bottom surface of the molding compound.

[0015] Specifically, the substrate is a conductive substrate; The conductive substrate and several first-side pins are integrated into one structure; A plurality of second-side pins are spaced apart from the conductive substrate and are electrically connected to the power chip via connectors; The top surface of the conductive substrate is exposed from the plastic encapsulation.

[0016] Specifically, the substrate is an insulating substrate, comprising a top metal layer, an insulating layer, and a bottom metal layer connected in sequence; The top surface of the top metal layer is exposed from the molding compound; a plurality of first side pins and a plurality of second side pins are electrically connected to the bottom metal layer respectively.

[0017] Specifically, the external solder feet include a mounting surface, a top surface, and multiple side surfaces; The external solder pad mounting surface is located on the outside of the molding compound, and the vertical distance between it and the bottom surface of the molding compound ranges from 0.01mm to 0.5mm.

[0018] Specifically, the side of the external solder pad is exposed outside the encapsulation body.

[0019] Specifically, the outer solder foot and the inner corner area of ​​the connection part are exposed outside the plastic encapsulation body, and the corner area has a smooth arc transition structure or a bent angle connection structure. When the connecting corner area has an angled connection structure, the sidewalls of the external solder feet are all exposed outside the encapsulation body.

[0020] Specifically, the connecting corner area is exposed through the recessed area at the bottom of the encapsulated body.

[0021] Specifically, the bottom surface of the encapsulated body is provided with an inwardly recessed groove, which extends laterally, extends longitudinally, or is arranged in a crisscross pattern.

[0022] Specifically, the bottom of the molding compound is provided with multiple downwardly extending positioning protrusions; The PCB board has multiple positioning grooves corresponding to the positioning protrusions.

[0023] Specifically, the pins are provided with a locking solder structure, which improves the reliability of soldering to the PCB board.

[0024] A lead frame, the lead frame including an outer frame and a plurality of pins disposed within the outer frame; The pin includes a connector and an external solder pad; The external welding feet are connected to the outer frame and are in the same plane; The connecting part includes a first bending area, a buffer zone, a second bending area, and an internal weld foot connected in sequence; the first bending area, the buffer zone, the second bending area, and the internal weld foot extend toward the center of the outer frame.

[0025] Specifically, one end of the bending area is connected to the external welding foot, and the included angle between the bending area and the outer frame is between 70° and 90°.

[0026] Specifically, the buffer zone extends downwards towards the center of the outer frame, with a downward tilt angle of 4° to 8° relative to the horizontal direction of the outer frame.

[0027] Specifically, the internal weld feet are inclined downwards, with an angle of 1° to 6° with the horizontal direction of the outer frame.

[0028] Specifically, the buffer length is set to 3 to 6 times the length of the internal solder pad.

[0029] Specifically, the bottom and / or top surfaces of the internal weld feet are provided with multiple pits.

[0030] Specifically, the first-side pins and second-side pins of the plurality of said pins are symmetrically arranged; The first side pin and / or the second side pin are respectively provided with a pair of symmetrically arranged central solder feet and a pair of symmetrically arranged side solder feet; The inner weld foot of the middle weld foot extends downward; the distance between the bottom end face of the middle weld foot and the upper surface of the outer frame is L1; The inner weld foot of the first side weld foot extends downward, and the distance between the bottom end face of the first side weld foot and the upper surface of the outer frame is L2; Where L2 is not less than L1.

[0031] Specifically, the difference between L2 and L1 is 0.005mm to 0.06mm.

[0032] Specifically, the first side pin and / or the second side pin also include a second side solder pad; The inner weld foot of the second side weld foot extends downward, and the distance between the bottom end face of the second side weld foot and the upper surface of the outer frame is L3; wherein, L3 is not less than L2.

[0033] This invention includes a substrate, a power chip, pins, and a molding compound. The pins include a connector and external solder pads. The connector is connected to the substrate and completely encapsulated within the molding compound. At least a portion of the lower surface of the external solder pads is exposed outside the molding compound, and the bottom surface of the external solder pads does not extend beyond the bottom surface of the molding compound. The vertical distance between the bottom surface of the external solder pads and the bottom surface of the molding compound ranges from 0.01mm to 0.3mm. This size matches the typical forming thickness of solder joints after SMT soldering (approximately 0.05mm). At this size, the bottom surface of the molding compound reliably adheres to the PCB during mounting, forming effective support and isolating the heat sink assembly clamping force to protect the solder joints. The external solder pads can also fully contact the solder paste to complete high-quality metallurgical soldering. This differentiated size matching design is customized for the pressure-bearing heat dissipation assembly scenario of this invention, differing from the general shape design of conventional unsupported structural components. It takes into account structural pressure protection, soldering process adaptability, and batch assembly consistency, effectively improving the problems of uneven thermal conductive adhesive thickness and premature high-temperature degradation of local components when assembling multiple components.

[0034] External solder pads are soldered onto the PCB using SMT (Surface Mount Technology). Specifically, the external solder pads are metallurgically bonded to the PCB pads using solder, thereby achieving electrical conductivity and mechanical fixation between the product and the PCB. The bottom surface of the molding compound is not flush with the bottom surface of the external solder pads; the bottom surface of the molding compound is the lowest end surface of the entire device. During SMT assembly, the bottom surface of the molding compound first contacts the PCB surface, and the external solder pads overlap the pre-printed solder paste on the PCB. After the solder melts and solidifies during reflow soldering, the external solder pads are soldered to the PCB pads to form a finished product. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the structure of Embodiment 2 of the present invention; Figure 3 This is a schematic diagram of the structure of Embodiment 3 of the present invention; Figure 4 This is a schematic diagram of the angled connection structure. Figure 5 This is a schematic diagram of the angled connection structure. Figure 6 This is a schematic diagram of a cross-shaped slot structure; Figure 7 This is a schematic diagram of the positioning protrusion structure; Figure 8 This is a schematic diagram of the connection structure between the positioning protrusion and the PCB board; Figure 9 This is a schematic diagram of a smooth arc transition structure; Figure 10 This is a schematic diagram of the weld protrusion structure; Figure 11 This is a schematic diagram of the structure for setting the welding recess; Figure 12 This is a schematic diagram of the assembly state structure of Embodiment 2 of the present invention; Figure 13 This is a schematic diagram of the connection structure between the outer frame and the pins. Figure 14 This is a schematic diagram of the outer frame cross-section with the buffer zone and internal weld feet in their unbent state (parallel to the outer frame); Figure 15 This is a schematic diagram of the outer frame cross-section when the buffer zone and the internal weld feet are bent. Figure 16 This is a schematic diagram of the pin-to-substrate soldering station structure; In the diagram, 100 is the substrate, 200 is the power chip, 300 is the pin, 310 is the connector, 311 is the first bending area, 312 is the buffer zone, 313 is the second bending area, 314 is the internal solder pad, 320 is the external solder pad, 321 is the solder pad protrusion, 322 is the solder pad recess, 400 is the molding compound, 401 is the groove, 402 is the first side surface, 403 is the second side surface, 410 is the recessed area, 420 is the slot, 430 is the positioning protrusion, and 500 is the PCB board. Detailed Implementation

[0036] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0037] In the description of this invention, it should be understood that the terms "upper," "lower," "left," "right," "vertical," and "horizontal," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0038] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0039] The following is for reference. Figure 1-16 Describe embodiments of the present invention; Example 1

[0040] A high-reliability pinless power module, comprising: The substrate 100, in this embodiment, is a conductive substrate and does not include an insulating structure. The portion of the substrate 100 exposed from the encapsulation has electrical and thermal pathways. In use, it typically contacts the heat sink through an insulating medium, such as ceramic or thermally conductive adhesive.

[0041] The power chip 200 is fixed to the substrate 100 by welding or sintering; the other electrode of the power chip 200 is electrically connected to the corresponding position of the substrate 100 through Al bonding wire or Cu bonding wire.

[0042] Multiple pins 300 include connected connecting portions 310 and external solder pads 320. The external solder pads 320 include a mounting surface, a top surface, and multiple side surfaces. The mounting surface is located outside the molding compound 400, and the vertical distance between it and the bottom surface of the molding compound 400 ranges from 0.01mm to 0.5mm. In this case, 0.05mm ± 0.2mm is preferred. This size matches the typical forming thickness of solder joints after SMT soldering (approximately 0.05mm). At this size, the bottom surface of the molding compound reliably adheres to the PCB during mounting, forming effective support and isolating the heat sink assembly clamping force to protect the solder joints. The external solder pads 320 can also fully contact the solder paste to complete high-quality metallurgical soldering. This differentiated size matching design is customized for the pressure-bearing heat dissipation assembly scenario of this invention, differing from the general shape design of conventional unsupported structural components. It balances structural pressure protection, soldering process adaptability, and batch assembly consistency, effectively improving the problems of uneven thermal conductive adhesive thickness and premature high-temperature degradation of local components during multi-component assembly.

[0043] The molding compound 400 encapsulates the power chip 200, a partial substrate 100, and a portion of the pins 300; the connecting portion 310 is connected to the substrate 100 and extends outward from the molding compound 400; the external solder pads 320 have at least their lower surfaces exposed outside the molding compound 400, and the bottom surface of the external solder pads 320 does not extend beyond the bottom surface of the molding compound 400.

[0044] At the bottom of the molding compound 400, a recessed area 360 is provided at a position flush with the external solder pads 320. The recessed area 360 is formed due to the constraints of the mold structure during the molding process.

[0045] like Figure 1 As shown, a portion of the pin 300 connection portion 310 extends to the substrate 100 and is integral with the substrate 100. The top of the substrate 100 is exposed from the encapsulation 400. The thickness of the substrate 100 is greater than the thickness of the pin 300, which is more conducive to the lateral diffusion of heat within the substrate 100 and improves the heat dissipation effect. The substrate 100 and the pin 300 are made of KFC copper alloy and are integrally formed by stamping.

[0046] The upper connection surface of the power chip 200 is electrically connected to the substrate 100, and the lower connection surface is electrically connected to the pins 300 of the remaining unconnected substrate 100 via a connector. The connector can be a bonding wire or a metal sheet.

[0047] like Figure 12As shown, the external solder pads 320 are soldered onto the PCB board 500 using SMT technology. Specifically, the external solder pads 320 are metallurgically bonded to the PCB pads with solder, thereby achieving electrical conductivity and mechanical fixation between the product and the PCB board 500. The bottom surface of the molding compound 400 is not flush with the bottom surface of the external solder pads 320; the bottom surface of the molding compound 400 is the lowest end surface of the entire device. During SMT mounting, the bottom surface of the molding compound 400 will first contact the PCB board surface, and the external solder pads 320 will overlap the pre-printed solder paste on the PCB board 500. After the solder melts and solidifies during reflow soldering, the external solder pads 320 are soldered to the PCB pads to form a shape.

[0048] After soldering, the entire PCB assembly is secured to the heatsink surface with screws. Thermally conductive adhesive is applied between the product's plastic encapsulation bottom and the heatsink interface. To achieve excellent heat dissipation performance, the adhesive layer thickness should be minimized during assembly. After assembly and tightening, the product will bear the assembly clamping force between the PCB board 500 and the heatsink. Thanks to the pre-supported structure of the plastic encapsulation bottom, the clamping load is borne by the product's plastic encapsulation body 400, preventing direct pressure on the solder joints and ensuring the structural safety of the solder joints. In practical applications, this product is generally used in multi-unit assembly. The product itself is integrally molded from a plastic encapsulation mold, resulting in small dimensional tolerances and good consistency in body height. Example 2

[0049] like Figure 2 As shown, the substrate 100 is an insulating substrate, including forms such as DBC, AMB, and IMS. Specifically, it includes a top metal layer, an insulating layer, and a bottom metal layer that are stacked and connected in sequence. The insulating layer is usually Al2O3, AlN, or Si3N4 ceramic, and the top and bottom metal layers are usually Cu metal layers or Al metal layers.

[0050] The pin 300 connection portion 310 is connected to the bottom metal layer of the substrate 100 by soldering, thereby realizing the electrical connection between the pin and the power chip 200. Alternatively, some of the pin 300 connection portions 310 are connected to the bottom metal layer of the substrate 100 by soldering, while other pins are connected to the power chip 200 or the bottom metal layer of the substrate 100 by bonding wires.

[0051] The top surface of the metal layer on the substrate 100 is exposed from the plastic package, and the connection surface on the power chip 200 is connected to the bottom metal layer of the substrate 100 by means of welding / sintering / bonding. The structure of the external solder pads 320 is the same as in Embodiment 1. Example 3

[0052] like Figure 3-5 As shown, the side of the external solder pad 320 is exposed outside the molding compound 400, and based on Embodiment 1 or Embodiment 2, the form of the corner area connecting the external solder pad 320 is expanded, namely: like Figure 9 As shown, the corner area where the outer weld foot 320 connects to the inner side of the connecting part 310 has a smooth, rounded transition structure, reducing stress concentration; as Figure 3-5 As shown, the connecting corner area has an angled connection structure.

[0053] like Figure 3 As shown, a groove 401 is provided in the corner area of ​​the external solder pad 320. The groove 401 allows the first side 402 of the external solder pad 320 to be exposed at least partially outside the encapsulation body 400. During soldering, the first side 402 can contact the solder to form a solder crawling effect. Figure 3 The connecting corner area has a 90-degree structure.

[0054] Figure 4 The groove 401 extends outward from the molded body 400 to form a recessed area 410, so that the second side 403 opposite to the outer solder pad 320 and the third side opposite to it are at least partially exposed outside the molded body 400.

[0055] Figure 5 A stepped boundary structure is adopted between the inner plastic seal 400 and the outer weld foot 320, exposing part of the side and part of the joint corner area of ​​the outer weld foot 320.

[0056] During the SMT reflow soldering process, the molten solder can climb up along the side wall of the outer solder pad 320 and wrap around the side area of ​​the outer solder pad 320, effectively increasing the effective welding bonding area between the outer solder pad 320 and the solder, strengthening the metallurgical bonding strength between the outer solder pad 320 and the PCB pad, and significantly improving the mechanical reliability and electrical connection stability of the overall welding structure.

[0057] According to AEC Q-007, plate-level temperature cycling reliability tests were conducted on structures with and without side exposure. The side-exposed structure can significantly improve temperature cycling capability, thereby improving reliability and extending service life. Example 4

[0058] like Figure 3 , 6As shown, the bottom surface of the molding compound 400 has inwardly recessed slots 420, which extend laterally, longitudinally, or in a crisscross pattern. After assembling the leadless power module of this invention on a PCB, during use, the power module will expand and contract due to temperature changes. This expansion and contraction will cause the module to expand and contract outward from the centroid of the bottom surface. The thermal stress caused by this expansion and contraction will be transmitted to the solder joints of the external solder pads, causing fatigue cracking and failure. This invention provides slots 420 of different shapes on the bottom surface to form multiple separate areas. That is, expansion and contraction will be centered on the centroid of these separate areas. This design can reduce the thermal stress on the solder joints, prevent premature fatigue failure, and improve solder joint lifespan.

[0059] The depth of the slot 420 should be greater than the height of the external solder pads 320 protruding from the plastic package. By setting the slot 420, the external solder pads 320 are placed in 4 independent islands. Although the stress of the external solder pads is still affected by the overall power module, it is significantly better than not dividing the area. Example 5

[0060] like Figure 7-8 As shown, the bottom of the molding compound 400 has multiple downwardly extending positioning protrusions 430; the PCB board 500 has multiple positioning grooves corresponding to the positioning protrusions 430. When this product is assembled on the PCB board 500, the positioning protrusions 430 can penetrate into the positioning grooves, playing a role in positioning, limiting, and blocking stress transmission; the shape of the positioning protrusions 430 includes spherical, cylindrical, or conical.

[0061] After the power module with positioning protrusion 430 is assembled on the PCB, it is connected to the heat sink via bolts or screws. During this process, the PCB may deform due to uneven stress, and the mechanical stress caused by the deformation will be transmitted to the solder joints of the external solder pads 320, affecting the life of the solder joints. This invention assembles the positioning protrusion 430 into the groove of the PCB, which avoids large PCB deformation and prevents the transmission of mechanical stress to the solder joints. Example 6

[0062] like Figure 10-11 As shown, pin 300 is provided with a lock soldering structure, which improves the reliability of soldering to PCB board 500.

[0063] Figure 10 The center-locking structure consists of downward-protruding protrusions 321 or elongated protrusions. The height of the protrusions does not exceed the bottom surface of the encapsulated body, meaning that the bottom surface of the encapsulated body will not be lifted after welding due to the height of the protrusions.

[0064] Figure 11The center-locked welding structure consists of an inwardly recessed pit 322 or groove welded to the outside. This structure is easy to process. After welding, the pit 322 stores solder, which increases the bonding force between the solder and the external weld foot. At the same time, it prevents the weld joint from cracking and continuing to expand inward, thus significantly improving the life of the weld joint.

[0065] In this case, pin 300 of a high-reliability leadless power module is formed by cutting a lead frame: The lead frame of the leadless power module, the structure of one unit is shown in the figure. Figure 13 As shown, it includes an outer frame 600, and the outer frame 600 is... Figure 14 In the mid-plane area, multiple pins 300 are located within the outer frame; Pin 300 includes a connection portion 310 and an external solder pad 320; like Figure 13 As shown, the outer weld foot 320 is connected to the outer frame 600 and is in the same plane; The connecting part 310 includes a first bending area 311, a buffer zone 312, a second bending area 313, and an inner weld foot 314 connected in sequence; the first bending area 311, the buffer zone 312, the second bending area 313, and the inner weld foot 314 extend toward the center of the outer frame 600.

[0066] like Figure 14 As shown, one end of the bending area 311 is connected to the outer weld foot 320. With the outer frame 600 as the reference, the included angle between the two is 70° to 90°. Preferably, the included angle is 80°.

[0067] The other end of the bending zone 311 bends towards the center of the outer frame 600, forming a buffer zone 312. The buffer zone 312 is basically parallel to the outer weld foot 320. However, to facilitate pressure transmission towards the bending zone 313, the buffer zone 312 is extended downwards towards the bending zone 313. Based on the horizontal direction of the outer frame 600, the downward tilt angle is 4° to 8°. Figure 15 As shown, preferably, the downward tilt angle is 5°. The buffer zone 312 is tilted towards the center of the outer frame, which allows the internal solder pads 314 to converge towards the center, thereby facilitating alignment and connection with the substrate 100.

[0068] The buffer zone 312 is bent into a second bending zone 313 at one end away from the first bending zone 311 and towards the center of the outer frame 600; the angle between the second bending zone 313 and the inner weld foot 314 is 70° to 90°, preferably 80°.

[0069] The end of the second bending zone 313 away from the buffer zone 312 is bent towards the center of the outer frame 600 and has an internal weld foot 314. Based on the horizontal extension direction of the outer frame 600, the angle between the internal weld foot 314 and this reference direction is 1° to 6°, preferably 4°. To ensure that the pressure borne by the outer frame 600 can be transmitted to the internal weld foot 314, the internal weld foot 314 is configured such that, based on the horizontal extension direction of the outer frame 600, as shown... Figure 15 As shown, the downward tilt is -1° to 6°, preferably 4°.

[0070] To facilitate frame processing and achieve better pressure transmission, the length of buffer zone 312 is set to 3 to 6 times the length of internal weld foot 314.

[0071] like Figure 16 As shown, when molding a leadless power module, the substrate 100 is bonded to the bottom of the mold. However, due to slight warping of the substrate 100, it is difficult to ensure that the molding compound will overflow onto the back of the substrate 100, resulting in excess adhesive. In this solution, after the substrate 100 is bonded to the bottom of the mold, the outer frame 600 of the frame still has a certain distance from the mold. After the upper and lower molds are closed, the outer frame 600 will be bonded to the surface of the lower mold under the pressure of the upper mold. At this time, the force of the outer frame 600 will be transmitted to the substrate 100 through the external solder pads 320, bending area one 311, buffer zone 312, bending area two 313, and internal solder pads 314, thereby making the substrate 100 bond more tightly with the lower mold cavity and effectively preventing the molding compound from overflowing onto the lower surface of the substrate 100.

[0072] This solution, through the design of the frame structure and the optimal selection of the angles of bending zone 1 311, buffer zone 312, bending zone 2 313, and internal solder feet 314, achieves the effect of pressure transmission and avoids plastic sealant overflow. It also effectively prevents the ceramic in the insulating substrate from cracking due to excessive pressure transmission.

[0073] After molding, the frame buffer 312 is basically parallel to the outer frame 600. The buffer 312 is set relatively long to form a larger contact area with the molding body 400 in the horizontal direction, thus preventing the external solder feet from separating from the molding body due to springback force after molding. In this design, the lead frame is made of copper alloy C19210 / TFe0.1 with a hardness of 1 / 2H and a frame thickness of 0.5mm.

[0074] In this case, the frame is typically manufactured using stamping. The stamping die contacts the internal solder pads on the same plane, meaning all internal solder pads are 600mm away from the outer frame during stamping. However, due to the long leads and several bends, the leads undergo both molding and elastic deformation after stamping. Molding deformation maintains the lead's shape, but elastic deformation causes it to spring back when the die pressure is removed. During frame assembly and welding to the substrate, the central solder pads contact the substrate, while the side solder pads often have a distance from it. After assembly, the side solders have a higher probability of incomplete soldering, affecting product yield or reliability due to rework. Furthermore, during the welding process, the frame may deform due to heat, causing the side solder pads to lift upwards, further increasing their distance from the substrate and contributing to incomplete soldering.

[0075] The following design was implemented to address the issue of incomplete soldering during assembly: The first-side pins 301 and second-side pins 302 of the plurality of pins 300 are symmetrically arranged; The first side pin 301 and / or the second side pin 302 are respectively provided with a pair of symmetrically arranged central solder pads 303, a pair of symmetrically arranged side solder pads 304, and a pair of symmetrically arranged second side solder pads 305. The inner weld foot 314 of the middle weld foot 303 extends downward; the distance between the bottom end face of the middle weld foot 303 and the upper surface of the outer frame 600 is L1; The inner weld foot 314 of the first side weld foot 304 extends downward, and the distance between the bottom end face of the first side weld foot 304 and the upper surface of the outer frame 600 is L2; The inner weld foot 314 of the second side weld foot 305 extends downward, and the distance between the bottom end face of the second side weld foot 305 and the upper surface of the outer frame 600 is L3; Where L2 is not less than L1. The difference between L2 and L1 is 0.005mm to 0.06mm. L3 is not less than L2.

[0076] The outer frame 600 is formed by stamping and is integrally flat; the pins 300 are relatively long and have multiple bending structures. After the stamping process, the springback deformation of the solder feet near the outer side of the outer frame 600 becomes significant, causing the internal solder feet to be out of plane. By using appropriate L1, L2, and L3 settings, the welding quality is improved, and the defects of cold solder joints 314 are avoided, thus affecting the product yield.

[0077] Regarding the information disclosed in this case, the following points need to be clarified: (1) The accompanying drawings of the embodiments disclosed in this case only involve the structures involved in the embodiments disclosed in this case. Other structures can refer to the general design. (2) Where there is no conflict, the embodiments and features disclosed in this case can be combined with each other to obtain new embodiments; The above are merely specific embodiments disclosed in this case, but the scope of protection of this disclosure is not limited thereto. The scope of protection disclosed in this case shall be determined by the scope of protection of the claims.

Claims

1. A high-reliability pinless power module, characterized in that, include: A semiconductor chip assembly includes a substrate (100) and a power chip (200) connected to the substrate (100). Multiple pins (300) include a plurality of first-side pins (301) and a plurality of second-side pins (302); the first-side pins (301) and the second-side pins (302) are electrically connected to the semiconductor chip assembly, respectively; A molding compound (400) covers the power chip (200), at least a portion of the substrate (100), and at least a portion of the pins (300). Each pin (300) includes a connected portion (310) and an external solder pad (320); the connected portion (310) is located inside the molding compound (400) and extends outward from the molding compound (400); the external solder pad (320) has at least its lower surface exposed outside the molding compound (400), and the bottom surface of the external solder pad (320) does not extend beyond the bottom surface of the molding compound (400).

2. The high-reliability pinless power module according to claim 1, characterized in that, The substrate (100) is a conductive substrate; The conductive substrate and several first-side pins (301) are integrated into one structure; A plurality of second-side pins (302) are spaced apart from the conductive substrate and are electrically connected to the power chip (200) via connectors; The top surface of the conductive substrate is exposed from within the encapsulation (400).

3. A high-reliability pinless power module according to claim 1, characterized in that, The substrate (100) is an insulating substrate, comprising a top metal layer, an insulating layer and a bottom metal layer connected in sequence; The top surface of the top metal layer is exposed from inside the encapsulation (400); a plurality of first side pins (301) and a plurality of second side pins (302) are electrically connected to the bottom metal layer respectively.

4. A high-reliability pinless power module according to claim 1, characterized in that, The external weld foot (320) includes a mounting surface, a top surface, and multiple side surfaces; The mounting surface of the external solder foot (320) is located on the outside of the encapsulation body (400), and the vertical distance between it and the bottom surface of the encapsulation body (400) ranges from 0.01mm to 0.5mm.

5. A high-reliability pinless power module according to claim 4, characterized in that, The side of the external solder pad (320) is exposed outside the encapsulation (400).

6. A high-reliability pinless power module according to claim 5, characterized in that, The inner corner area of ​​the connection between the external solder foot (320) and the connection part (310) is exposed outside the molding body (400), and the corner area has a smooth arc transition structure or a bent angle connection structure. When the connecting corner area has an angled connection structure, at least part of the sidewall of the external solder foot (320) is exposed outside the encapsulation body (400).

7. A high-reliability pinless power module according to claim 6, characterized in that, The connecting corner area is exposed through the recessed area (410) at the bottom of the encapsulated body (400).

8. A high-reliability pinless power module according to claim 1, characterized in that, The bottom surface of the encapsulated body (400) is provided with an inwardly recessed groove (420), which extends laterally, extends longitudinally, or is arranged in a crisscross pattern.

9. A high-reliability pinless power module according to claim 1, characterized in that, The bottom of the encapsulation body (400) is provided with one or more downwardly extending positioning protrusions (430). The PCB board (500) is provided with one or more positioning grooves corresponding to the positioning protrusions (430).

10. A high-reliability pinless power module according to claim 1, characterized in that, The pin (300) is provided with a locking structure, which improves the reliability of soldering to the PCB board.

11. A lead frame for use in the high-reliability leadless power module as described in claims 1-10, characterized in that, The lead frame includes an outer frame (600) and a plurality of pins (300) disposed within the outer frame (600). The pin (300) includes a connection portion (310) and an external solder pad (320). The external welding foot (320) is connected to the outer frame (600) and is in the same plane; The connecting part (310) includes a bending area one (311), a buffer zone (312), a bending area two (313), and an internal weld foot (314) connected in sequence; the bending area one (311), the buffer zone (312), the bending area two (313), and the internal weld foot (314) extend toward the center of the outer frame (600).

12. A lead frame according to claim 11, characterized in that, One end of the bending area (311) is connected to the outer welding foot (320), and the included angle between it and the outer frame (600) is 70° to 90°.

13. A lead frame according to claim 11, characterized in that, The buffer zone (312) extends downward toward the center of the outer frame (600) at an angle of 4° to 8° with the horizontal direction of the outer frame (600) as the reference.

14. A lead frame according to claim 11, characterized in that, The internal weld foot (314) is inclined downward, and the angle between it and the horizontal direction of the outer frame (600) is 1° to 6°.

15. A lead frame according to claim 11, characterized in that, The length of the buffer zone (312) is set to 3 to 6 times the length of the internal solder pad (314).

16. A lead frame according to claim 11, characterized in that, The bottom and / or top surfaces of the internal weld foot (314) are provided with multiple pits.

17. A lead frame according to claim 11, characterized in that, The first-side pins (301) and the second-side pins (302) of the plurality of said pins (300) are symmetrically arranged; The first side pin (301) and / or the second side pin (302) are respectively provided with a pair of symmetrically arranged central solder feet (303) and a pair of symmetrically arranged side solder feet (304). The inner weld foot (314) of the middle weld foot (303) extends downward; the distance between the bottom end face of the middle weld foot (303) and the upper surface of the outer frame (600) is L1; The inner weld foot (314) of the first side weld foot (304) extends downward, and the distance between the bottom end face of the first side weld foot (304) and the upper surface of the outer frame (600) is L2; Where L2 is not less than L1.

18. A lead frame according to claim 17, characterized in that, The difference between L2 and L1 is 0.005mm to 0.06mm.

19. A lead frame according to claim 17, characterized in that, The first side pin (301) and / or the second side pin (302) also include a second side solder pad (305); The inner weld foot (314) of the second side weld foot (305) extends downward, and the distance between the bottom end face of the second side weld foot (305) and the upper surface of the outer frame (600) is L3; Where L3 is not less than L2.

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