Leaf vein imitating fractal structure copper heat sink

Abstract

A vein-imitating fractal structure copper heat sink is arranged at the top of a chip packaging body through conductive adhesive and comprises a plurality of trunks arranged in a central symmetry mode and branches symmetrically arranged at the tail ends of the trunks, the tail ends of the branches are further provided with back-stage fractal trunks, and the number of the trunks at each stage is six. According to the invention, the Cu plate of the vein-imitating fractal structure is used as the heat sink, and the specific surface area of heat exchange between the QFN and air is increased by adopting the trunk and the branches of the vein-imitating fractal structure, so that the temperature of the packaging body is effectively reduced.

Description

Technical Field

[0001] This invention relates to a technology in the field of semiconductor heat dissipation, specifically a copper heat sink with a fractal structure inspired by leaf veins. Background Technology

[0002] With the rapid evolution of digital technology and the semiconductor industry, the integration, miniaturization, and performance of microelectronic components are constantly improving, leading to a continuous increase in heat generation. A lack of effective thermal management systems can cause microelectronic devices to overheat, affecting their normal function and even causing them to burn out. Existing honeycomb structures for heat conduction units cannot solve the heat dissipation problem of small-sized QFNs. Summary of the Invention

[0003] This invention addresses the heat dissipation problem of existing quad flat no-lead (QFN) packages by proposing a copper heat sink with a leaf vein-like fractal structure. By using a Cu plate with a leaf vein-like fractal structure as the heat sink, the specific surface area for heat exchange between the QFN and the air is increased through the use of the main trunk and branches of the leaf vein-like fractal structure, thereby effectively reducing the temperature of the package.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a copper heat sink with a fractal structure resembling leaf veins, which is disposed on the top of a chip package using conductive adhesive. It includes: several main trunks arranged symmetrically at the center and branches arranged symmetrically at the ends of the main trunks, wherein: the main trunks are arranged radially at fractal angles of 30°-90°, and the ends of the branches are further provided with main trunks of subsequent fractals.

[0006] There are two types of fractal forms: Y-shaped fractal and claw-shaped fractal. The Y-shaped fractal is formed from the end of the main trunk to both sides along the extension line of the main trunk, and the included angle between the two branches is the fractal angle. In the claw-shaped fractal, one branch is in the same direction as the main trunk, and the remaining branches are formed from the center point of the first branch head outwards at fractal angles of 30°-90°.

[0007] The number of branches is two or three, and the number of branches is the maximum number of branches that meet the package size requirements.

[0008] The length of the main trunk is 0.15-0.3 times the width of the package, the length ratio of the main trunk to the branches is 0.5-2, and the width ratio is 0.5-2.

[0009] The fractal is of level 2-4. Technical effect

[0010] This invention utilizes a leaf vein-inspired fractal structure Cu plate as a heat sink, comprising a fractal trunk and branches. Cross-linking between the branches forms a network structure. The pores in the network structure increase the specific surface area of ​​the heat sink in contact with air, and the closed network structure increases the directions of heat conduction, ultimately increasing the heat exchange between the QFN and the air, and reducing the chip's maximum junction temperature. The leaf vein-inspired fractal structure heat sink can be designed to be only a few millimeters in size and is adhered to the top of the package. The heat sink structure is manufactured through stamping, without altering the original chip package structure; it is directly adhered to the top of the package. It primarily addresses the heat dissipation difficulties of micro-miniature power devices. Compared to existing technologies, this invention improves the heat dissipation reliability of the package, is not limited by changes in application fields, and allows for flexible adjustment of the leaf vein-inspired fractal structure to adapt to different environments based on heat dissipation requirements. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the structure of an embodiment;

[0012] In the diagram: 1. Chip; 2. Package; 3. Lead solder; 4. Fractal heat sink; 5. Conductive adhesive; 6. Copper thermal pad.

[0013] Figure 2 (a) is a secondary 60° Y-shaped leaf vein fractal structure Cu heat sink as an example; Figure 2 (b) is a secondary 60° claw-shaped leaf vein fractal structure Cu heat sink;

[0014] Figure 3 The example shows the temperature change over time during thermal shock cycling.

[0015] Figure 4 The strain-time curve under thermal shock cycling is shown in the example. Detailed Implementation

[0016] like Figure 2 As shown, this embodiment relates to a copper heat sink with a fractal structure resembling leaf veins, comprising: several main trunks arranged symmetrically at the center and branches arranged symmetrically at the ends of the main trunks, wherein: the ends of the branches are further provided with main trunks of a subsequent fractal structure.

[0017] like Figure 2 As shown in (a), the number of branches is two; as Figure 2 As shown in (b), there are three branches, all of which are second-order fractal and have a fractal ratio of 1:1. With the widths fixed at 0.1 mm and 0.2 mm respectively, the fractal angles set in Table 1 are used for the QFN of the two leaf vein-like fractal structure Cu heat sinks according to the following program design.

[0018] like Figure 2 As shown in (a) and 2(b), the surface area of ​​the heat sink is 4 mm.2 and 5mm 2 .

[0019] like Figure 1 As shown, the QFN package, from top to bottom, consists of conductive adhesive 5, package body 2, chip 1, pins 7, copper thermal pad 3, and PCB board 6. In this QFN model, chip 1 has a size of 3.6 × 3.6 mm. 2 The thickness is 0.4 mm, and the material is Si; the dimensions of package 2 are 6.2 × 6.2 mm. 2 It has a thickness of 1mm and is made of EMC.

[0020] The copper heat sink is located on top of the package. Si has a Young's modulus of 131 GPa, a Poisson's ratio of 0.28, and a coefficient of thermal expansion of 2.8 ppm / ℃; EMC has a Young's modulus of 250 GPa, a Poisson's ratio of 0.3, and a coefficient of thermal expansion of 90 ppm / ℃; Cu has a Young's modulus of 120 GPa, a Poisson's ratio of 0.34, and a coefficient of thermal expansion of 18.9 ppm / ℃. Cu heat sinks with different fractal angles and leaf vein-like fractal structures (as shown in Table 1) are placed on the QFN. The ambient temperature is set to 25℃, and the natural air convection value is 25 W / (m²). 2 •K); Tetrahedral elements are used to mesh the QFN package, and hexahedral elements are used to mesh the remaining parts of the QFN. The mesh size is 0.05 mm, and then steady-state thermal analysis is performed.

[0021] The results are shown in Table 1. For the Y-shaped and claw-shaped leaf vein-inspired fractal structures of Cu heat sinks with a fractal width of 0.1 mm, the fractal angle gradually changed from 45° to 90°. The maximum temperature of the QFN also increased incrementally from 45.29℃ and 44.99℃ to 45.79℃ and 45.80℃, respectively. The claw-shaped structure had a lower maximum temperature than the Y-shaped structure. The reduction in maximum temperature was most significant when the fractal angle was 45°. The Y-shaped and claw-shaped leaf vein-inspired structures with a fractal width of 0.2 mm... The fractal angle of the Cu heat sink with a vein-like fractal structure gradually changes from 45° to 90°. The maximum temperature of the QFN also increases incrementally from 45.13℃ and 45.29℃ to 45.70℃ and 45.71℃. The claw-shaped heat sink shows a smaller decrease in maximum temperature compared to the Y-shaped heat sink. In particular, at a fractal angle of 45°, the maximum temperature of the QFN in the claw-shaped heat sink is abnormally higher than that of the Y-shaped heat sink due to the cross-linking between branches and the loss of the void heat dissipation process. When the fractal width is 0.1mm and the fractal angle is 45°, the maximum temperature of the QFN in the claw-shaped fractal heat sink is the lowest, at 44.99℃.

[0022] Table 1: Relationship between the highest temperature and fractal angle and width of Y-shaped leaf vein-inspired fractal structure Cu heat sink QFN.

[0023] As the fractal angle increases, the maximum junction temperature of the claw-shaped heat sink gradually increases compared to the Y-shaped fractal heat sink. When the fractal angle is constant, the maximum junction temperature of both leaf vein-inspired fractal heat sinks decreases as the fractal width increases, with the best reduction effect observed at a fractal angle of 60°. When the fractal width and fractal angle are constant, the claw-shaped heat sink has a lower maximum junction temperature than the Y-shaped heat sink, indicating better heat dissipation. Specifically, the 45° claw-shaped heat sink with a fractal width of 0.2mm exhibits better heat dissipation than the Y-shaped heat sink.

[0024] As shown in Table 2, due to the symmetrical structure of the leaf vein-inspired fractal heat sink, the fractal angle needs to be divisible by 360°, resulting in a non-uniform increase in the fractal angle. When the fractal angle changes from 30° to 90°, the maximum temperature of the QFN first decreases from 44.99℃ to 44.61℃ and then gradually increases to 45.80℃. The temperature reduction is most significant when the fractal angle is around 45°. At a fractal angle of 30°, the branching and cross-linking degree of the leaf vein-inspired fractal structure is very high, reducing the hollow area of ​​the heat sink to almost a single plate, resulting in a smaller convection area with air and less convective heat dissipation. Subsequently, as the fractal angle increases, the branching and cross-linking degree decreases, increasing the convection area with air and thus enhancing the heat dissipation capacity of the claw-shaped leaf vein-inspired fractal structure Cu heat sink QFN. In Table 1, when the width of the claw-shaped fractal is 0.2 mm, the maximum temperature of the claw-shaped leaf vein-like fractal structure heat sink increases. Therefore, the claw-shaped leaf vein-like fractal structure heat sink with a fractal width of 0.1 mm and a fractal angle of 45° has the best heat dissipation effect.

[0025] Table 2: Relationship between the highest temperature and fractal angle of the claw-shaped leaf vein-inspired fractal structure Cu heat sink QFN. Fractal Angle temperature 30° 44.99℃ 36° 44.61℃ 45° 44.99℃ 60° 45.35℃ 90° 45.80℃

[0026] In the above examples, the heat dissipation effect of the claw-shaped concentric circle Cu heat sink QFN first decreases and then gradually increases with the increase of the fractal angle. The maximum temperature of QFN is the lowest when the fractal angle is 45°. Combining the results in Tables 1 and 2, it can be expected that the claw-shaped leaf vein-inspired fractal structure heat sink with a fractal level of two, a fractal ratio of 1:1, a fractal width of 0.1 mm, and a fractal angle of 45° will have the best heat dissipation effect.

[0027] When the surface area of ​​the Cu heat sink with the fractal structure resembling leaf veins is 9mm 2 A secondary claw-shaped 1:1 fractal, with a thickness and fractal width of 0.1 mm, was subjected to transient thermal analysis. Temperature cycling from 100°C to -25°C was applied inside the chip. Figure 2 The cycle is 20 minutes. Finite element strain simulation is performed using a model built with ANSYS. The average and maximum strain values ​​based on the vein-like fractal structure Cu heat sink QFN are as follows: Figure 3As shown, the maximum warpage value of the Cu heat sink QFN based on the leaf vein fractal structure is less than that of the QFN without a heat sink. Obviously, the leaf vein fractal structure Cu heat sink can effectively reduce the thermal strain inside the package.

[0028] In contrast, the heat sink area of ​​a conventional disc-shaped QFN is controlled to 9mm. 2 Steady-state thermal analysis was conducted on a conventional disc-shaped heat sink and a secondary 45° claw-shaped fractal structure Cu heat sink QFN under the same conditions, with varying thicknesses. The results are shown in Table 3. According to Table 3, under the same geometric parameters and heat sink thickness, the maximum temperature of the fractal structure heat sink QFN is lower than that of the conventional disc-shaped heat sink QFN. Furthermore, when the heat sink thickness uniformly changes from 0.05 mm to 0.5 mm, the maximum temperature of the disc-shaped heat sink QFN decreases from 45.81℃ to 45.57℃, a decrease of 0.24℃; while the maximum temperature of the fractal structure heat sink QFN decreases from 45.27℃ to 42.98℃, a decrease of 2.29℃. The improved heat dissipation performance is significantly better than that of the disc-shaped heat sink.

[0029] Table 3: Relationship between maximum temperature and thickness of ordinary disc-shaped and leaf vein-like fractal structure copper heat sinks (QFN) thickness Temperature (disk) Temperature (fractal) 0.05mm 45.81℃ 45.27℃ 0.10mm 45.79℃ 44.99℃ 0.15mm 45.76℃ 44.71℃ 0.20mm 45.73℃ 44.44℃ 0.25mm 45.70℃ 44.18℃ 0.30mm 45.68℃ 43.93℃ 0.35mm 45.65℃ 43.68℃ 0.40mm 45.62℃ 43.44℃ 0.45mm 45.59℃ 43.21℃ 0.50mm 45.57℃ 42.98℃

[0030] The above examples demonstrate that, under the same geometric parameters such as heat sink surface area, the maximum temperature of the leaf vein-inspired fractal structure copper heat sink QFN is generally 0.5–2.6℃ lower than that of a conventional disc-shaped heat sink. Furthermore, the greater the thickness of the heat sink, the more pronounced the heat dissipation advantage of the leaf vein-inspired fractal structure heat sink. The heat dissipation effect of the leaf vein-inspired fractal structure Cu heat sink QFN is superior to that of a conventional disc-shaped heat sink QFN.

[0031] This invention marks the first use of a leaf vein-inspired fractal structure Cu plate as a heat sink. In this heat sink, the fractal design of the main trunks and branches plays a decisive role in heat dissipation, making it the most important part of the concentric circle Cu heat sink. Furthermore, the hollowed-out structure created by the branch cross-linking during the fractal process increases the lateral area of ​​the heat sink, thereby increasing the specific surface area for air convection, improving heat dissipation, reducing the package temperature, effectively preventing internal thermal strain caused by overheating within the QFN, and extending the chip's lifespan. This leaf vein-inspired fractal structure Cu heat sink differs from common heat dissipation technologies in the field, such as vacuum chamber vapor chamber cooling, immersion liquid cooling, and microchannel fluid cooling. On one hand, this technology allows for direct hot-press molding without altering the circuit layout and basic structure of the circuit board, omitting the process steps of adding external fluids, and avoiding the use of organic additives, thus simplifying the manufacturing process, saving production costs, and avoiding environmental pollution. On the other hand, the complexity and innovation of the fractal design for different packaging forms provide more possibilities for future optimization, contributing to the further development of heat dissipation technology.

[0032] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A copper heat sink with a fractal structure mimicking leaf veins, characterized in that, The conductive adhesive is applied to the top of the chip package, including: several main trunks arranged symmetrically at the center and branches arranged symmetrically at the ends of the main trunks, wherein: the ends of the branches are further provided with subsequent fractal main trunks, and each main trunk has six branches.

2. The leaf vein-inspired fractal structure copper heat sink according to claim 1, characterized in that, The number of branches is two or three. When there are two branches, the angle between the branches and between the branches and the trunk is 120°. When there are three branches, one branch is in the same direction as the trunk, and the other two branches are located on both sides of it with an angle of 60°.

3. The leaf vein-inspired fractal structure copper heat sink according to claim 1 or 2, characterized in that, The length of the main trunk is 0.15-0.3 times the width of the package, the length ratio of the main trunk to the branches is 0.5-2, and the width ratio is 0.5-2.

4. The leaf vein-inspired fractal structure copper heat sink according to claim 1, characterized in that, The fractal is of level 2-4.

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