Spaced pressurization combination method for power module with multiple power elements

Abstract

The application discloses a kind of interval pressurization combination method of power module with multiple power elements, comprising the following steps: multiple power elements are arranged at intervals on first ceramic substrate and a metal spacer block is arranged on each power element, wherein the metal spacer block is defined as a setting surface away from the first ceramic substrate direction;Second ceramic substrate with a layer of nano-silver layer is covered to the setting surface, and a spacer mold pad with a height exceeding the sum of power element and metal spacer block and lower than the sum of power element and metal spacer block plus the thickness of nano-silver layer is further arranged between the first and second ceramic substrates;Pressure is applied in the direction perpendicular to the first and second ceramic substrates, and the nano-silver layer is melted by heating to form a thin silver layer and electrically connected to the metal spacer block, and then cooled and solidified.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for manufacturing a power module with multiple power elements. BACKGROUND

[0002] With the global warming becoming more and more serious, and the environmental protection consciousness rising, more and more consumers choose to replace the traditional transportation tools powered by petrochemical fuel with electric transportation tools, such as replacing the traditional cars with electric cars and replacing the two-stroke motorcycles with electric motorcycles. These electric transportation tools rely on high-power electric motors to provide power, so the market demand for high-power power modules is growing, which has led to the investment and research and development of major suppliers to improve the yield and output of the production line. In addition, light source devices such as high-brightness LEDs or LDs are constantly being updated, making the power consumption of power devices continue to increase, and similarly, high-power and high-heat-dissipation power modules are needed to effectively support them.

[0003] High-power power modules inevitably convert part of the energy into heat energy due to their high energy consumption. With the continuous miniaturization of electronic devices, high-power elements in smaller spaces will be accompanied by higher heat generation, so how to remove excess heat energy and maintain the stability of the operating environment becomes crucial. In order to solve the problem of heat dissipation, the most common solution is to use ceramic materials as the insulating material layer of the circuit substrate. Ceramic substrates are a type of circuit board that has a thermal expansion coefficient close to that of semiconductors and high heat resistance. The most common ceramic material is a direct bonded copper (DBC) substrate made of aluminum oxide (Al2O3), which has a thermal conductivity of 35 W / mK in single-crystal structure and 20-27 W / mK in polycrystalline structure. Other common ceramic material substrates include aluminum nitride (AlN), beryllium oxide (BeO), and silicon carbide (SiC). Ceramic substrates have become the first choice for high-power power module substrates.

[0004] However, ceramic substrates have the problem of warping deformation, which may be tolerable in small sizes, but when the substrate size becomes larger, the severity of warping deformation becomes more obvious, causing the upper surface of the substrate to be uneven. A 5-6 cm ceramic substrate may be bent by about 0.2 mm, which has a significant impact on chips with a height of only about 0.2 mm. Especially when the current of the power module needs to reach hundreds of amperes or even hundreds of amperes, it is not possible for a single high-power element to withstand such a current, and multiple high-power elements need to be arranged in parallel on the same ceramic substrate plane to form a power module.

[0005] Therefore, ceramic substrates with dimensions exceeding several centimeters in length and width often suffer from unevenness and height due to warping and deformation, which can affect the overall component packaging and even performance. This is especially true for high-power power modules requiring heat dissipation through double-sided contact with the ceramic substrate. Maintaining optimal conductivity between each high-power module chip and both sides of the ceramic substrate presents a significant challenge. Unfortunately, taking a 200A-capable chip as an example, when conductivity is not optimal, high resistance may result from the high heat generated during current flow, reducing the actual current to only 100A. For power module chips handling high currents, even slight contact defects can cause substantial damage, and the remaining conductive chips must bear a greater load current. Therefore, ensuring good conductivity between each power module chip and the substrate is crucial, which is the problem this invention aims to solve.

[0006] To address these issues, researchers have proposed using nano-silver paste as an adhesive material. During the assembly process, heating causes the dopants within the nano-silver paste to vaporize, transforming it into pure molten silver. While this significantly reduces the thickness, it allows for the formation of pure silver connections between the ceramic substrate's pads and the chip's input / output electrodes. However, actual testing by the inventors revealed that while this technology works well for single chips, it becomes problematic when mounting chips containing six or more power components. The ceramic substrate must have sufficient area, making warping unavoidable. Furthermore, the significant thickness reduction of the nano-silver paste during heat treatment, combined with the limited thickness of the power component chips themselves, exacerbates the inherent warping issue in the thickness direction. Even before heating and soldering, inaccurate distance estimations can lead to impact damage to the power components, significantly impacting product yield and production efficiency. Summary of the Invention

[0007] In view of the above-mentioned shortcomings of the prior art, according to the embodiments of the present invention, it is desirable to provide an intermittent pressure bonding method for power modules with multiple power elements, which is a method for manufacturing high-power power modules, and aims to achieve the following objectives: (1) by using appropriate molds, the risk of damage to the ceramic substrate and power elements due to collision is reduced, thereby improving the manufacturing yield; (2) by using molds as a high guarantee, the poor contact between the nano silver paste on the ceramic substrate and the power elements is avoided, which leads to conductive defects in the finished product, thereby improving the reliability of the finished power module; (3) to ensure the conductive connection between individual power elements and the double-sided ceramic substrate.

[0008] According to an embodiment, the present invention provides an intermittent voltage bonding method for a power supply module with multiple power elements, comprising the following steps:

[0009] a) A plurality of power elements are spaced apart on a first ceramic substrate, wherein each of the aforementioned power elements has a pair of input and output electrodes located on the top and bottom surfaces respectively, and a pad circuit layer is formed on the first ceramic substrate for conductive bonding to the input and output electrodes on the bottom surface of the power elements, and a corresponding metal spacer is provided on the input and output electrodes on the top surface of each of the aforementioned power elements, wherein the direction of the metal spacer away from the first ceramic substrate is defined as a mounting surface.

[0010] b) A second ceramic substrate having a layer of nano-silver is covered with the connecting surface having the nano-silver layer, so that the mounting surfaces of the metal spacers are pressed into the nano-silver layer. Furthermore, in a separable manner, a plurality of spacer mold blocks with a height exceeding the sum of the power element and the metal spacers and lower than the thickness of the power element, the metal spacers, and the nano-silver layer are provided between the first ceramic substrate and the second ceramic substrate. This ensures that the metal spacers can penetrate into the nano-silver layer without directly contacting the second ceramic substrate and causing damage.

[0011] c) Pressurize and heat the nano-silver layer in a direction perpendicular to the first and second ceramic substrates to melt the nano-silver layer into a thinner silver layer and make it electrically bonded to the metal spacer block, and then cool it to solidify the silver layer.

[0012] According to one embodiment, in the aforementioned intermittent pressure bonding method for a power module with multiple power elements of the present invention, step a) further includes a sub-step a1) of forming the aforementioned pad circuit layer through photoresist etching.

[0013] According to one embodiment, in the aforementioned method for interleaved pressure bonding of a power module with multiple power elements, step a) further includes a sub-step a2) of forming chamfers at each corner of the aforementioned metal spacer block to avoid stress concentration.

[0014] According to one embodiment, in the aforementioned spaced-pressure bonding method for a power supply module with multiple power elements of the present invention, step a) further includes a sub-step a3 of silver plating on the surface of the aforementioned metal spacer block.

[0015] According to one embodiment, in the aforementioned intermittent voltage bonding method for a power supply module with multiple power elements of the present invention, step d) is further included before step a) to embed a ceramic substrate in the circuit board portion to form a first ceramic substrate.

[0016] According to one embodiment, in the aforementioned intermittent pressure bonding method for a power supply module with multiple power elements of the present invention, step e) is further included before step b) to embed a ceramic substrate in the circuit board portion to form a second ceramic substrate and cover it with a nano-silver layer.

[0017] Compared to existing technologies, the technical solution of this invention ensures that, before heating and welding, the presence of spacer mold pads ensures that the power components and metal spacers can be smoothly inserted into the nano-silver paste on the second ceramic substrate, regardless of how warped the ceramic substrate is, without directly impacting the second ceramic substrate. This avoids the risk of damage to the power component chip or ceramic substrate due to mechanical force during processing. On the other hand, it ensures that the metal spacers can be reliably pressed into the nano-silver paste without any contact issues.

[0018] Nano-silver paste possesses unique melting characteristics. Upon melting at 200°C, the dopants vaporize, and the nano-silver paste melts into liquid pure silver, reducing its overall height to approximately one-third of its original height. Because pressure is applied from both top and bottom during heating, the warping of the ceramic substrate is partially corrected by external force, reducing thickness errors. Furthermore, the fluidity of molten pure silver ensures that the contacted second ceramic substrate pads and metal spacers achieve conductive bonding due to the surface tension of silver. Even if the nano-silver layer shrinks during heating and eventually cools into a pure silver layer, it still forms an excellent conductive bond, tightly connecting the second ceramic substrate to the metal spacers. This invention ensures excellent conductive bonding between individual power components and the double-sided ceramic substrate, especially useful when power modules require larger dimensions, such as those exceeding 5-6 cm in length and width, thus solving the problem of warping and deformation of the double-sided ceramic substrates of the power components. Attached Figure Description

[0019] Figure 1 This is a flowchart of an intermittent voltage combination method for a power supply module with multiple power elements according to the present invention.

[0020] Figures 2 to 6 This is a side view schematic diagram of the structure of different steps in the first preferred embodiment of the present invention.

[0021] Figure 7 This is a side view schematic diagram of the structure of the second preferred embodiment of the present invention.

[0022] Wherein: 1, 1' are the first ceramic substrate; 11 is the pad circuit layer; 13' is part of the first ceramic substrate; 14' is the first dielectric material substrate; 2, 2' are power components; 21 is the bottom surface; 22 is the top surface; 211, 221 are input and output electrodes; 3, 3' are metal spacers; 31, 31' are mounting surfaces; 4, 4' are the second ceramic substrate; 41 is a nano-silver layer; 42, 42' are pure silver layers; 43' is part of the second ceramic substrate; 44' is the second dielectric material substrate; 411 is the connection surface; 5, 5' are spacer mold pads; 81 to 86 are steps. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. These embodiments should be understood as illustrative only and not as limiting the scope of protection of the present invention. After reading the description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

[0024] First preferred embodiment

[0025] like Figure 1 As shown, the first preferred embodiment of the present invention provides an intermittent voltage bonding method for a power supply module with multiple power elements. Firstly, in step 81... Figure 2 A plurality of power elements 2 are respectively disposed on a plurality of pads corresponding to the pad circuit layer 11 of the first ceramic substrate 1. Each power element 2 includes a bottom surface 21, an input / output electrode 211 soldered on the pad circuit layer 11 on the bottom surface 21, a top surface 22, and an input / output electrode 221 on the top surface 22. Subsequently, in step 82, a metal spacer 3, for example, copper-plated silver, is disposed on the input / output electrode 221 on the top surface 22 of the power element 2. Since the first ceramic substrate 1 is warped, the surface is uneven, resulting in different horizontal heights of the power elements 2 after placement. The upper surface of the metal spacer 3 in the direction away from the first ceramic substrate 1 also forms a placement surface 31 with different horizontal heights. The height difference here is only for illustration and is not an actual proportion.

[0026] Step 83 as follows Figure 3 As shown, a nano-silver layer 41 is coated on the second ceramic substrate 4. In this embodiment, the nano-silver layer 41 is approximately 600 μm thick, but in actual operation, it can be varied according to requirements and is not limited to a fixed thickness. Then, pressure devices (not shown in the figure) are respectively provided below the first ceramic substrate 1 and above the second ceramic substrate 4 to apply pressure relative to each other. To prevent the second ceramic substrate 4 and the nano-silver layer 41 from excessively pressing the power element 2 due to pressure approaching the first ceramic substrate 1, this embodiment includes step 84 as described above. Figure 4 As shown, a plurality of spacer mold blocks 5 are detachably disposed between or around individual power components 2 on the first ceramic substrate 1 and the second ceramic substrate 4. The height of the spacer mold blocks 5 exceeds the sum of the height of the power components 2 and the metal spacers 3, and is lower than the thickness of the power components 2, the metal spacers 3, plus the thickness of the nano-silver layer 41, forming a plurality of spacer devices that can limit the closest distance between the first ceramic substrate 1 and the second ceramic substrate 4.

[0027] like Figure 5As shown, at this time, the connecting surface 411 of the second ceramic substrate 4 with the nano-silver layer 41 covers and abuts the setting surface 31. Since the nano-silver layer 41 itself has some flexibility, when the nano-silver layer 41 contacts the setting surface 31 of the metal spacer block 3, it will... Figure 5 As shown, the metal spacer 3 is inserted therein. Since the nano-silver layer in this embodiment has a thickness of about 600μm, it can completely absorb the warping of the first ceramic substrate 1 and the second ceramic substrate 4 by up to about 200μm. There will be no gaps caused by lack of contact, and the metal spacer will not cause the second ceramic substrate 4 to hit and cause cracks or micro-gaps. It can completely compensate for the slight height difference between the above-mentioned setting surface 31 and the above-mentioned second ceramic substrate 4 caused by the warping of the first ceramic substrate 1 and the second ceramic substrate 4.

[0028] like Figure 6 As shown, in step 85, the nano-silver layer 41 is pressed and heated to melt in the direction perpendicular to the first ceramic substrate 1 and the second ceramic substrate 4. When the nano-silver layer 41 is heated and the dopants are vaporized, the nano-silver layer begins to melt and form a thin pure silver layer 42. Since it is already in contact with the above-mentioned setting surface 31 and the above-mentioned second ceramic substrate 4 respectively, due to the influence of surface tension, the silver in between will effectively conduct to the above-mentioned metal spacer block 3 and the above-mentioned second ceramic substrate 4 respectively. Even if the thickness of the nano-silver layer 41 is reduced to the pure silver layer 42 after heating, it can still ensure that each power element and the pad on the second ceramic substrate above have excellent conductive connection. Finally, in step 86, the pure silver layer 42 is cooled, solidified, and the above-mentioned spacer mold pad 5 is removed.

[0029] Due to the height design of the spacer mold pad 5, on the one hand, it limits the first ceramic substrate 1 and the second ceramic substrate 4 from getting too close, which would cause the metal spacer block 3 and the power component 2 to be damaged by impact, thereby improving the yield during the processing. On the other hand, the height of the spacer mold pad 5 can also ensure that even if the ceramic substrate warps, the metal spacer block 3 can still be firmly inserted into the nano silver layer 41, without poor contact that would cause poor conductivity in future use, thus improving reliability and achieving the above-mentioned objective of the present invention.

[0030] Of course, as those skilled in the art can easily understand, the first ceramic substrate and the second ceramic substrate mentioned here are not limited to a single complete ceramic substrate. Because ceramic substrates have good heat resistance and thermal conductivity, but their structure cannot be detailed, some people in the industry have proposed using a thermoelectric separation substrate of a ceramic substrate embedded in a dielectric material substrate. This allows high-heat-generating components, such as power components, to be placed on the ceramic substrate, while more complex components, such as control circuits, are placed on a multilayer circuit board of dielectric materials such as FR-4. This achieves a structure in which complex control circuits and high-power components with high heat dissipation circuits coexist and the advantages of both are combined.

[0031] Second preferred embodiment

[0032] like Figure 7 As shown, the parts identical to those in the previous preferred embodiment will not be repeated here, and similar components will use similar names and reference numerals; only the differences will be described. In the second preferred embodiment of the present invention, before step 81, a prior step of manufacturing a first ceramic substrate 1' is further included, in which a first ceramic substrate portion 13' is embedded in the first dielectric material substrate 14' at the position corresponding to the power element 2'; similarly, before step 83, a prior step of manufacturing a second ceramic substrate 4' is further included, in which a second ceramic substrate portion 43' is embedded in the second dielectric material substrate 44' at the position corresponding to the power element 2', and a nano-silver layer is covered in the second ceramic substrate portion 43' at the position corresponding to the power element 2', so that the nano-silver layer mentioned in step 84 covers and abuts against the setting surface 31', and is held abutted by the spacer mold pad 5'. Finally, in step 85, pressure is applied and the nano-silver layer is heated and melted in a direction perpendicular to the first ceramic substrate 1' and the second ceramic substrate 4' to form a pure silver layer 42' with a smaller thickness, so that the metal spacer 3' is electrically bonded to the second ceramic substrate portion 43' of the second ceramic substrate 4'.

Claims

1. A method for intermittently applying voltage to a power supply module with multiple power elements, characterized in that, Includes the following steps: a) A plurality of power elements are spaced apart on a first ceramic substrate, wherein each of the aforementioned power elements has a pair of input and output electrodes located on the top and bottom surfaces respectively, and a pad circuit layer is formed on the first ceramic substrate for conductive bonding to the input and output electrodes on the bottom surface of the power elements, and a corresponding metal spacer is provided on the input and output electrodes on the top surface of each of the aforementioned power elements, wherein the direction of the metal spacer away from the first ceramic substrate is defined as a mounting surface. b) A second ceramic substrate having a layer of nano-silver is covered with the mounting surface of the mounting surface of the metal spacer, so that the mounting surfaces of the metal spacers are pressed into the nano-silver layer respectively. In a separable manner, a plurality of spacer mold pads with a height exceeding the sum of the power element and the metal spacer and lower than the thickness of the power element, the metal spacer, and the nano-silver layer are provided between the first ceramic substrate and the second ceramic substrate. This ensures that the metal spacers can penetrate into the nano-silver layer without directly touching the second ceramic substrate and causing damage. c) Pressurize and heat the nano-silver layer in a direction perpendicular to the first and second ceramic substrates to melt the nano-silver layer into a thinner silver layer and make it electrically bonded to the metal spacer block, and then cool it to solidify the nano-silver layer.

2. The method for intermittent voltage application of a power supply module with multiple power elements as described in claim 1, characterized in that, Step a) further includes a sub-step a1 of forming the aforementioned pad circuit layer through photoresist etching.

3. The method for intermittent voltage application of a power supply module with multiple power elements as described in claim 1, characterized in that, Step a) further includes a sub-step a2) in which chamfers are formed at each corner of the aforementioned metal spacer block to avoid stress concentration.

4. The method for intermittent voltage application of a power supply module with multiple power elements as described in claim 1, characterized in that, Step a) further includes sub-step a3, which involves silver plating on the surface of the aforementioned metal spacer block.

5. The method for intermittent voltage application of a power supply module with multiple power elements as described in claim 1, characterized in that, Step a) further includes step d) which involves embedding a ceramic substrate in the circuit board portion to form a first ceramic substrate.

6. The method for intermittent voltage application of a power supply module with multiple power elements as described in claim 1, characterized in that, Step e) further includes embedding a ceramic substrate in the circuit substrate portion to form a second ceramic substrate and covering it with a nano-silver layer.

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