Packaging method and packaging structure

Abstract

The application provides a packaging method and a packaging structure. The packaging method comprises the following steps: providing a heat dissipation cover, a welding area of the heat dissipation cover is provided with a first magnetic structure; providing an indium-based solder, the indium-based solder is combined with a second magnetic structure; placing the indium-based solder between a chip and the heat dissipation cover and performing heating welding; during the heating process, a magnetic adsorption force is generated between the first magnetic structure and the second magnetic structure, so as to overcome the warping stress generated between the heat dissipation cover and the chip due to the mismatch of the thermal expansion coefficients and constrain the flow range of the molten indium-based solder. The packaging method can actively resist the warping stress, ensure the uniform spreading of the molten solder, avoid the loss or accumulation of indium in the welding area due to warping, and thus ensure the welding effect between the heat dissipation cover and the chip.

Description

Technical Field

[0001] This application relates to the field of chip packaging technology, and more specifically, to a packaging method and packaging structure. Background Technology

[0002] In flip-chip ball grid array (FCBGA) packaging, indium-based solder is typically used to connect the heat sink and the chip to achieve efficient heat conduction. However, during the packaging process, due to the mismatch in the coefficients of thermal expansion (CTE) between the chip 2, substrate 1, and heat sink 3, the product is highly susceptible to warping under high-temperature soldering conditions. Figure 3 As shown. This warping leads to uneven welding gaps. When the indium solder melts (approximately 220~240℃), due to differences in gravity and surface tension, the solder will flow and accumulate in areas with larger gaps or lower positions, causing solder loss or voids in other areas. Solder loss and accumulation can lead to a surge in thermal resistance and heat dissipation failure, or even cause solder joint cracking and poor soldering. Summary of the Invention

[0003] This application provides at least one packaging method and packaging structure. The packaging method can actively resist warping stress, ensure uniform spreading of molten solder, and avoid indium loss or accumulation in the welding area due to warping, thereby ensuring the welding effect between the heat sink and the chip.

[0004] In a first aspect, embodiments of this application provide an encapsulation method, including: A heat sink is provided, wherein the welding area of ​​the heat sink is provided with a first magnetic structure; An indium-based solder is provided, wherein a second magnetic structure is bonded to the indium-based solder; The indium-based solder is placed between the chip and the heat sink, and then heated and soldered. During the heating process, a magnetic attraction force is generated between the first magnetic structure and the second magnetic structure to overcome the warping stress caused by the mismatch of thermal expansion coefficients between the heat sink and the chip, and to constrain the flow range of the molten indium solder.

[0005] In one alternative embodiment, the first magnetic structure and the second magnetic structure have opposite magnetic poles to create an attractive magnetic field between them.

[0006] In one optional embodiment, both the first magnetic structure and the second magnetic structure are high-temperature resistant magnetic materials capable of maintaining magnetism at the peak temperature of heating and welding.

[0007] In one alternative embodiment, the first magnetic structure is a magnetic material layer formed in the welding area of ​​the heat sink.

[0008] In one optional embodiment, the method for manufacturing the heat sink includes: Provide coatings containing a first magnetic material; A welding area is positioned on the surface of the heat sink substrate, and the coating is sprayed or printed on the surface of the welding area to form a first magnetic structure.

[0009] In one alternative implementation, after forming the first magnetic structure, the method further includes: A wetting layer is formed on the surface of the first magnetic structure.

[0010] In one alternative embodiment, the second magnetic structure is a magnetic material dispersed in the indium-based solder.

[0011] In one optional embodiment, the method for preparing the indium-based solder includes: Provide a second magnetic material; A portion of the second magnetic material is uniformly mixed with indium powder and then pressed to obtain a solder blank. The solder blank is preheated and softened; The remaining second magnetic material is sprayed onto one surface of the softened solder blank.

[0012] In one alternative embodiment, the amount of the second magnetic material sprayed is half of the total amount.

[0013] Secondly, embodiments of this application also provide a packaging structure, which is prepared using the packaging method described above.

[0014] The above-mentioned technical solution of this application has the following beneficial technical effects: The packaging method of this application optimizes the heat sink and indium solder to actively resist warping stress, ensure uniform spreading of molten solder, and prevent indium loss or accumulation in the soldering area due to warping, thereby ensuring the soldering effect between the heat sink and the chip. Specifically, the method sets a first magnetic structure in the soldering area of ​​the heat sink and combines a second magnetic structure on the indium-based solder. Utilizing the magnetic attraction force generated by the two during the heating and soldering process, the solder can be tightly adsorbed onto the soldering area of ​​the heat sink and the chip, preventing solder displacement. This effectively overcomes warping stress caused by mismatch in the thermal expansion coefficients of the materials, constrains the flow range of the molten indium solder under warping extrusion, prevents disorderly loss and accumulation of solder in areas with larger or lower gaps, significantly reduces the risk of thermal resistance spikes, void formation, and solder joint cracking, and greatly improves the heat dissipation reliability and yield of the packaging structure.

[0015] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. These drawings are incorporated in and constitute a part of this specification. They illustrate embodiments conforming to this application and, together with the specification, serve to explain the technical solutions of this application. It should be understood that the following drawings only show some embodiments of this application and should not be considered as limiting the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 A flowchart of an encapsulation method provided in an embodiment of this application is shown; Figure 2 This illustration shows a schematic diagram of a packaging structure provided in an embodiment of this application; Figure 3 A schematic diagram of indium solder welding for a prior art packaging structure is shown; In the diagram: 1. Substrate; 2. Chip; 3. Heat sink; 4. First magnetic structure; 5. Indium-based solder; 6. Second magnetic structure. Detailed Implementation

[0018] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the present application.

[0019] The embodiments of this application will now be described in detail. Examples of these embodiments are illustrated 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 this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0020] The terms "first" and "second" in the specification and claims of this application may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise stated, "multiple" means two or more. Furthermore, "and / or" in the specification and claims indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0021] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application 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 this application.

[0022] In the description of this application, it should be noted that, unless otherwise expressly 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 between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0023] refer to Figure 1 This application provides a packaging method, which includes the following steps: S101, A heat sink is provided, wherein the welding area of ​​the heat sink is provided with a first magnetic structure; S102. Provide an indium-based solder, on which a second magnetic structure is bonded; S103. Place the indium-based solder between the chip and the heat sink and perform heat soldering (such as reflow soldering). During the heating process, a magnetic attraction force is generated between the first magnetic structure and the second magnetic structure to overcome the warping stress caused by the mismatch of thermal expansion coefficients between the heat sink and the chip, and to constrain the flow range of the molten indium-based solder.

[0024] This method optimizes the heat sink and indium solder to actively resist warping stress, ensure uniform solder spread, and prevent indium loss or accumulation in the soldering area due to warping, thereby guaranteeing the soldering effect between the heat sink and the chip. Specifically, this method uses a first magnetic structure in the soldering area of ​​the heat sink and a second magnetic structure combined with the indium-based solder. The magnetic attraction generated during the heating and soldering process tightly adheres the solder to the soldering area between the heat sink and the chip, preventing solder displacement. This effectively overcomes warping stress caused by mismatched thermal expansion coefficients, constrains the flow range of the molten indium solder under warping pressure, and prevents disordered loss and accumulation of solder in areas with larger or lower gaps. This significantly reduces the risk of thermal resistance spikes, void formation, and solder joint cracking, greatly improving the heat dissipation reliability and yield of the package structure.

[0025] It should be noted that in practical applications, chips are typically mounted on a substrate, and the heat sink is not only soldered to the chip using indium-based solder, but also fixed to the substrate using adhesives or other methods. Since the connections between the chip and the substrate, and between the heat sink and the substrate, are conventional prior art in this field and not the core improvements of this application, they will not be elaborated upon here.

[0026] In some embodiments, the magnetic poles of the first and second magnetic structures are opposite in polarity to create an attractive magnetic field between them. That is, the opposing surfaces of the first and second magnetic structures are configured as opposite magnetic poles. For example, along the bonding direction between the heat sink and the chip, the end of the first magnetic structure near the chip is the N pole, and the end of the second magnetic structure near the heat sink is the S pole. When the heat sink is placed on the chip, the N pole of the first magnetic structure and the S pole of the second magnetic structure face each other and attract each other. The resulting vertical pull (magnetic field force) can adsorb the molten solder, thereby constraining the flow range of the molten solder under warping and extrusion.

[0027] In some embodiments, both the first magnetic structure and the second magnetic structure are high-temperature resistant magnetic materials capable of maintaining magnetism at the peak heating and welding temperature. That is, both the first magnetic structure and the second magnetic structure are high-temperature resistant magnetic materials, and their Curie temperatures are higher than the peak heating and welding temperature. This prevents the first magnetic structure and the second magnetic structure from losing their magnetism due to excessively high heating and welding temperatures during the welding process, thus avoiding the loss of their effect in restraining the flow of molten indium solder.

[0028] It should be noted that in the reflow soldering process of FCBGA packaging, the melting temperature of indium-based solder is approximately 220~240℃ (depending on the ratio of indium silver or indium tin alloy), and the peak temperature may momentarily exceed 250℃. Ordinary neodymium iron boron magnets will experience irreversible magnetic decay at this temperature. Therefore, this embodiment can use samarium cobalt or iron cobalt vanadium as the first and second magnetic structures. The Curie temperature of these materials is much higher than the soldering peak temperature, ensuring a stable magnetic effect throughout the reflow soldering process.

[0029] In some embodiments, the first magnetic structure is a layer of magnetic material formed in the welding area of ​​the heat sink.

[0030] In this embodiment, a magnetic material layer design is adopted, which can ensure that the first magnetic structure provides sufficient adsorption force while having an extremely thin thickness, meeting the requirements of miniaturized packaging.

[0031] It should be noted that the magnitude of the magnetic adsorption force of the first magnetic structure is related to the thickness of the magnetic material layer and the type of magnetic material therein. In practical applications, the magnitude of the magnetic adsorption force can be precisely adjusted by selecting the thickness of the magnetic material layer or the type of magnetic material.

[0032] In some embodiments, the method of manufacturing a heat sink includes: A coating containing a first magnetic material is provided. For example, the coating may be made by mixing a high-temperature resistant magnetic powder (such as samarium cobalt powder or iron cobalt vanadium powder, with a particle size of 1-5 μm) with a high-temperature resistant resin binder.

[0033] A welding area is positioned on the surface of the heat sink substrate (usually copper or aluminum), and paint is sprayed or printed on the surface of the welding area to form the first magnetic structure.

[0034] In this embodiment, by employing a spraying or printing process to precisely coat the coating containing the first magnetic material onto the welding area, the patterning and customization of the magnetic material layer can be achieved, ensuring precise alignment between the magnetic structure and the welding area. Furthermore, compared to magnetron sputtering or electroplating, the printing / spraying process can significantly reduce equipment costs and allows for flexible adjustment of the thickness and pattern shape of the magnetic layer to adapt to the stress distribution of chips of different sizes.

[0035] It should be noted that in practical applications, the thickness of the magnetic material layer can be precisely controlled by adjusting parameters such as the thickness of the spraying or printing screen and the air pressure, thereby achieving customized adjustment of the magnetic adsorption force to match the warping stress of chips of different sizes.

[0036] It should also be noted that in practical applications, the particle size of the first magnetic material should be smaller than the thickness of the solder layer (i.e., the gap between the heat sink and the chip) to avoid damaging the chip due to excessive particle size.

[0037] In some embodiments, prior to forming the first magnetic structure, the method further includes forming a barrier layer on the surface of the welding area. For example, the barrier layer may be a nickel plating layer formed by electroplating.

[0038] In this embodiment, a barrier layer is formed on the surface of the welding area to prevent copper atoms in the heat sink substrate from diffusing to the surface and oxidizing under high temperature conditions, thereby ensuring the conductivity of the welding area and the reliability of the welding.

[0039] In some embodiments, after forming the first magnetic structure, the method further includes forming a wetting layer on the surface of the first magnetic structure. For example, the wetting layer may be a gold plating layer formed by electroplating.

[0040] In this embodiment, forming a wetting layer on the surface of the magnetic material layer can effectively improve the interfacial bonding force between the magnetic material and the indium-based solder, prevent welding defects (such as solder rejection, cold solder joints, etc.) caused by the poor wettability of the magnetic material itself, and thus effectively improve the overall metallurgical connection quality of the package.

[0041] It should be noted that, since magnetic materials typically have poor wettability, direct soldering can easily lead to incomplete soldering. The wetting layer serves two purposes: firstly, it protects the magnetic layer from oxidation, and secondly, it acts as a "metallurgical bridge," promoting the spread of indium-based solder on the surface of the magnetic layer and ensuring that the magnetic attraction force can be effectively transmitted.

[0042] In some embodiments, before forming the wetting layer, the method further includes forming a bonding layer on the surface of the first magnetic structure. That is, a bonding layer is added between the magnetic material layer and the wetting layer to improve the bonding strength between the first magnetic structure and the wetting layer. For example, the bonding layer may be a titanium film formed by sputtering.

[0043] In this embodiment, an additional bonding layer is added between the magnetic material layer and the wetting layer, which can play a mechanical anchoring role, significantly improve the bonding strength between the magnetic material layer and the wetting layer, and effectively prevent the wetting layer from peeling off under the high temperature impact of reflow soldering and the pulling force of magnetic adsorption, thereby helping to ensure the long-term reliability of the packaging structure.

[0044] In other embodiments, the first magnetic structure may also employ or include magnetic blocks embedded within the substrate, magnetic microstructures arranged in an array on the surface of the substrate, or magnetic films attached to the surface of the substrate.

[0045] In some embodiments, the second magnetic structure is a magnetic material dispersed in an indium-based solder.

[0046] In this embodiment, a magnetic material dispersed in the indium-based solder is used as the second magnetic structure. This allows the second magnetic structure to be directly mixed into the indium powder as a filler to form the indium-based solder. This simplifies the packaging process and does not increase the thickness of the solder, meeting the miniaturization requirements of advanced packaging. Furthermore, this dispersed design ensures that the magnetic attraction force is uniformly distributed throughout the solder melting and spreading process, thereby providing comprehensive and thorough constraint on the solder flow at the entire welding interface.

[0047] It should be noted that the amount of magnetic material incorporated is related to the strength of its magnetic adsorption force. In practical applications, the strength of the magnetic adsorption force can be precisely adjusted by controlling the amount of material incorporated.

[0048] In some embodiments, a method for preparing indium-based solder includes: Provide a second magnetic material (such as samarium cobalt powder or iron cobalt vanadium powder, with a particle size of 1-5 μm).

[0049] A portion of the second magnetic material is uniformly mixed with indium powder and then pressed to obtain a solder preform. For example, the uniformly mixed material is poured into a mold and pressed in the mold to obtain a solder preform. The internally mixed magnetic material increases the magnetic permeability of the solder body, making it more easily attracted by an external magnetic field.

[0050] The solder blank is preheated to soften it. For example, the preheating temperature is set below the recrystallization temperature of indium-based solder but within a range sufficient to cause plastic softening (e.g., 80°C-100°C). The softened solder surface has a slightly tacky quality, which is beneficial for the adhesion of subsequent surface magnetic materials.

[0051] The remaining second magnetic material is sprayed onto one surface of the softened solder blank. For example, the remaining second magnetic material is sprayed onto one surface of the solder blank, which is the top surface of the indium-based solder during soldering, by electrostatic spraying or dry spraying.

[0052] In this embodiment, the second magnetic material mixed into the indium powder can ensure the overall magnetic foundation of the solder body. The second magnetic material sprayed on the top surface of the solder blank can settle downwards during welding, so that the second magnetic material mixed into the indium powder can be kept as uniformly distributed as possible, which helps to ensure the adsorption effect of the first magnetic structure on the molten solder.

[0053] It should be noted that, in the molten state, the magnetic material on the top of the solder will precipitate to the bottom of the solder, while the magnetic material sprayed on the top surface of the solder will precipitate downwards to the top of the solder. This ensures that magnetic material is dispersed in both the top and bottom of the solder, which helps to guarantee the adsorption effect of the first magnetic structure on the molten solder.

[0054] It should also be noted that in practical applications, after the remaining magnetic material is sprayed onto the softened solder blank surface, the solder blank needs to undergo hot rolling, deoxidation, cold rolling, low-temperature annealing, and cutting to obtain the required indium-based solder. The annealing temperature must be lower than the melting point of indium and the Curie temperature of the magnetic material.

[0055] In some embodiments, the amount of the second magnetic material sprayed is half of the total amount. That is, 50% of the second magnetic material is mixed with indium powder and pressed to form a solder blank, and the remaining 50% of the second magnetic material is sprayed onto one surface of the solder blank.

[0056] In this embodiment, the amount of the second magnetic material sprayed on the surface is limited to half of the total amount, which ensures that half of the magnetic material is dispersed in both the upper and lower parts of the solder, thereby ensuring the adsorption effect of the first magnetic structure on the molten solder.

[0057] In other embodiments, the second magnetic structure may also employ or include magnetic blocks embedded within the substrate, magnetic microstructures arranged in an array on the surface of the substrate, magnetic coatings applied to the surface of the substrate, or magnetic films attached to the surface of the substrate.

[0058] refer to Figure 2 This application also provides a packaging structure, fabricated using the packaging method described above. Specifically, the packaging structure includes a substrate 1, a chip 2, and a heat sink 3. The chip 2 is disposed on the substrate 1, and the heat sink 3 is disposed on the substrate 1 and covers the chip 2. A first magnetic structure 4 is provided on the surface of the heat sink 3 facing the welding area of ​​the chip 2. The heat sink 3 and the chip 2 are welded together by indium-based solder 5 bonded with a second magnetic structure 6. During the heating and welding process, a magnetic attraction force can be generated between the first magnetic structure 4 and the second magnetic structure 6. This magnetic attraction force can tightly attract the molten solder to the welding area of ​​the heat sink 3 and the chip 2, preventing solder displacement. Figure 3 As shown, this effectively overcomes the warping stress caused by the mismatch of the thermal expansion coefficients of the materials, constrains the flow range of molten indium solder under warping extrusion, prevents the disorderly loss and accumulation of solder in areas with larger or lower gaps, significantly reduces the risk of thermal resistance spikes, void formation and solder joint cracking, and greatly improves the heat dissipation reliability and yield of the packaging structure.

[0059] One or more embodiments in this specification are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments in this specification should be included within the protection scope of this application.

[0060] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A packaging method, characterized in that, include: A heat sink is provided, wherein the welding area of ​​the heat sink is provided with a first magnetic structure; An indium-based solder is provided, wherein a second magnetic structure is bonded to the indium-based solder; The indium-based solder is placed between the chip and the heat sink, and then heated and soldered. During the heating process, a magnetic attraction force is generated between the first magnetic structure and the second magnetic structure to overcome the warping stress caused by the mismatch of thermal expansion coefficients between the heat sink and the chip, and to constrain the flow range of the molten indium solder.

2. The method according to claim 1, characterized in that, The first magnetic structure and the second magnetic structure have opposite magnetic poles, so as to form a magnetic field force that attracts each other between them.

3. The method according to claim 1, characterized in that, Both the first magnetic structure and the second magnetic structure are high-temperature resistant magnetic materials that can maintain magnetism at the peak temperature of heating and welding.

4. The method according to claim 1, characterized in that, The first magnetic structure is a magnetic material layer formed in the welding area of ​​the heat sink.

5. The method according to claim 4, characterized in that, The method for manufacturing the heat sink cover includes: Provide coatings containing a first magnetic material; A welding area is positioned on the surface of the heat sink substrate, and the coating is sprayed or printed on the surface of the welding area to form a first magnetic structure.

6. The method according to claim 5, characterized in that, After forming the first magnetic structure, the method further includes: A wetting layer is formed on the surface of the first magnetic structure.

7. The method according to claim 1, characterized in that, The second magnetic structure is a magnetic material dispersed in the indium-based solder.

8. The method according to claim 7, characterized in that, The method for preparing the indium-based solder includes: Provide a second magnetic material; A portion of the second magnetic material is uniformly mixed with indium powder and then pressed to obtain a solder blank. The solder blank is preheated and softened; The remaining second magnetic material is sprayed onto one surface of the softened solder blank.

9. The method according to claim 8, characterized in that, The amount of the second magnetic material sprayed is half of the total amount.

10. A packaging structure, characterized in that, It is prepared by the encapsulation method described in any one of claims 1-9.

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