A cover plate mounting method for improving wafer warpage

Abstract

The application discloses a cover plate mounting method for improving wafer warping, which comprises the following steps: placing the warped wafer on a heating platform, and fixing the wafer on the heating platform by adsorption after heating and flattening the wafer; providing a cover plate, coating AD glue on one side of the cover plate, and keeping the AD glue in a flowing state; turning over the cover plate, so that the side of the cover plate with the AD glue faces the flattened wafer, and aligning and mounting the cover plate and the wafer in a heating state; the AD glue forms a gradually solidified glue body under the action of the heat of the wafer; and rapidly solidifying the mounted wafer and cover plate, and integrally heating the wafer and the cover plate, so that the AD glue is completely solidified, thereby forming a stable structure of the mounted wafer and cover plate. The warped wafer is heated and flattened first, then the AD glue in a flowing state is spot-coated on the cover plate, and the AD glue is gradually solidified by the heat of the wafer during mounting, thereby forming a stable packaging structure, and the product yield is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of cover plate mounting technology, and more specifically to a cover plate mounting method for improving wafer warpage. Background Technology

[0002] In semiconductor wafer-level packaging processes, cover plate mounting is a key step used to protect the chip, enhance the strength of the package structure, and improve heat dissipation performance.

[0003] Current cover plate mounting methods involve applying adhesive (AD) to the warped wafer surface, then directly bonding the cover plate to the wafer, followed by rapid curing. However, in actual production, wafers naturally warp, leading to uneven stress during cover plate bonding, increasing the risk of wafer cracking, and thus reducing packaging yield. Furthermore, if the wafer is preheated and leveled, applying the adhesive directly while the wafer is at a high temperature causes the AD adhesive to cure instantly, making it difficult to form a uniform adhesive layer. This results in insufficient bonding strength and a higher risk of voids. Summary of the Invention

[0004] To overcome the above shortcomings, the purpose of this invention is to provide a cover plate mounting method to improve wafer warpage. First, the warped wafer is heated and leveled, and then flowing AD adhesive is applied to the cover plate. During bonding, the heat of the wafer causes the AD adhesive to gradually solidify, thereby forming a stable packaging structure and effectively improving product yield.

[0005] Technical solution: This invention discloses a cover plate mounting method for improving wafer warpage, comprising the following steps: The warped wafer is placed on a heating platform, and after the wafer is heated and flattened, it is fixed on the heating platform by vacuum adsorption. A cover plate is provided, and an AD adhesive is coated on one side of the cover plate, the area of ​​the AD adhesive being the same as the area of ​​the wafer, and the AD adhesive being kept in a flowing state; Flip the cover plate so that the side of the cover plate with the AD adhesive faces the flattened wafer, and align and attach the cover plate and the heated wafer, so that the AD adhesive forms a gradually curing colloid under the heat of the wafer; The laminated wafer and cover plate are rapidly cured, and the wafer and cover plate are heated as a whole to completely cure the AD adhesive, thereby forming a stable structure in which the cover plate and wafer are laminated.

[0006] Furthermore, the TG point of the wafer is 125°C, the heating and leveling temperature of the wafer is 0-10°C higher than the TG point, and the temperature of the heating platform is 125-135°C.

[0007] Furthermore, when the wafer is placed on the heating platform, a negative pressure adsorption method is used to keep the wafer flat and fixed under heating conditions.

[0008] Furthermore, when applying adhesive to the cover plate, the AD adhesive is applied to the surface of the cover plate at room temperature, thereby keeping the AD adhesive in a flowing state.

[0009] Furthermore, pressure is continuously applied to the cover plate during rapid curing of the wafer and the cover plate, with a curing pressure of 5-20 psi.

[0010] Furthermore, the heating time of the wafer placed on the heating platform is 30-300 seconds.

[0011] Furthermore, the cover plate is made of any one of glass, silicon wafer or ceramic.

[0012] Furthermore, the cover plate is flipped by a flipping mechanism and aligned and bonded with the wafer.

[0013] The beneficial effects of this invention are as follows: This invention first places the naturally warped wafer on a heating platform and heats it to flatten it, effectively reducing wafer warping and the risk of wafer cracking during mounting. At the same time, a fluid AD adhesive is coated on the surface of the cover plate, and then the cover plate is flipped and bonded to the heated wafer. This allows the AD adhesive to gradually cure using the heat of the wafer after contacting it, avoiding the problem of AD adhesive being directly applied to the wafer and instantly curing, which is not conducive to mounting.

[0014] In this invention, the AD adhesive gradually cures and fills the gap between the cover plate and the wafer during the bonding process, effectively reducing defects such as voids, local glue overflow, and uneven adhesive layer, thereby improving the product yield of the packaging structure. Compared with traditional mounting methods, it takes into account wafer leveling, adhesive flow and mounting reliability, and is more suitable for packaging products with high warp wafers. Attached Figure Description

[0015] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Furthermore, the shapes and proportions of the components in the drawings are merely illustrative to aid in understanding the invention and are not intended to specifically limit the shapes and proportions of the components. Those skilled in the art, guided by the teachings of this invention, can select various possible shapes and proportions to implement the invention according to specific circumstances. In the drawings: Figure 1 This is a schematic diagram of a wafer placed on a heating platform according to the present invention; Figure 2 This is a schematic diagram of the wafer being heated and leveled on a heating platform according to the present invention; Figure 3 This is a schematic diagram of the AD adhesive being applied to the cover plate according to the present invention; Figure 4 This is a schematic diagram of the AD adhesive being applied to the cover plate according to the present invention; Figure 5 This is a schematic diagram of the cover plate and wafer mounting process described in this invention; Figure 6 This is a schematic diagram showing the completed mounting of the cover plate and wafer according to the present invention.

[0016] In the diagram: 1. Heating platform; 2. Wafer; 3. Cover plate; 4. Adhesive. Detailed Implementation

[0017] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0018] In the description of this invention, it should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for 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. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. The embodiments of this invention will now be described according to its overall structure.

[0019] like Figures 1 to 6 As shown, this invention discloses a cover plate mounting method for improving wafer warpage, comprising the following steps: The warped wafer is placed on a heating platform, and after the wafer is heated and flattened, it is fixed on the heating platform by vacuum adsorption. A cover plate is provided, and an AD adhesive is coated on one side of the cover plate, the area of ​​the AD adhesive being the same as the area of ​​the wafer, and the AD adhesive being kept in a flowing state; Flip the cover plate so that the side of the cover plate with the AD adhesive faces the flattened wafer, and align and attach the cover plate and the heated wafer, so that the AD adhesive forms a gradually curing colloid under the heat of the wafer; The laminated wafer and cover plate are rapidly cured, and the wafer and cover plate are heated as a whole to completely cure the AD adhesive, thereby forming a stable structure in which the cover plate and wafer are laminated.

[0020] Using the above method, the wafer at room temperature is first placed on a heating platform. Since the wafer itself has natural warping, after heating the wafer to a certain temperature by the heating platform, the wafer is flattened and fixed on the heating platform by vacuum adsorption. This prevents the wafer from moving or returning to its warped state, and ensures that there will be no errors in the subsequent bonding operation.

[0021] Then, AD adhesive is applied to one side of the cover plate, and the AD adhesive is in a flowing state at this time. Since the cover plate itself is not heated, the AD adhesive on the cover plate will not cure instantly. Otherwise, the AD adhesive would cure instantly when exposed to high temperature, and it would not be able to form a uniform adhesive layer. The AD adhesive maintains optimal viscosity and fluidity at room temperature, and the area of ​​AD adhesive applied to the cover plate is the same as the area of ​​the wafer surface, to ensure that the AD adhesive can completely cover the surface of the wafer when the cover plate and the wafer are bonded.

[0022] After the cover plate with the AD adhesive side is flipped over to face the wafer and aligned and bonded, the heat from the wafer is transferred to the AD adhesive. Under the high temperature effect of the residual heat of the wafer, the AD adhesive gradually transforms into a gel. That is, the AD adhesive changes from a fluid colloid to a viscous gel, thus bonding the cover plate and the wafer on both sides of the AD adhesive. This is used to suppress the springback deformation of the wafer after it leaves the heating platform, keeping the wafer in a flat state.

[0023] Furthermore, during the gradual curing of the AD adhesive, the bonded cover plate and wafer undergo rapid curing. This involves heating and applying pressure to both the cover plate and wafer while maintaining wafer flatness. During this rapid curing process, the gel-state AD adhesive transforms into a fully cured colloid. In this process, the AD adhesive fully fills the interface between the cover plate and wafer, reducing air bubbles and gaps. The AD adhesive also utilizes the wafer's own high temperature for curing, effectively suppressing wafer springback.

[0024] The method described in this invention first coats the AD adhesive onto a cover plate. After the cover plate and the wafer are bonded together, the high temperature of the wafer is used to transfer the AD adhesive to the flowing AD adhesive, causing the AD adhesive to gradually solidify. This reduces the warping of the wafer caused by stress or temperature changes and effectively improves the cracking problem caused by direct bonding, significantly improving the product yield.

[0025] Furthermore, the TG point of the wafer is 125°C, which is the glass transition temperature of the wafer. The temperature for heating and leveling the wafer needs to be 0-10°C higher than the TG point, meaning the heating platform temperature is controlled within the range of 125-135°C, preferably 130°C. When the heating platform softens the wafer, the surface material of the warped wafer begins to soften after reaching the TG point, and the wafer becomes malleable and is placed flat on the heating platform. During the softening process, a cover plate coated with AD adhesive is bonded to the wafer. Utilizing the residual heat of the wafer, the AD adhesive on the cover plate gradually gels upon contact with the wafer, forming an adhesive layer that inhibits wafer springback and warping.

[0026] Preferably, the heating platform also includes a negative pressure adsorption structure. After the wafer is heated by the heating platform, it softens and adheres to the surface of the heating platform. The softened wafer and the heating platform maintain good contact. At this time, the wafer is stably fixed on the heating platform by the negative pressure adsorption structure, so that the wafer is stably positioned on the heating platform in a softened state. This also avoids the problem of warping caused by local temperature differences, which may affect subsequent bonding operations.

[0027] Because the wafer is adsorbed onto the heating platform by negative pressure, when the cover plate and the wafer are bonded together, the flowing AD adhesive comes into contact with the surface of the wafer. The flat wafer surface is conducive to the uniform spread of AD adhesive, thereby reducing the thickness difference of AD adhesive in some areas and the generation of bubbles.

[0028] In this application, when dispensing the cover plate, the AD adhesive is applied to the surface of the cover plate at room temperature, while still remaining in a fluid state. The AD adhesive exhibits good fluidity at room temperature, allowing it to spread evenly across the cover plate surface and ensuring a uniform thickness. Compared to directly dispensing the AD adhesive onto the wafer, the viscosity of the AD adhesive increases rapidly upon heating, and the curing speed also accelerates, which is detrimental to the alignment and bonding of the cover plate and the wafer, and makes it impossible to ensure a uniform thickness of the AD adhesive.

[0029] Understandably, the AD adhesive remains in a fluid state before bonding. Its curing process does not begin from the dispensing stage. Instead, after the AD adhesive comes into contact with the heated wafer, it gradually undergoes a curing reaction after being heated by the wafer, transforming into a viscoelastic gel. Subsequently, it enters a rapid curing stage, heating the overall structure of the bonded wafer and cover plate to ensure complete curing of the AD adhesive and ultimately forming a stable bonded structure.

[0030] Furthermore, during the rapid curing of the wafer and cover plate, continuous pressure is applied to the cover plate at a curing pressure of 5-20 psi. After the cover plate is bonded to the heated and leveled wafer, the AD adhesive between them, although having formed a preliminary gel structure under the residual heat of the wafer, is still in an incompletely cured state. At this stage, the adhesive layer still possesses a certain degree of fluidity and deformation capability. Therefore, continuous pressure is applied to the cover plate during the curing process to eliminate residual stress inside the wafer, prevent wafer springback, and allow the cover plate to act as a rigid support structure, continuously constraining the wafer and ensuring that the wafer remains in its leveled state until the AD adhesive is fully cured.

[0031] Preferably, the heating time for the wafer placed on the heating platform is 30–300 seconds. During the heating and leveling process, the warped wafer needs to be heated for a certain period to ensure that heat is fully transferred to the interior of the wafer, making the overall temperature of the wafer more uniform. Controlling the heating time within the range of 30–300 seconds also creates suitable heating conditions for the subsequent pre-curing of the AD adhesive. The heated wafer has a relatively uniform and stable temperature. When the cover plate coated with AD adhesive is bonded to the wafer, the heat carried by the wafer can be continuously transferred to the AD adhesive, causing the AD adhesive to gradually transform from a flowing state to a gel state, thereby forming an initial constraint on the wafer's springback.

[0032] In this application, the cover plate is made of any one of glass, silicon wafers, or ceramics. Glass, silicon wafers, or ceramics possess high rigidity, thermal stability, and good dimensional stability, providing reliable mechanical support during wafer capping. Furthermore, these materials ensure that the cover plate itself does not deform due to temperature changes or external pressure during wafer heating and leveling, AD adhesive pre-curing, and rapid curing, thereby guaranteeing the flatness and bonding accuracy of the wafer during the bonding process. Simultaneously, these materials can withstand the thermal and compressive stresses during rapid curing, are less prone to warping or cracking, maintain uniform contact between the cover plate and the wafer interface, and promote the formation of a stable and uniform cured layer of AD adhesive at the interface.

[0033] Furthermore, the cover plate is flipped using a flipping mechanism and aligned with the wafer. Flipping the cover plate using the flipping mechanism ensures that the side coated with the flowing AD adhesive faces the heated, leveled, and fixed wafer surface. This ensures that the cover plate remains stable during the flipping process and avoids tilting, vibration, and impact caused by manual or mechanical handling, thereby protecting the AD adhesive from disturbance and ensuring its uniformity.

[0034] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A cover plate mounting method for improving wafer warpage, characterized in that, Includes the following steps: The warped wafer is placed on a heating platform, and after the wafer is heated and flattened, it is fixed on the heating platform by vacuum adsorption. A cover plate is provided, and an AD adhesive is coated on one side of the cover plate, the area of ​​the AD adhesive being the same as the area of ​​the wafer, and the AD adhesive being kept in a flowing state; Flip the cover plate so that the side of the cover plate with the AD adhesive faces the flattened wafer, and align and attach the cover plate and the heated wafer, so that the AD adhesive forms a gradually curing colloid under the heat of the wafer; The laminated wafer and cover plate are rapidly cured, and the wafer and cover plate are heated as a whole to completely cure the AD adhesive, thereby forming a stable structure in which the cover plate and wafer are laminated.

2. The cover plate mounting method for improving wafer warpage according to claim 1, characterized in that, The TG point of the wafer is 125°C, the heating and leveling temperature of the wafer is 0-10°C higher than the TG point, and the temperature of the heating platform is 125-135°C.

3. The cover plate mounting method for improving wafer warpage according to claim 1, characterized in that, When the wafer is placed on the heating platform, negative pressure adsorption is used to keep the wafer flat and fixed under heating conditions.

4. The cover plate mounting method for improving wafer warpage according to claim 1, characterized in that, When applying adhesive to the cover plate, the AD adhesive is applied to the surface of the cover plate at room temperature, thereby keeping the AD adhesive in a flowing state.

5. The cover plate mounting method for improving wafer warpage according to claim 1, characterized in that, Pressure is continuously applied to the cover plate during rapid curing of the wafer and the cover plate, with a curing pressure of 5-20 psi.

6. The cover plate mounting method for improving wafer warpage according to claim 1, characterized in that, The wafer is placed on the heating platform and heated for 30-300 seconds.

7. The cover plate mounting method for improving wafer warpage according to claim 1, characterized in that, The cover plate is made of any one of glass, silicon wafer or ceramic.

8. The cover plate mounting method for improving wafer warpage according to claim 1, characterized in that, The cover plate is flipped by a flipping mechanism and aligned and bonded to the wafer.

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