A method for manufacturing a multi-chip co-planar tiled structure for an image sensor

Abstract

The application belongs to the field of sensor packaging process, and particularly relates to a manufacturing method of a multi-chip coplanar splicing structure for an image sensor, and aims to solve the problem of poor flatness of the multi-chip coplanar splicing structure. The application adopts a high-rigidity adapter plate as a base surface, optimizes the die-bonding area into a uniform plane, and uses the positioning balls of the adapter plate for coplanar positioning. The application uses the one-time chip mounting mode, ensures that all the chips are uniformly stressed during the picking, mounting and pressing processes, and can effectively improve the coplanarity of the multi-chip coplanar splicing and reduce errors.

Description

Technical Field

[0001] This invention belongs to the field of sensor packaging technology, and specifically relates to a method for fabricating a multi-chip coplanar splicing structure for image sensors. Background Technology

[0002] As image sensors are used more and more widely in various fields, the pixel size of image sensors continues to shrink, from the initial pixel size of 2.5μm to the current pixel size of 1.4μm for mobile phone camera sensors. The market demand for pixel size is as small as 1.1μm, or even 0.65μm.

[0003] As application scenarios become increasingly complex and diverse, single image sensors still struggle to meet the demands for high pixel counts, wide field of view, and high performance in certain fields. Furthermore, simply increasing the pixel count of a single chip places extremely high demands on the yield rate of the chip fabrication process, leading to an exponential increase in the cost per chip. Therefore, packaging multiple image sensors together—achieving higher pixel density and a wider field of view by combining multiple bare image sensor chips—to form a larger-scale, higher-performance image sensor array, thereby meeting the needs of high-performance image acquisition and processing, has become an effective way to solve this problem.

[0004] One of the key technologies in image sensor stitching and packaging is the packaging process, which directly affects the integration, stability, and reliability of the image sensor array. The goal is to achieve a doubling of pixel count and expand the field of view while reducing the packaging size. However, due to the large size of image sensor chips, their imaging quality is highly dependent on the flatness of the chip surface, requiring extremely high packaging precision. Therefore, there is an urgent need for a method for a highly coplanar multi-chip coplanar stitching structure for image sensors.

[0005] The main problems currently existing in the manufacturing process of multi-chip coplanar stitching structures used in image sensors in the industry are:

[0006] (1) During the fabrication of multi-chip coplanar splicing structures, the flatness is poor due to the large area of ​​the conventional ceramic shell bonding area, which is generally between 20μm and 70μm. However, the common bonding method uses liquid adhesive, which does not significantly restrict the flatness of the bonding. With conventional bonding methods, the bonding flatness of a single chip is between 50μm and 120μm, while the coplanarity of multiple chips is between 50μm and 170μm.

[0007] (2) In the fabrication of multi-chip coplanar splicing structures, the common method for mounting multiple products is to bond each chip individually using a single pick-and-place head and a pressure head. Therefore, the parameters of each chip after bonding are independent, and the flatness of each chip is controllable. However, the coplanarity between multiple chips is controlled by the repeatability and consistency of the mounting equipment. The error of this control method is approximately between 20μm and 80μm. Summary of the Invention

[0008] To address the aforementioned problem in the prior art, namely the poor flatness of multi-chip coplanar splicing structures, this invention provides a method for fabricating a multi-chip coplanar splicing structure for image sensors.

[0009] The technical solution of the present invention includes:

[0010] A method for fabricating a multi-chip coplanar stitching structure for an image sensor, characterized by the following steps:

[0011] Step (1): Using adhesive material (5), a grid array of adhesive blocks is formed on the mounting area (2) by screen printing.

[0012] Step (2): Use the adapter plate special suction tip (7) to place the adapter plate (6) on the processed mounting area (2);

[0013] Step (3): Place the limiting piece (8) above the adapter plate (6) and cure it according to the curing index requirements of the adhesive material (5);

[0014] Step (4): Use low-viscosity adhesive (9) to fill the gap between the adapter plate (6) and the mounting area (2). Fill the gap between the adapter plate (6) and the mounting area (2) with low-viscosity adhesive (9).

[0015] Step (5): Place the limiting piece (8) above the adapter plate (6), select a temperature between the curing temperature of the low viscosity adhesive (9) and the melting point of the positioning ball on the front of the adapter plate (6) for curing, and use the gravity of the limiting piece (8) to control the coplanarity of the upper surface of the positioning ball on the front of the adapter plate (6).

[0016] Step (6): Select UV fast-curing adhesive (10), apply adhesive to the four corners of the chip position on the upper surface of the adapter board (6), use a multi-chip special suction head (12) to pick up multiple chips (11) at the same time and place them in the set position, apply pressure at the same time to fix the chips, and use UV irradiation to make the chips fast-curing.

[0017] Step (7): Use low-viscosity adhesive (9) to fill the gap between the adapter board (6) and the chip (11). Fill the gap between the adapter board (6) and the chip (11) with low-viscosity adhesive (9).

[0018] Step (8): Curing is carried out according to the curing index requirements of the low viscosity adhesive (9).

[0019] As a preferred technical solution, the adhesive material (5) used in step (a) is a high-viscosity room temperature / low temperature curing resin, including one or a mixture of epoxy resin, cyanate ester, unsaturated polyester, and phenolic resin; and the viscosity of the adhesive material (5) is not less than 50000 cP, and the maximum temperature during the curing process does not exceed 80℃.

[0020] As a preferred technical solution, the low-viscosity adhesive (9) material used in step (iv) includes one or more of epoxy resin, cyanate ester, unsaturated polyester and phenolic resin, and its curing shrinkage rate shall not exceed ±5%; if the adhesive contains filler, the maximum diameter of the filler shall not be greater than 50μm, and the curing temperature of the low-viscosity adhesive (9) shall not be higher than the decomposition temperature of the adhesive material (5).

[0021] As a preferred technical solution, the adapter board (6) can be a bare board or a board with secondary wiring. When the adapter board is used for secondary wiring, the corresponding position of the chip needs to have a corresponding pad. The positioning ball is a solder ball, and the melting point of the solder ball cannot exceed 250°C. When the adapter board is a bare board, the area covered by each chip needs to have a sufficient number of positioning balls with a diameter range of 0.08mm to 0.30mm. There must be at least 3 positioning balls at the four corners, and the center of the positioning ball at the four corners must be within 0.2mm to 0.5mm from the edge of the chip. There must be at least 4 positioning balls at the center, and the center of the positioning ball at the center position only needs to be within 1mm of the diameter around the center point of the chip.

[0022] As a preferred technical solution, the size of the adapter board (6) is in the range of 40mm*40mm to 200mm*200mm, the thickness of the adapter board is in the range of 400μm to 800μm, the size of the chip is in the range of 15mm*15mm to 40mm*40mm, the thickness of the chip is in the range of 250μm to 800μm, and the coplanarity of the positioning ball of the adapter board is ≤10μm.

[0023] As a preferred technical solution, in step (5), during the glue filling process, an "L" shaped glue dispensing path is selected until the bottom of the adapter plate (6) is filled with glue.

[0024] As a preferred technical solution, in step (seven), during the glue filling process, any one of the "I", "L" or "U" type dispensing paths is selected according to the chip size until the bottom of the chip (11) is filled with glue. When planning the dispensing route, the influence of adjacent chips should be considered. When the distance between the edges of two chips is less than 1.5mm, dispensing in the space between the two chips should be avoided as much as possible.

[0025] As a preferred technical solution, the multi-chip dedicated suction head (12) in step (vi) has a suction port flatness of ≤10μm, and needs to ensure that the contact area between the chip and the suction head is greater than 60% of the chip area, and ensure that all chips can be picked up at once and placed at the same time. The pressure applied by the dedicated suction head is 0.5N to 5N.

[0026] As a preferred technical solution, in step (vi), adhesive is applied to each of the four corners, and the amount of adhesive applied to a single point shall not exceed 10% of the chip's side length.

[0027] As a preferred technical solution, the weight of the limiting piece (8) is 0.5N to 5N.

[0028] The beneficial effects of this invention are:

[0029] (1) The present invention provides a method for fabricating a multi-chip coplanar splicing structure for an image sensor. By using a high-rigidity adapter plate as the base surface, the bonding area is optimized into a uniform plane, and the positioning ball on the adapter plate is used for coplanar positioning. The chip is mounted on top of the positioning ball, and the positioning ball is placed below the chip as a support, so that the upper-layer chips can be on the same plane, realizing the fabrication of a highly coplanar multi-chip coplanar splicing structure, which can ensure that the error is within a set range.

[0030] (2) By using a one-time chip mounting method, the present invention ensures that all chips are subjected to uniform force during the picking, mounting and pressurizing process, which can effectively improve the coplanarity of multi-chip coplanar splicing and reduce errors. Attached Figure Description

[0031] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0032] Figure 1(a) is a schematic diagram of a process flow of the fabrication method of the multi-chip coplanar splicing structure for image sensors according to the present invention;

[0033] Figure 1(b) is a schematic diagram of a process flow of the fabrication method of the multi-chip coplanar splicing structure for image sensors according to the present invention;

[0034] Figure 1(c) is a schematic diagram of a process flow of the fabrication method of the multi-chip coplanar splicing structure for image sensors according to the present invention;

[0035] Figure 1(d) is a schematic diagram of a process flow of the fabrication method of the multi-chip coplanar splicing structure for image sensors according to the present invention;

[0036] Figure 1(e) is a schematic diagram of a process flow of the fabrication method of the multi-chip coplanar splicing structure for image sensors according to the present invention;

[0037] Figure 1(f) is a schematic diagram of a process flow of the fabrication method of the multi-chip coplanar splicing structure for image sensors according to the present invention;

[0038] Figure 1(g) is a schematic diagram of a process flow of the fabrication method of the multi-chip coplanar splicing structure for image sensors according to the present invention;

[0039] Figure 1(h) is a schematic diagram of a process flow of the fabrication method of the multi-chip coplanar splicing structure for image sensors according to the present invention;

[0040] Figure 1(i) is a schematic diagram of a process flow of the fabrication method of the multi-chip coplanar splicing structure for image sensors according to the present invention;

[0041] Figure 1(j) is a schematic diagram of a process flow of the fabrication method of the multi-chip coplanar splicing structure for image sensors according to the present invention;

[0042] Figure 2 This is a schematic diagram showing the arrangement of the positioning balls on the front of the adapter plate;

[0043] Figure 3 This is a schematic diagram of a multi-chip dedicated suction head structure;

[0044] The attached figures are labeled as follows:

[0045] 1-Screen mesh, 2-Packaging area, 3-Ceramic housing for image sensor chip, 4-Glue head, 5-Adhesive material, 6-Adapter board, 7-Adapter board dedicated suction head, 8-Limiting piece, 9-Low viscosity adhesive, 10-UV fast curing adhesive, 11-Chip, 12-Multi-chip dedicated suction head. Detailed Implementation

[0046] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0047] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0048] This invention provides a method for fabricating a multi-chip coplanar stitching structure for image sensors.

[0049] Figures 1(a), 1(b), 1(c), 1(d), 1(e), 1(f), 1(g), 1(h), 1(i), and 1(j) are schematic diagrams of the various processes in the fabrication method of the multi-chip coplanar splicing structure for image sensors according to the present invention.

[0050] The corresponding processes are as follows:

[0051] Step 1: Using adhesive head 4 and adhesive material 5, screen printing is used to form a grid array of adhesive blocks on the mounting area 2, in combination with screen 1 and image sensor ceramic housing 3, as shown in Figure 1(a), Figure 1(b), and Figure 1(c).

[0052] The adhesive material 5 is a high-viscosity room temperature / low temperature curing resin, including one or a mixture of epoxy resin, cyanate ester, unsaturated polyester, and phenolic resin.

[0053] The viscosity of adhesive material 5 is not less than 50,000 cP, and the maximum temperature during the curing process does not exceed 80℃.

[0054] Step 2: Use the adapter plate special suction head 7 to place the adapter plate 6 on the processed mounting area 2, as shown in Figure 1(d);

[0055] The third step is to place the limiting piece 8 above the adapter plate 6 and cure it according to the curing index requirements of the adhesive material 5, as shown in Figure 1(e).

[0056] The size of the adapter board 6 is in the range of 40mm*40mm to 200mm*200mm, and the thickness of the adapter board is in the range of 400μm to 800μm.

[0057] The coplanarity of the positioning ball that comes with adapter plate 6 is ≤10μm.

[0058] The size of chip 11 ranges from 15mm*15mm to 40mm*40mm, and the chip thickness ranges from 250μm to 800μm.

[0059] The weight of the limiting piece 8 is 0.5N to 5N.

[0060] Step 4: Use low-viscosity adhesive 9 to fill the gap between the adapter plate 6 and the mounting area 2. Fill the gap between the adapter plate 6 and the mounting area 2 with low-viscosity adhesive 9, as shown in Figure 1(f).

[0061] The low-viscosity adhesive 9 material includes one or a mixture of epoxy resin, cyanate ester, unsaturated polyester and phenolic resin, and the curing shrinkage rate shall not exceed ±5%; if the adhesive contains filler, the maximum diameter of the filler shall not exceed 50μm.

[0062] The curing temperature of the low-viscosity adhesive 9 must not exceed the decomposition temperature of the adhesive material 5.

[0063] During the glue filling process, use an "L" shaped glue dispensing path until the bottom of the adapter plate is filled with glue.

[0064] Step 5: Place the limiting piece 8 above the adapter plate 6, and select the higher of the curing temperature of the low viscosity adhesive 9 and the melting point of the positioning ball on the front of the adapter plate 6 for curing. Use the gravity of the limiting piece 8 to control the coplanarity of the upper surface of the positioning ball on the front of the adapter plate 6, as shown in Figure 1(g).

[0065] The weight of the limiting piece 8 is 0.5N to 5N.

[0066] Step 6: Apply UV fast-curing adhesive 10 to the four corners of the chip placement position on the upper surface of the adapter board 6. Use the multi-chip special suction head 12 to pick up multiple chips 11 at the same time and place them in the set position. Apply pressure to fix the chips 11. At the same time, use UV irradiation to make the chips 11 cure quickly, as shown in Figure 1(h) and Figure 1(i).

[0067] The multi-chip dedicated suction tip 12 has a suction nozzle flatness of ≤10μm.

[0068] The pressure applied by the multi-chip dedicated suction tip 12 is 0.5N to 5N.

[0069] The structure of the multi-chip dedicated suction head 12 needs to ensure that the contact area between the chip and the suction head is greater than 60% of the chip area, and that all chips can be picked up at once and placed simultaneously.

[0070] Figure 3 The diagram shows a schematic of a dedicated chip pick-up tip for 4 chips.

[0071] When applying adhesive to each of the four corners, the amount of adhesive applied to a single spot must not exceed 10% of the chip's side length.

[0072] Step 7: Use low-viscosity adhesive 9 to fill the gap between the adapter board 6 and the chip 11. Fill the gap between the adapter board 6 and the chip 11 with low-viscosity adhesive 9, as shown in Figure 1(j).

[0073] During the glue filling process, select any one of the following dispensing paths—"I," "L," or "U"—based on the chip size until the bottom of the chip is filled with glue. When planning the dispensing route, the influence of adjacent chips should be considered. When the distance between the edges of two chips is less than 1.5mm, try to avoid dispensing glue in the space between the two chips.

[0074] Step 8: Curing should be carried out according to the curing index requirements of low viscosity adhesive 9.

[0075] In the process flow of the multi-chip coplanar splicing structure fabrication method for image sensors of the present invention, the adapter board (6) can be a bare board or a board with secondary wiring. When the adapter board is used for secondary wiring, the corresponding position of the chip needs to have a corresponding pad, the positioning ball is a solder ball, and the melting point of the solder ball cannot exceed 250°C. When the adapter board is a bare board, the area covered by each chip needs to have a sufficient number of positioning balls with a diameter range of 0.08mm to 0.30mm. There must be at least 3 balls at the four corners, and the center of the positioning ball at the four corners is within 0.2mm to 0.5mm from the edge of the chip. There must be at least 4 balls at the center, and the center of the positioning ball at the center position only needs to be within 1mm of the diameter around the center point of the chip.

[0076] Figure 2 The diagram shows the arrangement of the positioning balls on the front of the adapter plate.

[0077] In summary, for image sensors, the imaging quality is most dependent on the flatness of the chip surface, and the chip mounting process is the direct factor determining the chip flatness. For structures with an overall imaging area exceeding 40mm*40mm in size, the coplanarity of the mounting area is limited by factors such as the flatness of the outer shell mounting area, the thickness of the mounting adhesive material, the stress of the mounting adhesive material, and the mounting process. The manufacturing process of the multi-chip coplanar splicing structure of the image sensor of this invention utilizes a high-rigidity adapter plate as a base surface to optimize the mounting area into a uniform plane. Coplanar positioning is achieved using the positioning ball built into the adapter plate. The chip is mounted on top of the positioning ball, and the positioning ball is placed below the chip as support, so that the upper-layer chips can be on the same plane, realizing the fabrication of a highly coplanar multi-chip coplanar splicing structure to ensure that the error is within the set range.

[0078] Moreover, by using a single chip mounting method, this invention ensures that all chips are subjected to uniform force throughout the picking, mounting, and pressurizing process, effectively improving the coplanarity of multi-chip coplanar splicing and reducing errors.

[0079] In the description of this invention, terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," which indicate direction or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. These are used merely for ease of description and do not indicate or imply that the device or element 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.

[0080] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0081] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent in such process, method, article, or apparatus / device.

[0082] 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 these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for fabricating a multi-chip coplanar stitching structure for an image sensor, characterized in that... The steps are as follows: Step (1): Using adhesive material (5), a grid array of adhesive blocks is formed on the mounting area (2) by screen printing. Step (2): Use the adapter plate special suction head (7) to place the high rigidity adapter plate (6) on the processed mounting area (2); the front of the adapter plate (6) facing away from the adhesive material (5) has a positioning ball, and the coplanarity of the positioning ball of the adapter plate is ≤10μm; Step (3): Place the limiting piece (8) above the adapter plate (6) and cure it according to the curing index requirements of the adhesive material (5); Step (4): Use low-viscosity adhesive (9) to fill the gap between the adapter plate (6) and the mounting area (2). Fill the gap between the adapter plate (6) and the mounting area (2) with low-viscosity adhesive (9). Step (5): Place the limiting piece (8) above the adapter plate (6), select a temperature between the curing temperature of the low viscosity adhesive (9) and the melting point of the positioning ball on the front of the adapter plate (6) for curing, and use the gravity of the limiting piece (8) to control the coplanarity of the upper surface of the positioning ball on the front of the adapter plate (6). Step (6): Select UV fast-curing adhesive (10), apply adhesive to the four corners of the chip position on the upper surface of the adapter board (6), use a multi-chip special suction head (12) to pick up multiple chips (11) at the same time and place them in the set position, apply pressure at the same time to fix the chips, use the positioning ball on the adapter board to perform coplanar positioning, install the chips on the top of the positioning ball, use the positioning ball to place the chips below as support, so that the upper layer chips can be on the same plane, and use UV irradiation to make the chips fast-curing. Step (7): Use low-viscosity adhesive (9) to fill the gap between the adapter board (6) and the chip (11). Fill the gap between the adapter board (6) and the chip (11) with low-viscosity adhesive (9). Step (8): Curing is carried out according to the curing index requirements of the low viscosity adhesive (9).

2. The method for fabricating a multi-chip coplanar stitching structure for an image sensor according to claim 1, characterized in that: The adhesive material (5) used in step (a) is a high-viscosity room temperature / low temperature curing resin, including one or a mixture of epoxy resin, cyanate ester, unsaturated polyester, and phenolic resin; and the viscosity of the adhesive material (5) is not less than 50000 cP, and the maximum temperature during the curing process does not exceed 80℃.

3. The method for fabricating a multi-chip coplanar stitching structure for an image sensor according to claim 1, characterized in that: The low-viscosity adhesive (9) used in step (iv) includes one or more of epoxy resin, cyanate ester, unsaturated polyester and phenolic resin, and its curing shrinkage rate shall not exceed ±5%; if the adhesive contains filler, the maximum diameter of the filler shall not be greater than 50μm, and the curing temperature of the low-viscosity adhesive (9) shall not be higher than the decomposition temperature of the adhesive material (5).

4. The method for fabricating a multi-chip coplanar stitching structure for an image sensor according to claim 1, characterized in that: The adapter board (6) is a bare board or has secondary wiring. When the adapter board has secondary wiring, pads need to be set at the positions corresponding to the chips. The positioning balls are solder balls, and the melting point of the solder balls cannot exceed 250°C. When the adapter board is a bare board, there must be a sufficient number of positioning balls in the area covered by each chip, with a diameter range of 0.08mm to 0.30mm. There must be at least 3 positioning balls at the four corners, and the center of the positioning balls at the four corners must be within 0.2mm to 0.5mm from the edge of the chip. There must be at least 4 positioning balls at the center, and the center of the positioning ball at the very center must be within 1mm of the diameter around the center point of the chip.

5. The method for fabricating a multi-chip coplanar stitching structure for an image sensor according to claim 1, characterized in that: The size of the adapter board (6) is in the range of 40mm*40mm~200mm*200mm, the thickness of the adapter board is in the range of 400μm~800μm, the size of the chip is in the range of 15mm*15mm~40mm*40mm, and the thickness of the chip is in the range of 250μm~800μm.

6. The method for fabricating a multi-chip coplanar stitching structure for an image sensor according to claim 1, characterized in that: In step (5), during the glue filling process, an "L" shaped glue dispensing path is selected until the bottom of the adapter plate (6) is filled with glue.

7. The method for fabricating a multi-chip coplanar stitching structure for an image sensor according to claim 1, characterized in that: In step (seven), during the glue filling process, select any one of the "I", "L" or "U" type dispensing paths according to the chip size until the bottom of the chip (11) is filled with glue. When planning the dispensing route, the influence of adjacent chips should be considered. When the distance between the edges of two chips is less than 1.5mm, avoid dispensing glue in the space between the two chips.

8. The method for fabricating a multi-chip coplanar stitching structure for an image sensor according to claim 1, characterized in that: The multi-chip dedicated suction head (12) mentioned in step (six) has a suction port flatness of ≤10μm, and needs to ensure that the contact area between the chip and the suction head is greater than 60% of the chip area, and ensure that all chips can be picked up at once and placed at the same time. The pressure applied by the multi-chip dedicated suction head (12) is 0.5N~5N.

9. The method for fabricating a multi-chip coplanar stitching structure for an image sensor according to claim 1, characterized in that: In step (six), when applying adhesive to the four corners, the amount of adhesive applied to a single point shall not exceed 10% of the chip's side length.

10. The method for fabricating a multi-chip coplanar stitching structure for an image sensor according to claim 1, characterized in that: The weight of the limiting piece (8) is 0.5N~5N.

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