A method for manufacturing a high planarity die bonding structure for a sensor chip

Abstract

The application discloses a manufacturing method of a high-flatness die-bonding structure for a sensor chip, comprising the following steps: dispensing: adopting thermoplastic resin as a bonding material, and adopting an automatic dispensing / manual dispensing mode to dispense the bonding material on a chip die-bonding area of a ceramic shell according to a specified dispensing path; shaping: after the bonding material is cooled and solidified, mechanical processing is performed to obtain a boss array; die mounting: placing a chip on the boss array; flatness control: placing a limiting sheet with a certain mass above the chip, and controlling the flatness by using the gravity of the limiting sheet; solidification: after the bonding material is heated and melted, the bonding material is cooled and solidified again. Through the method, the die-bonding flatness of a large-size chip can be effectively controlled, the die-bonding flatness of a large-size image sensor chip can be realized, the die-bonding flatness is less than or equal to 20 microns, and the die-bonding flatness is far superior to that of a similar device without using the method.

Description

Technical Field

[0001] This invention belongs to the field of sensor packaging technology, and particularly relates to a method for fabricating a high-flatness die-bonding structure for sensor chips. Background Technology

[0002] With advancements in large-scale integrated circuit design and signal processing technologies, CMOS image sensors have gained increasing attention and become a hot research area in solid-state image sensors. In recent years, with significant progress in integrated circuit design and manufacturing processes, CMOS image sensors are primarily used in commercial applications such as smartphones, automobiles, security, medical devices, and industrial applications. For example, cameras serving advanced driver assistance systems and 360° parking assistance systems have seen a multiplier effect on revenue across the industry due to improved camera performance and increased numbers. As the size of photosensitive pixels gradually decreases from 10μm to 0.5μm, the light-sensing range will be significantly improved. When the pixel size reaches 0.5μm, the pixel count can exceed 1 billion. The trend in image sensor development is towards smaller pixel sizes and larger chip sizes. The flatness of the photosensitive area plays a crucial role in image quality. When the pixel size decreases to 1μm, the depth of focus decreases, requiring the flatness of the chip's photosensitive area to be controlled within 20μm. This enables the single-chip packaging of high-precision, large-size image sensor circuits. Compared to multi-chip sensors, single large-size image sensors offer significant advantages in terms of high pixel count, low power consumption, and fewer blind spots. Therefore, innovative methods are needed to achieve high flatness bonding of large-size image sensor chips.

[0003] The main problems currently existing in the high-flatness die bonding process for image sensor chips in the industry are: (1) In the die bonding and packaging of large-size image sensor chips, the traditional die bonding adhesive is a thermosetting resin, and its curing is an irreversible reaction. If expansion or contraction occurs during the curing process, the flatness of the chip will exceed 20μm, which will directly lead to failure. The die bonding adhesive uses thermoplastic resin, and its curing is a reversible reaction. If the flatness is not up to standard, rework can be carried out, which can effectively improve the product pass rate. (2) In the die bonding of large-size image sensor chips, since the conventional die bonding method uses liquid adhesive, the liquid adhesive has strong fluidity. Even if the adhesive is dispensed in a quantitative manner, the flow of the die bonding adhesive cannot be avoided. The flow will cause changes in the amount of adhesive in a local area, which will lead to the chip being recessed or raised in that area, and ultimately the flatness will exceed 20μm. Summary of the Invention

[0004] The technical problem solved by the present invention is to overcome the shortcomings of the prior art and provide a method for fabricating a high-flatness die-bonding structure for sensor chips, which can effectively control the die-bonding flatness of large-size chips.

[0005] To address the aforementioned technical problems, this invention discloses a method for fabricating a high-planarity die-attach structure for sensor chips, comprising: Step 1, dispensing: Thermoplastic resin is used as the adhesive material. The chip bonding area on the ceramic shell is dispensed using automatic / manual dispensing methods, following the specified dispensing path. Step 2, Shaping: After the bonding material cools and solidifies, it is machined to obtain an array of bosses; Step 3, Wafer mounting: Place the chip on the boss array; Step 4, control flatness: Place a limiting piece of a certain mass above the chip and use the gravity of the limiting piece to control flatness; Step 5, Curing: After heating and melting the adhesive material, cool and cure it again.

[0006] In the above method for fabricating a high-flatness adhesive structure for sensor chips, in step 1, the specified dispensing path is any one of the following: "dot matrix", "rice-shaped", "bow-shaped" and "zigzag".

[0007] In the above-mentioned method for fabricating a high-flatness adhesive structure for sensor chips, in step 2, after the adhesive material cools and solidifies, it is machined. First, the adhesive material is flattened into a cuboid by machining, and then a mesh groove and a boss array are machined at certain intervals. The upper surfaces of each boss in the boss array are on the same plane.

[0008] In the above-mentioned method for fabricating a high-flatness adhesive structure for sensor chips, the adhesive material naturally forms an upper dome shape after cooling and solidification. The adhesive material is then flattened into a cuboid using mechanical leveling, and the thickness of the adhesive is controlled by the height of the cuboid. The adhesive thickness is ≥150μm, and the upper surface of the cuboid is a plane with a flatness of ≤10μm.

[0009] In the above-mentioned method for fabricating a high-planarity adhesive structure for sensor chips, the trenches are arranged in a mesh pattern, with a trench depth of 50μm~200μm and a trench width of 1mm~4mm.

[0010] In the above-mentioned method for fabricating a high-flatness bonding structure for sensor chips, the boss is circular with a diameter of 0.2mm to 2mm; or, the boss is a cube or cuboid with a side length of 0.2mm to 2mm.

[0011] In the above-mentioned method for fabricating a high-planarity bonding structure for sensor chips, the distance between the edge of the boss and the inner edge of the chip bonding area is 0.3mm~1.5mm; the height of the boss is 50μm~200μm; the center distance between two adjacent bosses is 0.3mm~3mm; and the coplanarity of the boss array is ≤10μm.

[0012] In the above method for fabricating a high-flatness adhesive structure for sensor chips, in step 4, the weight of the limiting piece is 0.5N~5N.

[0013] In the above-described method for fabricating a high-planarity adhesive structure for sensor chips, the thermoplastic resin is one or a mixture of several of the following: polyethylene, polypropylene, polyacrylic acid, and acrylonitrile / butadiene / styrene copolymer.

[0014] In the above-mentioned method for fabricating a high-planarity die-attach structure for sensor chips, the length and width of the chip are in the range of 20mm*20mm to 40mm*40mm, and the thickness is in the range of 80μm to 800μm.

[0015] The present invention has the following advantages: (1) This invention discloses a method for fabricating a high-flatness adhesive structure for sensor chips. The method of mechanically leveling and repeatedly curing adhesive materials can effectively control the flatness of large-size image sensor chips and ensure that the error is within a certain range.

[0016] (2) The present invention discloses a method for fabricating a high-flatness die-bonding structure for sensor chips, which can effectively improve the die-bonding qualification rate and reduce costs. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the fabrication process of a high-flatness die-bonding structure for a sensor chip according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the morphology of an adhesive material after processing, according to an embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments disclosed in the present invention will be described in further detail below with reference to the accompanying drawings.

[0019] For image sensors, the imaging quality depends most on the flatness of the chip surface, and the chip mounting process is the factor that directly determines the chip flatness. For chips larger than 20mm×20mm, the flatness of the mounting area is limited by factors such as the flatness of the housing mounting area, the thickness of the mounting adhesive material, the stress of the mounting adhesive material, and the mounting process.

[0020] Reference Figure 1and Figure 2 This invention discloses a method for fabricating a high-planarity die-attach structure for sensor chips, comprising: Step 1, dispensing: Thermoplastic resin is used as the adhesive material 4. The chip bonding area 2 on the ceramic shell 1 is dispensed using an automatic / manual dispensing method, following the specified dispensing path.

[0021] In this embodiment, any one of the following dispensing paths—"dot matrix," "star-shaped," "bow-shaped," and "zigzag"—can be selected as the prescribed dispensing path based on the chip size. Thermoplastic resin is used as the adhesive material 4. The chip bonding area 2 on the ceramic shell 1 is dispensed via an automatic / manual dispensing method using the glue head 3, following the prescribed dispensing path. The dispensing starting point should be 0.5mm to 3mm from the edge of the chip bonding area 2. The adhesive must not overflow beyond the chip bonding area 2. The dispensing width (or glue dot diameter) is 0.5mm to 1.5mm, and the dispensing amount is 10% to 50% greater than the actual adhesive amount. The minimum softening temperature of the adhesive material used must be higher than room temperature (20°C). Specific thermoplastic resin materials include, but are not limited to, one or more mixtures of polyethylene, polypropylene, polyacrylic acid, and acrylonitrile / butadiene / styrene copolymers. It should be noted that the dispensing path includes, but is not limited to, "dot matrix," "star-shaped," "bow-shaped," and "zigzag" paths.

[0022] Step 2, Shaping: After the bonding material 4 cools and solidifies, it is machined to obtain a boss array.

[0023] In this embodiment, the bonding material 4 is machined after cooling and solidification. First, the bonding material 4 is flattened into a cuboid by machining, and then a mesh groove and a boss array are machined at certain intervals. The upper surfaces of each boss in the boss array are on the same plane.

[0024] Preferably, after the adhesive material 4 cools and solidifies, it naturally takes on an upper dome shape. A mechanical leveling method is used to flatten the adhesive material 4 into a cuboid, and the thickness of the adhesive is controlled by the height of the cuboid. Specifically, the thickness of the adhesive is ≥150μm, and the upper surface of the cuboid is a flat surface with a flatness ≤10μm.

[0025] Preferably, the trenches are arranged in a mesh pattern, with a trench depth of 50μm to 200μm and a trench width of 1mm to 4mm.

[0026] Preferably, the boss is circular with a diameter of 0.2mm to 2mm; or, the boss is a cube or cuboid with a side length of 0.2mm to 2mm.

[0027] Preferably, the inner distance from the edge of the boss to the inner edge of the chip bonding area 2 is 0.3 mm to 1.5 mm; the height of the boss is 50 μm to 200 μm; the center distance between two adjacent bosses is 0.3 mm to 3 mm; the coplanarity of the boss array is ≤ 10 μm.

[0028] Step 3, chip mounting: Place the chip 5 on the boss array.

[0029] Step 4, flatness control: Place a limiting piece 6 with a certain mass above the chip 5, and use the gravity of the limiting piece 6 for flatness control. Among them, the gravity of the limiting piece 6 is 0.5 N to 5 N.

[0030] Step 5, curing: Heat and melt the bonding material and then cool and cure it again.

[0031] In this embodiment, the minimum secondary softening time of the bonding material must be higher than 10 min.

[0032] In this embodiment, the length and width of the chip 5 are within the range of 20 mm * 20 mm to 40 mm * 40 mm, and the thickness is within the range of 80 μm to 800 μm.

[0033] In this embodiment, let: the total volume of the bonding material be V, the effective bonding area (the part where the glue is connected to the chip is regarded as the effective bonding area) be S, the side length of the chip be a, the thickness of the bonding material be h, and the thickness of the boss be k; then: when satisfying 0.75[(h - k)a

[0033] + Sk]<V<(1.25a 2 h + Sk - a 2 k), this constraint condition can well ensure the quality of chip mounting.

[0034] In this embodiment, let: the side length of the boss be b, and the pitch be l; then: when satisfying 2(l - b) 2 < 3b 2 < 6(l - b) <​​​​​​​​​​​A chip with dimensions of 24mm x 24mm and a thickness of 350μm was selected. Polypropylene thermoplastic resin was used as the adhesive. An automated dispensing method was employed in the chip bonding area, using a zigzag dispensing path until the adhesive reached the specified flow state. After the adhesive material cooled and cured, it underwent machining. First, it was flattened into a cuboid, ensuring the top surface was flat (9μm flatness). Then, a mesh of grooves and a boss array were machined, ensuring all bosses had their top surfaces on the same plane. The boss width was 0.5mm, the distance from the edge of the boss to the inner edge of the chip bonding area was 0.75mm, the boss height was 100μm, and the center-to-center distance between adjacent bosses was 1mm. The chip was placed on the boss array, and then a locating plate was placed on top of the chip. The flatness was controlled by the weight of the locating plate, which weighed 0.2kg. The mixture was heated to 180℃ and maintained for 15 minutes to melt the adhesive material, then cooled again to room temperature for curing.

[0038] The method described above effectively controls various parameters of large-size image sensor chip bonding, achieving high flatness bonding. Testing showed that the flatness of the formed chip is 17 μm, with a deviation of ±3 μm.

[0039] Example 2 A chip with dimensions of 27mm x 27mm and a thickness of 450μm was selected. Acrylonitrile / butadiene / styrene copolymer thermoplastic resin was used as the adhesive. An automatic dispensing method was employed in the chip bonding area, using a "bow-shaped" dispensing path until the adhesive reached the specified flow state. After the adhesive material cooled and cured, it was machined. First, it was leveled into a cube, ensuring the upper surface of the adhesive material was flat (flatness 7.5μm). Then, a mesh of grooves and a boss array were machined, ensuring that the upper surfaces of all bosses were on the same plane. The boss width was 0.8mm, the distance from the edge of the boss to the inner edge of the chip bonding area was 1mm, the boss height was 80μm, and the center distance between two adjacent bosses was 1.5mm. The chip was placed on the boss array, and then a locating plate was placed on top of the chip. The flatness was controlled by the gravity of the locating plate, which weighed 0.3kg. The mixture was heated to 200℃ and maintained for 15 minutes to melt the adhesive material, and then cooled again to room temperature for curing. The method described above effectively controls various parameters of large-size image sensor chip bonding, achieving high flatness bonding. Testing showed that the flatness of the formed chip is 16 μm, with a deviation of ±3 μm.

[0040] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

[0041] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for fabricating a high-planarity die-attach structure for a sensor chip, characterized in that, include: Step 1, dispensing: Thermoplastic resin is used as the adhesive material (4). The chip bonding area (2) on the ceramic shell (1) is dispensed using an automatic / manual dispensing method, following the specified dispensing path. Step 2, Shaping: After the material to be bonded (4) is cooled and cured, it is machined to obtain a boss array. The coplanarity of the boss array is ≤10μm. Step 3, Wafer mounting: Place the chip (5) on the boss array; wherein, the total volume V of the adhesive material and the effective adhesive area S, the chip side length a, the adhesive material thickness h, and the boss thickness k satisfy the following relationship: 0.75[(hk)a 2 +Sk] <V<(1.25a 2 h+Sk-a 2 k); The side length b of the boss and the pitch l satisfy: 2(lb) 2 <3b 2 <6 (lb) 2 The distance L from the geometric center point of the boss to the chip edge satisfies the following relationship with the number of bosses on one side, n: 0.3(n-1). <a-2L<3(n-1); Step 4, control flatness: Place a limiting piece (6) of a certain mass above the chip (5) and use the gravity of the limiting piece (6) to control the flatness; Step 5, Curing: Heat and melt the adhesive material for at least 10 minutes, then cool and cure it again. Among them, the length and width of chip (5) are in Within the range, the thickness is in the range of 80μm to 800μm.

2. The method for fabricating a high-planarity die-attach structure for a sensor chip according to claim 1, characterized in that, In step 1, the specified dispensing path is any one of the following: "dot matrix", "rice pattern", "bow pattern" and "zigzag pattern".

3. The method for fabricating a high-planarity die-attach structure for a sensor chip according to claim 1, characterized in that, In step 2, after the adhesive material (4) is cooled and cured, it is machined. First, the adhesive material (4) is flattened into a cuboid by machining, and then a mesh groove and a boss array are machined at certain intervals. The upper surfaces of each boss in the boss array are on the same plane.

4. The method for fabricating a high-planarity die-attach structure for a sensor chip according to claim 3, characterized in that, After the adhesive material (4) cools and solidifies, it naturally presents an upper dome shape. The adhesive material (4) is flattened into a cuboid by mechanical leveling. The thickness of the mounting adhesive is controlled by the height of the cuboid. The thickness of the mounting adhesive is ≥150μm, and the upper surface of the cuboid is a plane with a flatness of ≤10μm.

5. The method for fabricating a high-planarity die-attach structure for a sensor chip according to claim 3, characterized in that, The trenches are arranged in a mesh pattern, with a depth of 50μm to 200μm and a width of 1mm to 4mm.

6. The method for fabricating a high-planarity die-attach structure for a sensor chip according to claim 3, characterized in that, The boss is a circular boss with a diameter of 0.2mm to 2mm; or, the boss is a cube or cuboid boss with a side length of 0.2mm to 2mm.

7. The method for fabricating a high-planarity die-attach structure for a sensor chip according to claim 3, characterized in that, The distance between the edge of the protrusion and the edge of the chip bonding area (2) is 0.3mm~1.5mm; the height of the protrusion is 50μm~200μm; the center distance between two adjacent protrusions is 0.3mm~3mm.

8. The method for fabricating a high-planarity die-attach structure for a sensor chip according to claim 1, characterized in that, In step 4, the weight of the limiting piece (6) is 0.5N~5N.

9. The method for fabricating a high-planarity die-attach structure for a sensor chip according to claim 1, characterized in that, Thermoplastic resin is one or a mixture of several of the following: polyethylene, polypropylene, polyacrylic acid, and acrylonitrile / butadiene / styrene copolymer.

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