A method for manufacturing a high flatness die bonding structure of a large-size sensor chip

Abstract

The application discloses a kind of for large size sensor chip high flatness die-bonding structure production method, comprising: evenly applying flux in chip bonding area, positioning ball is placed in chip bonding area;Limiting sheet is pasted according to design specified position, positioning ball is welded with chip bonding area;The device obtained after welding is cleaned and dried, flux is cleaned, then the limiting sheet is stripped;Chip is placed in design specified position, chip four corners are bonded with chip bonding area respectively, and fast curing is carried out under the condition that certain pressure P is applied;Edge position is filled with glue head along the edge of chip in any direction until the bottom of chip is filled with glue solution;A certain mass of pressing block is applied above chip, then curing is carried out according to the process specification of filled glue solution.The method can effectively control the die-bonding flatness of large size chip, and the die-bonding flatness is ≤20 μm, which is much better than similar devices 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 large-size sensor chips. Background Technology

[0002] With advancements in image sensor chip technology, the size of photosensitive pixels has gradually decreased from 10μm to 5μm, and currently, 1μm pixels have been developed. While maintaining the original chip size, this reduction in pixel size significantly increases the light-sensing range of image sensors. For example, reducing the pixel size from 5μm to 1μm increases the light-sensing range by 5×5 times. Therefore, large-scale ultra-small pixel imaging chips are the current development trend and will play a significant role in space-based and airborne applications. It is known that the smallest pixel size currently available in China is 0.5μm, and the pixel scale can reach over 1 billion pixels.

[0003] 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, necessitating that the flatness of the chip's photosensitive area be controlled within 20μm. Solving the problem of wafer flatness allows for 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. However, when the chip size exceeds 20mm*20mm, achieving a flatness ≤20μm using methods such as controlling the flatness of the housing mounting area and the mounting process becomes difficult. Therefore, innovative methods are needed to achieve high flatness wafer bonding for large-size image sensor chips.

[0004] 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 of large-size image sensor chips, the conventional die bonding method uses resin-based adhesives, which are thermosetting resins that undergo irreversible curing. Furthermore, the curing process inevitably results in expansion or contraction. Without proper control during dispensing and curing, the chip thickness, currently less than 1mm, is easily affected by changes in the curing volume of the adhesive, leading to chip curvature and exceeding flatness standards. Domestic and international manufacturers use multiple chip splicing or splicing of multiple image sensor circuits to achieve this; direct bonding of the entire chip remains impossible.

[0005] (2) In the die bonding of large-size image sensor chips, it is necessary to control the die thickness to facilitate heat dissipation of the chip; the thinner the die adhesive, the better the thermal conductivity. Therefore, the die thickness should preferably not exceed 300μm. Summary of the Invention

[0006] 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 large-size sensor chips, which can effectively control the die-bonding flatness of large-size chips.

[0007] To address the aforementioned technical problems, this invention discloses a method for fabricating a high-planarity die-attach structure for large-size sensor chips, comprising: Step 1: Apply flux evenly to the chip bonding area, and then place the solderable positioning ball in the chip bonding area; Step 2: Install the limiting pieces at the positions specified in the design, and weld the positioning balls to the chip bonding area at the set temperature; Step 3: Clean and dry the device obtained after welding in Step 2, remove the flux completely to ensure no residue, and then peel off the limiting piece. Step 4: Place the chip in the designated position, and use spot bonding to bond the four corners of the chip to the chip bonding area, and then quickly cure it under a certain pressure P. Step 5: Use the glue applicator to fill the chip with glue along any edge in any direction until the bottom of the chip is filled with glue. Step 6: Apply a pressure block of a certain mass on top of the chip, and then cure it according to the process instructions of the applied adhesive.

[0008] In the above method for fabricating a high-planarity die-attach structure for large-size sensor chips, in step 1: A solderable positioning ball device is used to evenly place solderable positioning balls at designed intervals in the chip bonding area; or, Using screen printing, solderable positioning balls are evenly placed at designed intervals in the chip bonding area; the screen openings are circular with a diameter ranging from 15μm to 350μm, and the flux thickness ranges from 100μm to 300μm; or, By using a ball-planting method, solderable positioning balls are placed in the chip bonding area: the size of the recessed part of the chip bonding area is measured, and the balls are precisely planted according to the size of the recessed part to place the solderable positioning balls in the chip bonding area.

[0009] In the above-mentioned method for fabricating a high-flatness bonding structure for large-size sensor chips, in step 1, the positioning balls are placed in a dot matrix pattern in the chip bonding area. The outermost positioning ball is 0.3mm to 1.5mm from the inner edge of the chip bonding area, and the center distance between two adjacent positioning balls is 0.3mm to 3mm.

[0010] In the above-mentioned method for fabricating a high-flatness bonding structure for large-size sensor chips, in step 2, during the welding process, the positioning ball is heated and melted. Under the action of gravity, a plane with a flatness of ≤20μm is formed on the upper side of the positioning ball, while the lower side of the positioning ball is welded together with the chip bonding area.

[0011] In the above-described method for fabricating a high-flatness bonding structure for large-size sensor chips, in step 2, any one of vacuum welding, reflow welding, and infrared welding is used to weld the positioning ball to the chip bonding area; wherein, the set temperature is the temperature recommended in the positioning ball welding instruction manual.

[0012] In the above-mentioned method for fabricating a high-flatness bonding structure for large-size sensor chips, in step 5, depending on the chip, any one of the "I", "L" and "U" type dispensing paths is selected, and glue is filled along the edge of the chip in any direction until the bottom of the chip is filled with glue.

[0013] In the above-mentioned method for fabricating a high-planarity die-bonding structure for large-size sensor chips, the length and width of the chip are in the range of 20mm*20mm~40mm*40mm, and the thickness is in the range of 80μm~800μm.

[0014] In the above-mentioned method for fabricating a high-flatness bonding structure for large-size sensor chips, the length and width of the limiting piece are consistent with the length and width of the chip.

[0015] In the above method for fabricating a high-planarity bonding structure for large-size sensor chips, the positioning ball is made of any one or more of Ag, SnAg, SnPb, SnAgCu, Sn, and AuSn; the diameter of the positioning ball is in the range of 50μm to 350μm.

[0016] In the above method for fabricating a high-flatness bonding structure for large-size sensor chips, in step 4, the applied pressure P is in the range of 0.5N to 5N; in step 6, the weight of the pressing block is in the range of 0.5N to 5N.

[0017] The present invention has the following advantages: (1) This invention discloses a method for fabricating a high-flatness bonding structure for large-size sensor chips. The method of using a positioning ball to control the height can effectively control the flatness of large-size image sensor chips and ensure that the error is within a certain range.

[0018] (2) This invention discloses a method for fabricating a high-flatness die-bonding structure for large-size sensor chips, which can effectively control the die thickness and is beneficial to the heat dissipation of the chip. Attached Figure Description

[0019] Figure 1This is a schematic diagram of a high-flatness bonding structure for large-size sensor chips in an embodiment of the present invention; Figure 2 This is a schematic diagram of the fabrication process for a high-flatness die-bonding structure for large-size sensor chips in an embodiment of the present invention. Detailed Implementation

[0020] 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.

[0021] 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.

[0022] like Figure 1 and Figure 2 As shown, this invention discloses a method for fabricating a high-planarity die-attach structure for large-size sensor chips, comprising: Step 1: Apply flux 5 evenly to the chip bonding area 4, and then place the solderable positioning ball 3 in the chip bonding area 4.

[0023] In this embodiment, the solderable positioning ball 3 can be placed in the chip bonding area 4 in any of the following ways: Method 1: Use a solder ball suction device to evenly place the solderable positioning balls 3 at the designed distance intervals in the chip bonding area 4.

[0024] Method 2: Using screen printing, solderable positioning balls 3 are evenly placed in the chip bonding area 4 at designed intervals. The screen openings are circular with a diameter ranging from 15μm to 350μm, and the flux 5 has a thickness ranging from 100μm to 300μm.

[0025] Method 3: Using ball placement, solderable positioning balls 3 are placed in the chip bonding area 4. The dimensions of the recessed portion of the chip bonding area 4 are measured, and the balls are precisely placed according to these dimensions to position the solderable positioning balls 3 in the chip bonding area 4. The size of the ball placement must be 20μm~50μm larger than the size of the recessed portion.

[0026] In both methods 1 and 2, the positioning balls 3 can be placed in a dot matrix pattern in the chip bonding area 4. The outermost positioning ball is 0.3mm to 1.5mm from the inner edge of the chip bonding area 4, and the center distance between two adjacent positioning balls is 0.3mm to 3mm.

[0027] Step 2: Mount the limiting piece 6 in the position specified in the design, and weld the positioning ball 3 to the chip bonding area 4 at the set temperature (the temperature recommended in the positioning ball welding instruction manual).

[0028] In this embodiment, any one of the following welding methods—vacuum welding, reflow welding, and infrared welding—can be used to weld the positioning ball 3 to the chip bonding area 4. During the welding process, the positioning ball 3 melts upon heating, and under the influence of gravity, a plane with a flatness of ≤20μm is formed on the upper side of the positioning ball 3. Simultaneously, the lower side of the positioning ball 3 is welded together with the chip bonding area 4. The length and width of the limiting piece 6 are consistent with the length and width of the chip 1.

[0029] Step 3: Clean and dry the device obtained after welding in step 2, clean the flux 5 to ensure no residue, and then peel off the limiting piece 6.

[0030] Step 4: Place chip 1 in the designated position, and use spot bonding to bond the four corners of chip 1 to chip bonding area 4 respectively, and then perform rapid curing under a certain pressure P (0.5N~5N).

[0031] In this embodiment, when the four corners of the chip are bonded to the chip bonding area using spot bonding, and rapid curing is performed under a certain pressure P (0.5N~5N), the diameter of the adhesive dots at the four corners must not exceed 1 / 10 of the chip's side length, and the curing time must not exceed 10 minutes. Step 5: Use the glue applicator 7 to fill the chip 1 with glue along any edge in any direction until the bottom of the chip 1 is filled with glue 2.

[0032] In this embodiment, the positioning ball 3 is located at a fixed position between the chip 1 and the chip bonding area 4, so the thickness of the adhesive (i.e. the filling thickness of the adhesive liquid) can be controlled by the positioning ball 3.

[0033] Preferably, any one of the "I", "L", and "U" type dispensing paths can be selected based on the chip 1. The glue head 7 is used to fill the chip 1 along its edge in any direction until the bottom of the chip 1 is filled with glue 2. Specifically: after the chip 1 is mounted and fixed, any one of the "I", "L", and "U" type dispensing paths is selected, and glue is dispensed at a distance of 0.3mm to 1mm along the edge of the chip 1 in any direction. The dispensing width is 0.5mm to 1.5mm, and the total amount of glue dispensed and the amount dispensed each time are proportional to the size of the chip 1. The interval between each filling is 5s to 30s, and the interval time is proportional to the size of the chip 1.

[0034] Preferably, the matrix material of the positioning adhesive used to bond the four corners of the chip 1 to the chip bonding area in step 4 should be the same as the matrix material of the adhesive filled in this step, which is one or several of epoxy resin, unsaturated polyester, phenolic resin, or cyanate ester. Moreover, the maximum curing temperature of the selected adhesive shall not exceed the melting point of the positioning ball 3.

[0035] Step 6, apply a certain mass of pressure block 8 above the chip 1, and then cure it according to the process specification of the filled adhesive liquid 2.

[0036] In this embodiment, the pressure provided by the pressure block 8, that is, the gravity of the pressure block 8, is within the range of 0.5 N to 5 N.

[0037] In this embodiment, the length and width of the chip 1 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. The material of the positioning ball 3 is any one or more of Ag, SnAg, SnPb, SnAgCu, Sn, AuSn; the diameter of the positioning ball 3 is within the range of 50 μm to 350 μm.

[0038] In this embodiment, let: the volume of the flux be V, the printing thickness be h, and the radius of the positioning ball be r; then: when satisfying 1.13r 2 h < V < 3.82r 2 This constraint condition of h can well ensure the quality and consistency of the positioning ball welding.

[0039] In this embodiment, let: the volume of the adhesive under the chip be V (volume); the long side length of the chip be a, the short side length be b; the diameter of the positioning ball be d, and the number be n; then: when satisfying 0.8abd - 0.25nπd 3 < V < 1.5abd - 0.25nπd 3 This constraint condition can ensure that the amount of filled adhesive is sufficient to achieve good bonding.

[0040] In this embodiment, let: the distance from the center of the positioning ball to the edge of the chip be L, and the number of unilateral positioning balls be m; then: when satisfying 0.3(m - 1) < a - 2L < 3(m - 1) this constraint condition, it can ensure that the number and interval of the positioning balls are reasonable.

[0041] Based on the above embodiments, two specific examples are described below.

[0042] Example 1 A chip with dimensions of 20mm x 20mm and a thickness of 400μm was selected. Positioning balls made of 63Sn37Pb material were used, with a diameter of 200μm, 19 balls on each side, and a total of 361 balls. The balls were placed using screen printing, with a 150μm opening on the solder mask and a 1mm dot spacing. The positioning tabs (matching the chip's dimensions) were mounted in the designated positions. Vacuum soldering (using a peak temperature curve of 200℃) was employed. After soldering, the devices were cleaned and dried, and all flux was thoroughly removed to ensure no residue. The positioning tabs were then peeled off. The actual product chip was placed in the designated positions, and the four corners of the chip were bonded to the chip bonding area using dot bonding. Epoxy resin with a dot diameter of 0.8mm was used, and rapid curing was performed under a force of 2N at 150℃ for 10 minutes. After curing, use an "L" shaped path to fill the adhesive along the right side of the chip marking position until the bottom of the chip is filled with adhesive; preferably, apply a force of 3N above the chip and then cure at 150℃ / 1h.

[0043] 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 18 μm, with a deviation of ±3 μm.

[0044] Example 2 A chip with dimensions of 30mm x 30mm and a diameter of 300μm was selected. Positioning balls made of SAC305 material were used, with a diameter of 100μm, 19 balls on each side, and a total of 361 balls. The balls were placed using screen printing, with an 80μm opening on the solder mask and a 1.5mm dot spacing. The positioning tabs (matching the chip's dimensions) were mounted in the designated positions. Vacuum soldering (using a peak temperature curve of 235℃) was employed. After soldering, the devices were cleaned and dried, and all flux was thoroughly removed to ensure no residue. The positioning tabs were then peeled off. The actual product chip was placed in the designated positions, and the four corners of the chip were bonded to the chip bonding area using dot bonding. Epoxy resin with 1mm diameter dots was used, and rapid curing was performed under a force of 3N at 150℃ for 10 minutes. After curing, use an "L" shaped path to fill the adhesive along the right side of the chip marking position until the bottom of the chip is filled with adhesive; preferably, apply a force of 3N above the chip and then cure at 150℃ / 1h.

[0045] 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 19 μm, with a deviation of ±3 μm.

[0046] 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.

[0047] 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 large-size sensor chips, characterized in that, include: Step 1: Apply flux (5) evenly to the chip bonding area (4), and then place the solderable positioning ball (3) in the chip bonding area (4). Step 2: The limiting piece (6) is mounted in the position specified in the design, and the positioning ball (3) is welded to the chip bonding area (4) at the set temperature. During the welding process, the positioning ball (3) is heated and melted. Under the action of gravity, a plane with a flatness of ≤20μm is formed on the upper side of the positioning ball (3), and the lower side of the positioning ball (3) is welded together with the chip bonding area (4). Step 3: Clean and dry the device obtained after welding in step 2, clean the flux (5) to ensure no residue, and then peel off the limiting piece (6). Step 4: Place the chip (1) at the designated location, and use spot bonding to bond the four corners of the chip (1) to the chip bonding area (4) respectively, and then perform rapid curing under a certain pressure P. Step 5: Use the glue head (7) to fill the edge of the chip (1) in any direction until the bottom of the chip (1) is filled with glue (2). Step 6: Apply a pressure block (8) of a certain mass above the chip (1), and then cure it according to the process instructions of the filled adhesive (2); Among them, the volume V of the underfill of the chip satisfies the following relationships with the long side length a of the chip, the short side length b of the chip, the diameter d of the positioning ball, and the number n of positioning balls: 0.8abd - 0.25nπd 3 <V < 1.5abd - 0.25nπd 3 ; the distance L from the center of the positioning ball to the edge of the chip satisfies the following relationship with the number m of unilateral positioning balls: 0.3(m - 1) < a - 2L < 3(m - 1); the length and width of the chip (1) are within a certain range, and the thickness is within the range of 80 μm to 800 μm.

2. The method for fabricating a high-planarity die-bonding structure for large-size sensor chips according to claim 1, characterized in that, In step 1: A solder ball suction device is used to evenly place solderable positioning balls (3) at designed intervals in the chip bonding area (4); or, Using screen printing, solderable positioning balls (3) are evenly placed at designed intervals in the chip bonding area (4); wherein the screen opening is circular with a diameter in the range of 15μm to 350μm, and the flux (5) thickness is in the range of 100μm to 300μm; or, By using the ball-planting method, the solderable positioning ball (3) is placed in the chip bonding area (4): the size of the recessed part of the chip bonding area (4) is measured, and the ball is precisely planted according to the size of the recessed part so that the solderable positioning ball (3) can be placed in the chip bonding area (4).

3. The method for fabricating a high-planarity die-bonding structure for large-size sensor chips according to claim 1, characterized in that, In step 1, the positioning ball (3) is placed in the chip bonding area (4) in a dot matrix manner. The distance between the outermost positioning ball and the inner edge of the chip bonding area (4) is within the range of 0.3mm to 1.5mm, and the center distance between two adjacent positioning balls is within the range of 0.3mm to 3mm.

4. The method for fabricating a high-planarity die-bonding structure for large-size sensor chips according to claim 1, characterized in that, In step 2, the positioning ball (3) is welded to the chip bonding area (4) using any one of the following welding methods: vacuum welding, reflow welding, and infrared welding; wherein the temperature is set to the temperature recommended in the positioning ball welding instruction manual.

5. The method for fabricating a high-planarity die-bonding structure for large-size sensor chips according to claim 1, characterized in that, In step 5, select any one of the "I", "L" and "U" dispensing paths according to the chip (1), and use the glue head (7) to fill the glue along the edge position of the chip (1) in any direction until the bottom of the chip (1) is filled with glue (2).

6. The method for fabricating a high-planarity die-bonding structure for large-size sensor chips according to claim 1, characterized in that, The length and width of the limiting piece (6) are the same as those of the chip (1).

7. The method for fabricating a high-planarity die-bonding structure for large-size sensor chips according to claim 1, characterized in that, The positioning ball (3) is made of any one or more of Ag, SnAg, SnPb, SnAgCu, Sn, and AuSn; the diameter of the positioning ball (3) is in the range of 50μm to 350μm.

8. The method for fabricating a high-planarity die-bonding structure for large-size sensor chips according to claim 1, characterized in that, In step 4, the applied pressure P is in the range of 0.5N to 5N; in step 6, the weight of the pressure block (8) is in the range of 0.5N to 5N.

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