Optimization method for glue filling of high-density pixel infrared focal plane device

Abstract

The invention discloses an optimization method for glue filling of a high-density pixel infrared focal plane device, and the method comprises the steps: selecting underfill glue with better fluidity, carrying out natural flow filling of the underfill glue in a linear or L-shaped manner, standing, then putting the underfill glue into a vacuum device, carrying out vacuum pumping and discharging, and observing, and vacuumizing is repeated until the underfill glue overflows around the chip. According to the invention, the filling defect of the underfill is reduced, the connection strength of the chip and the readout circuit is enhanced, and the reliability of the device is improved. The method is especially suitable for large-scale small-center-distance infrared focal planes.

Description

Technical Field

[0001] The invention relates to the manufacturing field of infrared focal plane devices, in particular to a method for optimizing the filling of high-density pixel infrared focal plane devices. Technical Background

[0002] At present, with the vigorous development of infrared focal planes, the scale of arrays is getting larger and larger, and the pixel pitch is getting smaller and smaller, which poses new challenges to the reliability of high-density and small-center-distance infrared focal plane devices. Infrared focal plane devices are mainly composed of chips, readout circuits and lead substrates. The chips and readout circuits are interconnected by indium pillars. When the device drops from room temperature to the operating temperature (about 80K), the large thermal stress between the device chip and the readout circuit will cause the chip to separate from the readout circuit and fail. Therefore, in the preparation process of infrared focal plane devices, epoxy resin glue must be filled between the chip and the readout circuit for curing to improve the low-temperature reliability of the focal plane device.

[0003] However, the existing filling process of epoxy resin glue as the bottom fill glue mainly relies on the capillary surface tension effect so that the gas between the chip and the readout circuit can be driven out by the flowing bottom fill glue, reducing the residual bubbles. However, due to the slow capillary flow, it is easy to cause bottom fill glue filling defects, especially in the high-density and small center-to-center infrared focal plane, because the small gap between adjacent indium columns creates a certain resistance, especially when the gap between the indium columns is less than 7 microns, or the height of the indium column, that is, the gap between the chip and the readout circuit is less than 7 microns, the bottom fill glue will stagnate after flowing to a certain extent, resulting in insufficient bottom fill glue filling, so that the gap between the chip and the readout circuit is not filled with bottom fill glue, and even bubbles are left in the filled bottom fill glue. The smaller the indium column gap or the indium column height, the more obvious the filling defects, such as Figure 1 As shown, this situation reduces the reliability of the device.

[0004] In summary, it is necessary to design a focal plane underfill method suitable for large-scale and high-density applications to reduce filling defects, enhance the connection strength between the chip and the readout circuit, and improve solder joint reliability issues caused by thermal mismatch. Summary of the invention

[0005] The purpose of the present invention is to provide an optimization method for filling glue of a high-density pixel infrared focal plane device, which solves the problem that the bottom filling glue cannot be fully filled between the chip and the readout circuit in the existing infrared focal plane device, resulting in poor reliability of the infrared focal plane device.

[0006] To achieve the above object, the technical solution of the present invention is:

[0007] A method for optimizing the filling of a high-density pixel infrared focal plane device, wherein the high-density pixel infrared focal plane device comprises a chip, a readout circuit and a lead substrate, wherein the chip and the readout circuit are connected by an indium column; an underfill is required between the chip and the readout circuit, and the method comprises the following steps:

[0008] Step 1: Prepare low-temperature bottom filler and select bottom filler with good fluidity;

[0009] Step 2: Fill the gap between the chip and the readout circuit with the bottom filler in a straight or L-shaped manner, and let it sit horizontally for 5-10 minutes.

[0010] Step 3, placing the high-density pixel infrared focal plane device in a vacuum device with a vacuum pressure of less than 2000 Pa for 5-10 minutes;

[0011] Step 4: Quickly remove the vacuum, then let it stand for 3-5 minutes and observe the overflow of the bottom fill glue around the chip.

[0012] The bottom filling glue is epoxy resin glue.

[0013] The vacuum pressure in step 3 is 500Pa.

[0014] After completing step 4, if the underfill glue does not overflow on all four sides of the chip, repeat steps 3 and 4 and continue to observe until the underfill glue overflows on all four sides of the chip.

[0015] The advantages of the present invention are as follows: Different from the existing filling process, a vacuum pumping and releasing step is added after filling the bottom filling glue, so that the space between the chip and the readout circuit is filled with the bottom filling glue. Through multiple vacuum pumping and releasing, the bubbles between the chip and the readout circuit can be completely removed, further enhancing the connection strength between the chip and the readout circuit, improving the reliability of the device, and being more suitable for high-density small center distance infrared focal plane devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a photo of bubbles between the chip and the readout circuit when the underfill glue is filled using the existing technology;

[0017] Figure 2 Schematic diagram of the optimization method of the present invention;

[0018] Figure 3 The photo shows the bubble-free effect of filling the bottom filling glue using the method of the present invention. DETAILED DESCRIPTION

[0019] In order to more concisely describe the present embodiment, some parts known to those skilled in the art but not related to the main content of the present invention are omitted in the drawings or descriptions. In addition, for the convenience of description, some parts in the drawings are omitted, enlarged or reduced, but they do not represent the size or entire structure of the actual product.

[0020] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0021] The present invention is further described below in conjunction with the accompanying drawings, which are only used for exemplary description and cannot be understood as limiting the present invention.

[0022] The present invention will now be further described with reference to the embodiments and the accompanying drawings:

[0023] The invention relates to an optimization method for filling glue of a high-density pixel infrared focal plane device. The high-density pixel infrared focal plane device comprises a chip, a readout circuit and a lead substrate. The chip and the readout circuit are connected by an indium column. An underfill glue needs to be filled between the chip and the readout circuit.

[0024] like Figure 2 As shown in the figure, taking the focal plane with a pixel center distance of 7.5 microns and a scale of 2560×2048 as an example, the size of the indium pillars connecting the chip and the readout circuit is 4×4 microns, the height of the indium pillars is 4 microns, and the gap between adjacent indium pillars is 3.5 microns. After compression through the indium pillar reverse solder connection, the gap between the chip and the readout circuit is only about 4 microns. The specific steps for filling glue in such a high-density and small-pitch focal plane device are as follows:

[0025] Step 1: prepare low-temperature bottom fill glue and select bottom fill glue with good fluidity; usually, the bottom fill glue is epoxy resin glue.

[0026] Step 2: Fill the bottom filler with natural flow in a straight line or L-shaped manner between the chip and the readout circuit, that is, fill the bottom filler in a straight line along one side of the chip, or in an L-shaped manner along two adjacent sides of the chip, and let it stand horizontally for 5-10 minutes after filling;

[0027] Step 3: Place the high-density pixel infrared focal plane device in a vacuum device with a vacuum pressure of less than 2000Pa for 5-10 minutes. Through experiments, it is found that when the vacuum pressure is greater than 2000Pa, the fluidity of the bottom fill glue is insufficient and cannot fill the gap between the chip and the readout circuit. The higher the vacuum degree, that is, the smaller the vacuum pressure, the better the filling effect. Preferably, the vacuum pressure of this embodiment is 500Pa and is placed for 10 minutes.

[0028] Step 4: quickly release the vacuum, then let it stand for 3-5 minutes, and observe the overflow of the bottom fill glue around the chip. Preferably, let it stand for 5 minutes.

[0029] If after completing step 4, the underfill glue does not overflow on all four sides of the chip, repeat steps 3 and 4 for multiple times and continue to observe until the underfill glue overflows on all four sides of the chip. This ensures that the space between the chip and the readout circuit is filled with underfill glue without filling defects. Figure 3 shown.

[0030] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. That is, any equivalent changes and modifications made according to the content of the patent application scope of the present invention should be within the technical scope of the present invention.

Claims

1. A method for optimizing the filling of a high-density pixel infrared focal plane device, wherein the high-density pixel infrared focal plane device comprises a chip, a readout circuit and a lead substrate, wherein the chip and the readout circuit are connected by an indium column; characterized in that: The bottom filler needs to be filled between the chip and the readout circuit, including the following steps: Step 1: Prepare low-temperature bottom filler and select bottom filler with good fluidity; Step 2: Fill the gap between the chip and the readout circuit with the bottom filler in a straight or L-shaped manner, and let it sit horizontally for 5-10 minutes. Step 3, placing the high-density pixel infrared focal plane device in a vacuum device with a vacuum pressure of less than 2000 Pa for 5-10 minutes; Step 4: Quickly remove the vacuum, then let it stand for 3-5 minutes and observe the overflow of the bottom fill glue around the chip.

2. The method for optimizing the filling of a high-density pixel infrared focal plane device according to claim 1, characterized in that: The bottom filling glue is epoxy resin glue.

3. The method for optimizing the filling of a high-density pixel infrared focal plane device according to claim 1, characterized in that: The vacuum pressure in step 3 is 500Pa.

4. The method for optimizing the filling of a high-density pixel infrared focal plane device according to claim 1, characterized in that: After completing step 4, if the underfill glue does not overflow on all four sides of the chip, repeat steps 3 and 4 and continue to observe until the underfill glue overflows on all four sides of the chip.

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