Flip-chip inspection sample and preparation method thereof

Abstract

The invention discloses a flip-chip inspection sample and a preparation method thereof. The preparation method comprises the following steps: (1) pasting a chip on a base film, then scribing the chip along the transverse or longitudinal direction to form a plurality of long strips, and then taking down the long strips from the base film to obtain a primary inspection sample; and (2) polishing the cutting section of the primary inspection sample in the step (1), and washing after polishing to obtain the flip-chip inspection sample. According to the method, the flip-chip bonding chip is subjected to scribing and polishing treatment to obtain a test sample, the test sample is detected by an optical microscope, a scanning electron microscope, X-ray tomography and other methods, and the connection condition between the salient points of the chip and the colloid underfilling condition can be clearly seen; the problem of checking the bump connection condition of the flip-chip can be solved.

Description

Technical Field

[0001] The invention belongs to the technical field of material performance characterization, and in particular relates to a flip-chip inspection sample and a preparation method thereof. Background Art

[0002] The flip-chip device consists of three parts from top to bottom: chip, bump (indium column) and readout circuit. The active side of the chip is facing downward, opposite to the bottom readout circuit. With the help of the solder bump array in the middle, several independent electrical paths are formed to realize independent circuit connection between the chip and the corresponding unit of the readout circuit. The core content of the flip-chip packaging method is to replace the traditional bonding wire interconnection with the bump interconnection method, so as to achieve high-density and high-efficiency electrical connection. Due to the limitation of the wire arrangement, the pads of the traditional wire bonding method are generally distributed around the edge of the device, and the wire density is low. The flip-chip technology realizes the longitudinal expansion of the device in space. The bumps can be arranged in a planar array on the inner surface of the chip and the readout circuit, and its electrode density is much higher than that of the wire bonding. In addition, the device using the flip-chip technology also has the advantages of high alignment accuracy, small device size, small interconnection parasitic parameters, and fast transmission rate. It is precisely because of the collection of a large number of advantages that the flip-chip packaging form is the representative of contemporary advanced packaging forms. At present, the performance test of flip-chip interconnected devices is basically non-destructive electrical parameters, such as focal plane detectivity, noise equivalent temperature difference (NETD), etc. However, electrical parameters cannot directly reflect the bump interconnection process and the colloid bottom filling after interconnection. Therefore, there is no effective method to test the bump connection of flip-chip devices. Summary of the invention

[0003] The invention provides a flip-chip inspection sample and a preparation method thereof, so as to achieve the purpose that the inspection sample can be used to observe the connection status of bumps.

[0004] The present invention provides a method for preparing a flip-chip inspection sample, which adopts the following technical scheme: A method for preparing a flip chip inspection sample comprises the following steps: (1) Paste the chip on the base film, then cut the chip in the horizontal or vertical direction into several strips, and then remove the strips from the base film to obtain a primary test sample; (2) The cut cross section of the primary inspection sample in step (1) is polished, and after polishing, it is washed to obtain a flip chip inspection sample.

[0005] Preferably, in step (1), the base film is a blue film; and the width of the long strip during dicing is 0.8-1.2 mm.

[0006] Preferably, in step (1), a dicing machine is used for dicing; the spindle speed of the dicing machine is 28000-32000 rpm, and the feed speed is 0.9-1.1 mm / s.

[0007] Preferably, in step (1), the type of scribing knife used for scribing is a hubless electroformed soft knife; the diamond particle size of the hubless electroformed soft knife is 3000#~4000#, and the diamond volume concentration is 60~90%.

[0008] Preferably, in step (2), the polishing liquid used in the polishing treatment is a mixed solution of silicon dioxide solution and hydrogen peroxide solution.

[0009] Further preferably, the mass concentration of the silicon dioxide solution is 12% to 13%, and the mass concentration of the hydrogen peroxide solution is 40% to 50%; the volume ratio of the silicon dioxide solution to the hydrogen peroxide solution in the mixed solution is (90 to 100):(9 to 10).

[0010] Preferably, in step (2), during the polishing process, the rotation speed of the polishing fixture is 40-50 rpm, and the rotation speed of the working disc is 40-50 rpm.

[0011] Preferably, in step (2), during the polishing process, the flow rate of the polishing liquid is 10-12 mL / min; the pressure of the polishing process is 180-220 g / cm 2 The polishing time is 10~15min.

[0012] Preferably, in the step (2), after washing, a nitrogen drying step is also included.

[0013] Based on the same inventive concept, the present invention provides a flip-chip inspection sample prepared by the above preparation method.

[0014] The above one or more technical solutions of the present invention can achieve at least one of the following beneficial effects: In the method of the present invention, the flip-chip chip is diced and polished to obtain a test sample. By using an optical microscope, a scanning electron microscope, an X-ray tomography detection method and the like, the connection between the bumps of the chip and the bottom filling glue condition can be clearly seen, and the problem of bump connection condition inspection of the flip-chip chip can be solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is an electron microscope image of the cross section of the flip chip inspection sample prepared in Example 1.

[0016] Figure 2 This is an electron microscope image of the cross-section of the flip-chip inspection sample prepared in Comparative Example 1.

[0017] Figure 3 This is an electron microscope image of the cross-section of the flip-chip inspection sample prepared in Example 2.

[0018] Figure 4 This is an electron microscope image of the cross-section of the flip-chip inspection sample prepared in Example 3. DETAILED DESCRIPTION

[0019] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments. Unless otherwise defined, all the professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0020] Example 1 The preparation method of the infrared focal plane flip chip (model VM1215MB) test sample in this embodiment is as follows: (1) Place the infrared focal plane flip-chip on the blue film; use a dicing machine to cut the chip into 5 strips of 1 mm width along the X-axis; when dicing, the spindle speed of the dicing machine is 30,000 rpm, the feed speed is 1 mm / s, the dicing knife type is a hubless electroformed soft knife, the blade width is 0.1 mm, the diamond particle size is 3000#, and the diamond volume concentration is 80%. Gently press the back of the blue film with your fingers to lift up the diced strips, and remove the strips with tweezers to obtain the strips to be polished.

[0021] (2) Heat the polishing fixture to 75°C on a heating table, then apply paraffin wax on the polishing fixture. The area of ​​the paraffin wax coating should be larger than the chip area. Then, use tweezers to pick up the strip to be polished, with the cut section of the strip facing upward, and stick it to the area of ​​the polishing fixture coated with paraffin wax. After the polishing fixture cools to room temperature, use a dust-free cloth dipped in alcohol to wipe off the wax on the cross section of the strip. This will give you a fixture that fixes the strip to be polished.

[0022] (3) Install the fixture that fixes the strip to be polished on the CMP polishing machine, polish the cross section of the strip to be polished, and obtain a polished test sample, wherein: the polishing solution used for polishing is a mixed solution of silicon dioxide solution (silicon dioxide particle size is 100nm) and hydrogen peroxide solution. The mixed solution is obtained by mixing a silicon dioxide solution with a mass concentration of 12% and a hydrogen peroxide solution with a mass concentration of 45% in a volume ratio of 10:1. The rotation speed of the fixture is 40rpm, the rotation speed of the working disk is 40rpm, the flow rate of the polishing solution is 12mL / min, and the polishing pressure is 200g / cm 2 The polishing time is 10 minutes. After the surface of the polished test sample is cleaned with pure water, it is blown dry with nitrogen to obtain the infrared focal plane flip chip test sample.

[0023] Comparative Example 1 In this comparative example, no polishing treatment was performed. The long strip cross section to be polished in step (1) of Example 1 was directly washed with pure water and dried with nitrogen to serve as an infrared focal plane flip-chip inspection sample.

[0024] The cross sections of the infrared focal plane flip-chip test samples of Example 1 and Comparative Example 1 were observed by electron microscope, and the cross sections were as follows: Figure 1 and Figure 2 As shown, it can be seen that in Comparative Example 1, polishing is not performed, and the observed cross section is uneven and blurred, and the connection of the bumps and the condition of the underfill cannot be clearly observed. After polishing in Example 1, the cross section is very clear, and the connection of the bumps and the condition of the underfill can be clearly observed.

[0025] Example 2 The preparation method of the infrared focal plane flip chip (VM0615MB) test sample in this embodiment is as follows: (1) Stick the infrared focal plane flip-chip chip on the blue film; use a dicing machine to cut the chip into 4 strips with a width of 1.2 mm along the X-axis direction; when dicing, the spindle speed of the dicing machine is 28000 rpm, the feed speed is 0.9 mm / s, the dicing knife type is a hubless electroformed soft knife, the blade width is 0.1 mm, the diamond particle size is 4000#, and the diamond volume concentration is 80%. Press the back of the blue film gently with your fingers to lift up the diced strips, and remove the strips with tweezers to obtain the strips to be polished.

[0026] (2) Heat the polishing fixture to 80°C on a heating table, then coat the polishing fixture with paraffin wax. The area of ​​the paraffin wax coating should be larger than the chip area. Then, use tweezers to pick up the strip to be polished, with the cross section of the strip facing upward, and stick it to the area of ​​the polishing fixture coated with paraffin wax. After the polishing fixture cools to room temperature, use a dust-free cloth dipped in alcohol to wipe off the paraffin wax on the cross section of the strip. This will give you a fixture that holds the strip to be polished.

[0027] (3) Install the fixture that holds the strip to be polished on the CMP polishing machine, and then polish the cross section of the strip to be polished to obtain a polished test sample, wherein: the polishing solution used for polishing is a mixed solution of a silicon dioxide solution (the particle size of silicon dioxide is 100nm) and a hydrogen peroxide solution. The mixed solution is obtained by mixing a silicon dioxide solution with a mass concentration of 13% and a hydrogen peroxide solution with a mass concentration of 40% in a volume ratio of 9:1. The rotation speed of the fixture is 45rpm, the rotation speed of the working disk is 45rpm, the flow rate of the polishing solution is 10mL / min, and the polishing pressure is 180g / cm 2 The polishing time is 15 minutes. After the surface of the polished test sample is cleaned with pure water, it is blown dry with nitrogen to obtain an infrared focal plane flip-chip.

[0028] The polished cross section of the infrared focal plane flip chip test sample prepared in this embodiment was observed by electron microscope. The results are as follows: Figure 3 As shown, the cross section is relatively clear, and the connection status of the bumps and the bottom filling glue can be clearly observed.

[0029] Example 3 The preparation method of the infrared focal plane flip chip (VM0615MB) test sample in this embodiment is as follows: (1) Stick the infrared focal plane flip-chip chip on the blue film; use a dicing machine to cut the chip into 6 strips with a width of 0.8 mm along the X-axis direction; when dicing, the spindle speed of the dicing machine is 32000 rpm, the feed speed is 1.1 mm / s, the dicing knife type is a hubless electroformed soft knife, the blade width is 0.1 mm, the diamond particle size is 3000#, and the diamond volume concentration is 90%. Press the back of the blue film gently with your fingers to lift up the diced strips, and remove the strips with tweezers to obtain the strips to be polished.

[0030] (2) Heat the polishing fixture to 80°C on a heating table, then coat the polishing fixture with paraffin wax. The area of ​​the paraffin wax coating should be larger than the chip area. Then, use tweezers to pick up the strip to be polished, with the cross section of the strip facing upward, and stick it to the area of ​​the polishing fixture coated with paraffin wax. After the polishing fixture cools to room temperature, use a dust-free cloth dipped in alcohol to wipe off the paraffin wax on the cross section of the strip. This will give you a fixture that holds the strip to be polished.

[0031] (3) The fixture holding the strip to be polished is installed on the CMP polishing machine, and then the cross section of the strip to be polished is polished to obtain a polished test sample, wherein: the polishing solution used for polishing is a mixed solution of a silicon dioxide solution (the particle size of silicon dioxide is 100nm) and a hydrogen peroxide solution. The mixed solution is obtained by mixing a silicon dioxide solution with a mass concentration of 12% and a hydrogen peroxide solution with a mass concentration of 50% in a volume ratio of 100:9. The rotation speed of the fixture is 50rpm, the rotation speed of the working disk is 50rpm, the flow rate of the polishing solution is 10mL / min, and the polishing pressure is 220g / cm 2 The polishing time is 12 minutes. After the surface of the polished test sample is cleaned with pure water, it is blown dry with nitrogen to obtain the infrared focal plane flip chip test sample.

[0032] The polished cross section of the infrared focal plane flip chip test sample prepared in this embodiment was observed by electron microscope. The results are as follows: Figure 4 As shown, the cross section is relatively clear, and the connection status of the bumps and the bottom filling glue can be clearly observed.

[0033] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a flip chip inspection sample, characterized in that: The following steps are involved: (1) Paste the chip on the base film, then cut the chip in the horizontal or vertical direction into several strips, and then remove the strips from the base film to obtain a primary test sample; (2) The cut cross section of the primary inspection sample in step (1) is polished, and after polishing, it is washed to obtain a flip chip inspection sample.

2. The method for preparing a flip chip inspection sample according to claim 1, characterized in that: In the step (1), the base film is a blue film; and the width of the long strip during dicing is 0.8-1.2 mm.

3. The method for preparing a flip chip inspection sample according to claim 1, characterized in that: In the step (1), a dicing machine is used for dicing; during dicing, the spindle speed of the dicing machine is 28000-32000 rpm, and the feed speed is 0.9-1.1 mm / s.

4. The method for preparing a flip chip inspection sample according to claim 1 or 3, characterized in that: In the step (1), the type of scribing knife used for scribing is a hubless electroformed soft knife; the diamond particle size of the hubless electroformed soft knife is 3000#~4000#, and the diamond volume concentration is 60~90%.

5. The method for preparing a flip chip inspection sample according to claim 1, characterized in that: In the step (2), the polishing liquid used in the polishing process is a mixed solution of silicon dioxide solution and hydrogen peroxide solution.

6. The method for preparing a flip chip inspection sample according to claim 5, characterized in that: The mass concentration of the silicon dioxide solution is 12% to 13%, and the mass concentration of the hydrogen peroxide solution is 40% to 50%; the volume ratio of the silicon dioxide solution to the hydrogen peroxide solution in the mixed solution is (90 to 100):(9 to 10).

7. The method for preparing a flip chip inspection sample according to claim 1 or 5, characterized in that: In the step (2), during the polishing process: the rotation speed of the polishing fixture is 40-50 rpm, and the rotation speed of the working disc is 40-50 rpm.

8. The method for preparing a flip chip inspection sample according to claim 1 or 5, characterized in that: In the step (2), during the polishing process, the flow rate of the polishing liquid is 10-12 mL / min; the pressure of the polishing process is 180-220 g / cm 2 The polishing time is 10~15min.

9. The method for preparing a flip chip inspection sample according to claim 1, characterized in that: In the step (2), after washing, a nitrogen drying step is also included.

10. A flip chip inspection sample, characterized in that: The method is prepared by any one of claims 1 to 9.

Images