A sintering bonding method for reducing the porosity of nano-metallic paste and application

Abstract

The application belongs to the technical field of device packaging, and particularly relates to a sintering bonding method for reducing the void rate of nano metal paste and application. The sintering bonding method for reducing the void rate of nano metal paste comprises the following steps: S1, printing a nano paste body onto a bonded substrate; S2, placing an electronic device on the nano silver paste; S3, performing freeze drying on the substrate with the electronic device; and S4, performing sintering on the dried product. The freeze drying comprises the following operations: a first stage: pre-freezing, the pre-freezing temperature is below 10 DEG C; a second stage: primary drying; a third stage: secondary drying; and a fourth stage: final drying; or a first stage: pre-freezing, the pre-freezing temperature is below 10 DEG C; a second stage: primary drying; and a third stage: final drying. The sintering bonding method can effectively reduce the void rate of metal bonding, improve the thermal conductivity and bonding strength, and finally improve the reliability of the device.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of device packaging, and particularly relates to a sintering bonding method for reducing the void rate of nano metal paste and application. BACKGROUND

[0002] The existing connection technology between nano-sintered silver / copper and other sintered metals can be divided into the following processes: organic solvent volatilization, decomposition and volatilization of nano-particle surface dispersant or bonding agent, and nano-particle sintering. Among them, the volatilization of organic solvent / dispersant is a key step. Some nano-sintering connection technologies use a wet process. After the electronic device and the nano paste are placed on the substrate, the organic solvent is expanded and vaporized under the action of heat flow and then volatilized. In the vaporization process, large pores are formed in the nano paste. At the same time, due to the coverage of the electronic device, the volatilization channel of the solvent / dispersant in the nano paste is too small, so that the solvent is difficult to volatilize in the nano paste and small pores are easily aggregated to form larger pores (large voids), and even the electronic device is moved or tilted. The pores generated in the subsequent sintering process cannot be healed, forming permanent pores, thereby reducing the bonding strength and the reliability of the bonding. Although there is a dry process in the prior art, which involves baking the nano silver paste first and then placing the electronic device. However, if the thickness of the nano paste required is thick, the nano paste itself will block the volatilization channel and form large pores. Therefore, it is urgent to develop a bonding method capable of reducing the void rate of nano metal paste to effectively improve the bonding strength between nano-sintered metals. SUMMARY

[0003] The application aims to provide a sintering bonding method for reducing the void rate of nano metal paste and application. The sintering bonding method of the application can effectively reduce the void rate of metal bonding, improve the thermal conductivity and the bonding strength, and ultimately improve the reliability of the device.

[0004] To achieve the above-mentioned purpose, the application adopts the following technical scheme: a sintering bonding method for reducing the void rate of nano metal paste, comprising the following steps:

[0005] S1, printing the nano paste onto the bonded substrate;

[0006] S2, placing the electronic device on the nano silver paste;

[0007] S3, freeze-drying the substrate with the electronic device;

[0008] S4, sintering the dried product;

[0009] The freeze-drying in step S3 includes the following operations:

[0010] The first stage is pre-freezing at a temperature below 10℃; the heat is removed by pre-freezing to cool the nano-sintered metal paste and freeze it into a solid;

[0011] The second stage is primary drying; during this process, the solvent ice crystals on the surface of the nano-sintered metal paste begin to sublimate, and as the process continues, the solvent ice crystals inside the paste also gradually sublimate, and the solvent atmosphere produced by sublimation is discharged from the nano-channels produced by previous drying. It should be noted that the speed of solvent atmosphere drying depends on the vacuum degree, and as the continuous drying process ends, the solvent in the nano-sintered paste is basically completely sublimated;

[0012] The third stage is secondary drying; the fourth stage is final drying;

[0013] Or the first stage is pre-freezing at a temperature below 10℃; the second stage is primary drying; and the third stage is final drying.

[0014] The secondary drying or final drying steps in the present application are both to remove as much residual solvent as possible from the nano-sintered metal paste. Because the capillary force of the solvent needs to be overcome during secondary drying or final drying, and because increasing the temperature to remove residual solvent will cause pores to gather and cause glue to overflow, resulting in short circuits in electronic devices, the removal of the solvent needs to be achieved by increasing the vacuum degree in a gradient manner.

[0015] Preferably, the pre-freezing temperature in the first stage of the freeze-drying is below -10℃.

[0016] More preferably, the pre-freezing temperature in the first stage of the freeze-drying is between -20℃ and -40℃.

[0017] Preferably, the temperature of the primary drying in step S3 is the temperature of the first stage.

[0018] Preferably, the vacuum value of the primary drying in step S3 is below 10mbar. More preferably, the vacuum value of the primary drying is below 5mbar. The best results can be achieved when the vacuum value of the primary drying is below 1mbar.

[0019] Preferably, the time of the primary drying in step S3 is between 30min and 60min.

[0020] In the first stage of freeze-drying, if the vacuum degree and temperature are too high, the initial solvent will volatilize rapidly, resulting in a large number of pores. If the vacuum degree and temperature are too low, the drying rate will be too low, affecting production efficiency.

[0021] Preferably, the temperature of the secondary drying or final drying in step S3 is the temperature of the first stage.

[0022] Preferably, the vacuum value of the secondary drying or final drying in step S3 is lower than 1 mbar.

[0023] More preferably, the vacuum value of the secondary drying or final drying in step S3 is 0.8 mbar to 0.05 mbar.

[0024] Preferably, the time of the secondary drying or final drying in step S3 is 30 to 60 minutes.

[0025] Preferably, the sintering condition in step S4 is sintering for 5 to 10 minutes under 10 to 20 MPa. The sintering condition in the present application can be the sintering condition suitable for all sintered products in the industry.

[0026] In the present application, the entire drying process is carried out at a low temperature, so the organic solvent does not expand by vaporization, and at the same time, since the nano-paste skeleton is frozen, the formation of large pores is inhibited, so that the dried connection bonding layer is uniform and dense, thereby reducing the void rate of the metal bonding, improving the thermal conductivity, and enhancing the bonding strength, and finally greatly improving the reliability of the device. At the same time, due to the sublimation of the solvent, nanometer / micrometer channels are left, which are uniformly distributed in the entire metal bonding layer. In the use of the device, these channels can absorb stress, thereby further improving the reliability of the metal bonding.

[0027] The present application also claims an electronic device prepared by the sintering bonding method for reducing the void rate of nano-metal paste.

[0028] The present application also claims the application of the sintering bonding method for reducing the void rate of nano-metal paste in the field of electronic device bonding.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] The sintering bonding method of the present application can effectively reduce the void rate of the metal bonding, improve the thermal conductivity, and enhance the bonding strength, thereby finally improving the reliability of the device. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The failure microscope image (partial enlargement) of the metal bonding section of the product prepared in Example 1 of the present application.

[0032] Figure 2 The failure microscope image (partial enlargement) of the metal bonding section of the product prepared in Example 4 of the present application.

[0033] Figure 3 The failure microscope image (overall) of the metal bonding section of the product prepared in Example 1 of the present application.

[0034] Figure 4Failure microscope image (overall) of the product metal bonding section prepared for Invention Comparative Example 1. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0036] In the embodiments and comparative examples, the experimental methods used are conventional methods, and the materials, reagents, etc. used are commercially available unless otherwise specified.

[0037] Example 1

[0038] S1, printing the nano paste onto the bonded substrate;

[0039] S2, placing the electronic device onto the nano silver paste;

[0040] S3, freeze-drying the substrate with the electronic device attached;

[0041] S4, sintering the dried product at 15 MPa for 5 minutes.

[0042] The specific operation of freeze-drying is as follows:

[0043] First stage: pre-freezing at -10°C for 10 minutes;

[0044] Second stage: primary drying, 1 mbar, -10°C, 10 minutes;

[0045] Third stage: final drying, 0.05 mbar, -10°C, 10 minutes.

[0046] Example 2

[0047] S1, printing the nano paste onto the bonded substrate;

[0048] S2, placing the electronic device onto the nano silver paste;

[0049] S3, freeze-drying the substrate with the electronic device attached;

[0050] S4, sintering the dried product at 10 MPa for 10 minutes.

[0051] The specific operation of freeze-drying is as follows:

[0052] First stage: pre-freezing at 10°C for 10 minutes;

[0053] Second stage: primary drying, 1 mbar, 10°C, 10 minutes;

[0054] Third stage: final drying, 0.05 mbar, 10°C, 10 minutes.

[0055] Example 3

[0056] S1, printing the nano-paste onto the adherend substrate;

[0057] S2, placing the electronic device onto the nano-silver paste;

[0058] S3, freeze-drying the substrate with the electronic device attached;

[0059] S4, sintering the dried product at 15 MPa for 5 minutes.

[0060] The specific operation of freeze-drying is as follows:

[0061] First stage: pre-freezing at -10°C for 30 minutes;

[0062] Second stage: primary drying, 5 mbar, -10°C, 30 minutes;

[0063] Third stage: final drying, 0.05 mbar, -10°C, 30 minutes.

[0064] Example 4

[0065] S1, printing the nano-paste onto the adherend substrate;

[0066] S2, placing the electronic device onto the nano-silver paste;

[0067] S3, freeze-drying the substrate with the electronic device attached;

[0068] S4, sintering the dried product at 15 MPa for 5 minutes.

[0069] The specific operation of freeze-drying is as follows:

[0070] First stage: pre-freezing at -10°C for 10 minutes;

[0071] Second stage: primary drying, 0.5 mbar, -10°C, 10 minutes;

[0072] Third stage: final drying, 0.05 mbar, -10°C, 10 minutes.

[0073] Example 5

[0074] S1, printing the nano-paste onto the substrate to be bonded;

[0075] S2, placing the electronic device onto the nano-silver paste;

[0076] S3, freeze-drying the substrate with the electronic device attached;

[0077] S4, sintering the dried product at 15 MPa for 5 minutes.

[0078] The freeze-drying is carried out as follows:

[0079] First stage: pre-freezing at -20°C for 10 minutes;

[0080] Second stage: primary drying, 1 mbar, -20°C, 10 minutes;

[0081] Third stage: secondary drying, 0.05 mbar, -20°C, 10 minutes;

[0082] Fourth stage: final drying, 0.05 mbar, -20°C, 10 minutes.

[0083] Example 6

[0084] S1, printing the nano-paste onto the substrate to be bonded;

[0085] S2, placing the electronic device onto the nano-silver paste;

[0086] S3, freeze-drying the substrate with the electronic device attached;

[0087] S4, sintering the dried product at 15 MPa for 5 minutes.

[0088] The freeze-drying is carried out as follows:

[0089] First stage: pre-freezing at -20°C for 30 minutes;

[0090] Second stage: primary drying, 1 mbar, -20°C, 30 minutes;

[0091] Third stage: secondary drying, 0.05 mbar, -20°C, 30 minutes;

[0092] Fourth stage: final drying, 0.05 mbar, -20°C, 30 minutes.

[0093] Example 7

[0094] S1, printing the nano-paste onto the substrate to be bonded;

[0095] S2, placing the electronic device onto the nano-silver paste;

[0096] S3, freeze-drying the substrate with the electronic device attached;

[0097] S4, sintering the dried product at 15 MPa for 5 minutes.

[0098] The freeze-drying is performed according to the following procedure:

[0099] First stage: pre-freezing at -40°C for 30 minutes;

[0100] Second stage: primary drying, 1 mbar, -40°C, 30 minutes;

[0101] Third stage: secondary drying, 0.05 mbar, -40°C, 30 minutes;

[0102] Fourth stage: final drying, 0.05 mbar, -40°C, 30 minutes.

[0103] Example 8

[0104] S1, printing the nano-paste onto the substrate to be bonded;

[0105] S2, placing the electronic device onto the nano-silver paste;

[0106] S3, freeze-drying the substrate with the electronic device attached;

[0107] S4, sintering the dried product at 15 MPa for 5 minutes.

[0108] The freeze-drying is performed according to the following procedure:

[0109] First stage: pre-freezing at -10°C for 10 minutes;

[0110] Second stage: primary drying, 1 mbar, -5°C, 10 minutes;

[0111] Third stage: final drying, 0.05 mbar, -5°C, 10 minutes.

[0112] Example 9

[0113] S1, printing the nano-paste onto the substrate to be bonded;

[0114] S2, placing the electronic device onto the nano-silver paste;

[0115] S3, freeze-drying the substrate with the electronic device attached;

[0116] S4, sintering the dried product at 15 MPa for 5 minutes.

[0117] The freeze-drying is performed according to the following procedure:

[0118] First stage: pre-freezing at -10°C for 10 minutes;

[0119] Second stage: primary drying, 1 mbar, -10°C, 10 minutes;

[0120] Third stage: final drying, 0.8 mbar, -10°C, 10 minutes.

[0121] Comparative Example 1

[0122] S1, printing the nano-paste onto the adherend substrate;

[0123] S2, placing the electronic device onto the nano-silver paste;

[0124] S3, drying the solvent by baking the substrate with the electronic device directly, placing the substrate with the electronic device into a 100°C oven for 1 hour to volatilize the solvent;

[0125] S4, sintering the dried product at 15 MPa for 5 minutes.

[0126] The difference between the comparative example and Example 1 is only that the drying method of the substrate in step S3 is different.

[0127] Comparative Example 2

[0128] S1, printing the nano-paste onto the adherend substrate;

[0129] S2, placing the electronic device onto the nano-silver paste;

[0130] S3, freeze-drying the substrate with the electronic device;

[0131] S4, sintering the dried product at 15 MPa for 5 minutes.

[0132] The specific operation of freeze-drying is as follows:

[0133] First stage: pre-freezing at 15°C for 10 minutes;

[0134] Second stage: primary drying, 1 mbar, 15°C, 10 minutes;

[0135] Third stage: final drying, 0.05 mbar, 15°C, 10 minutes.

[0136] The difference between the comparative example and Example 1 is only that the pre-freezing temperature is 15°C.

[0137] Comparative Example 3

[0138] S1, printing the nano-paste onto the adherend substrate;

[0139] S2, placing the electronic device on the nano-silver paste;

[0140] S3, freeze-drying the substrate with the electronic device;

[0141] S4, sintering the dried product at 15 MPa for 5 minutes.

[0142] The specific operation of freeze-drying is as follows:

[0143] First stage: pre-freezing at -10°C for 10 minutes;

[0144] Second stage: primary drying, 15 mbar, -10°C, 10 minutes;

[0145] Third stage: final drying, 0.05 mbar, -10°C, 10 minutes.

[0146] Compared with Example 1, the only difference of the present comparative example is that the vacuum value of primary drying is 15 mbar.

[0147] Comparative Example 4

[0148] S1, printing the nano-paste to the bonding substrate;

[0149] S2, placing the electronic device on the nano-silver paste;

[0150] S3, freeze-drying the substrate with the electronic device;

[0151] S4, sintering the dried product at 15 MPa for 5 minutes.

[0152] The specific operation of freeze-drying is as follows:

[0153] First stage: pre-freezing at -10°C for 30 minutes;

[0154] Second stage: primary drying, 5 mbar, -10°C, 30 minutes;

[0155] Third stage: final drying, 1.4 mbar, -10°C, 30 minutes.

[0156] Compared with Example 3, the only difference of the present comparative example is that the vacuum value of final drying is 1.4 mbar.

[0157] Performance test

[0158] The products prepared in Examples 1-9 and Comparative Examples 1-4 were tested in the following items, and the test standards are shown in Table 1, and the performance test results are shown in Table 2.

[0159] Table 1 Performance test standards

[0160] Table 1 Performance test standards

[0160] Table 1 Performance test standards

[0160]

[0161] Table 2: Performance test results of each sample

[0162]

[0163]

[0164] From the data in Table 2, it can be seen that the products prepared by the embodiments of the present application all have a low void rate, and the thermal conductivity, shear strength, cold-heat shock times and other performances can all meet the standard requirements, and can better meet the requirements of semiconductor metal interconnection.

[0165] Comparative Example 1 is a prior art directly using a baking drying solvent method, and the sample prepared thereby has a void rate of 65.3%, and the thermal conductivity, shear strength, cold-heat shock times and other performances are all significantly poorer than the embodiments; Comparative Example 2 selects a too high freezing temperature in the freeze drying process, resulting in an increased void rate of the sample; Comparative Example 3 has an unsuitable vacuum value for the initial drying in the freeze drying, and Comparative Example 4 has an unsuitable vacuum value for the final drying in the freeze drying, both of which result in poorer performances such as thermal conductivity and shear strength of the prepared sample than the embodiments.

[0166] From the attached Figures 1 to 4 It can be seen that the void rate of Example 4 of the present application is slightly lower than that of Example 1, and the bonding (fitting) surface of Example 1 of the present application has no obvious large holes, while the bonding (fitting) surface of Comparative Example 1 using a traditional baking drying process has a giant hole of more than 1 mm.

[0167] The above examples are only illustrative of the principles and effects of the present application, and are not intended to limit the present application. Any person skilled in the art can modify or change the above examples without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical thought disclosed by the present application should still be covered by the claims of the present application.

Claims

1. A sintering bonding method for reducing the void ratio of a nano metal paste, characterized by, The method comprises the following steps: S1, printing nano-silver paste onto a bonding substrate; S2, placing an electronic device onto the nano-silver paste; S3, freeze-drying the substrate with the electronic device; S4, sintering the dried product; The freeze-drying in step S3 comprises the following operations: a first stage: pre-freezing at a temperature of -10℃ or below; a second stage: primary drying; a third stage: secondary drying; and a fourth stage: final drying; or a first stage: pre-freezing at a temperature of -10℃ or below; a second stage: primary drying; and a third stage: final drying; The vacuum value of the primary drying in step S3 is lower than 10 mbar; The vacuum value of the secondary drying or final drying in step S3 is lower than 1 mbar; The pre-freezing time in step S3 is 10 min or 30 min; The freeze-drying is performed in a gradient manner; The drying time is consistent with the pre-freezing time; The temperature of the primary drying in step S3 is the temperature of the first stage; The temperature of the secondary drying or final drying in step S3 is the temperature of the first stage.

2. The sintering bonding method for reducing the void ratio of a nano metal paste according to claim 1, wherein The pre-freezing temperature of the first stage in the freeze-drying is -20~ -40℃.

3. The method of claim 1, wherein the nano metal paste has a sintering temperature of 300-400°C. The vacuum value of the primary drying in step S3 is lower than 5 mbar.

4. The method of claim 1, wherein the nano metal paste has a sintering temperature of 300-400°C. The sintering condition in step S4 is sintering at 10~20 MPa for 5~10 min.

5. An electronic device prepared by the sintering bonding method for reducing the void rate of nano-metal paste according to any one of claims 1~4.

6. Application of the sintering bonding method for reducing the void rate of nano-metal paste according to any one of claims 1~4 in the field of electronic device bonding.

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