Solder paste, solder joint body, and method for manufacturing solder joint body

Abstract

To provide a solder paste capable of uniformizing thickness of a solder layer formed when members are joined to each other, and capable of suppressing generation of voids in the solder layer.SOLUTION: A solder paste contains a solder powder and a spacer, where the content of the spacer is 1 mass% or less, the spacer has melting temperature higher than melting temperature of the solder powder and does not dissolve in solder even when heated at temperature of a melting point of the solder powder +20°C for 5 minutes, the spacer has a columnar or tubular shape, and diameter variation σ / D of the spacer calculated from average diameter D and standard deviation σ of the spacer is 6.0% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a solder paste containing solder powder, a soldered joint in which a first member and a second member are joined via a solder layer, and a method for manufacturing the soldered joint. [Background technology]

[0002] For example, various devices such as LEDs and power modules have a structure in which electronic components such as semiconductor elements are bonded onto a circuit board. When electronic components such as semiconductor elements are joined to a circuit board, methods using solder materials are widely used, as shown in Patent Documents 1 and 2, for example.

[0003] Here, when the electronic component is a semiconductor chip with a large area, a power semiconductor that generates a lot of heat, or a flip-chip mounted chip with multiple electrical connections, the thickness of the solder layer between the electronic component and the substrate varies, making it difficult to maintain a constant distance between the electronic component and the substrate. When the solder layer thickness varies and the electronic component is joined to the board at an angle, the thermal resistance changes within the chip, which is the electronic component, and the expected heat dissipation cannot be achieved. Also, when the electronic component is a high-brightness LED, the light emission angle from the LED does not meet the expected angle.

[0004] Therefore, for example, Patent Document 3 discloses a solder paste that uses Ni balls with a diameter of 1 to 300 μm and a sphericity of 0.90 or more that do not melt at soldering temperatures. Patent Document 1 describes that self-alignment properties can be ensured when the Ni balls are mounted on electrodes of semiconductor elements, and that because the Ni balls do not melt at soldering temperatures, variations in height in solder joints can be suppressed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-271782 [Patent Document 2] Patent Publication No. 2021-010152 [Patent Document 3] Patent No. 5585752 Summary of the Invention [Problem to be solved by the invention]

[0006] However, Patent Document 3 describes a solder paste using Ni balls with a diameter of 1 to 300 μm and a sphericity of 0.90 or more that do not melt at soldering temperatures, but does not disclose details such as the percentage of Ni balls contained in the solder paste. In particular, in the case of Ni powder, which is an aggregate of Ni balls, the percentage of Ni powder contained in the solder paste was not disclosed. As a result, there was a risk that the Ni balls in the solder layer would not be able to fully suppress tilting of electronic components. Furthermore, if the content of Ni balls is increased in order to suppress tilting of electronic components, voids are more likely to form in the solder layer, which may prevent the heat generated by the electronic components from being efficiently transferred to the substrate side through the solder layer.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a solder paste that can make the thickness of the solder layer formed when joining components uniform and can suppress the occurrence of voids in the solder layer, a solder joint in which a first component and a second component are joined via a solder layer of uniform thickness and with few voids, and a method for manufacturing a solder joint. [Means for solving the problem]

[0008] In order to solve the above problems, the solder paste of aspect 1 of the present invention contains solder powder and spacers, the content of the spacers is 1 mass % or less, the melting temperature of the spacers is higher than the melting temperature of the solder powder, and the spacers do not dissolve in the solder even when heated for 5 minutes at a temperature 20°C above the melting point of the solder powder, the spacers are cylindrical or tubular, and the diameter variation σ / D of the spacers calculated from the average diameter D and standard deviation σ of the spacers is 6.0% or less.

[0009] According to the solder paste of aspect 1 of the present invention, the melting temperature is higher than that of the solder powder and the spacer is contained, which does not dissolve in the solder even when heated for 5 minutes at a temperature 20°C above the melting point of the solder powder. The diameter variation σ / D of the spacer calculated from the average diameter D and standard deviation σ of the spacer is 6.0% or less, so that it is possible to make the thickness of the solder layer formed by applying and heating the solder paste uniform. Furthermore, since the content of the spacer is set to 1 mass % or less, it is possible to suppress the formation of voids in the solder layer. Furthermore, because the spacers are cylindrical or tubular, cutting cylindrical or tubular materials with little variation in diameter in the longitudinal direction can reduce the diameter variation σ / D of the spacers, calculated from the average diameter D and standard deviation σ of the spacers. Furthermore, the spacer content can be reduced, making it possible to suppress the occurrence of voids in the solder layer.

[0010] The solder paste of aspect 2 of the present invention is characterized in that in the solder paste of aspect 1 of the present invention, the average diameter D of the spacers is in the range of 1 μm or more and 300 μm or less. According to the solder paste of aspect 2 of the present invention, the average diameter D of the spacers is set within the range of 1 μm or more and 300 μm or less, so that a solder layer of the desired thickness can be formed uniformly within the range of 1 μm or more and 300 μm or less.

[0011] A solder joint of aspect 3 of the present invention is a solder joint in which a first member and a second member are joined via a solder layer, and the solder layer has dispersed therein spacers whose melting temperature is higher than that of the solder layer and which do not melt even when heated for 5 minutes at a temperature 20°C above the melting point of the solder layer, and is characterized in that the tilt angle of the first member is less than 1.0° and the void fraction of the solder layer is 20% or less.

[0012] According to the soldered joint of the third aspect of the present invention, the solder layer contains dispersed spacers whose melting temperature is higher than that of the solder layer and which do not melt even when heated for 5 minutes at a temperature 20°C above the melting point of the solder layer. This allows the solder layer to be formed with a uniform thickness, and the inclination angle of the first member to be less than 1.0°. Furthermore, the void fraction of the solder layer is 20% or less, allowing stable heat transfer between the first member and the second member via the solder layer.

[0013] A soldered joint according to a fourth aspect of the present invention is the soldered joint according to the third aspect of the present invention, characterized in that the average height of the spacers is within the range of 1 μm to 300 μm. According to the solder joint of aspect 4 of the present invention, the average height of the spacers is within the range of 1 μm or more and 300 μm or less, so that the thickness of the solder layer is within the range of 1 μm or more and 300 μm or less, and the distance between the first member and the second member can be made constant.

[0014] A soldered joint of aspect 5 of the present invention is characterized in that, in the soldered joint of aspect 3 or aspect 4 of the present invention, the first member is a circuit board and the second member is a semiconductor element. According to the solder joint of aspect 5 of the present invention, the first member is a circuit board and the second member is a semiconductor element. This prevents the semiconductor element and the circuit board from being joined at an angle, and also allows the heat generated in the semiconductor element to be efficiently transferred to the circuit board via the solder layer, making it possible to construct a semiconductor device with stable performance.

[0015] The method for manufacturing a solder joint of aspect 6 of the present invention is a method for manufacturing a solder joint in which a first member and a second member are joined via a solder layer, and includes a paste application process in which the solder paste of aspect 1 or aspect 2 is applied to either or both of the joining surface of the first member and the joining surface of the second member; a lamination process in which the first member and the second member are stacked via the applied solder paste; and a solder joining process in which the first member and the second member stacked via the solder paste are heat-treated to form a solder layer and join the first member and the second member via the solder layer, and is characterized in that the heating temperature in the solder joining process is equal to or higher than the melting temperature of the solder powder and lower than the melting temperature of the spacer.

[0016] According to the method for producing a soldered joint of the sixth aspect of the present invention, the solder paste of the first or second aspect of the present invention is used, so that spacers are dispersed in the molten solder powder during the soldering process, and the thickness of the solder layer can be determined by these spacers. Furthermore, because a solder paste with a low spacer content is used, the occurrence of voids in the solder layer can be suppressed. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a solder paste that can make the thickness of the solder layer formed when joining components uniform and can suppress the occurrence of voids in the solder layer, a solder joint in which a first component and a second component are joined via a solder layer of uniform thickness and with few voids, and a method for manufacturing a solder joint. [Brief explanation of the drawings]

[0018] [Figure 1] 1A and 1B are schematic explanatory diagrams of a solder paste and a solder joint according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged explanatory view of a solder layer according to an embodiment of the present invention. [Figure 3]1 is an explanatory diagram of the plane filling rate of a solder paste and a solder joint (solder layer) according to one embodiment of the present invention. [Figure 4] FIG. 1 is a flow diagram showing a method for manufacturing a solder joint according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, a solder paste, a soldered joint, and a method for manufacturing a soldered joint according to embodiments of the present invention will be described with reference to the drawings.

[0020] 1, the soldered joint 10 according to this embodiment is formed by joining a first member 11 and a second member 12 via a solder layer 20. In this embodiment, the soldered joint 10 is a semiconductor device in which a circuit board (first member 11) and a semiconductor element (second member 12) are joined via the solder layer 20.

[0021] Here, the circuit board (first member 11) is made of a material with excellent thermal conductivity, such as copper or a copper alloy, aluminum or an aluminum alloy, iron or an iron alloy, or aluminum nitride, and in this embodiment, is made of an iron alloy (Kovar). Note that it is preferable that a film of Au or the like is formed on the joining surface of the circuit board (first member 11) to ensure wetting with solder. Furthermore, it is preferable that a film of Au or the like be formed on the joining surface of the semiconductor element (second member 12) in order to ensure wettability with the solder.

[0022] The solder layer 20 is formed from the solder paste of this embodiment, and as shown in FIG. 2, spacers 21 are dispersed inside the solder layer 20. In this embodiment, the spacer 21 has a cylindrical or tubular shape, as shown in FIG.

[0023] The solder paste of this embodiment will be described below. The solder paste of this embodiment contains solder powder and spacers 21. In this embodiment, the content of the spacers 21 in the solder paste is set to 1 mass % or less. The upper limit of the content of the spacers 21 is preferably 0.5% by mass or less, while the lower limit of the content of the spacers 21 is preferably 0.01% by mass or more, and more preferably 0.1% by mass or more.

[0024] The solder powder is appropriately selected depending on the materials of the joining surfaces of the first member 11 and the second member 12 to be joined. In this embodiment, when the joining surfaces of the circuit board (first member 11) and the semiconductor element (second member 12) are made of a precious metal (Au), for example, Sn-Ag-Cu based solder, Au-Sn based solder, Sn-Cu based solder, etc. can be used as the solder powder. In this embodiment, the solder powder is an Au—Sn solder containing 10 mass % or more and 80 mass % or less of Sn, with the remainder being Au and unavoidable impurities. The average particle size of the solder powder is preferably within the range of 1 μm to 300 μm.

[0025] The spacer 21 is made of a material whose melting temperature is higher than that of the solder powder and which does not melt even when heated for 5 minutes at a temperature 20°C above the melting point of the solder powder. Examples of materials that can be used for the spacer 21 include Cu, Ag, Au, Ni, Pt, Pd, W, and composites of these metals coated on the surfaces of different materials. In this embodiment, since the solder powder is the above-mentioned Au—Sn solder, the spacer 21 has a melting temperature higher than the melting temperature (280° C.) of the solder powder (Au—Sn solder).

[0026] 3, in this embodiment, the spacers 21 are cylindrical or tubular, and the diameter variation σ / D of the spacers 21 calculated from the average diameter D and standard deviation σ of the spacers 21 is set to 6.0% or less. It is more preferable that the diameter variation σ / D is 2.0% or less. Here, the diameter of the cylindrical or tubular spacer 21 is the distance between the two most distant points within one spacer on a cross section perpendicular to the longitudinal direction of the cylinder or tube.

[0027] In this embodiment, the average diameter D of the spacers 21 is preferably within the range of 1 μm to 100 μm. Furthermore, in this embodiment, the aspect ratio (ratio of average diameter D to length L) L / D of the spacer 21 is preferably 1 or more and 50 or less.

[0028] Furthermore, it is preferable that the surface of the spacer 21 is made of a material that has good wettability with the molten solder powder. In this embodiment, since the solder powder is the above-mentioned Au-Sn solder, it is preferable that at least the surface of the spacer 21 is made of a metal material consisting of one or two types selected from Ni and Cu.

[0029] Next, a method for manufacturing the semiconductor device (soldered joint 10) according to this embodiment will be described with reference to the flow chart of FIG.

[0030] (Paste application process S01) First, the solder paste of this embodiment is applied to one or both of the joining surface of the circuit board (first member 11) and the joining surface of the semiconductor element (second member 12). The method for applying the solder paste is not particularly limited, but for example, a metal mask method, a screen printing method, a dispensing method, or the like can be applied.

[0031] (Lamination process S02) The circuit board (first member 11) and the semiconductor element (second member 12) are laminated together via the solder paste applied as described above.

[0032] (Soldering process S03) The circuit board (first member 11) and the semiconductor element (second member 12) laminated together with the solder paste therebetween are subjected to a heat treatment. The heating temperature during this heat treatment is set to be equal to or higher than the melting temperature of the solder powder and lower than the melting temperature of the spacer 21.

[0033] The molten solder paste is solidified to form a solder layer 20, and the circuit board (first member 11) and the semiconductor element (second member 12) are joined together via the solder layer 20. Here, since the spacers 21 are dispersed in the molten solder powder, the thickness of the solder layer 20 (the distance between the circuit board (first member 11) and the semiconductor element (second member 12)) is constant.

[0034] The solder paste of this embodiment configured as described above contains spacers 21 whose melting temperature is higher than that of the solder powder and which do not dissolve in solder even when heated for 5 minutes at a temperature 20°C above the melting point of the solder powder. The diameter variation σ / D of the spacers 21 calculated from the average diameter D and standard deviation σ of the spacers 21 is 6.0% or less, so that it is possible to make the thickness of the solder layer 20 formed by applying and heating the solder paste uniform. Furthermore, since the content of the spacers 21 in the solder paste is set to 1 mass % or less, the formation of voids in the formed solder layer 20 can be suppressed.

[0035] Furthermore, in this embodiment, when the average diameter D of the spacers 21 is within the range of 1 μm or more and 300 μm or less, the thickness of the formed solder layer 20 can be formed uniformly within the range of 1 μm or more and 300 μm or less.

[0036] Furthermore, in this embodiment, when the spacers 21 are cylindrical or tubular, cutting a cylindrical or tubular material with little variation in diameter in the longitudinal direction can reduce the diameter variation σ / D of the spacers 21, calculated from the average diameter D and standard deviation σ of the spacers 21. In addition, the content of the spacers 21 can be reduced, further reducing the occurrence of voids in the formed solder layer 20.

[0037] In the solder joint 10 of this embodiment, spacers 21 having a melting temperature higher than that of the solder layer 20 are dispersed in the solder layer 20, and the diameter variation σ / D of the spacers 21 calculated from the average diameter D and standard deviation σ is 6.0% or less. Therefore, the thickness of the solder layer 20 can be formed uniformly, and the circuit board (first member 11) and the semiconductor element (second member 12) are prevented from being joined at an angle, and the angle of inclination of the circuit board (first member 11) is less than 1.0°. Furthermore, since the content of the spacers 21 in the solder paste is set to 1 mass % or less, the void ratio of the solder layer 20 is 20% or less. Therefore, it is possible to configure a semiconductor device (soldered joint 10) with stable performance.

[0038] Furthermore, in this embodiment, when the average diameter of the spacers 21 is within the range of 1 μm or more and 300 μm or less, the thickness of the solder layer 20 can be formed uniformly within the range of 1 μm or more and 300 μm or less, the distance between the circuit board (first member 11) and the semiconductor element (second member 12) becomes constant, and a semiconductor device (solder joint 10) with stable performance can be manufactured.

[0039] Although the embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the technical idea of ​​the invention. In this embodiment, the solder joint 10 is described as a semiconductor device in which a circuit board (first member 11) and a semiconductor element (second member 12) are joined via a solder layer 20, but this is not limited to this and other solder joints may also be used. Furthermore, although the solder powder has been described as being made of Au-Sn solder, the present invention is not limited to this and other solder materials may be used, such as Sn-based solder, Pb-based solder, etc. It is preferable to select the material of the spacer 21 appropriately depending on the material of the solder powder. [Example]

[0040] The results of confirmation experiments conducted to confirm the effectiveness of the present invention will be described below.

[0041] A solder paste containing the solder powder and spacers shown in Table 1 was prepared. The average diameter of the cylindrical or tubular spacers was measured as follows: The spacers were dispersed on the surface of a carbon tape and spread out with a force that did not deform the spacers. SEM images of the spacers were taken at 500x magnification using a Hitachi TM303 tabletop microscope. Five spacers were randomly selected from the SEM image, and the distance between the two furthest points on each spacer in the direction perpendicular to the length of the spacer was measured. This was taken as the diameter of that spacer. The average of the diameters measured for the five spacers was taken as the average diameter D.

[0042] The above solder paste was applied to a substrate made of Al2O3 with a surface that had been subjected to an Au metallization treatment, so that the thickness after reflow heating would be the diameter of the spacer. Formula for calculating the appropriate paste application thickness: ((solder volume excluding spacers under the chip) / (volume ratio of solder in the solder paste excluding spacers)+(volume of spacers under the chip)) / (chip area) Here, the solder volume is calculated on the assumption that it is the thickness of one spacer, and the spacer volume is calculated from the spacer concentration in the solder paste. A chip (1 mm x 1 mm) was stacked on top of the applied solder paste.

[0043] Then, a reflow oven (SRS-1C manufactured by Malcom) was used to perform a heat treatment in a nitrogen atmosphere according to the following heating pattern, thereby soldering the circuit board and the chip together. Heat from room temperature to 200°C at a rate of 1.5°C / sec, hold at 200°C for 2 minutes, heat from 200°C to 300°C at a rate of 1.5°C / sec, hold at 300°C for 5 seconds.

[0044] The soldered joints obtained as described above were evaluated for voids in the solder layer and tilt of the chip as follows: Furthermore, a comprehensive evaluation of the soldered joints was made from these evaluations.

[0045] (voids in the solder layer) The chip was observed from directly above using a transmission X-ray device, and the ratio of the total area of ​​the voids observed by projecting them to the chip area was taken as the void ratio. The measurement was performed three times, and the average void ratio was calculated.

[0046] (Tilt of the chip) The soldered joint was cut along a plane perpendicular to the center line of the chip surface, and the angle between the substrate surface and the chip surface was measured, which was taken as the inclination of the chip. This measurement was carried out three times to measure the inclination of the chip.

[0047] [Table 1]

[0048] In Comparative Example 1, the solder paste did not contain spacers, and the tilt of the chip was large, at 1.6°. In Comparative Example 2, the spacer content was as high as 30 mass %, and the void ratio in the solder layer was as high as 35%. In Comparative Example 3, the spacer diameter variation σ / D was large at 10.0%, the void rate in the solder layer was high at 25%, and the chip tilt was large at 1.0°. It became. In Comparative Example 4, the spacer diameter variation σ / D was large at 10.0%, and the tip tilt was large at 1.4°.

[0049] In contrast to this, in Examples 1 to 9 of the present invention, it was possible to suppress the occurrence of voids in the solder layer and also to suppress the tilt of the chip.

[0050] From the results of the above confirmation experiments, it was confirmed that the present invention can provide a solder paste that can make the thickness of the solder layer formed when joining components uniform and can suppress the occurrence of voids in the solder layer, a solder joint in which a first component and a second component are joined via a solder layer of uniform thickness and with few voids, and a method for manufacturing a solder joint. [Explanation of symbols]

[0051] 10 Solder joint 11 First member 12 Second member 20 solder layer 21 Spacer

Claims

1. The solder paste contains a solder powder and a spacer, and the content of the spacer is 1 mass % or less, the spacer has a melting temperature higher than that of the solder powder, and is not dissolved in the solder even when heated at a temperature 20°C higher than the melting point of the solder powder for 5 minutes; A solder paste characterized in that the spacers are cylindrical or tubular, and the diameter variation σ / D of the spacers calculated from the average diameter D and standard deviation σ of the spacers is 6.0% or less.

2. 2. The solder paste according to claim 1, wherein the average diameter D of the spacers is in the range of 1 μm to 300 μm.

3. A soldered joint in which a first member and a second member are joined via a solder layer, The solder layer has dispersed therein a spacer having a melting temperature higher than that of the solder layer and not melting even when heated at a temperature of the melting point of the solder layer plus 20°C for 5 minutes, A soldered joint, characterized in that the tilt angle of the first member is less than 1.0° and the void ratio of the solder layer is 20% or less.

4. 4. The solder joint according to claim 3, wherein the average height of the spacers is in the range of 1 μm to 300 μm.

5. 5. The solder joint according to claim 3, wherein the first member is a circuit board and the second member is a semiconductor element.

6. A method for manufacturing a soldered joint in which a first member and a second member are joined via a solder layer, comprising: a paste application step of applying the solder paste according to claim 1 or 2 to one or both of the joining surfaces of the first member and the second member; a lamination step of laminating the first member and the second member via the applied solder paste; a solder bonding process in which the first member and the second member laminated with the solder paste interposed therebetween are heat-treated to form a solder layer, and the first member and the second member are bonded to each other via the solder layer; It has A method for producing a soldered joint, wherein the heating temperature in the soldering step is equal to or higher than the melting temperature of the solder powder and lower than the melting temperature of the spacer.

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