Manufacturing method of preform solder

Abstract

With a method for manufacturing a solder preform that includes a step in which lead-free solder particles and particles of a metal with a higher melting point than the lead-free solder are mixed by stirring, a step in which a homogeneous powder is obtained in a particulate state, a step in which the mixed powder is compression-molded to obtain a compression-molded article, and a step in which the compression-molded article is molded into a prescribed shape by an extrusion molding device to obtain an extrusion-molded article, it is possible to provide a method for manufacturing a solder preform that allows a solder preform in which metal particles are dispersed uniformly in a lead-free solder to be obtained with simpler size management of the metal particles than was previously possible, without the metal particles becoming smaller, flux being left behind, or the like.

Description

[Technical field]

[0001] The present invention relates to a method for producing a solder preform. [Background technology]

[0002] Conventionally, when soldering terminals of electronic components such as integrated circuits (ICs) to printed circuit boards or attaching semiconductor chips to boards, a method of placing solder paste or solder sheet at required locations and heating in a reflow furnace or the like may be adopted. In such reflow soldering methods, the solder melted by heating may be pushed out from between the joined members by the weight of the electronic components, semiconductor chips, etc., which may result in a decrease in the joining strength. In addition, when an electronic component is joined to a board at an angle, thermal stress may be applied to the thinned solder joints as a result of long-term use, which may cause cracks in the solder joints.

[0003] As a measure to improve these problems, for example, a composite material in which metal particles are dispersed in a solder alloy and a method for manufacturing the composite material have been proposed (Patent Documents 1 and 2).

[0004] Patent documents 1 and 2 disclose a method for manufacturing a solder preform, in which a mixed master alloy is prepared from a mixture of a thermally decomposable flux and high-melting point metal particles, the mixed master alloy is poured into and stirred with a large amount of molten solder to prepare a billet, and the billet is then subjected to extrusion, rolling and punching processes to form pellets or washers. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-99789 A [Patent Document 2] International Publication No. 2007 / 032429 Summary of the Invention [Problem to be solved by the invention]

[0006] The technology for incorporating metal particles disclosed in Patent Documents 1 and 2 involves preparing a mixed master alloy from a mixture of thermally decomposable flux and high-melting point metal particles, and then introducing and stirring the mixed master alloy into a large amount of molten solder to produce a billet.Compared to the conventional method of directly introducing a specified amount of metal particles into the molten solder, the technology is described as solving the problems of metal particles being eroded by the molten solder and becoming smaller in size, or flux remaining behind.

[0007] However, in the conventional method of directly introducing metal particles into molten solder and the method described in Patent Documents 1 and 2 of preparing a mixed master alloy and introducing and stirring the mixed master alloy into a large amount of molten solder to prepare a billet, both methods involve introducing metal particles into molten solder, which not only poses the problem of dispersing the metal particles uniformly in the molten solder, but also creates the possibility that the metal particles will be eroded by the molten solder and become smaller. Furthermore, since the melting point and characteristics during melting vary depending on the composition of the molten solder, it becomes complicated to manage the size of the metal particles.

[0008] Therefore, the present invention aims to provide a method for manufacturing preform solder, which can produce preform solder in which metal particles are uniformly dispersed in lead-free solder without the metal particles becoming small or leaving flux behind, by simply managing the size of the metal particles more simply than in the past. [Means for solving the problem]

[0009] As a result of extensive research into a manufacturing method that can uniformly disperse metal particles in lead-free solder and easily maintain and control the particle size, the inventors discovered that the above-mentioned problems can be solved by obtaining a uniform mixed powder of lead-free solder particles and metal particles having a higher melting point than the lead-free solder, pressurizing and molding this to obtain a pressurized molded product, and then molding the pressurized molded product into a predetermined shape via the extrusion molding to obtain a preform solder.

[0010] The present invention relates to a method for manufacturing a preformed solder, the method including the steps of mixing and stirring particles of lead-free solder with particles of a metal having a melting point higher than that of the lead-free solder to obtain a uniform mixed powder in a particulate state, pressurizing and molding the mixed powder to obtain a pressurized molded product, and molding the pressurized molded product into a predetermined shape in an extrusion molding device to obtain an extrusion molded product.

[0011] In an embodiment of the present invention, the method may further include a step of forming the extrusion into a predetermined shape to obtain a solder preform. Effect of the Invention

[0012] According to the present invention, a method for producing a preform solder can be provided that can produce a preform solder in which metal particles are uniformly dispersed in lead-free solder without the metal particles becoming small or without leaving any flux, by simply managing the size of the metal particles more simply than in the past. [Brief description of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view showing a schematic diagram of a powder compaction apparatus for compacting a mixed powder of lead-free solder particles and metal particles into a billet, which is a compact. [Diagram 2] FIG. 2 is a photograph showing the appearance of the extrusion product obtained in the examples when it was divided into three parts in the longitudinal direction, that is, the front, middle, and rear portions. [Diagram 3] FIG. 3 is a photograph showing a cross section of each of the three divided extrusion molded products shown in FIG. 2 cut in the length direction. [Figure 4] (a) is a photograph showing an enlargement of a part of the dotted square of the extrusion molded product labeled "before" in Fig. 3. (b) is a photograph showing an enlargement of a part of the dotted square of the extrusion molded product labeled "center" in Fig. 3. (c) is a photograph showing an enlargement of a part of the dotted square of the extrusion molded product labeled "after" in Fig. 3. [Diagram 5] FIG. 5 is a photograph showing an enlarged view of one of the metal particles 6 in FIG. 4(a). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] A method for manufacturing a solder preform according to an embodiment of the present invention includes a step of mixing and stirring lead-free solder particles and metal particles having a higher melting point than the lead-free solder (hereinafter, sometimes referred to as "predetermined metal particles" or "metal particles") to obtain a mixed powder uniform in a particulate state (also referred to as step 1), a step of pressurizing and molding the mixed powder to obtain a pressurized product (also referred to as step 2), and a step of forming the pressurized product into a predetermined shape using an extrusion molding device to obtain an extrusion product (also referred to as step 3).The method further includes a step of forming the extrusion product into a predetermined shape to obtain a solder preform (also referred to as step 4).

[0015] In this way, a mixed powder in which the lead-free solder particles and the predetermined metal particles are uniformly mixed is obtained, and then the mixed powder is pressure molded to obtain a pressure molded product in which the metal particles are uniformly dispersed in the lead-free solder phase. Therefore, the extrusion molded product obtained from this pressure molded product and the preformed solder obtained from the extrusion molded product also have the metal particles uniformly dispersed in the lead-free solder phase. Moreover, since the preformed solder is obtained without melting the predetermined metal particles through the mixed powder, the shape and size of the metal particles do not change substantially. Therefore, it is possible to control the shape and size of the metal particles in the preformed solder by controlling the shape and size of the metal particles before forming the mixed powder without considering the component composition of the lead-free solder.

[0016] The mixing and stirring means that can be used in step 1 is not particularly limited as long as it can uniformly mix the lead-free solder and the predetermined metal particles, and for example, a known stirring and mixing device used when mixing powders can be used. Examples of such stirring and mixing devices include a container rotation type, a mechanical stirring type, and a non-stirring type. Examples of the container rotation type include a horizontal cylinder type, an inclined cylinder type, a V type, and a double cone type. The inner wall of the container may or may not have a protrusion. In addition, the container may have one rotation shaft, or may have two or more rotation shafts. In the mechanical stirring type, the rotation axis of the stirring blade may be horizontal or vertical, or may have a predetermined inclination angle other than these. Examples of the non-stirring type include a so-called static mixer. In addition, when mixing and stirring a small amount, the container may be manually shaken using a sealable container having a volume selected according to the amount.

[0017] The temperature condition for uniformly mixing and stirring the lead-free solder particles and the specified metal particles may be room temperature. If heat is generated during mass processing, a stirring and mixing device equipped with a cooling device may be used. From the viewpoint of preventing oxidation of the lead-free solder particles and the specified metal particles, it is preferable to carry out step 1 under reduced pressure or in an inert gas atmosphere.

[0018] The lead-free solder particles may be either powder or granular. The shape of the particles may be any of spherical and amorphous, but spherical is preferred. The size of the particles may be as specified by JIS Z3282, but Type 4 and Type 5 are preferred.

[0019] Lead-free solder is an alloy mainly composed of Sn, and examples thereof include lead-free solder alloys such as Sn-Ag, Sn-Ag-Cu, Sn-Zn, Sn-Sb, Sn-Ag-Bi, Sn-Ag-In, Sn-Cu-Ni, Sn-Cu, Sn-Bi, Sn-In, etc. Among these, lead-free solder compositions such as Sn-Cu-Ni and Sn-Cu are preferred.

[0020] The particle size of the predetermined metal particles can be set arbitrarily depending on the purpose for which the preform solder is used, and can be, for example, 50 μm to 100 μm.

[0021] The predetermined metal particles may be any metal having a melting point higher than that of the lead-free solder, and examples thereof include metals such as Cu and Ni, alloys of Cu and Ni, etc. In the case of an alloy of Cu and Ni, a Cu-Ni alloy with a Ni content of 0.1 to 44 mass% is suitable for dispersion in a Sn-Cu-Ni or Sn-Ag-Cu lead-free solder alloy.

[0022] The pressure molding means applicable in step 2 is not particularly limited as long as it can pressurize the mixed powder obtained in step 1 and mold it into a predetermined shape, and a known pressurizing device used for pressurizing powder can be used. For example, as shown in FIG. 1, a cylinder 1 with both ends open is placed on a bottom plate 2 placed horizontally so that the length direction of the cylinder 1 is vertical, one end of the cylinder is sealed with the bottom plate 2, a push rod 3 is provided that can slide while pressing the mixed powder 4 (lead-free solder particles 5, metal particles 6) filled in the cylinder 1 from above in the vertical direction, and a pressurizing device is provided that presses the push rod 3 from above in the vertical direction. The load pressure and temperature during pressure molding are not particularly limited, and may be under conditions that allow the pressure molded product to be shaped to an extent that it can be placed in an extrusion molding device in step 3 without collapsing. The shape of the pressure molded product is not particularly limited as long as it is a shape suitable for use in step 3, but a cylindrical shape is preferable from the viewpoint of uniform pressure. The pressure molded product is also called a billet.

[0023] The extrusion molding device applicable in step 3 is not particularly limited as long as it can extrude the pressure-molded product obtained in step 2 into a predetermined shape and can mold a preform solder of the desired quality from the extrusion molded product in step 4. For example, an extrusion molding device used in manufacturing a general solder wire can be used. The extrusion molding conditions can be appropriately determined, such as the extrusion speed and the set temperature of the extrusion die, depending on the composition of the lead-free solder, the shape and characteristics of the pressure-molded product and the extrusion molded product. For example, when the pressure-molded product (billet) is converted from a cylindrical shape to a linear extrusion molded product with a circular cross section, the molding conditions can be set to mold a linear extrusion molded product with a diameter of 1 / 5 or less of the diameter of the billet. In addition, for example, when a Sn-Cu-Ni-based lead-free solder is used, it is possible to extrude a linear extrusion molded product with a wire diameter of 1 / 5 or less of the billet by heating the extrusion part of the extrusion molding device to 100°C or more. In addition, the obtained extrusion molded product has an appearance equivalent to that of a general solder wire, and can also have flexibility depending on the type of lead-free solder composition.

[0024] The shape of the extrusion molded product is not particularly limited, and may be any shape suitable for use in step 4. For example, it may be a linear body with a circular cross section.

[0025] In step 4, the extrusion product obtained in step 3 is molded into a desired shape using a known molding device or the like to obtain a preform solder. The shape of the preform solder is not particularly limited and can be appropriately selected depending on the application. For example, a sheet shape, a ribbon shape, a wire shape, a sphere shape, a pellet, a washer, etc. can be mentioned. When the extrusion product is a linear cylinder as described above, for example, it may be molded into a sheet shape or the like using a known rolling device, and further processed into a desired shape as necessary.

[0026] The preform solder obtained by the above-mentioned manufacturing method is a lead-free solder in which metal particles with a higher melting point than the lead-free solder are dispersed. Furthermore, since the shape and size of the metal particles contained in the preform solder do not change even when molded into a preform shape from the shape and size before mixing, the preform solder is particularly suitable for bonding semiconductor elements. EXAMPLES

[0027] A method for producing a solder preform according to an embodiment of the present invention will be described based on an example.

[0028] (Process 1) 2000g and 6g of SN100C powder (powder size: type 4) manufactured by Nihon Superior Co., Ltd. as lead-free solder particles and Cu-30Ni alloy particles (particle size: passing through 75μm mesh) manufactured by Fukuda Metal Foil and Powder Co., Ltd. as metal particles with a higher melting point than lead-free solder were filled into a sealable cylindrical container and mixed in a sealed state.

[0029] The container was rotated around the central axis of the cylinder in the length direction as the rotation axis at a rotation speed of 120 to 130 rpm for about 5 minutes to mix and stir. Then, the container was rotated 10 times around the direction perpendicular to the central axis as the rotation axis, and then mixed and stirred again for 5 minutes at the same rotation speed with the central axis as the rotation axis.

[0030] In this manner, the lead-free solder powder and the metal particles were uniformly dispersed. When the dispersion state of the obtained mixed powder was visually confirmed, there was no uneven distribution of the metal particles.

[0031] (Process 2) The mixed powder obtained in step 1 was filled into the hollow inside of the cylinder 1 of a 50 ton press-equipped powder compaction device manufactured by Tanizawa Iron Works, as shown in Figure 1. The device was then covered with a pressing rod 3 and pressed for 5 minutes at a pressure of 50 ton to produce a billet (pressure-molded product) with a diameter of approximately 60 mm.

[0032] (Step 3) The billet formed in step 2 was molded into a linear extrusion product with a diameter of 8 mm using a Yamaguchi Seisakusho 150t press-type extrusion molding device (model: SPC-2C) under the following conditions: die heater temperature: 110°C, cylinder heater temperature: 110°C, extrusion die dimensions: inner diameter 8 mmΦ.

[0033] Figure 2 shows a photograph of the linear extrusion product with a diameter of 8 mm obtained in step 3, divided lengthwise into three sections: front, middle, and rear. Figure 3 shows a photograph of the cross-sections of each section cut lengthwise. Figures 4 (Figures 4(a), 4(b), and 4(c)) show enlarged photographs of the areas enclosed by dotted squares in Figure 3. Figure 5 shows an enlarged photograph of one of the metal particles 6 in Figure 4(a).

[0034] From FIG. 2, it can be seen that the obtained extrusion molding has a good appearance and has a metallic luster similar to that of a general solder wire. It was also confirmed that the extrusion molding before division had flexibility that allowed it to be bent into a horseshoe shape. From FIG. 4, it can be seen that metal particles 6 are dispersed in the lead-free solder phase. Furthermore, when the size of the metal particles 6 was measured, it was confirmed that they were 50 μm or more and that their irregular shape matched the size and shape of the lead-free solder before mixing (see FIG. 5, for example). Furthermore, from FIG. 3, FIG. 4, and FIG. 5, it can be seen that there are no voids in the formed linear solder, and that the metal particles 6 are uniformly dispersed in the state before mixing.

[0035] As described above, by going through the above-mentioned process, the extrusion molding has no voids, the metal particles maintain their original particle size, and are uniformly dispersed in the lead-free solder phase, so that the preform solder finally obtained using this has similar properties. In addition, the above-mentioned process is much simpler than the conventional method. Therefore, it is possible to easily manufacture a preform solder in which the metal particles are uniformly dispersed while maintaining their original particle size. [Explanation of symbols]

[0036] 1 Cylinder 2 Bottom plate 3 Push Stick 4 Mixed powder 5. Lead-free solder particles 6 Metal particles

Claims

1. A process for producing a uniform mixed powder in a particulate state by filling a sealable container with particles of a lead-free solder selected from a Sn-Cu-Ni alloy and a Sn-Cu alloy, and particles of a Cu-Ni alloy having a Ni content of 0.1 to 44 mass %, which is a metal having a higher melting point than the lead-free solder, and mixing and stirring the mixture in a sealed state using a container-rotating stirring and mixing device having two or more rotating shafts; A step of pressure-molding the mixed powder to obtain a pressure-molded product; and The press-molded product is molded into a predetermined shape by an extrusion molding device to obtain an extrusion molded product. A method for manufacturing solder preforms.

2. 2. The method of claim 1, further comprising the step of forming the extrusion into a predetermined shape to obtain a solder preform.

Images