JP7553755B2 - Soldering elastomer - Google Patents

Description

The present invention relates to an elastic body for soldering.

As shown in Patent Document 1, a conductive contact member is known that is mounted on a wiring board and provides electrical continuity between the wiring board and a case or the like. This conductive contact member is made by combining a base portion formed from a thin metal material and a contact portion formed by filling an elastomer such as silicone with a conductive filler. The metallic base portion of the conductive contact member is soldered to the circuit pattern on the wiring board by reflow soldering.

As shown in Patent Document 2, a conductive rubber part that can be mounted by soldering based on surface mounting technology is known. This conductive rubber part has a conductive rubber unit made of radical reaction curing silicone rubber mixed with a conductive filler made of silver-coated glass powder. A metal coating that can be electrically connected to a wiring board by soldering is formed on a part of the surface (compressed surface) of the conductive rubber unit. The metal coating has two or more layers, and the outermost layer is made of gold. Such a metal coating is formed on the conductive rubber unit by sputtering.

JP 2003-168507 A Patent No. 5340485

Although the conductive contact member has excellent conductivity and solderability, it is composed of two parts, a base part and a contact part, and there is room for improvement in terms of reducing the number of parts and manufacturing costs.

In addition, the conductive rubber parts use a metal coating that is prepared separately from the conductive rubber alone to ensure solderability to the wiring board, which makes the manufacturing cost high and the manufacturing process complicated.

The object of the present invention is to provide an elastic body for soldering that can be constructed as a single component and has at least solderability. Another object of the present invention is to provide an elastic body for soldering that is furthermore electrically conductive.

As a result of intensive research conducted by the inventors to achieve the above object, they discovered that a filler with a Sn film, which is a core material covered with a Sn film made of Sn or a Sn alloy, can be exposed from the surface of an insulating elastomer containing insulating rubber, and that the surface containing the exposed Sn film-covered filler can be soldered to a counterpart. This led to the completion of the present invention.

The means for solving the above problems are as follows.
<1> A soldering elastomer comprising an insulating elastomer containing insulating rubber, a core material coated with a Sn film made of Sn or a Sn alloy, and a filler with a Sn film contained in the insulating elastomer, the filler having a Sn film being included in the insulating elastomer, the filler having a Sn film being exposed from a surface of the insulating elastomer, and the soldering surface being capable of being soldered to a counterpart.

<2> The soldering elastic body described in <1>, in which the content (mass%) of the Sn-filmed filler is 55 mass% or more.

<3> The soldering elastic body according to <1> or <2>, wherein the insulating rubber is a heat-resistant rubber having a heat-resistant temperature of 200°C or higher.

According to the present invention, it is possible to provide an elastic body for soldering that can be configured as a single component and has at least solderability. In addition, according to another aspect of the present invention, it is possible to provide an elastic body for soldering that is furthermore conductive.

FIG. 1 is a perspective view showing a schematic configuration of an elastic body for soldering according to a first embodiment; An explanatory diagram showing a schematic diagram of the bottom surface of the soldering elastomer Schematic cross-sectional view of a filler with a Sn film An explanatory diagram showing a schematic view of a part of a cross section of a soldering elastomer FIG. 1 is an explanatory diagram showing a state in which a soldering elastic body is fixed by soldering onto a wiring layer provided on the surface of a wiring board. 11A and 11B are perspective views each showing a schematic configuration of a cubic and a sheet-shaped soldering elastic body according to another embodiment; 1 is a side view of an elastomer for soldering according to another embodiment;

[Elastic body for soldering]
Hereinafter, a soldering elastic body 1 according to a first embodiment of the present invention will be described. Fig. 1 is a perspective view showing a schematic configuration of the soldering elastic body 1 according to the first embodiment, and Fig. 2 is an explanatory view showing a schematic bottom surface 3 of the soldering elastic body 1.

The soldering elastic body 1 of this embodiment 1 is generally cylindrical and has a top surface 2, a bottom surface 3, and a peripheral surface 4. Such a soldering elastic body 1 is made of a cylindrical insulating elastic body 5 containing insulating rubber, which contains a predetermined amount of Sn-filmed filler 6.

The insulating elastomer 5 is a base material containing the Sn-filmed filler 6, and contains insulating rubber as a main component. The insulating rubber is contained in a proportion of 90 mass % or more, preferably 95 mass % or more, and more preferably 98 mass % or more, relative to the total mass (100 mass %) of the insulating elastomer 5. In this specification, the "insulating" of the insulating elastomer 5 and the insulating rubber means that, for example, the volume resistivity is 1 x 10 ¹⁰ Ω·cm or more in the state of the composition and/or the cured product. In this specification, the volume resistivity is determined by a measurement method in accordance with JIS K 7194.

In particular, the insulating rubber is preferably heat-resistant rubber with a heat resistance of 200°C or higher so that it can be used in the reflow soldering process. Examples of such insulating rubber include silicone rubber and fluorine-based rubber.

There are no particular limitations on the silicone rubber as long as it does not impair the objectives of the present invention, but millable silicone rubber is preferred from the viewpoint of ease of mixing with the Sn-filmed filler 6. Millable silicone rubber is a silicone rubber compound whose pre-cured state is similar to unvulcanized compounded rubber such as natural rubber or ordinary synthetic rubber, and which can be plasticized and mixed using a kneading roll machine or an enclosed mixer.

As the millable type silicone rubber, for example, KE-571-U, KE-1571-U, KE-951-U, KE-541-U, KE-551-U, KE-561-U, KE-961T-U, KE-1541-U, KE-1551-U, KE-941-U, KE-971T-U, etc. manufactured by Shin-Etsu Chemical Co., Ltd. can be used. These silicone rubbers may be used alone or in combination of two or more kinds.

There are no particular limitations on the fluororubber as long as it does not impair the object of the present invention, but examples of usable fluorosilicone rubber, tetrafluoroethylene-propylene rubber, vinylidene fluoride-hexafluoropropylene rubber, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene rubber, fluorinated polyether, etc. may be used. These may be used alone or in combination of two or more.

In addition, the insulating elastomer 5 may contain a base material rubber component or a resin component in addition to the insulating rubber, as long as the object of the present invention is not impaired. In addition, the insulating elastomer 5 may contain a vulcanizing agent, a hardener, a plasticizer, a foaming agent, etc., as necessary.

2, on the bottom surface 3 of the soldering elastomer 1, a number of Sn-filmed fillers 6 are exposed from the surface 50 of the insulating elastomer 5 in a planar, scattered manner. Such a bottom surface 3 is composed of the surface 50 of the insulating elastomer 5 and a number of Sn-filmed fillers 6 exposed from the surface 50, and constitutes a soldering surface 3 that can be soldered to a counterpart, as described below. In this embodiment, the top surface 2 and peripheral surface 4 of the soldering elastomer 1 are also exposed from the surface 50 of the insulating elastomer 5 in a planar, scattered manner, similar to the bottom surface 3. In particular, the top surface 2 can be a soldering surface that can be soldered, similar to the bottom surface 3.

Figure 3 is a schematic cross-sectional view of a Sn-filmed filler 6. The Sn-filmed filler 6 is made of a core material 61 coated with a Sn film 62 made of Sn or a Sn alloy.

The core material 61 is a conductive or non-conductive material in the shape of a typical filler. The shape of the core material 61 is not particularly limited as long as it does not impair the object of the present invention, and examples of the shape include needle-shaped, spherical, flat, block-shaped, disk-shaped, and dendritic shapes. In addition, the conductive core material 61 is not particularly limited as long as it does not impair the object of the present invention, and examples of the shape include metal/alloy powders such as copper powder, copper alloy powder, silver powder, and silver alloy powder. These can be used alone or in combination of two or more types.

The shape of the core material 61 is preferably flat, for example, from the viewpoint of making it easier to ensure contact between the Sn-filmed fillers 6 within the insulating elastomer body 5. A method for producing the flat core material 61 is, for example, to mechanically process spherical metal powder (e.g., copper powder) into a flat shape to obtain the flat metal powder.

The non-conductive core material 61 is not particularly limited as long as it does not impair the object of the present invention, but examples include plastic powder, glass powder, and the like. These may be used alone or in combination of two or more. A conductive Sn film 62 made of Sn (tin) or a Sn (tin) alloy is formed so as to cover the surface of such a core material 61.

There are no particular limitations on the method for forming the Sn film 62 on the surface of the core material 61 as long as it does not impair the object of the present invention. For example, when coating the surface of copper powder, which is the core material, with Sn, electroless Sn plating may be used. Examples of electroless Sn plating include substitution type Sn plating, in which Sn ions in the plating solution are reduced and precipitated as the underlying copper powder (core material) dissolves; reduction type Sn plating, in which Sn coating is performed by reducing Sn ions in the plating solution with a reducing agent; and disproportionation reaction type Sn plating, in which Sn coating is performed by utilizing the disproportionation reaction of Sn ions to become metallic Sn.

When coating an Sn alloy with Sn alloy plating, a Sn alloy coating can be formed by adding soluble salts of alloy-constituting silver, bismuth, zinc, etc. to a substitution type Sn plating solution, reduction type Sn plating solution, or disproportionation reaction type Sn plating solution, and precipitating these metals simultaneously with Sn.

When the Sn-coated filler 6 is spherical, lumpy, or the like, its particle size (average particle size) is not particularly limited as long as it does not impair the object of the present invention, but may be, for example, 10 μm to 20 μm. The particle size (average particle size) is the volume-based average particle size (D50) determined by a laser diffraction scattering type particle size distribution measurement method.

When the Sn-coated filler 6 is needle-like, flat, etc., its particle size (average particle size) is expressed by the average major axis diameter and the average minor axis diameter. The average major axis diameter of the Sn-coated filler 6 is not particularly limited as long as it does not impair the object of the present invention, but may be, for example, 5 μm to 50 μm. The average major axis diameter of the Sn-coated filler 6 may be 4 to 30 times its average minor axis diameter. The average minor axis diameter of the Sn-coated filler 6 is not particularly limited as long as it does not impair the object of the present invention, but may be, for example, 0.2 μm to 1.1 μm.

The average major axis diameter and the average minor axis diameter of the Sn-coated filler 6 were determined by measuring the major axis diameter (maximum diameter) and minor axis diameter of 100 Sn-coated fillers 6 based on images obtained by a scanning electron microscope or a transmission electron microscope, and calculating the average value. The minor axis diameter of the Sn-coated filler 6 was defined as the length of the axis perpendicular to the major axis diameter.

The Sn-filmed filler 6 is mixed into the insulating elastomer 5 at a predetermined ratio that takes into consideration ensuring the solderability of the soldering elastomer 1. In the soldering elastomer 1 (100 mass%), the content (mass%) of the Sn-filmed filler is preferably 55 mass% or more. When the content of the Sn-filmed filler is in this range, it is easy to ensure the solderability of the soldering elastomer 1.

In addition to ensuring solderability, the content (mass %) of the Sn-filmed filler may be set in consideration of ensuring electrical conductivity. The content (mass %) of the Sn-filmed filler is preferably 60 mass % or more, and more preferably 65 mass % or more. There is no particular upper limit to the content (mass %) of the Sn-filmed filler as long as it does not impair the object of the present invention, but from the viewpoint of ease of molding the soldering elastic body 1, it is preferably 75 mass % or less, and more preferably 70 mass % or less.

Figure 4 is an explanatory diagram showing a schematic representation of a part of a cross section of the soldering elastic body 1. In Figure 4, a part of a cross section of the soldering elastic body 1 cut along the vertical direction is shown. As shown in Figure 4, inside the insulating elastic body 5, a conductive path 7 is formed in which the Sn-filmed fillers 6 are connected to each other. If many such conductive paths 7 are formed inside the insulating elastic body 5, the conductivity of the soldering elastic body 1 is ensured. The conductive paths 7 are formed in various directions, and the conductivity of the soldering elastic body 1 is isotropic. The soldering elastic body 1 is used, for example, to ensure conductivity between the top surface 2 and the bottom surface 3. The conductive paths 7 may be formed on the surfaces (top surface 2, bottom surface 3, peripheral surface 4) of the soldering elastic body 1.

The soldering elastomer 1 may contain other components such as antioxidants, UV absorbers, colorants, fillers, and flame retardants in addition to the Sn-filmed filler 6, as long as the purpose of the present invention is not impaired.

The soldering elastomer 1 can be produced, for example, by the following method. The insulating rubber (e.g., silicone rubber) having fluidity is mixed with the Sn-filmed filler 6 to fill the insulating rubber with the Sn-filmed filler 6. Methods for mixing the insulating rubber and the Sn-filmed filler 6 include a method of kneading using a machine such as a vacuum degassing mixer, a method of kneading using extrusion, a two-roll mill, a kneader, a Banbury mixer, etc. If necessary, a hardening retarder, an antioxidant, a flame retardant, a plasticizer, etc. may be added to the insulating rubber having fluidity. In another embodiment, the insulating rubber to be mixed with the Sn-filmed filler 6 may be in a semi-solid form such as a pellet.

Next, the mixture composition obtained by mixing the insulating rubber having fluidity with the Sn-filmed filler 6 is molded. Examples of molding methods include known molding methods such as press molding, injection molding, extrusion molding, coater, and calendar roll. The soldering elastomer 1 shown in FIG. 1 is manufactured, for example, by press molding using a specified mold.

Figure 5 is an explanatory diagram showing a state in which the soldering elastic body 1 is fixed by soldering on the wiring layer E provided on the surface of the wiring board. In Figure 5, a cross section of the soldering elastic body 1 is shown typically. The bottom surface 3 of the soldering elastic body 1 is a solderable soldering surface 3, and the soldering surface 3 is joined to the wiring layer E via a solder layer 8. During such soldering, the Sn film 62 of the Sn film-attached filler 6 exposed from the soldering surface 3 melts and joins to the solder layer 8. In addition, the wiring layer (copper foil) E is joined while forming an alloy layer between it and the solder layer 8. Note that, in part, the Sn film 62 of the Sn film-attached filler 6 exposed from the soldering surface 3 may be directly joined to the wiring layer (copper foil) E. A fillet 9 made of solder is formed around the soldering surface (bottom surface) 3 of the soldering elastic body 1. In this way, the soldering elastic body 1 is soldered to the mating wiring layer E. For ease of explanation, FIG. 5 shows only the Sn-filmed filler 6 near the bottom surface 3.

Such a soldering elastic body 1 can be soldered and mounted using surface mount technology (SMT), and is mounted, for example, on a wiring board (printed wiring board, etc.) of an electronic device. The process for soldering the soldering elastic body 1 may be a flow soldering process or a reflow soldering process.

The soldering elastic body 1 may be used in a clamped state so that it is compressed in the vertical direction. For example, the bottom surface (soldering surface) 3 of the soldering elastic body 1 may be mounted on a wiring board, and the top surface 2 may be brought into contact with a housing (ground) that houses the wiring board.

As described above, the soldering elastic body 1 of this embodiment can be configured as a single component, and can be soldered to a mating part such as a wiring board (has solderability). Furthermore, the soldering elastic body 1 of this embodiment also has electrical conductivity as described above.

When the soldering elastomer 1 has electrical conductivity, the volume resistivity is preferably less than 1×10 ¹⁰ Ω·cm, for example.

The present invention will be described in more detail below with reference to examples. Note that the present invention is not limited to these examples.

Example 1
Silicone rubber (product name "KE-941-U", manufactured by Shin-Etsu Chemical Co., Ltd.) was prepared as insulating rubber (heat-resistant rubber). In addition, Sn-plated copper powder was prepared by plating the surface of flat copper powder with Sn as the Sn-filmed filler. The Sn-plated copper powder was flat, with an average major axis diameter of 7 μm and an average minor axis diameter of 1 μm. The Sn plating content in the Sn-plated copper powder was 26.03 mass%. 100 mass parts of this silicone rubber were mixed with 129.6 mass parts of flat Sn-plated copper powder and 1 mass part of vulcanizing agent, and the resulting mixed composition was press-molded to obtain an elastic body for soldering (diameter 9 mm x height 10 mm, cylindrical shape) of Example 1.

Example 2
An elastic body for soldering of Example 2 was produced in the same manner as in Example 1, except that the blending amount of the Sn-plated copper powder was changed to 194.4 parts by mass.

Comparative Example 1
An elastic body for soldering of Example 2 was produced in the same manner as in Example 1, except that the blending amount of the Sn-plated copper powder was changed to 116.6 parts by mass.

[Implementation test]
For each of the soldering elastomers of Examples 1 and 2 and Comparative Example 1, a mounting test was carried out in the following manner.

A substrate (polyimide substrate) with a copper foil wiring pattern formed on its surface was prepared. Solder paste was applied to the wiring pattern of the substrate, and a soldering elastomer was placed on the solder paste with its bottom surface in contact with the solder paste. The substrate with the soldering elastomer placed on it was placed in a specified heating furnace, and heated for 30 to 60 seconds (5 to 10 seconds at 250°C) while increasing the temperature from 220°C to 250°C. The substrate was then removed from the heating furnace and air-cooled to obtain a substrate with a soldering elastomer mounted on it (hereinafter referred to as a "mounted product").

(Implementation Experiment A)
The mounted product obtained as described above was first placed so that the soldering elastic body faced downward and was maintained in this state for 300 seconds. Then, while maintained in this state, it was confirmed whether the soldering elastic body of the mounted product peeled off from the board and fell due to its own weight.

(Implementation Experiment B)
Next, the mounted product was placed so that the soldering elastic body was facing sideways and the board surface (mounting surface) was aligned vertically (i.e., the soldering elastic body was laid on its side), and this state was maintained for 300 seconds. Then, while this state was maintained, it was confirmed whether the soldering elastic body of the mounted product peeled off from the board and fell due to its own weight.

In either case of the above mounting experiment A or B, if the soldering elastomer did not peel off from the board, the result of the mounting experiment was good, and is indicated in Table 1 as "O." In addition, in either case of the above mounting experiment A or B, if the soldering elastomer peeled off from the board, the result of the mounting experiment was not good, and is indicated in Table 1 as "X." The results are shown in Table 1.

As shown in Table 1, it was confirmed that the soldering elastomers of Examples 1 and 2 had excellent solderability. In contrast, it was confirmed that the soldering elastomer of Comparative Example 1 had a lower content of Sn-plated copper powder than Examples 1 and 2, and did not have sufficient solderability. Specifically, during the above mounting experiment B, the soldering elastomer peeled off from the board.

<Other embodiments>
The present invention is not limited to the embodiments described above and illustrated in the drawings, and the following embodiments, for example, are also included within the technical scope of the present invention.

(1) In the above embodiment, a soldering elastomer formed into a cylindrical shape is exemplified, but the present invention is not limited to this, and the soldering elastomer may have various shapes depending on the application, etc. For example, as shown in FIG. 6, it may be a cubic soldering elastomer 1A or a sheet-like soldering elastomer 1B. In still another embodiment, it may be a soldering elastomer 1C having a cylindrical shape with a narrowed circumferential surface, as shown in FIG. 7. When this soldering elastomer 1C is compressed in the vertical direction, even if the narrowed portion deforms so as to spread outward, it is prevented from protruding outward beyond the top or bottom surface.

(2) The solder used when soldering the soldering elastomer is not particularly limited as long as it does not impair the objective of the present invention. For example, common solder containing tin or lead, lead-free solder, etc. can be used.

(3) In the soldering elastomer, the Sn-filmed filler may be uniformly dispersed in the insulating elastomer, or may be contained so as to be partially unevenly distributed, as long as the object of the present invention is not impaired. For example, the Sn-filmed filler may be contained in the insulating elastomer so as to be unevenly distributed only near the surface of the insulating elastomer, or the Sn-filmed filler may be contained in the insulating elastomer so as to be gathered along a specific direction.

(4) In the above embodiment 1, the Sn-filmed filler was exposed on the soldering surface of the soldering elastic body in a dotted manner, but the present invention is not limited to this. For example, a large number of Sn-filmed fillers may be exposed in a regular or irregular pattern (concentric circles, mosaic) as a whole.

1...elastic body for soldering, 2...upper surface, 3...bottom surface (soldering surface), 4...periphery, 5...insulating elastic body, 6...filler with Sn film, 61...core material, 62...Sn film, 7...conductive path, 8...solder layer, 9...fillet, E...wiring layer

Claims (2)

an insulating elastomer including an insulating rubber made of a heat-resistant rubber having a heat-resistant temperature of 200° C. or higher;
The insulating elastomer comprises a flat core material covered with a Sn film made of Sn or a Sn alloy, and a filler with a Sn film is contained in the insulating elastomer;
a soldering surface including a surface of the insulating elastomer and the Sn-filmed filler exposed from the surface, the soldering surface being capable of being soldered to a counterpart;
The content (mass%) of the Sn-filmed filler is 55 mass% or more and 75 mass% or less,
The elastic body for soldering , wherein the average major axis diameter of the Sn film-attached filler is 5 μm to 50 μm, and the average minor axis diameter of the Sn film-attached filler is 0.2 μm to 1.1 μm . 2. The elastomer for soldering according to claim 1 , wherein said insulating rubber is silicone rubber.

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