Conductive particle processing method, conductive particle manufacturing method, and wiring-forming member

Abstract

This conductive particle processing method comprises: a step A in which conductive particles X are subjected to bottom cut processing for removing small-diameter particles having a particle diameter equal to or less than a prescribed value XU; and a step B in which the conductive particles A obtained through step A are disintegrated to obtain conductive particles B.

Description

Method for processing conductive particles, method for manufacturing conductive particles, and component for forming wiring

[0001] The present invention relates to a method for processing conductive particles, a method for manufacturing conductive particles, and a component for forming wiring.

[0002] Conductive particles are used as materials for manufacturing electronic components such as semiconductor packages. For example, Patent Document 1 below proposes a wiring-forming member in which a metal foil layer is laminated on an adhesive layer containing conductive particles, as a material for easily forming a wiring layer of a printed circuit board containing electronic components such as IC chips.

[0003] International Publication No. 2022 / 030634 Brochure

[0004] In the above-mentioned components, it is desirable that the fluidity of the adhesive layer be stable from the viewpoint of reducing resistance during substrate connection. Conductive particles are usually selected based on indicators such as median diameter, but because there is a distribution in particle size, even when wiring forming components are used under the same conditions, problems such as an increase in connection resistance may occur due to changes in the fluidity of the adhesive layer.

[0005] Therefore, the present invention aims to provide a method for processing conductive particles that can stabilize the fluidity of an adhesive layer. Furthermore, the present invention aims to provide a method for manufacturing conductive particles that can stabilize the fluidity of an adhesive layer, and a component for forming wiring.

[0006] The present invention includes the following aspects. [1] A method for processing conductive particles, comprising: Step A of performing an undercut process on conductive particles X to remove small-diameter particles having a particle diameter equal to or less than a predetermined value XU; and Step B of disintegrating the conductive particles A obtained through Step A to obtain conductive particles B. [2] The method for processing conductive particles according to [1], wherein the undercut process includes classification using a classification mesh having an opening size corresponding to the predetermined value XU. [3] The method for processing conductive particles according to [1] or [2], wherein in Step A, a top-cut process of removing large-diameter particles having a particle diameter equal to or larger than a predetermined value XT is further performed on the conductive particles X. Ａ１０ [4] The method for processing conductive particles according to [3], wherein the top-cut process includes classification using a classification mesh having an opening size corresponding to the predetermined value XT. [5] The method for processing conductive particles according to any one of [1] to [4], wherein in Step B, the conductive particles A are disintegrated using a jet mill. Ｂ１０ [6] The method for processing conductive particles according to any one of [1] to [5], wherein in Step B, when AU represents the cumulative frequency of particles having a particle diameter equal to or less than the predetermined value XU in the volume-based particle size distribution of the conductive particles A, and BU represents the cumulative frequency of particles having a particle diameter equal to or less than the predetermined value XU in the volume-based particle size distribution of the conductive particles B, the condition of the following formula (B-1) is satisfied: 10 ≤ (BU - AU) ≤ 40 ... (B-1) [7] The method for processing conductive particles according to any one of [1] to [6], wherein when the 50% cumulative particle diameter in the volume-based particle size distribution of the conductive particles X is D Ｘ５０ and the conditions of the following formula (X-1) and the following formula (A-1) are satisfied, and when D Ｘ５０ and D Ｘ５０ respectively represent the 10% cumulative particle diameters in the volume-based particle size distributions of the conductive particles A and the conductive particles B, the condition of the following formula (B-2) is satisfied: 40 µm ≤ D Ａ１０ ≤ 55 µm ... (X-1) 0.8D Ｂ１０ ≤ XU ≤ 0.9D Ａ１０ ... (A-1) 10 ≤ (D - D Ｂ１０ ) × 100 / D Ａ１０ ≤ 25 ... (B-2) [8] The method for processing conductive particles according to any one of [1] to [7], further comprising Step C of performing a surface treatment on the conductive particles B.

[0007] According to the method described in [1] above, it is possible to reduce fine particles that excessively reduce the fluidity of the resin component in the adhesive layer, while moderately suppressing the flow of the resin component with small-diameter particles generated by crushing. This makes it possible to stabilize the fluidity of the adhesive layer.

[0008] Furthermore, the present invention includes the following aspects: [9] A method for producing conductive particles, comprising a method for processing conductive particles according to any one of [1] to [8].

[10] The conductive particles B obtained through step B have a ratio of 10% cumulative particle size to 90% cumulative particle size in the volume-based particle size distribution [D Ｂ１０ / D Ｂ９０ A method for producing conductive particles according to [9], wherein ] is 0.4 to 0.7.

[11] A wiring forming member comprising a metal layer and an adhesive layer provided on the metal layer, wherein the conductive particles are obtained by the method according to [9].

[12] A metal layer and an adhesive layer provided on the metal layer, wherein the conductive particles have a 50% cumulative particle size in the volume-converted particle size distribution of 40 to 55 μm and a 90% cumulative particle size D in the volume-converted particle size distribution. ９０ 10% cumulative particle size D １０ The proportion [D １０ / D ９０ A wiring forming member having a ratio of 0.4 to 0.7 and a cumulative frequency of 22.8 to 26.1 μm particles in the volume-reduced particle size distribution of 0.5 to 3%.

[0009] According to the present invention, a method for processing conductive particles that can stabilize the fluidity of an adhesive layer can be provided. Furthermore, the present invention can provide a method for manufacturing conductive particles that can stabilize the fluidity of an adhesive layer, and a component for forming wiring.

[0010] Embodiments of the present invention will be described below. However, the present invention is not limited to the following embodiments.

[0011] In this specification, numerical ranges indicated using "~" represent a range that includes the numbers listed before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages within this specification, the upper or lower limit of one numerical range may be replaced by the upper or lower limit of another numerical range described in stages.

[0012] [Method for processing conductive particles] The method for processing conductive particles according to this embodiment comprises: step A, which involves performing an undercut process on conductive particles X to remove small-diameter particles having a particle diameter of a predetermined value XU or less; and step B, which involves crushing the conductive particles A obtained through step A to obtain conductive particles B.

[0013] The conductive particles X may be metal particles such as Au, Ag, Ni, Cu, Sn, or solder, or conductive carbon particles composed of conductive carbon. Copper particles can be used from the viewpoint of low resistance and heat dissipation during connection. The copper particles can be particles containing one or more of Cu and alloys of Cu with other metals. Examples of alloys of Cu with other metals include silver, zinc, nickel, gold, lead, tin, aluminum, manganese, beryllium, tungsten, and iron. The Cu content in the copper particles may be 50% by mass or more, 70% by mass or more, or 100% by mass.

[0014] The shape of the conductive particle X may be spherical, approximately spherical, flake-shaped, columnar, rod-shaped, needle-shaped, plate-shaped, or fibrous.

[0015] The conductive particle X may have a volume-reduced particle size distribution (hereinafter simply referred to as "volume-reduced particle size distribution") measured by laser diffraction / scattering particle size distribution measurement, which may be in the range of 8 to 100 μm, 20 to 80 μm, or 39 to 65 μm.

[0016] Conductive particle X has a 50% cumulative particle size in the volume-reduced particle size distribution (hereinafter referred to as "D"). Ｘ５０ In some cases, the diameter may be 48-53 μm, 38-47 μm, or 54-64 μm, and in order to obtain even smaller diameter conductive particles, D Ｘ５０ The thickness may be 8 to 12 μm, or 18 to 22 μm.

[0017] The undercut treatment can be performed, for example, using a sieve having a classification mesh. As the classification mesh, a metal mesh such as stainless steel, a resin mesh such as nylon, or the like can be used. Further, as the sieve, an acoustic sieve, an ultrasonic powder sieve, a horizontal rotary sieve, or the like can be used.

[0018] The opening diameter of the classification mesh can be appropriately set according to the particle diameter of the small-diameter particles to be removed. Further, the frequency, intensity, and treatment time of the sieve can be appropriately set according to the amount of the small-diameter particles to be removed.

[0019] The undercut treatment may include, for example, classification with a classification mesh having an opening size of a predetermined value XU. The predetermined value XU is D of the conductive particles X Ｘ５０ can be set using as an index. For example, the predetermined value XU is D Ｘ５０ may be 0.8 to 1.2 times the particle diameter of D Ｘ５０ may be 0.9 to 1.1 times the particle diameter of D Ｘ５０ may be 0.8 to 0.9 times the particle diameter of .

[0020] D of the conductive particles X Ｘ５０ satisfies the following formula (X-1), from the viewpoint of reducing connection resistance, the predetermined value XU may satisfy the condition of the following formula (A-1). 40 μm≦D Ｘ５０ ≦55 μm ...(X-1) 0.8D Ｘ５０ ≦XU≦0.9D Ｘ５０ ...(A-1)

[0021] D of the conductive particles X Ｘ５０ satisfies the following formula (X-2), from the viewpoint of reducing connection resistance, the predetermined value XU may satisfy the condition of the following formula (A-2). 8 μm≦D Ｘ５０ ≦12 μm ...(X-2) 0.8D Ｘ５０ ≦XU≦1.2D Ｘ５０ ...(A-2)

[0022] D of the conductive particles X Ｘ５０When the following formula (X-3) is satisfied, from the perspective of reducing the connection resistance value, the predetermined value XU may satisfy the condition of the following formula (A-3). 18μm≤D Ｘ５０ ≤22μm ...(X-3) 0.8D Ｘ５０ ≤XU≤0.9D Ｘ５０ ...(A-3)

[0023] In step A, for conductive particles X, a top-cut treatment for removing large-diameter particles with a particle diameter equal to or larger than a predetermined value XT can be performed before or after the undercut treatment, or simultaneously with the undercut treatment.

[0024] The top-cut treatment can use the same means as the above-mentioned undercut treatment.

[0025] The top-cut treatment may include classification by a classification mesh having an opening size corresponding to the predetermined value XT. The predetermined value XT is based on D of the conductive particles X Ｘ５０ can be set based on this indicator. For example, the predetermined value XT may be a particle diameter of 1.05 to 1.5 times D Ｘ５０ and may be 1.1 to 1.3 times D Ｘ５０ .

[0026] The conductive particles A obtained through step A, from the perspective of reducing the connection resistance value, the ratio of the 10% cumulative particle diameter to the 90% cumulative particle diameter in the volume-based particle size distribution [D Ａ１０ / D Ａ９０ may be 0.4 to 0.7, or may be 0.5 to 0.7.

[0027] For disintegration of conductive particles A, for example, an airflow pulverizer such as a jet mill that can disintegrate particles only with compressed air can be used. The treatment conditions by the jet mill can be set to satisfy the following conditions.

[0028] For example, when AU represents the cumulative frequency of particles having a particle diameter equal to or smaller than the predetermined value XU in the volume-based particle size distribution of conductive particles A, and BU represents the cumulative frequency of particles having a particle diameter equal to or smaller than the predetermined value XU in the volume-based particle size distribution of conductive particles B, the conductive particles A may be disintegrated to satisfy the condition of the following formula (B-1). 10≤(BU-AU)≤40 ...(B-1)

[0029] In other words, by increasing the cumulative frequency of particles with a particle diameter of XU or less by 10 to 40%, the effect of reducing the connection resistance value by suppressing the flow of the resin component becomes easier to obtain. In addition, in step B, the cumulative frequency of particles with a particle diameter of XU or less may be increased by 10 to 20%.

[0030] Furthermore, from a similar viewpoint, the 10% cumulative particle size in the volume-reduced particle size distribution of conductive particle A and conductive particle B is set to D Ａ１０ and D Ｂ１０ In this case, conductive particles A may be crushed to satisfy the following condition (B-2): 10 ≤ (D Ａ１０ -D Ｂ１０ ) × 100 / D Ａ１０ ≦25...(B-2)

[0031] From the viewpoint of reducing connection resistance, step A, which satisfies the above-described equations (X-1) and (A-1), may be combined with step B, which satisfies the conditions of the above-described equation (B-1) or (B-2).

[0032] The conductive particles B obtained in step B may have a cumulative frequency of fine particles with a particle size smaller than a predetermined particle size S1 of less than 0.5%, and it is desirable that such particles are substantially absent, from the viewpoint of easily obtaining the effect of reducing connection resistance by suppressing the flow of the resin component. The particle size S1 may be, for example, the minimum diameter of the conductive particle X, or 2 to 5 μm.

[0033] When conductive particles A are crushed using a jet mill, the crushed material can be collected in a way that prevents the aforementioned fine particles from being included due to the airflow.

[0034] In step B, if the conductive particles are copper particles or the like, the oxide film on the particle surface can be removed. This reduces the volume resistivity of conductive particles B.

[0035] Furthermore, if the conductive particle X has impurities unevenly distributed on its surface, in step B, it is possible to obtain conductive particle B with a low concentration of impurities on its surface.

[0036] The conductive particles B obtained through step B have a ratio of 10% cumulative particle size to 90% cumulative particle size in the volume-converted particle size distribution [D Ｂ１０ / D Ｂ９０ ] may be between 0.4 and 0.7, and may be between 0.5 and 0.6.

[0037] The method for processing conductive particles in this embodiment may further include a step C in which the conductive particles B are subjected to a surface treatment.

[0038] Surface treatments include rust prevention treatment, which involves contacting conductive particles B with a treatment solution containing a rust inhibitor, as well as metal coating treatment and chelation treatment.

[0039] The conductive particle processing method of this embodiment described above can be applied as a method for manufacturing conductive particles to obtain conductive particles B or a surface-treated product thereof. In other words, the method for manufacturing conductive particles of this embodiment may have the conductive particle processing method of this embodiment described above.

[0040] [Conductive Particles] The conductive particles of this embodiment have a 50% cumulative particle size of 40 to 55 μm in the volume-based particle size distribution, and a 90% cumulative particle size D in the volume-based particle size distribution. ９０ 10% cumulative particle size D １０ The proportion [D １０ / D ９０ The ratio is 0.4 to 0.7, and the cumulative frequency of particles between 22.8 and 26.1 μm in the volume-reduced particle size distribution is 0.5 to 3%.

[0041] The conductive particles of this embodiment can be obtained by the processing method described above.

[0042] According to the conductive particles of this embodiment, the proportion of conductive particles contributing to conductivity is sufficiently large, and the flow of the resin component of the adhesive layer can be suppressed, thereby reducing the connection resistance of wiring forming members and the like. The wiring forming member may be one in which a metal layer, such as metal foil, is laminated on an adhesive layer containing conductive particles.

[0043] [Wiring Forming Member] The wiring forming member of this embodiment comprises, for example, a metal layer and an adhesive layer provided on the metal layer, the adhesive layer containing conductive particles and an adhesive component, wherein the conductive particles may be the conductive particles of this embodiment, or may be obtained by the method for manufacturing the conductive particles of this embodiment.

[0044] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples.

[0045] (Example 1) [Preparation of copper particles X] Commercially available copper particles were prepared as copper particles X, and the volume-reduced particle size distribution was measured by laser diffraction / scattering particle size distribution measurement, and the following information was obtained: Minimum diameter: 6.7 μm Maximum diameter: 262.4 μm 10% cumulative particle size: 19.4 μm 50% cumulative particle size: 43.8 μm 90% cumulative particle size: 81.1 μm

[0046] [Step A] The copper particles X prepared above were subjected to the following top-cut treatment. <Top-cut treatment> Sieve: Ultrasonic sieve (manufactured by Tsutsui Rikagakuki Co., Ltd., SW-20AT, frequency 115 Hz, LEVEL (7), treatment time 15 minutes) Classification mesh: Stainless steel mesh (aperture size: 53 μm) / Nylon mesh (aperture size: 48 μm) / Stainless steel mesh (aperture size: 46 μm)

[0047] Next, the following undercutting process was performed. <Undercutting Process> Sieving equipment: Ultrasonic powder sieving equipment (Artech Co., Ltd., DGS35-50, frequency 35kHz, LEVEL 80%, processing time 15 minutes) + horizontal swivel sieving equipment (Taiyo Co., Ltd., SKH-01, rotation speed 200rpm, processing time 15 minutes) Classification mesh: Stainless steel mesh (aperture size: 38μm)

[0048] The volume-reduced particle size distribution of copper particles A obtained through the above process was measured by laser diffraction / scattering particle size distribution measurement, and the following information was obtained: Minimum diameter: 29.9 μm Maximum diameter: 116.2 μm 10% cumulative particle size: 40.2 μm 50% cumulative particle size: 51.2 μm 90% cumulative particle size: 67.3 μm

[0049] [Step B] The copper particles A obtained above were crushed using a Super Jet Mill SJ-100 (manufactured by Nisshin Engineering Co., Ltd.) under the conditions of an air pressure of 0.5 MPa and a processing speed of 10 g / min.

[0050] The volume-reduced particle size distribution of copper particles B obtained through the above process was measured by laser diffraction / scattering particle size distribution measurement, and the following information was obtained: Minimum diameter: 22.8 μm Maximum diameter: 116.2 μm 10% cumulative particle size: 33.1 μm 50% cumulative particle size: 43.1 μm 90% cumulative particle size: 58.1 μm

[0051] Furthermore, the cumulative frequency of copper particle B particles between 22.8 μm and 26.1 μm in the volume-reduced particle size distribution was 0.8%. In addition, step B increased the cumulative frequency of copper particle B particles 38 μm or smaller in the volume-reduced particle size distribution by 12% compared to the cumulative frequency of copper particle A particles 38 μm or smaller in the volume-reduced particle size distribution.

[0052] [Preparation of Wiring Forming Components] 5.00 g of NC-3000H (biphenyl aralkyl type epoxy resin, manufactured by Nippon Kayaku Co., Ltd., trade name, epoxy equivalent: 289 g / eq) as epoxy resin, 4.69 g of YL983U (bisphenol F type epoxy resin, manufactured by Mitsubishi Chemical Corporation, trade name, epoxy equivalent: 170 g / eq), 4.08 g of KA-1163 (cresol novolac type phenol resin, manufactured by DIC Corporation, trade name, hydroxyl group equivalent: 118 g / eq) as phenol resin, and YP-70 (BPA / B) as phenoxy resin. 2.68 g of PF copolymer (manufactured by Nippon Steel Chemical & Material Co., Ltd., trade name) and 0.025 g of G-8009L (isocyanate mucimidazole, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name) as a curing accelerator were dissolved in 19.1 g of methyl ethyl ketone (MEK). Then, 5.36 g of SC-2050KC (phenylaminosilane-treated silica filler, average particle size 0.5 μm, manufactured by Admatex Co., Ltd., trade name) and 4.21 g of copper particles B were added to prepare a coating solution for forming an adhesive layer.

[0053] This coating solution was applied to one side (surface roughness Rz: 3.0 μm) of copper foil (manufactured by Mitsui Mining & Smelting Co., Ltd., product name: "3EC-M3-VLP", thickness: 12 μm) using a coating device (manufactured by Yasui Seiki Co., Ltd., product name: Precision Coating Machine), and then dried with hot air at 70°C for 5 minutes to form an adhesive layer with a thickness of 54 μm on the copper foil. In this way, a component for forming wiring was manufactured.

[0054] (Comparative Example 1) Copper particles X were crushed using a Super Jet Mill SJ-100 (manufactured by Nisshin Engineering Co., Ltd.) under conditions of an air pressure of 0.5 MPa and a processing speed of 10 g / min to obtain comparative copper particles 1. Next, a wiring forming member was manufactured in the same manner as in Example 1, except that comparative copper particles 1 were used instead of copper particles B.

[0055] (Comparative Example 2) A wiring forming member was manufactured in the same manner as in Example 1, except that copper particle A was used instead of copper particle B.

[0056] [Evaluation of the fluidity of the adhesive layer] A 5 mm × 5 mm × 54 μm sheet was prepared using the adhesive layer forming coating solution prepared in the examples and comparative examples. A constant pressure was applied to this sheet according to the method described below, and the elongation of the sheet (in the longitudinal and transverse directions) was measured. The sheet was sandwiched between two glass plates (18 mm × 18 mm × 0.15 mm), and heated and pressurized at 180°C, 2 MPa for 10 minutes using a heat-sealing device, and the elongation rate of the sheet was measured. The elongation rate of the sheet was calculated with the value before heating and pressurizing set to 100%.

[0057] Example 1 yielded 173%, Comparative Example 1 yielded 218%, and Comparative Example 2 yielded 239%.

[0058] [Evaluation of Wiring Forming Components] For the wiring forming components prepared as described above, evaluation samples were prepared and their connection resistance values ​​were measured according to the following method, and the connection resistance values ​​were evaluated according to the following criteria.

[0059] [Measurement of connection resistance] <Preparation of evaluation sample> Wiring forming material was attached to a circuit board (PWB) having three copper circuits with a line width of 1000 μm, a pitch of 10000 μm, and a thickness of 15 μm on a glass cloth-reinforced epoxy substrate. This was then heated and pressurized at 180°C and 2 MPa for 60 minutes using a thermocompression bonding device (heating method: constant heat type, manufactured by Toray Engineering Co., Ltd.) to connect them over a width of 2 mm and to produce a connected body.

[0060] The sample, with a resist formed on the fabricated connector, was immersed in an etching solution and agitated. The etching solution was prepared with copper chloride: 100 g / L and hydrochloric acid: 100 ml / L. Once the desired copper foil portion was removed, it was washed with pure water. After that, the resist was peeled off to obtain the desired evaluation sample.

[0061] <Evaluation of the initial evaluation sample> The resistance between the remaining copper foil portion on the circuit and the copper circuit on the substrate was measured with a multimeter immediately after bonding. The connection resistance value was calculated by taking the average of 37 resistance points between the remaining copper foil portion on the circuit and the copper circuit on the substrate.

[0062] The resistance values ​​were 0.3 mΩ for Example 1, 1.7 mΩ for Comparative Example 1, and 5.4 mΩ for Comparative Example 2.

Claims

1. A method for processing conductive particles, comprising: step A, which involves applying an undercut treatment to conductive particles X to remove small-diameter particles having a particle diameter of a predetermined value XU or less; and step B, which involves crushing the conductive particles A obtained through step A to obtain conductive particles B.

2. The method for processing conductive particles according to claim 1, wherein the undercutting process includes classification using a classification mesh having an aperture size of a predetermined value XU.

3. The method for processing conductive particles according to claim 1, wherein in step A, a top-cut treatment is further applied to the conductive particles X to remove large-diameter particles having a particle diameter of a predetermined value XT or greater.

4. The method for processing conductive particles according to claim 3, wherein the top-cutting process includes classification using a classification mesh having an opening size of a predetermined value XT.

5. The method for processing conductive particles according to claim 1, wherein in step B, the conductive particles A are crushed using a jet mill.

6. The method for processing conductive particles according to claim 1, wherein in step B, when AU is the cumulative frequency of particles whose particle diameter in the volume-converted particle size distribution of conductive particle A is less than or equal to the predetermined value XU, and BU is the cumulative frequency of particles whose particle diameter in the volume-converted particle size distribution of conductive particle B is less than or equal to the predetermined value XU, the following condition (B-1) is satisfied: 10 ≤ (BU - AU) ≤ 40 … (B-1) 7. When the 50% cumulative particle size in the volume-based particle size distribution of said conductive particles X is D Ｘ５０ , the conditions of the following formula (X-1) and the following formula (A-1) are satisfied; when the 10% cumulative particle sizes in the volume-based particle size distributions of said conductive particles A and said conductive particles B are respectively D Ａ１０ and D Ｂ１０ , the condition of the following formula (B-2) is satisfied. The method for treating conductive particles according to claim 1. 40μm≦D Ｘ５０ ≦55μm ...(X-1) 0.8D Ｘ５０ ≦XU≦0.9D Ｘ５０ ...(A-1) 10≦(D Ａ１０ -D Ｂ１０ )×100 / D Ａ１０ ≦25 ...(B-2) 8. The method for treating conductive particles according to claim 1, further comprising step C of applying a surface treatment to the conductive particles B.

9. A method for producing conductive particles, comprising a method for processing conductive particles according to any one of claims 1 to 8.

10. The conductive particles B obtained through step B have a volume-based particle size distribution with a ratio of 10% cumulative particle size to 90% cumulative particle size [D Ｂ１０ / D Ｂ９０ A method for producing conductive particles according to claim 9, wherein [ ] is 0.4 to 0.

7.

11. A wiring forming member comprising a metal layer and an adhesive layer provided on the metal layer, wherein the conductive particles are obtained by the method described in claim 9.

12. A metal layer and an adhesive layer provided on the metal layer, the adhesive layer comprising conductive particles and adhesive components, wherein the conductive particles have a 50% cumulative particle size of 40 to 55 μm in the volume-based particle size distribution and a 90% cumulative particle size D in the volume-based particle size distribution. ９０ 10% cumulative particle size D １０ The proportion [D １０ / D ９０ A wiring forming member having a ratio of 0.4 to 0.7 and a cumulative frequency of 22.8 to 26.1 μm particles in the volume-reduced particle size distribution of 0.5 to 3%.