CONDUCTIVE PASTE

Abstract

The present invention addresses the problem of providing a conductive paste that achieves both low resistance and high adhesion strength (die shear strength) of the resulting conductive body after firing.

The present invention provides a conductive paste comprising: (A) copper fine particles having an average particle diameter of 50 nm to 400 nm and a crystallite diameter of 20 nm to 50 nm; (B) copper particles having an average particle diameter of 0.8 μm to 5 μm and a ratio of a crystallite diameter to the crystallite diameter of the copper particles (A) of 1.0 to 2.0; and (C) a solvent.

Claims

1. A conductive paste comprising: (A) copper fine particles having an average particle diameter of 50 nm to 400 nm and a crystallite diameter of 20 nm to 50 nm; (B) copper particles having an average particle diameter of 0.8 μm to 5 μm and a ratio of a crystallite diameter to the crystallite diameter of the (A) copper fine particles of 1.0 to 2.0; and (C) a solvent.

2. The conductive paste according to claim 1, wherein the (B) copper particles have an aspect ratio of 1.0 to 2.0.

3. The conductive paste according to claim 1, further comprising (D) an amine compound.

4. The conductive paste according to claim 1, wherein a content of the (B) copper particles is 20 parts by mass to 80 parts by mass based on a total 100 parts by mass of the (A) copper fine particles and the (B) copper particles.

5. A die attach agent comprising the conductive paste according to claim 1.

6. A semiconductor device fabricated using the die attach agent according to claim 5.

7. The semiconductor device according to claim 6, wherein a surface to which the die attach agent is applied is copper.

Description

EXAMPLES

[0072] The invention will be described in more detail by means of examples and comparative examples, but the invention is not limited to these examples.

[0073] [Preparation of Conductive Paste]

[0074] Each conductive paste was prepared by mixing the following components in the proportions of Examples 1 to 4 and Comparative Examples 1 and 2 listed in Table 1. The proportions of each component shown in Table 1 are all in parts by mass, and a blank column means that the component is not blended.

(A) Copper Fine Particles

[0075] When 400 g (4.5 mol) of 3-methoxypropylamine was added to the reaction vessel and 450 g (2.0 mol) of copper formate was added while maintaining the reaction temperature below 40° C. with stirring, the copper formate dissolved into a dark blue solution. When 100 g (2.0 mol) of hydrazine was slowly added to the solution, and the reaction temperature was maintained at 5-60° C., copper fine particles were formed with the addition of hydrazine, and the dark blue solution gradually changed to dark brown. After the reaction was terminated by dropping the entire amount of hydrazine, methanol was added to the resulting reaction mixture with stirring, and the mixture was then separated into two layers when left to stand at 25° C. The upper layer was a pale yellow clear liquid, and brownish (A) copper fine particles settled in the lower layer. The liquid in the upper layer was removed by decantation, and then methanol addition, standing, and decantation were repeated to obtain a paste. To the resulting paste, 10 g of 2-ethyl-1,3-hexanediol was added and mixed, and the remaining methanol was removed by evaporator to obtain a copper particles slurry containing the (A) copper fine particles with a copper content of 90% by mass. The amount of the (A) copper fine particles shown in Table 1 is the amount of copper component. Of the remaining 10% by mass of the copper particles slurry, 2% by mass is 3-methoxypropylamine and 8% by mass is 2-ethyl-1,3-hexanediol. This was confirmed by using a thermogravimetric differential thermal analysis (TG/DTA) system.

(B) Copper Particles 1

[0076] EFC-09 (manufactured by Fukuda Metal Foil & Powder Co., Ltd.)

(B) Copper Particles 2

[0077] CS-10D (manufactured by Mitsui Mining & Smelting Co., Ltd.)

(B) Copper Particles 3

[0078] HXR-Cu (manufactured by Nippon Atomized Metal Powders Corporation)

(B) Copper Particles 4

[0079] DCX-99 (manufactured by DOWA Electronics Materials Co., Ltd.)

(C) Solvent

[0080] 2-Ethyl-1,3-hexanediol (manufactured by FUJIFILM Wako Pure Chemical Corporation)

[0081] Table 1 shows the total amount of 2-ethyl-1,3-hexanediol contained in the copper particles slurry including the (A) copper fine particles with a copper content of 90% by mass, and 2-ethyl-1,3-hexanediol added separately if a solvent is required.

(D) Amine Compound

[0082] 3-Methoxypropylamine (Tokyo Chemical Industry Co., Ltd.)

[0083] Table 1 shows the amount of 3-methoxypropylamine contained in a copper particles slurry including the (A) copper fine particles with a copper content of 90% by mass.

[0084] The measurement methods in Examples and Comparative Examples are as follows.

[0085] [Average Particle Diameter]

[0086] The average particle diameter is an average value of the diameters of 200 arbitrary particles observed with a scanning electron microscope (SEM) (number average value). The scanning electron microscope (SEM) used was an S-3400N (manufactured by Hitachi High-Tech Corporation).

[Crystallite Diameter]

[0087] The crystallite diameter was obtained by the measurement by a powder X-ray diffraction method using CuKα ray as a line source to obtain full width at half maximum of the peak of Miller index (111) plane, and the calculation using Scherrer's equation. The Scherrer constant used was 1.33. An Ultima IV X-ray diffractometer (Rigaku Corporation) was used as the X-ray diffractometer.

[0088] [Measurement of Crack Occurrence]

[0089] The conductive paste of each of Examples and Comparative Examples was applied to a glass substrate in the shape of 5 mm in width, 50 mm in length, and 0.05 mm in thickness, and the temperature was raised from room temperature (25° C.) to 250° C. at a rate of 10° C./minute, and then fired by holding at 250° C. for 20 minutes to form a conductive body. The presence or absence of cracks in the conductive body (presence or absence of shrinkage in the thin film) were observed visually.

[0090] Not occurred: The number of cracks in the conductive body is 0.

[0091] Occurred: The number of cracks in the conductive body is 1 or more.

[0092] [Measurement of Specific Resistance]

[0093] The test piece prepared in the crack occurrence measurement above was used for the measurement of specific resistance. Using an LCR meter, the specific resistance (resistivity) was measured using the four-terminal method.

[0094] [Die Shear Strength]

[0095] A 1 mm×1 mm gold-coated silicon chip was mounted on a copper lead frame using the conductive paste of each of Examples and Comparative Examples. Under a non-oxidizing atmosphere (nitrogen-hydrogen mixed gas (hydrogen concentration of about 3-5%)), the temperature was raised from room temperature (25° C.) to 250° C. at a rate of 10° C./min and held at 250° C. for 20 minutes. After firing, the die shear strength was measured at room temperature (25° C.) using a bond tester. The bond tester was a 4000 universal bond tester (manufactured by Nordson DAGE).

TABLE-US-00001 TABLE 1 Average particle Crystallite diameter diameter Comparative Comparative (μm) (nm) Example 1 Example 2 Example 3 Example 4 Example 1 Example 2 (A) Copper fine particles 0.14 30.79 45 45 45 45 100 — (B) Copper particles EFC-09 1.07 50.10 50 — — — — 100 CS-10D 0.93 43.43 — 50 — — — — HXR-Cu 1.48 41.95 — — 50 — — — DCX-99 2.76 57.62 — — — 50 — — (C) Solvent 2-ethyl-1,3-hexanediol 11 11 11 11 8 14 (D) Amine compound 1 1 1 1 2 0 Ratio of crystallite diameters (B)/(A) 1.63 1.41 1.36 1.87 — — Evaluation items Crack occurrence Not Not Not Not Occurred Not occcured occurred occurred occurred occurred Specific resistance value 8.0 9.0 11.5 7.4 Not 139.4 (μΩ .Math. cm) measurable Die shear strength (MPa) 47.0 32.3 24.2 34.2 Not Not measurable measurable

[0096] As can be seen from the results shown in Table 1, the conductive bodies obtained by firing the conductive pastes of Examples 1-4 were free of cracks, had low specific resistance, and had high die shear strength. More precisely, as “crystallite diameter of (B) copper particles”/“crystallite diameter of (A) copper fine particles” became larger, the specific resistance value became smaller. It can also be seen that the die shear strength decreases as the “crystallite diameter of (B) copper particles”/“crystallite diameter of (A) copper particles” approaches 1.0 or 2.0, with the maximum at 1.6. In contrast, the conductive body obtained by firing the conductive paste of Comparative Example 1 showed cracks, and it was not possible to prepare a test piece sufficient for measuring the specific resistance and die shear strength. The conductive body obtained by firing the conductive paste of Comparative Example 2 did not have crack, but the conductive body was brittle and the die shear strength could not be measured. In addition, the specific resistance value was high.

[0097] The disclosure of Japanese Patent Application No. 2018-183879 (filing date: Sep. 28, 2018) is incorporated herein by reference in its entirety.

[0098] All references, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if the individual references, patent applications, and technical standards were specifically and individually noted as being incorporated by reference.