US-12617013-B2 - Silver powder and method of producing same

Abstract

Provided are a silver powder having powder physical properties enabling reduction of volume resistivity after firing and a method of producing this silver powder. The silver powder has a tap density of 4.8 g/mL or more, a TAP/D50 value (value determined by dividing the tap density (g/mL) by the volume-based median diameter (μm)) of not less than 7 and not more than 15, and a specific surface area of not less than 0.75 m 2 /g and not more than 1.3 m 2 /g.

Inventors

• Kaori TOKUSADA
• Hikaru HAYASHIDA

Assignees

• DOWA ELECTRONICS MATERIALS CO., LTD.

Dates

Publication Date

20260505

Application Date

20220302

Priority Date

20210310

Claims (1)

1. 1 . A method of producing a silver powder comprising: a milling step of using a pneumatic mill to accelerate and mill a silver powder produced by a wet reduction method; and a classification step of classifying the silver powder, performed after the milling step, wherein the milling step is performed with the silver powder having a powder concentration during milling of 0.2 kg/m 3 or less, the classifying is performed such that after the classification step, the silver powder has powder physical properties of: a tap density of 4.8 g/mL or more; a TAP/D50 value that is a value determined by dividing the tap density by volume-based median diameter, in units of μm, of not less than 7 and not more than 15; and a specific surface area of not less than 0.75 m 2 /g and not more than 1.3 m 2 /g, a milling device in the milling step, a classifying device in the classification step, and a collecting device are connected in series in this order, an exhaust ventilator is connected at a downstream side of the collecting device and performs suction such that silver powder that has been supplied to the milling device is pneumatically conveyed to the collecting device, and a powder concentration during pneumatic conveyance determined by dividing a supply rate of silver powder in the milling step by an airflow rate of the exhaust ventilator is 0.08 kg/m 3 or less.

Description

TECHNICAL FIELD The present disclosure relates to a silver powder and a method of producing the same. BACKGROUND Silver pastes are used as conductive pastes in the formation of electrodes and wiring patterns of substrates in electronic components, for example. A silver paste serving as a conductive paste is produced by kneading silver powder with a vehicle and so forth. It is desirable for the silver powder of a conductive paste to have a suitably small particle diameter and a sharp particle size distribution in order to comply with miniaturization of electronic components, formation of conductor patterns with higher density and finer lines, and so on. Patent Literature (PTL) 1 identifies a problem that with a silver powder produced by a conventional technique, there are instances in which the condition of a coating film or line properties are poor, resulting in the inability to obtain a good fired film and to comply with increased density and finer line formation in a pattern. PTL 1 describes a silver powder and method of producing the same for solving this problem. In the method of producing a silver powder that is described in PTL 1, a silver powder produced by a wet reduction method is subjected to a surface smoothing process in which particles are caused to mechanically collide with one another, and then large agglomerates of silver are removed by classification. PTL 1 reports that a paste in which a silver powder produced by this production method is used enables improvement of line properties, for example. CITATION LIST Patent Literature PTL 1: JP2007-186798A SUMMARY Technical Problem In a conventional technique such as described above, reduction of the particle diameter (volume-based median diameter) of silver particles in a silver powder in production of the silver powder by a wet reduction method tends to be accompanied by an increase of specific surface area of the silver powder and a decrease of tap density of the silver powder. This makes it difficult to fill in voids after a conductive film is formed with a conductive paste in which this silver powder is used and is then fired, and leaves room for improvement of electrical conductivity such as by reducing volume resistivity. The present disclosure is made in light of the circumstances set forth above, and an object thereof is to provide a silver powder having powder physical properties that enable reduction of volume resistivity after firing and a method of producing this silver powder. Solution to Problem A silver powder according to the present disclosure for achieving the object set forth above has: a tap density of 4.8 g/mL or more;a TAP/D50 value that is a value determined by dividing the tap density, in units of g/mL, by volume-based median diameter, in units of μm, of not less than 7 and not more than 15; anda specific surface area of not less than 0.75 m2/g and not more than 1.3 m2/g. A method of producing a silver powder according to the present disclosure for achieving the object set forth above comprises: a milling step of using high-pressure airflow to accelerate and mill a silver powder produced by a wet reduction method; anda classification step of classifying the silver powder, performed after the milling step, whereinthe milling step is performed with the silver powder having a concentration of 0.2 kg/m3 or less, andthe classifying is performed such that after the classification step, the silver powder has powder physical properties of:a tap density of 4.8 g/mL or more;a TAP/D50 value that is a value determined by dividing the tap density by volume-based median diameter, in units of μm, of not less than 7 and not more than 15; anda specific surface area of not less than 0.75 m2/g and not more than 1.3 m2/g. Advantageous Effect Provided are a silver powder having powder physical properties that enable reduction of volume resistivity after firing and a method of producing this silver powder. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: FIG. 1 illustrates one example of a plant for producing silver powder. DETAILED DESCRIPTION A silver powder according to a present embodiment is a powder that is a collection of fine silver particles. The following describes the silver powder according to the present embodiment and a method of producing this silver powder. (Silver Powder) The silver powder according to the present embodiment has a tap density of 4.8 g/mL or more. Moreover, when a value determined by dividing the tap density of the silver powder by the volume-based median diameter (μm) of fine silver particles in the silver powder is defined as a TAP/D50 value, this TAP/D50 value is not less than 7 and not more than 15. Furthermore, the silver powder has a specific surface area of not less than 0.75 m2/g and not more than 1.3 m2/g. As a result of the silver powder having powder physical properties such as set forth above, it is possible to achieve reduction of volume resistivity of a conductive film that is obtain