Silver powder made of silver particles, each to which fine silver particles adhere and process of producing the same

Abstract

This invention is a silver powder having a low-temperature sintering performance and dispersibility, which allows the powder particles to be agglomerated to a small degree and be nearly in the monodisperse state. Employed is silver powder of fine silver particles each to which fine silver particles adhere, wherein fine silver particles of nano-order particle size are adhered to the surface of each silver powder particle. The powder particles of the silver powder of fine silver particles each to which fine silver particles adhere have excellent dispersibility. In the production of the silver powder of fine silver particles each to which fine silver particles adhere, a process of including the steps of: adding a silver nitrate and a neutralizing agent into a slurry of silver powder in a dispersing medium; dissolving the mixture while stirring to allow fine silver oxide particles to be precipitated on the surface of each silver powder particle; washing the resultant silver powder; and exposing the fine silver oxide particles to UV rays to reduce the same to fine silver particles.

Description

TECHNICAL FIELD [0001] The present invention relates to a silver powder made of silver particles, each to which fine silver particles adhere and a process of producing the same. BACKGROUND ART [0002] Silver ink (silver paste) has been conventionally used not only for forming circuit boards by co-firing it with a ceramic substrate at a relatively high temperature but also for forming a wiring circuit on a printed wiring board, via-hole-fillers through such a board and adhesives for mounting electrical parts thereon by mixing and curing the silver ink (silver paste) with various types of resin ingredients, as described in the Patent Document 1. In the latter application, in general, an electrical conductivity has been obtained simply by mutually having the particles of silver powder touched, as a conductive filler without mutually sintering the particles. [0003] However, there have been a demand in recent years for lowering an electrical resistance for conductor portions formed using ...

AI Technical Summary

Benefits of technology

[0018] The “silver powder made of silver particles whose center part is regarded as a core material, in which silver particles each being finer than the silver particle of the center part adheres to the core material”(i.e., silver powder made of silver particles, each to which fine silver particles adhere) relating to the present invention is in other words expressed by “silver powder made of silver particles each being made adhered to the surface of each of the silver powder particles”. Specifically, the surface of each powder particle of the silver powder 2 as a core material is further coated with much finer silver particles 3, just like the image shown in FIG. 1. Thus, the fine silver particles 3 existing on the surface of each particle of the silver powder 2, each allows the fine silver particles 2 to exhibit a low-temperature sintering performance, independent of the shape and size of the powder particles of the core material, thereby making easier the sintering of the adjacent powder particles of the silver powder made of silver particles 1 made to adhere thereto.

[0064] In the meantime, the process for producing silver powder made of silver particles each to which fine silver particles adhere according to the present invention is excellent in running stability through the production process, and therefore, it can produce silver powder made of silver particles to each which fine silver particles adhere very effectively. The process can also produce silver powder used as the core material effectively, because it employs a process for producing silver powder using the above-described dilute solution.

Problems solved by technology

However, in a metal powder such as a silver powder, it is generally said that both the size-refinement of powder particles and the dispersibility meant by that powder particles nearly in a mono-disperse state are hard to become satisfied.

In such a case, generally the decomposition temperature of the dispersant is higher than the sintering temperature of the silver nanoparticles, resulting in that the low-temperature sintering performance of the silver nanoparticles themselves cannot be used to the full.

Further, in case of the silver ink containing the silver nanoparticles, because the content of the filler is less than conventional, a thick film is difficult to form while a thin film is easy to form.

This makes it difficult to use such silver ink for application to form wiring circuits having a large cross-sectional area sufficient to be usable for power-supply circuit such carries a relatively large amount of current or for application to form a low-resistance circuit.

Further, in the use of the silver ink for adhesives for mounting components thereon, not only its conductivity, but also its adhesive strength is required severely.

Thus, there remain many problems that cannot be overcome by conventional silver-nanoparticles-containing silver ink.

In the meantime, it goes without saying that silver powder used for commonly-used silver pastes has had a limitation in terms of its low-temperature sintering performance judging from its particle size.

Thus, the conventional silver powder has been unsuitable when forming recent circuits where fine-pitched wiring patterns are drawn.

As a result, a silver powder has been merely obtained such that its crystallinity is low, and additionally its agglomeration significantly occurs easily.

Images