133

Original Research Paper

J. Jpn. Soc. Colour Mater., 93〔5〕，133–137（2020）

Spatial Distribution of Metal Particles in Dried Metal Paste
Tatsuo A ikawa＊,†, Kyoko Miyauchi＊, Makiko Ito＊＊ and Ken Nakajima＊＊＊ Materials Laboratories, Technology Division, Sumitomo Metal Mining Co., Ltd. 1-6-1 Suehiro-cho, Ome, Tokyo 198-8601, Japan＊＊ Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology,

2-12-1 O-okayama, Meguro, Tokyo 152-8552, Japan†Corresponding Author, E-mail: tatsuo.aikawa.m8@smm-g.com(Received January 30, 2020; Accepted March 17, 2020 )Abstract
Metal paste is a viscous fluid containing polymeric resin as a binder that can bind particles onto a substrate. The spatial distribution of metal
particles after the paste dries plays an important role in the properties of the final product. In this study, we focused on whether phase separationof binder resins influences distribution of metal particles in the dried paste. To study this relationship, the spatial distribution of metal particles
and resins must be clear. The spatial distribution of metal particles and phase separated resins was studied based on difference in surface
moduli among components (particles, resins). To measure the surface modulus of the components, the nano-palpation method with an atomicforce microscope (AFM) was used. The result indicated that phase separation of binder resins affected the distribution of metal particles.
Key-words: Metal paste, Resin, Phase separation, AFM, Nano-palpation

1．Introduction
Metal paste is a viscous fluid, and is a functional painting
material for manufacturing small, high performanceelectronic components such as conductive printed circuits 1 ).
As shown in Scheme 1, a typical metal paste consists ofmetal particles, a binder resin, solvent and additives. The
binder resin is used to increase the adhesiveness of the paste,
which enables the paste to attach to a substrate after thesubstrate is coated with it and it dries. Organic solvent isused for diluting the paste to adjust the coating properties. A
certain type of additive is used to tune the dispersibility ofthe particles and the rheological properties. The applicationof metal paste is determined by the type of metal particles
in the paste 2 ). For example, when using conductive metal
particles, such as nickel, copper, or silver, the resulting metal
paste can be used for producing conductive components.
Other applications are shown in Table 1.
Furthermore, metal paste is classified into two types
depending on whether a firing process is employed or not.
A firing process produces thin metallic layers which haveconductive properties, and in this study we deal with metal
paste that requires a firing process. A typical usage of themetal paste is for manufacturing conductive components, andthis is described as follows (Scheme 2 ). Firstly, a substrate
is coated with metal paste. When coating the substrate with
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－1－Scheme 1 Typical components of metal paste.
Table 1 Application of metal paste depending on type of metal

particles.

Types of particles Constituent element Application of metal paste
Ni, Cu, Ag, Pt, Au
Electric conductive
Metal particles
Cu, Ag
Thermal conductive
Al, AgLight scattering
RuO 2
Electronic resistive
Metallic oxideparticles
BaTiO 3Dielectric, piezoelectric

the paste, the printing technique should be chosen carefully(e.g, screen printing, gravure printing, inkjet printing, and soon) because the printing technique determines the structureof the final product, so choosing a suitable printing technique
is important 3-5 ). After printing, the paste is dried to remove
the solvent contained in the paste. After drying, the paste isburned out to remove the binder resin, and then fired. Finally,
the only thing that remains is the metal component, which
can work as a conductive circuit.
These processes influence the properties of the finalproduct. In particular, the distribution of metal particles inthe dried paste is an important factor for the conductivity of© 2020 Journal of the Japan Society of Colour Material