JAPAN-based Tanaka Holdings says it has developed a silver paste that allows circuits to be screen-printed and cured with ultraviolet light only.
The UV700-SR1J does not require thermal curing to form conductive electronic circuits. According to Tanaka Holdings, the circuit can be screen printed on a base material using its silver paste, then cured by exposing it to UV light for around 10 seconds, which instantly hardens the printed film even at room temperature.
The technology enables narrower width than in conventional screen printing, resulting in the creation of micro wiring with a width of 70 micrometers and electrical resistivity of 10-4 ohm-cm (10 to the power of minus 4 ohm per 1 centimeter) on surface-treated PET film. This level of electrical conductivity is comparable to UV-curable and thermally curable silver pastes used in conventional flexographic printing.
Even at a film thickness of 10 micrometers, the silver paste can be cured using UV. By eliminating the need for thermal curing, Tanaka Holdings says it is now possible to screen print circuits on flexible base materials that may be susceptible to heat, such as PET film. Shortened treatment time (10 seconds UV curing vs hours for thermal curing) and the use of screen printing techniques also helps with applications such as rapid prototyping or small manufacturing runs.
Because screen printing is a method that applies paste through a mesh with openings in the plate, the ink needs to be a paste with thixotropy to prevent bleeding when the plate is separated and adhesiveness suitable for adhering to the base material, and the silver particles contained in the paste must be fine enough to pass through the mesh.
Furthermore, while flexographic printing, which is a type of letterpress printing can create wires with a thickness of 5 um, screen printing produces wires with paste more than double the thickness of ink due to the thickness of the mesh plate.
By reviewing the composition of the resin and silver particles that are the main components of silver paste, Tanaka Holdings succeeded in developing a UV-curable product that enables the formation of submicroscopic circuits while ensuring the stable electrical conductivity required for printed electronics.