A one-step react-on-demand (RoD) method for fabricating flexible circuits with ultra-low sheet resistance, enhanced safety and durability. With the special functionalized substrate, a real-time three-dimensional synthesize of silver plates in micro scale was triggered on-demand right beneath the tip in the water-swelled PVA coating, forming a three-dimensional metal-polymer (3DMP) hybrid structure of 7 m with one single stroke. The as-fabricated silver traces show an enhanced durability and ultralow sheet resistance down to 4 m/sq which is by far the lowest sheet resistance reported in literatures achieved by direct writing. Meanwhile, PVA seal small particles inside the film, adding additional safety to this technology. Since neither nanomaterials nor a harsh fabrication environment are required, the proposed method remains low-cost, user friendly and accessible to end-users. the RoD approach can be extended to various printing systems, offering a particle-free, sintering-free solution for high resolution, high speed production of flexible electronics.

A method of forming a solder connection between a carrier and a component includes a) printing an electrically conductive layer containing metal particles on a surface of the carrier by a printing process, b) printing a solder onto the electrically conductive layer by a printing process, c) arranging the component on the carrier so that the component is in direct contact with the solder, and d) melting the solder and then solidifying the solder to form the solder connection, wherein e) prior to printing the solder, the metal particles of the electrically conductive layer are coated with a precious metal coating, and f) a solder mediator agent including a precious metal salt or a precious metal oxide from which a precious metal is released to form the precious metal coating is applied onto the electrically conductive layer by a printing process.

The present invention provides a solder paste free of reducing agents and activators, and a method for producing a soldered product in which the solder paste is used to achieve solder bonding. The solder paste for reducing gas of the present invention is a solder paste for reducing gas used together a reducing gas. The solder paste contains a solder powder; a thixotropic agent that is solid at normal temperature; and a solvent, and is free of reducing agents for removal of oxide films and free of activators for improvement of reducibility.

The disclosure relates to flocs of metallic, geometrically discrete copper nanoparticles. Specifically, the disclosure relates to a process for obtaining flocs, or clusters of oxidation-resistant, stable Copper nano-particles, the flocs being capable of being sintered in ambient environment at relatively low temperatures.

Copper inks are provided that include a plurality of core-shell nanostructures, with each nanostructure including a copper core and a barrier metal shell, a diameter of less than about 500 nm, and a distinct boundary between the copper core and the barrier metal shell. Methods of forming a copper ink are further provided and include an initial step of synthesizing an amount of copper nanoparticles in an aqueous solution. An amount of a barrier metal is then added to the copper nanoparticles to form a dispersion of the barrier metal and the copper nanoparticles, and a reducing agent is subsequently added to the dispersion to produce a copper ink comprising core-shell nanostructures having a copper core and a barrier metal shell. Copper films are then formed by applying that copper ink to a substrate and sintering the copper ink.

A conductive pattern having high dispersion stability and a low resistance over a board is formed. A dispersing element (1) contains a copper oxide (2), a dispersing agent (3), and a reductant. Content of the reductant is in a range of a following formula (1). Content of the dispersing agent is in a range of a following formula (2).

0.0001(reductant mass/copper oxide mass)0.10(1)

0.0050(dispersing agent mass/copper oxide mass)0.30(2)

The dispersing element containing the reductant promotes reduction of copper oxide to copper in firing and promotes sintering of the copper.

Disclosed is copper powder having an average primary particle size D of 0.15 to 0.6 m, having a ratio of D to D.sub.BET, D/D.sub.BET, of 0.8 to 4.0 wherein D.sub.BET is a sphere-equivalent average particle diameter calculated from a BET specific surface area, and having no layer for preventing agglomeration on the surface thereof. The copper powder is suitably produced by a method which includes a step of mixing (1) hydrazine and (2) a reactant mixture including a monovalent or divalent copper source and a liquid medium which includes water and an organic solvent having water miscibility and capable of reducing the surface tension of water, to reduce the copper source to form copper particles.

In some embodiments, a method comprises leaching a surface of a glass or glass ceramic substrate to form a leached layer. The glass or glass ceramic substrate comprises a multi-component material. The material has a bulk composition, in mol % on an oxide basis: 51% to 90% SiO.sub.2; 10% to 49% total of minority components RO.sub.x. Leaching comprises selectively removing components RO.sub.x of the glass or glass ceramic substrate preferentially to removal of SiO.sub.2. In the leached layer, the RO.sub.x concentration is 50% or less than the RO.sub.x concentration of the bulk composition.

To provide a method for firing a copper paste, which improves sinterability of copper particles for the purpose of forming a copper wiring line that is decreased in the electrical conductivity. A method for firing a copper paste, which comprises: an application step wherein a copper paste is applied over a substrate; a first heating step wherein the substrate is heated in a nitrogen gas atmosphere containing from 500 ppm to 2,000 ppm (inclusive) of an oxidizing gas in terms of volume ratio after the application step, thereby oxidizing and sintering copper particles in the copper paste; and a second heating step wherein the substrate is heated in a nitrogen gas atmosphere containing 1% or more of a reducing gas in terms of volume ratio after the first heating step, thereby reducing the oxidized and sintered copper oxide.

A method for manufacturing a printed circuit board, comprising in order steps (i) providing a non-conductive substrate having on a surface copper circuitry with a copper surface, wherein said surface is chemically treated by (a) oxidation and subsequent reduction reaction and/or (b) organic compound attached to said surface, a permanent, non-conductive, not fully polymerized cover layer covering at least partially said surface, (ii) thermally treating the substrate with the cover layer at temperature from 140 C. to 250 C. in atmosphere containing molecular oxygen at 100000 ppm or less, based on the total volume of the atmosphere, wherein a substrate with a permanent, non-conductive cover layer is obtained, with the provisos that (ii) is after (i) but before any metal or metal alloy is deposited onto the cover layer, and that in (ii) the cover layer is fully polymerized in one thermal treating step, if the cover layer is a solder mask.