A circuit forming method, comprising: a coating step of applying a metal-containing liquid and a metal paste in an overlapping manner on a base, the metal-containing liquid containing fine metal particles and the metal paste containing a resin binder and metal particles larger than the fine metal particles in the metal-containing liquid; and a heating step of making the metal-containing liquid and the metal paste coated in the coating step conductive by heating the metal-containing liquid and the metal paste.

The present disclosure relates to the field of circuit testing technologies and discloses a flexible circuit board and a test fixture. The flexible circuit board comprises: a flexible body which has a first crimping portion and an extension portion, the first crimping portion being used to be laminated with a second crimping portion of a substrate to be tested; a first electrically connected structure which is located on a first side of the flexible body, arranged on the first crimping portion, and used to be laminated with a second electrically connected structure on the second crimping portion; a support structure which is located on the first side of the flexible body and includes a first support portion and a second support portion; the first support portion is arranged on the extension portion and configured to support the extension portion in the laminating state.

A circuit forming method, comprising: a coating step of applying a metal-containing liquid and a metal paste in an overlapping manner on a base, the metal-containing liquid containing fine metal particles and the metal paste containing a resin binder and metal particles larger than the fine metal particles in the metal-containing liquid; and a heating step of making the metal-containing liquid and the metal paste coated in the coating step conductive by heating the metal-containing liquid and the metal paste.

Provided is an electronic component mounting structure and method for mounting electronic components on the side of a printed circuit board by means of simple fabrication and enlarging the surface area for mounting electronic components. A cut face of a conductive plating layer, which is obtained by cutting along a via in which a conductive plating layer covering an inner wall face of a via hole is electrically connected to a conductive pattern layer of the printed circuit board, is exposed at a cut end face and used as a land pattern which is solder-connected to a mount connecting portion of the electronic component. The end face at which the land pattern is exposed is a surface parallel to the side of the printed circuit board, and therefore electronic components can be mounted on the end face parallel to the side.

A chip package includes a circuit board, a chip and an underfill. A solder resist layer formed on the circuit board is modified in edge profile so as to reduce required amount of the underfill. The fewer underfill is still enough to be filled between the circuit board and the chip, and still can cover circuit lines that are not covered by the solder resist layer to protect the circuit lines from oxidation.

Provided is an electronic component mounting structure and method for mounting electronic components on the side of a printed circuit board by means of simple fabrication and enlarging the surface area for mounting electronic components. A cut face of a conductive plating layer, which is obtained by cutting along a via in which a conductive plating layer covering an inner wall face of a via hole is electrically connected to a conductive pattern layer of the printed circuit board, is exposed at a cut end face and used as a land pattern which is solder-connected to a mount connecting portion of the electronic component. The end face at which the land pattern is exposed is a surface parallel to the side of the printed circuit board, and therefore electronic components can be mounted on the end face parallel to the side.

A substrate for a printed circuit board according to an embodiment of the present invention includes a resin film and a metal layer stacked on at least one of surfaces of the resin film. An average diffusion depth of a main metal of the metal layer in the resin film is 100 nm or less after a weather resistance test in which the substrate is held at 150 C. for seven days. The average diffusion depth is preferably 80 nm or less before the weather resistance test.

The present disclosure relates to the field of circuit testing technologies and discloses a flexible circuit board and a test fixture. The flexible circuit board comprises: a flexible body which has a first crimping portion and an extension portion, the first crimping portion being used to be laminated with a second crimping portion of a substrate to be tested; a first electrically connected structure which is located on a first side of the flexible body, arranged on the first crimping portion, and used to be laminated with a second electrically connected structure on the second crimping portion; a support structure which is located on the first side of the flexible body and includes a first support portion and a second support portion; the first support portion is arranged on the extension portion and configured to support the extension portion in the laminating state.

A substrate for a printed circuit board according to an embodiment of the present invention includes a resin film and a metal layer stacked on at least one of surfaces of the resin film. An average diffusion depth of a main metal of the metal layer in the resin film is 100 nm or less after a weather resistance test in which the substrate is held at 150 C. for seven days. The average diffusion depth is preferably 80 nm or less before the weather resistance test.

The present invention provides a silver powder that has an appropriate viscosity range at the time of paste production, can be easily kneaded, and prevents flake occurrence. The silver powder has a dibutyl phthalate absorption amount, measured by a method of JIS-K6217-4, of 7.0 to 9.5 ml/100 g, and has an oil absorption profile at the time of measurement of the absorption amount, having two peaks, or one peak having a half width of not more than 1.5 ml/100 g.