A method of making an assembly can include forming a first conductive element at a first surface of a substrate of a first component, forming conductive nanoparticles at a surface of the conductive element by exposure to an electroless plating bath, juxtaposing the surface of the first conductive element with a corresponding surface of a second conductive element at a major surface of a substrate of a second component, and elevating a temperature at least at interfaces of the juxtaposed first and second conductive elements to a joining temperature at which the conductive nanoparticles cause metallurgical joints to form between the juxtaposed first and second conductive elements. The conductive nanoparticles can be disposed between the surfaces of the first and second conductive elements. The conductive nanoparticles can have long dimensions smaller than 100 nanometers.

A method of making an assembly can include forming a first conductive element at a first surface of a substrate of a first component, forming conductive nanoparticles at a surface of the conductive element by exposure to an electroless plating bath, juxtaposing the surface of the first conductive element with a corresponding surface of a second conductive element at a major surface of a substrate of a second component, and elevating a temperature at least at interfaces of the juxtaposed first and second conductive elements to a joining temperature at which the conductive nanoparticles cause metallurgical joints to form between the juxtaposed first and second conductive elements. The conductive nanoparticles can be disposed between the surfaces of the first and second conductive elements. The conductive nanoparticles can have long dimensions smaller than 100 nanometers.

A component built-in board comprises stacked therein a plurality of printed wiring bases having a wiring pattern and a via formed on/in a resin base thereof, and comprises an electronic component built in thereto, wherein at least a portion of the plurality of printed wiring bases include a thermal wiring in the wiring pattern and include a thermal via in the via, at least one of the plurality of printed wiring bases has formed therein an opening where the electronic component is built, and has formed therein a heat-conducting layer and closely attached to a surface on an opposite side to an electrode formation surface of the electronic component built in to the opening, and the electronic component is fixed in the opening by an adhesive layer stacked on the heat-conducting layer, via a hole formed in a region facing onto the opening of the heat-conducting layer.

A component built-in board comprises stacked therein a plurality of printed wiring bases having a wiring pattern and a via formed on/in a resin base thereof, and comprises an electronic component built in thereto, wherein at least a portion of the plurality of printed wiring bases include a thermal wiring in the wiring pattern and include a thermal via in the via, at least one of the plurality of printed wiring bases has formed therein an opening where the electronic component is built, and has formed therein a heat-conducting layer and closely attached to a surface on an opposite side to an electrode formation surface of the electronic component built in to the opening, and the electronic component is fixed in the opening by an adhesive layer stacked on the heat-conducting layer, via a hole formed in a region facing onto the opening of the heat-conducting layer.

A method of making an assembly can include forming a first conductive element at a first surface of a substrate of a first component, forming conductive nanoparticles at a surface of the conductive element by exposure to an electroless plating bath, juxtaposing the surface of the first conductive element with a corresponding surface of a second conductive element at a major surface of a substrate of a second component, and elevating a temperature at least at interfaces of the juxtaposed first and second conductive elements to a joining temperature at which the conductive nanoparticles cause metallurgical joints to form between the juxtaposed first and second conductive elements. The conductive nanoparticles can be disposed between the surfaces of the first and second conductive elements. The conductive nanoparticles can have long dimensions smaller than 100 nanometers.

A method of making an assembly can include forming a first conductive element at a first surface of a substrate of a first component, forming conductive nanoparticles at a surface of the conductive element by exposure to an electroless plating bath, juxtaposing the surface of the first conductive element with a corresponding surface of a second conductive element at a major surface of a substrate of a second component, and elevating a temperature at least at interfaces of the juxtaposed first and second conductive elements to a joining temperature at which the conductive nanoparticles cause metallurgical joints to form between the juxtaposed first and second conductive elements. The conductive nanoparticles can be disposed between the surfaces of the first and second conductive elements. The conductive nanoparticles can have long dimensions smaller than 100 nanometers.