A method of making an assembly can include juxtaposing a top surface of a first electrically conductive element at a first surface of a first substrate with a top surface of a second electrically conductive element at a major surface of a second substrate. One of: the top surface of the first conductive element can be recessed below the first surface, or the top surface of the second conductive element can be recessed below the major surface. Electrically conductive nanoparticles can be disposed between the top surfaces of the first and second conductive elements. The conductive nanoparticles can have long dimensions smaller than 100 nanometers. The method can also include elevating a temperature at least at interfaces of the juxtaposed first and second conductive elements to a joining temperature at which the conductive nanoparticles can cause metallurgical joints to form between the juxtaposed first and second conductive elements.

A method of making an assembly can include juxtaposing a top surface of a first electrically conductive element at a first surface of a first substrate with a top surface of a second electrically conductive element at a major surface of a second substrate. One of: the top surface of the first conductive element can be recessed below the first surface, or the top surface of the second conductive element can be recessed below the major surface. Electrically conductive nanoparticles can be disposed between the top surfaces of the first and second conductive elements. The conductive nanoparticles can have long dimensions smaller than 100 nanometers. The method can also include elevating a temperature at least at interfaces of the juxtaposed first and second conductive elements to a joining temperature at which the conductive nanoparticles can cause metallurgical joints to form between the juxtaposed first and second conductive elements.

A micro light emitting diode (LED) transfer device includes a transfer part configured to transfer a relay substrate having at least one micro LED; a mask having openings corresponding to a position of the at least one micro LED; a first laser configured to irradiate a first laser light having a first wavelength to the mask; a second laser configured to irradiate a second laser light having a second wavelength different from the first wavelength to the mask; and a processor configured to: control the at least one micro LED to contact a coupling layer of a target substrate, and based on the coupling layer contacting the at least one micro LED, control the first laser to irradiate the first laser light toward the at least one micro LED, and subsequently control the second laser to irradiate the second laser light toward the at least one micro LED.

A micro light emitting diode (LED) transfer device includes a transfer part configured to transfer a relay substrate having at least one micro LED; a mask having openings corresponding to a position of the at least one micro LED; a first laser configured to irradiate a first laser light having a first wavelength to the mask; a second laser configured to irradiate a second laser light having a second wavelength different from the first wavelength to the mask; and a processor configured to: control the at least one micro LED to contact a coupling layer of a target substrate, and based on the coupling layer contacting the at least one micro LED, control the first laser to irradiate the first laser light toward the at least one micro LED, and subsequently control the second laser to irradiate the second laser light toward the at least one micro LED.

A method of making an assembly can include juxtaposing a top surface of a first electrically conductive element at a first surface of a first substrate with a top surface of a second electrically conductive element at a major surface of a second substrate. One of: the top surface of the first conductive element can be recessed below the first surface, or the top surface of the second conductive element can be recessed below the major surface. Electrically conductive nanoparticles can be disposed between the top surfaces of the first and second conductive elements. The conductive nanoparticles can have long dimensions smaller than 100 nanometers. The method can also include elevating a temperature at least at interfaces of the juxtaposed first and second conductive elements to a joining temperature at which the conductive nanoparticles can cause metallurgical joints to form between the juxtaposed first and second conductive elements.

A semiconductor package of a pin-grid-array type includes a bump pad on a first substrate, a metal socket on a second substrate, a core material for reverse reflow on the bump pad, and solder paste or a solder bump forming a solder layer on the core material for reverse reflow. The solder paste or the solder bump is in contact with the bump pad. The core material for reverse reflow and the solder paste or the solder bump bonded to the core material for reverse reflow are used as a pin and detachably attached to the metal socket. The core material for reverse reflow includes a core, a first metal layer directly coated on the core, and a second metal layer directly coated on the first metal layer.

A semiconductor package of a pin-grid-array type includes a bump pad on a first substrate, a metal socket on a second substrate, a core material for reverse reflow on the bump pad, and solder paste or a solder bump forming a solder layer on the core material for reverse reflow. The solder paste or the solder bump is in contact with the bump pad. The core material for reverse reflow and the solder paste or the solder bump bonded to the core material for reverse reflow are used as a pin and detachably attached to the metal socket. The core material for reverse reflow includes a core, a first metal layer directly coated on the core, and a second metal layer directly coated on the first metal layer.

A micro light emitting diode (LED) transfer device includes a transfer part configured to transfer a relay substrate having at least one micro LED; a mask having openings corresponding to a position of the at least one micro LED; a first laser configured to irradiate a first laser light having a first wavelength to the mask; a second laser configured to irradiate a second laser light having a second wavelength different from the first wavelength to the mask; and a processor configured to: control the at least one micro LED to contact a coupling layer of a target substrate, and based on the coupling layer contacting the at least one micro LED, control the first laser to irradiate the first laser light toward the at least one micro LED, and subsequently control the second laser to irradiate the second laser light toward the at least one micro LED.

A micro light emitting diode (LED) transfer device includes a transfer part configured to transfer a relay substrate having at least one micro LED; a mask having openings corresponding to a position of the at least one micro LED; a first laser configured to irradiate a first laser light having a first wavelength to the mask; a second laser configured to irradiate a second laser light having a second wavelength different from the first wavelength to the mask; and a processor configured to: control the at least one micro LED to contact a coupling layer of a target substrate, and based on the coupling layer contacting the at least one micro LED, control the first laser to irradiate the first laser light toward the at least one micro LED, and subsequently control the second laser to irradiate the second laser light toward the at least one micro LED.

A method of making an assembly can include juxtaposing a top surface of a first electrically conductive element at a first surface of a first substrate with a top surface of a second electrically conductive element at a major surface of a second substrate. One of: the top surface of the first conductive element can be recessed below the first surface, or the top surface of the second conductive element can be recessed below the major surface. Electrically conductive nanoparticles can be disposed between the top surfaces of the first and second conductive elements. The conductive nanoparticles can have long dimensions smaller than 100 nanometers. The method can also include elevating a temperature at least at interfaces of the juxtaposed first and second conductive elements to a joining temperature at which the conductive nanoparticles can cause metallurgical joints to form between the juxtaposed first and second conductive elements.