A circuit substrate that includes a substrate having a major surface, a multilayer body on the major surface, and an insulating layer that covers the major surface. The multilayer body includes a first layer and a second layer that overlies the first layer. The first layer is made of a first metal as a main material thereof, and the second layer is made of a second metal as a main material thereof. The second metal has a higher solder wettability than the first metal. As viewed perpendicular to the major surface, the insulating layer is spaced from and surrounds the surface of the second layer so as to define a recess between the multilayer body and the insulating layer.

A heat exchanger includes a plurality of flat tubes and a coupling header. The flat tubes are disposed in multiple tiers along a predetermined tube tier direction and in multiple rows so as to be adjacent to each other in a tube row direction intersecting the tube tier direction and the longitudinal direction of the flat tubes. The coupling header is formed by joining a first member to a plurality of second members in the tube tier direction. The first member has a plurality of through holes through which pass the first end portions of the flat tubes. The second members when joined to the first member forming a plurality of coupling passages where the first end portions of the flat tubes adjacent to each other in the tube row direction communicate with each other.

A workpiece composite and a method for producing the workpiece composite having at least two workpieces are provided. A first workpiece and a second workpiece are positioned relative to each other, and an integral connection between the end face of the first workpiece and the second workpiece is formed in a joint section by way of a thermal joining method. Prior to forming the integral connection, the first workpiece is provided with an indentation or embossing, which adjoins the end face, at least in the joint section, whereby the thickness of the first workpiece is reduced in the region of the end face.

A workpiece composite and a method for producing the workpiece composite having at least two workpieces are provided. A first workpiece and a second workpiece are positioned relative to each other, and an integral connection between the end face of the first workpiece and the second workpiece is formed in a joint section by way of a thermal joining method. Prior to forming the integral connection, the first workpiece is provided with an indentation or embossing, which adjoins the end face, at least in the joint section, whereby the thickness of the first workpiece is reduced in the region of the end face.

A plate fin heat exchanger 1 includes a corrugated fin 3 and tube plates 2. An intermediate portion 33 of the corrugated fin between crest and trough portion 31 and 32 thereof has a plurality of protruding ribs 34 protruding beyond a surface of the corrugated fin and arranged in a first direction. Surfaces of the crest and trough portions being in contact with the tube plates are configured as contact surfaces 310, 320 with no protruding rib. Gently sloping portions 341 are provided between the protruding ribs and the contact surfaces of the crest and trough portions to gradually protrude from the surface of the corrugated fin with increasing distance from the contact surfaces, and are continuous with the protruding ribs.

A plate fin heat exchanger 1 includes a corrugated fin 3 and tube plates 2. An intermediate portion 33 of the corrugated fin between crest and trough portion 31 and 32 thereof has a plurality of protruding ribs 34 protruding beyond a surface of the corrugated fin and arranged in a first direction. Surfaces of the crest and trough portions being in contact with the tube plates are configured as contact surfaces 310, 320 with no protruding rib. Gently sloping portions 341 are provided between the protruding ribs and the contact surfaces of the crest and trough portions to gradually protrude from the surface of the corrugated fin with increasing distance from the contact surfaces, and are continuous with the protruding ribs.

A ceramic-metal structure in which a metallic body (2) is inserted into or disposed above a through hole (4h) of a ceramic substrate (4) and which includes an annular pad layer (6) disposed around the through hole; an annular ring member (8) joined to the pad layer via a first brazing filler portion (10) and having a coefficient of thermal expansion smaller than that of the metallic body; a second brazing filler portion (12) intervening between the ring member and metallic body; and brazing filler flow prevention layers (7a, 7b) covering an outer surface of the pad layer so as to expose a central region (6c) of the outer surface of the pad layer facing the first brazing filler portion. The first brazing filler portion joins the central region and the ring member without projecting to a radially inner or outer side of the flow prevention layers.

A ceramic-metal structure in which a metallic body (2) is inserted into or disposed above a through hole (4h) of a ceramic substrate (4) and which includes an annular pad layer (6) disposed around the through hole; an annular ring member (8) joined to the pad layer via a first brazing filler portion (10) and having a coefficient of thermal expansion smaller than that of the metallic body; a second brazing filler portion (12) intervening between the ring member and metallic body; and brazing filler flow prevention layers (7a, 7b) covering an outer surface of the pad layer so as to expose a central region (6c) of the outer surface of the pad layer facing the first brazing filler portion. The first brazing filler portion joins the central region and the ring member without projecting to a radially inner or outer side of the flow prevention layers.

A copper-ceramic joint body having high joint strength is provided. The copper-ceramic joint body includes: a copper member made of Cu or Cu alloy; a ceramic member joined to the copper member and made of nitride of Si or Al; and a joint layer formed on joint surfaces of the copper member and the ceramic member, and containing Cu and Mg and further containing at least one type of active metal elements selected from a group of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ca, Y, Ce, La, Sm, Yb, Nd, Gd and Er, and shear strength of the joint layer is equal to or higher than 10 MPa.

A copper-ceramic joint body having high joint strength is provided. The copper-ceramic joint body includes: a copper member made of Cu or Cu alloy; a ceramic member joined to the copper member and made of nitride of Si or Al; and a joint layer formed on joint surfaces of the copper member and the ceramic member, and containing Cu and Mg and further containing at least one type of active metal elements selected from a group of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ca, Y, Ce, La, Sm, Yb, Nd, Gd and Er, and shear strength of the joint layer is equal to or higher than 10 MPa.