Resin multilayer substrate and method for manufacturing resin multilayer substrate

A resin multilayer substrate comprising:

• a metal foil layer, an upper resin layer, and a lower resin layer;
• wherein
• the metal foil layer includes a metal foil layer upper main surface, a metal foil layer lower main surface with a surface roughness greater than a surface roughness of the metal foil layer upper main surface, and a metal foil layer side surface that is a surface of the metal foil layer excluding the metal foil layer upper main surface and the metal foil layer lower main surface;
• the metal foil layer upper main surface is in contact with the upper resin layer;
• the metal foil layer lower main surface is in contact with the lower resin layer;
• a portion of a lower main surface of the upper resin layer and a portion of an upper main surface of the lower resin layer are in contact with each other to define a layer interface;
• in a cross section of the metal foil layer parallel or substantially parallel to a multilayer body up-down direction, a direction from an inner side of a region surrounded by a surface of the metal foil layer toward an outer side portion of a region surrounded by the surface of the metal foil layer of directions perpendicular or substantially perpendicular to the multilayer body up-down direction is defined as an inside-outside direction;
• in a cross section of the metal foil layer parallel or substantially parallel to a multilayer body up-down direction, the metal foil layer side surface includes an outer point and an inner point located at a portion where the upper resin layer is in contact with the side surface;
• and
• the inner point is located below the outer point and is located inward of the outer point in the inside-outside direction.