Three-dimensional multi-layer circuit structure and method for forming the same

A method of forming a circuit structure comprising the steps of:

• forming a partially etched pre-circuit by,
• providing a metallic foil formed of a first metal having a first coefficient of thermal expansion,
• applying a second metal having second coefficient of thermal expansion to selected areas of said foil,
• etching said metallic foil in an etching solution, and
• removing said metallic foil from said etching solution after said etching solution partially etches said metallic foil to undercut said second metal;
• bending said partially etched pre-circuit into a shape;
• inserting said partially etched pre-circuit into a mold cavity so that at least one surface of said circuit structure is adjacent said mold;
• filling said mold with a molten dielectric so that said molten dielectric encapsulates at least a portion of said partially etched pre-circuit and fills said undercuts, said dialectic having a third coefficient of thermal expansion within a range of the first and second coefficients of thermal expansion;
• removing said partially etched pre-circuit from said mold;
• and
• further etching said foil to form air bridges.