Method of making a two-sided fluid cooled assembly

A method of making a fluid cooled assembly, comprising:

• (a) providing a work piece that forms a partial enclosure defining an interior void space and having a top wall having a top surface, and that has a bottom wall having a bottom surface, and that defines at least one top opening through said top wall to said void space, said work piece further having a pair of opposed ledges between said top opening and said void space said work piece further defining fluid entrance and exit ports into said void space, said top wall and said bottom wall both being made of material that can be friction stir welded;
• (b) providing a top lid having a size and shape substantially conformal to said top opening, having a top surface that at least at the margins, is formed of a material that can be friction stir welded to said work piece, and having a bottom surface that has a set of heat sink protrusions extending downwardly but has a pair of opposed regions matching said opposed ledges, which are free of heat sink protrusions;
• and
• (d) placing said top lid into said top opening so that said opposed regions are set onto said ledges thereby placing said top lid top surface flush with said top surface of said work piece top wall and friction welding said top lid to said work piece.