A fluid-containing cooling plate includes a bottom plate, a top plate, and metal wire or tubing formed into a circuit and sandwiched between the plates to form a chamber. The wire is plated or otherwise coated with a brazeable or solderable alloy which bonds it to the plates when the assembly is heated, thereby sealing the chamber. To make a two-phase cooling plate, slugs of plated metal are placed in the chamber and are bonded to the plates to provide support against collapse. The chamber is provided with a wicking structure, and is partially filled with an evaporable fluid via an inlet. A partial vacuum is then drawn, and the inlet is closed off. To make a single-phase cooling plate, wire partitions serving as baffles are provided in lieu of the slugs. These partitions can be arranged to provide a serpentine flow path between the inlet and an outlet, and are likewise plated with an alloy which melts to bond them to the plates.