Compression molding of metals is used to make microchannel heat exchangers. Heat transfer can be improved by employing controlled microchannel surface roughness. Flux-free bonding is achieved using a eutectic thin-film intermediate layer. Seals are leak-tight, mechanically strong, and uniform across multiple contact areas. The metal heat exchangers may be mass-produced inexpensively, and are useful for applications including the cooling of computer chips and other high-power electronic devices, air conditioning, refrigeration, condenser plates, radiators, fuel cell heat management, and instant water heating.