NOVELTY - The process comprises forming open microchannels on a surface of a first homogeneous metal piece, supplying a second homogeneous metal piece when bonded to the first metal piece to convert the microchannels into closed microchannels, supplying a eutectic layer or eutectic precursor layer at the surface of the first metal piece, a surface of the second metal piece or between the first and second metal pieces, simultaneously applying pressure to and heating the first and second metal pieces, and cooling the first and second metal pieces to a temperature below the eutectic melting temperature.    USE - The process is useful for making a metal microchannel heat exchanger, which is useful for cooling computer chips, high-power electronic devices, air conditioning, refrigeration, condenser plates, radiators, fuel cell heat management and instant water heating.    ADVANTAGE - The method ensures efficient and economical mass production of the metal microchannel heat exchanger with high efficiency and high thermal conductivity using controlled microchannel surface roughness thus providing rapid and effective heat absorption and dissipation to the microprocessor to maintain safe microprocessor operating temperatures.    DETAILED DESCRIPTION - The process comprises forming open microchannels on a surface of a first homogeneous metal piece, supplying a second homogeneous metal piece when bonded to the first metal piece to convert the microchannels into closed microchannels, supplying a eutectic layer or eutectic precursor layer at the surface of the first metal piece, a surface of the second metal piece or between the first and second metal pieces, simultaneously applying pressure to and heating the first and second metal pieces, and cooling the first and second metal pieces to a temperature below the eutectic melting temperature while maintaining the pressure during a portion of the cooling, such that the first and second metal pieces fuse together and such that the open microchannels are converted into the closed microchannels, where the closed microchannels are adapted to transport liquid without substantial leakage and are enclosed entirely by the fused first and second metal pieces and the eutectic layer so that the fused first and second homogeneous pieces and eutectic layer form a microchannel heat exchanger. During the step of applying the pressure to and heating the first and second metal pieces: the pressure pushes the first and second metal pieces toward each other with the eutectic layer or eutectic precursor layer; the pieces are heated to a temperature at which the eutectic layer or eutectic precursor layer melts or at which the eutectic layer or eutectic precursor layer interacts with the metal pieces to form a molten eutectic composition between the first and second metal pieces; and the temperature to which the metal pieces are heated is below the melting temperature of the first and second metal pieces to avoids substantial deformation of the microchannels. The microchannels have a width of 30-1000 mu m and a depth of 30-1000 mu m. The heat exchanger withstands an internal pressure in the closed microchannels of greater than or equal to 100. The microchannel is formed by compression molding of metal pieces with a refractory metal mold insert. The closed microchannels have a surface roughness of 3-15 mu m. An INDEPENDENT CLAIM is included for a metal microchannel heat exchanger.    DESCRIPTION OF DRAWING(S) - The diagram shows a detailed view of a transition from a microchannel array to a fluid supply channel formed by a single cut with a micro electrical discharge machine.