Abstract: Fuel cell stacks comprising stacked separator/membrane electrode assembly cells in which the separators comprise a series of stacked thin sheet platelets having individually configured serpentine micro-channel reactant gas humidification, active area and cooling fields therein. The individual platelets are stacked with coordinate features precisely aligned in contact with adjacent platelets and bonded to form a monolithic separator. Post bonding processing includes passivation, such as nitriding. Preferred platelet material is 4-25 mil Ti in which the features, serpentine channels, tabs, lands, vias, manifolds and holes, are formed by chemical or laser etching, cutting, pressing or embossing, with combinations of depth and through-etching being preferred. The platelet manufacturing process is continuous and fast. By employing CAD based platelet design and photolithography, rapid change in feature design to accommodate a wide range of thermal management and humidification techniques. 100 cell H.sub.2 --O.sub.