In the past, a unique hybrid IC processing approach which combines wet-metallized copper, air-fired (ruthenium-based) RuO2paste, and photoactive polyimide, was presented by the authors , Now, a further improved and advanced new copper/polyimide hybrid technology Mitsubishi Copper Polyimide Hybrid (MCPH) has been developed. The new MCPH was processed using a large (106 x 106 mm) Al2O3substrate, full copper system (all layers) with 50-µm fine lines. For the first layer, the full-additive process was adopted, while for the other layers, a semiadditive process was employed. The photoactlve polyimide interlayer insulation is screen printed, and after the exposure and development steps, is cured using a conveyor belt furnace. This new process has many excellent features, such as uniform coating thickness, better mass-production capability, etc. The MCPH fundamental processes were evaluated and established using an MCPH Test Element Group (TEG). This TEG has fine lines, small diameter vias and/or pads, matrix lines, etc. To compare characteristics, the same circuit as a conventional hybrid IC was fabricated by applying the MCPH technology. As a result, this functional MCPH (MCPH ES) is a compact size (less than 1/2 the circuit area), has excellent electrical parameters, and high reliability. This MCPH ES uses a flip-chip IC (2.9 mmx 3.4 mm) with 30 small solder bumps (100 µm, min. 170-µm pitch). Important MCPH process factors and/or reliability factors were fully evaluated by using the TEG and functional ES. Through various tests (thermal cycle, voltage loaded, humidity, pressure cooker, break-down or leak, etc.), the MCPH shows excellent reliability characteristics. Consequently, a unique MCPH has been developed using a simple, reliable, cost-effective and excellent massproduction multilayer-hybrid process.