Mitsuyuki Takada

Advanced Copper/Polyimide Hybrid Technology

In the past, a unique hybrid IC processing approach which combines wet-metallized copper, air-fired (ruthenium-based) RuO 2 paste, and photoactive polyimide, was presented by the authors [1], 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) Al 2 O 3 substrate, 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.

A novel manufacturing technology of buried RuO/sub 2/-based thick film resistors in copper-polyimide substrate

A novel manufacturing technology of buried RuO/sub 2/-based thick-film resistor (TFR) in copper-polyimide system has been studied. Since electrodes of copper thin film are formed on the TFR by using photolithography and a plating method and the resistance of TFR has a widely linear relation, the resistance is determined only by the geometry of the TFR within 10% variation to the designed value. A specially optimized pulse laser irradiates the TFR through the polyimide film in order to accurately adjust the resistance without any degradation of the overcoating polyimide film on the TFR. The surface of the TFR is modified, and the resistance decreases with the shot number of the laser. Analysis by heat conduction theory suggests that the non-degradation of the polyimide film is based on the shortness of the laser pulse duration. Results of reliability tests show the stability of the resistance of laser-modified buried TFR.<<ETX>>