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We have developed a new alumina multi-layer ceramic substrate material, whose properties of low resistance conductor and excellent mechanical and thermal characteristics, providing a new and unique substrate solution for automotive ECU applications. Unique to this material is the circuit conductor which is made from a composite material of tungsten and copper, providing low electric resistance and high thermal diffusivity. This material system (AO600) utilizes a low-temperature, co-fireable alumina with a low resistance metal conductor composite. Electric current path is made by copper in the composite to effectively reduce the resistance. Thick film on the alumina substrates surface is also effective for the resistance reduction. Using this material system, substrates with miniaturized design, high strength and high thermal diffusivity have been realized. We have also tested reliability by temperature cycle tests between -40 and 150 degrees centigrade.

A new process for a highly reliable ceramic substrate with electric circuit has been developed for power devices of automotive applications. The circuit conductor has high conductivity to accept a current of 10 to 200 Amperes, and has strong joining strength to ceramic substrates. The conductor is made of sintered copper powders with several kinds of diameters to get a porous structure, for reducing Young's modulus and thermal stress between the circuit conductor and ceramic substrate. Sintering shrinkage of the circuit conductor has been restrained, and joining strength to the ceramic substrates kept strong by an anchor effect. The copper circuit conductor realized electric resistivity of 2.3×10-6 ohm-cm, and coefficient of thermal conductivity, 290 W/mK. We have also confirmed superior reliabilities in the joining strength and conductivity by thermal cycling tests.

A new alumina ceramic substrate has been developed for an Electronic Control Unit (ECU). This substrate has a thick conductor circuit made of molybdenum for a power line, accepting high electric current up to 50 Amperes (standard design). The design concept can integrate control and power circuits in one substrate, directly mountable on engines or power train system without any forced cooling system. Cross-sectional shape of the conductor is designed to minimize thermal stress and reduce cracking in the substrate, caused by a thermal expansion mismatch between alumina and molybdenum. Optimization of the design is performed by FEM analyses and X-ray diffraction measurement. We confirmed that the substrate can work after 10,000 cycles of temperature cycle test, and 600,000 cycles of electric cycle test.

Alumina substrates have been developed for a flip-chip mount ECU ( Electronic Control Unit ). On this substrate, large sized IC chips as a flip-chip and other electronic components have been mounted. Cu thick film circuit has also been mounted on the other surface. This circuit consists of printed resistors by connecting tungsten metallized layer and Cu thick film through Cu plating. In order to mount the large sized flip-chip IC, the substrate needs strictly precise dimensions. The tolerance of the dimensions are within ± 0.1 % and the warp of the flip-chip area is less than 10 μm per 10 mm.