CONVENTIONAL PROCESSING

Japanese industry, as exemplified by companies such as Nippondenso, Hitachi, Mitsubishi Electric Company (MELCO), and many others, maintains R&D programs that improve precision and manufacturability in large as well as small devices. This is particularly true in fields such as low temperature bonding. Hitachi uses high vacuum sputter cleaning to produce oxide-free bonding surfaces prior to vacuum bonding via applied pressure and temperature. The company reports good results for many metal systems with areas ranging from several square centimeters to fractions of a square centimeter. Mitsubishi Electric is also active is this area, and reports silicon to silicon bonding and silicon to silver bonding at room temperature without applied pressure after sputter etching in 10(-9) Torr vacuum. A second area, not reflected in the site reports, is precision polishing. At Nippondenso, improved polishing techniques have been used to produce thin piezoelectric ceramics for use in stacked actuators for active suspensions. Results from these polishing techniques are reflected in sensor manufacturing, where precision polishing is of major concern, as demonstrated by the devices that Lucas-Nova Sensor, Inc., a U.S.-based company, markets.

A third area that fits well into the conventional and lithographic processing world is that of electro-discharge machining (EDM). This area has received long-term attention in Japan. The results are not only interesting devices but also the marketing of equipment that can perform this function. Thus, Matsushita makes and sells EDM machines that can be used for metals and semiconductors, and are capable of holding tolerances to 0.1 mm with minimum dimensions of 5 mm.

This type of tool and other precision tools are used by Seiko Instruments, Incorporated (SII) to make a variety of commercially available millimotors. Alternating current (AC), direct current (DC), and ultrasonic actuation are used. A three-phase stepping motor with 60 stepping angle, with speeds up to 13,000 rpm and output torques of 1.2 x 10(-6) Newton-meter, can be purchased for roughly $1,000. Its length is 5 mm and its diameter is 2.8 mm; its 0.5 mm output shaft can be coupled to a 23:1 reduction gear box which is also available.

This motor and gear box are simply examples of several similar devices that SII produces and markets. The design of these structures is obviously labor intensive, and profits from a mechanical CAE/CAD/CAM system that SII has developed and is using. This multiple-option system is also marketed by SII.

Precision injection molding also fits into the conventional and lithographic processing category. Research in this area is supported by private companies and national laboratories. The view expressed by representatives of the Mechanical Engineering Laboratory (MEL) -- that polymer injection molding is already under control -- is somewhat surprising. Precision injection molding for metals and ceramics are high priority R&D projects.

Industrial attitudes towards lithographic processing also profit from the willingness to adapt available processes and processing tools to the task at hand. This is particularly true in magnetics. Thus, Mitsubishi Electric experiments with sputtered films of Sendust (85% Fe, 9.5% Si, 5.5% Al), a material that is used extensively in magnetic recording. Permalloys, typically 80% Ni and 20% Fe, play a major role in read/write heads and have been studied extensively for several decades. MELCO uses sputtered and electroplated films for magnetic micromechanical devices. NTT adapts its skill and knowledge in permalloys to produce optimized relay springs from 2-micron thick sputtered alloy films.

A willingness to invest time and energy in process tool development is exemplified by Hitachi. The company uses its silicon machining skill (which originated in ultrasonics, particularly lens production) to produce large half-spheres, about 4 cm in diameter, from a silicon ingot. These structures, which contain all possible silicon crystallographic directions, are etched in potassium hydroxide etches to produce etch rate versus orientation data for several etch conditions. The data are used in a computer simulation tool to predict etched geometries as a function of etch time. Two-dimensional simulations are fully functional, and three-dimensional predictions will be in the near future. The tool is being applied to silicon sensors and reflects itself in particular in accelerometer development for automotive applications at Hitachi (Wise 1994).


Published: September 1994; WTEC Hyper-Librarian