Laser structuring of printed layers on thick film ceramic substrates

Abstract

The market for automatic transmissions continues to grow. In addition to what originally attracted interest to the product – enhanced driver convenience – the prospect of greater fuel efficiency is now a further factor in their favor. Continental has been offering transmission control units (TCU) since 1982, starting with those for simple three-gear conventional automatic transmissions, followed by all-wheel applications in 1985, CVT applications in 1999, truck applications in 2000, and arriving at the double clutch transmissions in widespread use today. At present Continental Business Unit Transmission is technology leader worldwide in the market for transmission controls for the full spectrum of automatic drives. Continental TCU's are divided in “Stand alone”, “Attached to” and “Integrated” TCU's. However the “Stand alone” and “Attached to” TCU's are normally equipped with standard PCB substrates. Because of the highest requirements in temperature, vibration and typical medias (aggressive Transmission oils – liquid & gaseous), standard organic substrates cannot be used, ceramic substrates are typically preferred. A common technology in that case is the ceramic based thick film technology, where conductor and resistor pastes are printed on the surface of a ceramic alumina substrate by using a common screen printing process. The printed layers (Au, Ag, AgPd, AgPt) have to be dried and thermally sintered after appliance. The increasing functionality of the TCU's and the increasing requirements due to miniaturization inherently show that thickfilm technology, as applied in a standard printing process, is not possible to reach those requirements. Continental has developed a concept to realize higher miniaturization of the circuit boards. Therefore a innovative laser structuring process has been installed for the newest generations of TCU's in cooperation with a leading machine and system manufacturer. By using the laser structuring of conductor lines it allows Continental to increase the connection density by keeping the substrate size unchanged. Typical common printing pitches in thickfilm production are 300μm, however pitches of 100μm are possible by laser structuring in mass production.