Product Code: ICAL08_M308

Laser Based Contacting of Thin Metal Coated Active Elements
Authors:
Stephan Neugebauer, Bayerisches Laserzentrum Gmbh; Erlangen Germany
Florian Albert, Bayerisches Laserzentrum Gmbh; Erlangen Germany
Michael Schmidt, Bayerisches Laserzentrum Gmbh; Erlangen Germany
Thomas Frick, Bayerisches Laserzentrum; Erlangen Germany
Presented at ICALEO 2008

Present research in the field of active noise absorption at automotive assemblies deals with piezoelectric elements embedded into parts like gear boxes or car bodies. Under closed loop operation, these elements are able to modify the oscillation behaviour of the whole body. This may significantly reduce the assemblys noise emission. Essential for the operation of the active noise damping is the existence of reliable joints between the different parts of the electric circuit. The piezoelectric elements are covered with thin metal films, e.g. Cu/Ni, Ag or Au. These metal films need to be connected to circuit carriers like leadframes. The joints need to provide electrical and mechanical stability during a complete vehicle lifetime. Temperatures of round 180 degrees Celsius and contemporaneous vibration have to be sustained. The connection between the piezo element and the electric circuit is normally achieved by means of clamping or soldering. However, these methods have disadvantages. Such connections show a lack of reliability, they are not qualified for the use under permanently oscillating conditions or may not withstand high temperatures and rough environment. The fabrication of high-temperature-resistant joints fails, in most cases, due to the low resistance of the ceramics and its metallization against the process conditions.
This paper deals with the production of thermally and mechanically stable joints achieved by the use of two laser-based technologies. First, the two different laser processes are described. A newly constructed double-beam Laser Droplet Welding (LDW) processing head allows the deposition of molten metal droplets. The deposited droplet welds the joining partners. The limited energy of the droplet prevents the ceramics and its metallization from being immoderately damaged. The second process system is laser micro brazing for the manufacture of high-temperature resistant joints. Here a temperature control reduces overheating of the process area.
In a next part creating of the joints is being investigated. Two different piezoceramics have been used. These are PIC 151 of PI Ceramics with sputtered Cu/Ni metallization and Sonox P508 by CeramTec with a screen-printed Ag metallization. Then the joints will be characterized. The contact quality will be discussed in terms of formation of intermetallic phases and the long-term stability after artificial aging.