Lead-oxide-free copper thick-film paste for alumina substrates

The present paper relates to a lead-oxide-free copper thick-film paste for printing on ceramic substrates, especially on alumina. Commercialized copper thick-film pastes usually consist of copper powder with lead-oxide glass, which should be avoided in regard to the RoHS Certificate of Conformity. The screen printing technology could be an alternative method instead of the standard DCB process, particularly for structured and thinner films. In this case it is meaningful to use thick-film pastes to form such structures. In the first steps of the paste development process the rheological properties could successfully realized. That means a paste with high solid content and good structured conductor lines was established. Furthermore the adherence of the copper thick-film on alumina substrates could be highly improved by adding additives. Also the solder ability was achieved to 95% by adding another additive, which acts as a wetting agent. FESEM and EDX characterizations show the mechanical adhesion process, which belongs to the formation of a ceramic-metal-interlayer, where copper aluminate is build. Moreover cross section images of the examined copper thick-film layers show a sinter body with pores in the copper film, which have to be minimized, to improve the electrical and mechanical properties. In summary can be said, that previous investigations showed measured values, which nearly achieve the aim values and a lead-oxide-free copper thick-film paste is developed, which can be tested for DCB-applications.