An Introduction of RoHS Legislation in SMD Thick-Film Hybrid Technology - a Case Study

In this paper a case study of the introduction of European environmental regulations on the restriction of the use of hazardous substances (RoHS) in thick-film hybrid technology is presented. The ecologically "hazardous" materials in conventional thick-film hybrid circuits can be found mainly in the solder for soldering SMD components and in the conventional thick-film materials. The substitution of ecologically "hazardous" materials with acceptable alternatives is possible with lead-free soldering technology and with the new, emerging thick-film pastes. But using the new materials and a modified manufacturing process require research and an assessment of the reliability of the new "green" hybrid circuits in comparison with the "conventional" ones. As a case study the authors designed a thick-film hybrid circuit that was produced using "ecologically friendly" as well as "conventional" materials. The circuits were aged under accelerated conditions, including temperature cycling and humidity testing. The measured functional characteristics of both sets of samples before and after ageing show that a humidity/temperature test at 93%RH/+40degC up to 1000 hours has no significant influence on the circuits' characteristics. On the other hand, failure rates after 1000 temperature cycles (-40/+125degC) are rather high - especially for some combinations of thick-film conductor materials and solders used for soldering discrete SMD electronic components