Reliability of thin film conductors and air gap crossovers for hybrid circuits: Tests, results and design criteria

Abstract

The paper presents the results of a long study on the reliability of thin film conductors and cross-overs metallization for hybrid circuits. Three failure mechanisms are examined: electromigration, humidity corrosion and mechanical fatigue, which affect the complex hybrid circuits as a consequence of the current load, of the humidity and the electrical load and of the mechanical stresses induced by the encapsulant. For the humidity corrosion a new general quantitative formulation is proposed which relate temperature, polarization and R.H. with medium time to fail. The agreement between the proposed formulation and the results is verified both on unencapsulated and on encapsulated components and give an activation energy for NiCr-Au or TiPdAu materials of g ́ f = 0.53 eV . Finally same cautelative design rules are proposed in order to have an acceptable reliability level from the design.