Reliability of silkscreen printed planar capacitors and inductors under accelerated thermal cycling and humidity bias life testing

The reliability of silkscreen printed capacitors and inductors were assessed based on thermal cycling (0-100°C) and humidity bias life (85°C/85%RH) tests. The used fabrication materials were Melinex ST504 polyester as a substrate, Asahi LS-411AW silver paste as a conductor and Asahi CR-18□-KT1 as the dielectric of capacitors and crossover insulator of inductors. Several components' geometries, with and without encapsulation, were studied to find out the influence of size and encapsulation effect on long term reliability. The results show, that thermal cycling induced stresses are not critical for the technology considered. The capacitance increased approximately 20% during the first 3000 cycles, while inductance kept quite constant (±3%). However, the inductor loss resistance decreased almost 10-20%. Humidity bias tests showed quite different results. For example, capacitance of all tested capacitor geometries increased more than 60% after approximately 2500h in an 85°C/85%RH environment. The Weibull analysis showed that larger capacitors are more vulnerable to combined temperature and humidity bias than smaller ones. The Weibull parameters obtained for the large (15mm × 15mm) capacitors under 85°C/85%RH were β = 2.8 and η = 1623. The failure criterion was the total failure of the dielectric. Furthermore, under temperature cycling, the corresponding parameters were β = 3.7 and η = 2486. In these, the failure criterion was the 1^st electrical indication of the dielectric deterioration, i.e., a clear drop in the DC resistance. None of the encapsulated components failed during the 85°C/85%RH tests, which suggest that simple lamination enhances the component reliability.