Reliability Performance of Conductive Ink Subjected to Hygrothermal Aging

In the era of rapid technological development, the popularity in printed technologies and electronic packaging have resulted in a tremendous increase in the use of carbon-based conductive ink due to their advantageous features such as being environmental-friendly, low cost and lower assembly temperature. From the literature, it has been highlighted that the interconnect material are exposed to some degree of humidity and elevated temperature during the service life in an actual application. To-date, there is not yet a great length of literature reporting on the reliability performance of such materials when exposed to hygrothermal aging. Therefore, the objective of this research work is to investigate the reliability performance of the conductive ink when subjected to hygrothermal aging. In this study, the samples were exposed to either the room temperature condition with temperature of 20°C and humidity of 60% RH and secondly when subjected to hygrothermal aging in an environmental chamber with humidity of 85% RH and a temperature of 85°C up to 24 hours. Following these, the samples were tested in terms of electrical conductivity using a four-point-probe (ASTM F390) and lap shear test (ASTM D1002) via tensile loading to evaluate the bonding strength at the interface between the adhesive and the substrate. Next, morphological study was done using Scanning Electron Microscopy (SEM). With the presence of water molecule in the conductive ink, the molecule of carbon black and epoxy become unstructured and traces of riverlines are evident. In addition, there is a dramatic decrease in the sheet resistance following hygrothermal aging relative to the samples conditioned at room temperature, possibly due to enhancement in the conductivity of the ink. In contrast, as for the mechanical shear stress, the lap shear stress following hygrothermal aging process becomes weaken compared to those conditioned at room temperature, which could be associated with weak surface energy, brittle and weak bonding between carbon black molecules and the aluminium substrate interface.