Reliability of Ag ink jet printed traces on polyimide substrate

Printable electronics is a new emerging technology with capabilities of producing high volumes, low price and flexible electronic devices. Printing techniques using nano-size material particles at low temperatures can revolutionize the electronics industry in coming years. However, a number of questions, mainly related reliability of such devices, are still pending. Reliability of electronic devices can be accessed through the use of accelerated life testing and degradation analysis. In this sense, conductive traces printed through in inkjet method on flexible substrates can have its reliability estimated. Such analysis provides valuable information in order to allow the mass production of devices which utilizes this technology. In this paper, metal nanoparticles based ink was printed on flexible polyimide substrates. After curing, the microstructure was analyzed through scanning electron microscope (SEM) and trough profilometer. Printed traces underwent two different environmental tests: 85/85 test (85°C and RH 85%) and Thermal Cycling (-40°C to 125°C with a dwell time of 30 min and a ramp time of 1h). The number of conductive layers printed was modified and these samples were grouped. A variation of 20% in the trace resistance was considered as a failure. Curves of reliability versus time were obtained for the different analyzed groups. It was possible to observe that samples with 1 and 5 layers have similar reliability in the 85/85 tests. Moreover, it was not possible to observe delamination in the samples submitted to cycling tests. Probably, the porous traces microstructure has a key influence in the reliability.