Comparative Study of Process-Reliability Interaction of Additive Circuits with Low-Temperature Solders ECAs and Magnetically Oriented ACAs

The paper focuses on component attachment using low-temperature solders (LTS), electrically conductive adhesives (ECA), magnetically oriented anisotropic conductive adhesives (ACA) on direct-write and aerosol-jet additively printed circuits for signal processing and charging applications. The realization of flexible hybrid electronics using additively printed circuits requires the development of component attachment methods with low-temperature processing. While polyimide may be processed at normal reflow temperatures, thermally stabilized PET and PEN require a peak processing temperature of less than 150°C. Low-temperature solder materials have emerged capable of being processed at 130-150°C. Low-temperature processing has additional benefits: lower warpage, lower energy consumption, and lower carbon footprint. This paper presents process-performance-reliability relationships for Sn-Bi-Ag and Sn-In solders, ECAs, and magnetically-oriented ACA on additively printed circuits using direct-write and aerosol-jet processes. Electrical and mechanical performance has been studied by characterizing the assembled components. In addition, the viability of charging circuits has been studied. Reliability and the performance degradation of the additively printed circuits have been quantified in dynamic-flexing applications. In addition, SEM/EDAX has been used to study the intermetallics at the interface of LTS and additively printed circuits.