Relationship Between Process Recipe-Print Consistency-Performance for Additively Printed Z-axis Interconnects in Multilayer Circuits
Traditionally, the printed circuit assemblies have been fabricated through a combination of imaging and plating based subtractive processes involving use of photo-exposure followed by baths for plating and etching to form the needed circuitry on rigid and flexible laminates. The emergence of a number of additive technologies poses an opportunity for the development of processes for manufacture of flexible substrates using mainstream additive processes, which are now commercially available. In this paper, the correlation of the mechanical properties of aerosol jet printed multi-layer substrates and z-axis interconnects with process parameters has been studied. The reliability of the aerosol-jet printed traces has been correlated to the mechanical properties and electrical properties of the printed lines. The elastic modulus, the shear modulus or shear load to failure, resistivity of the printed line have been used for selection of suitable ink type, process parameters, and sintering times and temperatures. Process parameters studied include sheath flow rate, ink flow rate, stage speed, standoff height, chiller temperature, platen temperature. A better understanding of the effect of each process parameter in the printed lines will allow users to select appropriate process parameters for design functional performance. In addition, the development of process-property relationships will provide visibility into the critical parameters, which require added level of attention for process-control. In addition, the process parameter drift over a long production run may be important for a high-volume production environment. The effect on the print process may be in the form of line consistency, and resistance – both of which have been quantified in this study. A procedure for finding process parameters that minimize the resistivity of printed lines has been developed. The effect of sintering time and sintering temperature on the mechanical and electrical properties of the printed lines has been quantified. Scanning electron micrographs have been used to understand the electrical and mechanical behavior of printed traces.