Direct Ink Write Processing of Signal Crossovers Using Aerosol Jet Printing Method

Lucas A. Clark, Wright State University


Electronics in different applications, such as in medical imaging devices, radar systems, communication transmitters, and optical drives, often require various power and signal lines to be integrated at board level. In such cases, different lines may cross over one another in three-dimensional space for efficient electronic integration. Crossovers are usually achieved by adding additional layers to a PCB. However, these additional layers increase the cost, weight, and complexity of the component. By creating a process and structure to offer board-level heterogenous integration, these factors may be reduced. RF-DC crossovers were designed and additively manufactured using an aerosol jet printer. Benzocyclobutene (BCB), a thermally curable dielectric material, and Norland Electronic Adhesive 121 (NEA), a UV curable dielectric ink, were printed as crossover materials on boards containing an RF transmission line. Electroninks 615 (EI-615), a conductive silver ink, was printed on the crossover’s surface to complete the DC circuit trace. Two different toolpath designs were explored to serve for the digital printing of the crossover structure. A network analyzer was used to measure the scattering parameters (S12 and S21) across the RF transmission line in X-band (8-12 GHz). A thermal camera was used to capture the heat spread across the crossover region. The printed ramp design resulted in a more gradual slope as expected, requiring a single print of the conductive trace while the steep pad design required tilting of the crossover and multiple printing sessions. The NEA 121 and BCB showed no significant changes in the S21 parameter as DC power increased; however, slight coupling occurred in both. The largest S21 difference recorded at 10 GHz was 0.339 dB. The BCB crossovers exhibited higher power handling than the NEA 121 crossovers, reaching up to 6.93 W. The maximum breakdown temperature occurred at 273.0°C in the NEA 121 and at 248.6°C in the BCB crossovers.