Experimental investigation and quantitative analysis of resistance variations and control in printed thick film resistors

Polymer Thick Film Resistors (PTFRs) are low cost resistors with a wide resistivity range. Its low processing temperature makes it a potential candidate in the application of embedded resistors in polymer substrates. The electrical resistance variation of these resistors is approximately ±10% after deposition and the resistors require additional trimming procedure to tune the resistances to meet specifications. This adds to the cost and complicates the fabrication process when the resistors are embedded. In this study, the influences of PTFRs geometries on the resistance tolerances were conducted. Results indicated that the accuracy of stencil printed resistors was markedly higher than the screen printed resistors. The screen printed resistor edge geometries were observed to be irregular under the microscope, and FEM analyses revealed that the resistance tolerances were associated with irregular edge geometry. Remedies to the variations were proposed and the relationship between resistance tolerances and aperture orientations was also outlined.