Quantitative analysis of resistance of printed resistors

Surface-mounted resistors on an electronic circuit board are inexpensive and accurate, but resistors embedded in circuit boards can attain the same accuracy only after costly post-deposition trimming. Improved low cost methodologies of resistor fabrication are needed for cost effective embedding of resistors into polymeric substrates. Polymer Thick Film Resistors (PTFRs) are low temperature processable, low cost resistors with a wide resistivity range. The electrical resistance variation of these resistors is approximately /spl plusmn/10% after deposition and 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 investigated. 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 rough. FEM analyses revealed that the resistance tolerances were associated with edge roughness. Remedies to the variations were proposed and the relationship between resistance tolerances and aperture orientations was also outlined.