Polymer thick-film resistor printed on planar circuit board surface

DETAILED DESCRIPTION According to the present invention, there is provided a method of manufacturing a printed circuit board with a polymer thick-film (PTF) resistor whose dimensions can be defined with improved precision by providing a circuit board construction having a planar surface where the resistor is to be deposited.
To achieve the desired board construction, the interconnect for the resistor is electrolytically pattern plated using a permanent photodielectric layer as a plating mask instead of a sacrificial plating resist.
The interconnect can be patterned before or after the PTF resistor ink is printed.
The x and z dimensions (width and thickness, respectively) of the resistor are determined by the deposition process, while the y dimension (electrical length) is accurately determined by copper terminations.
The method of this invention generally entails forming a first electrically-conductive layer on a dielectric substrate, forming an opening in the first electrically-conductive layer to expose a surface portion of the substrate, and then forming a dielectric layer that covers a part of the exposed surface portion of the substrate and preferably adjacent surface portions of the first electrically-conductive layer, while exposing a surface portion of the first electrically-conductive layer.
Using the dielectric layer as a mask, a second electrically-conductive layer is then deposited on the first electrically-conductive layer so that the dielectric layer and the second electrically-conductive layer define a substantially coplanar surface.
In a preferred embodiment, portions of the first and second electrically-conductive layers are then removed to define a pair of terminations separated by the dielectric layer, after which a polymer thick-film resistive material is screen printed on the dielectric layer and the terminations to define a polymer thick-film resistor.
Alternatively, the polymer thick film resistive material can be screen printed on the dielectric layer and the second electrically-conductive layer prior to the terminations being defined