Embedded passive electrical circuit components are commonly designed as individual components that are individually fabricated and embedded into a substrate. For example, resistors and capacitors are typically designed as individual electrical circuit components that may be formed using thick film materials, usually applied in the form of a thick film ink applied via a printing technique.
Conventional thick film resistors can be formed by printing an ink film of copper compatible resistor material, such as resistor formulations utilizing LaB6 as a functional phase, on a copper foil substrate. The printed thick film ink is then fired at an elevated temperature to cure. An encapsulation material may be printed on top of the resistor. The copper foil may be etched and laser trimming may be employed to achieve desired electrical resistance characteristics. The resistor circuit is then embedded into a substrate, such as a laminated substrate.
Conventional thick film capacitors can similarly be formed by printing and firing a thick film dielectric material on top of a copper foil and forming a capacitor electrode on top of the dielectric material. The resulting capacitor may be encapsulated and laminated onto a core of a substrate. Additionally, the capacitor electrode may be laser trimmed to achieve desired electrical capacitive characteristics. The capacitor circuit is then embedded into a substrate, such as a laminated substrate.
The conventional methodology for fabricating individual resistors and capacitors is generally limited to achieving certain circuit component densities which limits the number of passive components in a given amount of space that is available. Additionally, the embedded resistor and capacitor components typically can only be tested and trimmed after being laminated into the inner layer of the substrate which risks performing valuable steps on a potentially defective foil.
What is desired is a passive circuit that provides multiple circuit components and does not suffer the space limitations of conventional thick film passive circuit designs. In particular, it is desirable to provide for a resistor and capacitor circuit that may be easily employed in a laminated circuit board. Additionally, it is desirable to provide for a fabrication method that achieves enhanced embedded passive circuit densities. It is also desired to test and adjust the resistors and capacitors prior to lamination into the core of a substrate.