New Methods for Circuit Fabrication on Poly(tetrafluoroethylene) Substrates

Abstract

By combining conventional integrated‐circuit processing techniques with chemical etching for strong Cu film adhesion, three processes for the fabrication of the fine (≤20 μm, a factor of five smaller than existing technology), adherent, conducting features on poly(tetrafluoroethylene) (PTFE) substrates have been developed. Metal features are defined using a lift‐off technology, electroless plating, or a combination of electroless and electroplating. The third process requires additional processing steps but is also the most versatile technique enabling 4 μm thick metal features with high lateral resolution. These three processes result in a less expensive process for patterning metal features on an etched PFTE substrate with resolution of at least a factor of five better than existing processes. Adhesion of the metal features depends upon successful substrate preparation by etching the PTFE in a sodium naphalenide solution. Using the three processes discussed above, coupled‐line quadrature (Lange) couplers that demonstrate equal power splitting between 5 and 14 GHz have been fabricated on a PTFE substrate. Lange couplers have extensive applications as passive hybrid device components in microwave and radio‐frequency (RF) systems.