New Low Cost Substrate (Duroid) for Hybrid Microwave Integrated Circuits (MICs) in Wide Band Available to Purchase

Because of its lower dielectric constant and loss tangent, and its greater surface smoothness, fused silica is very suitable for use in the KU band and above, but its cost is very high. The purpose of this paper is therefore to select a new substrate which competes with fused silica on the grounds of lower cost; to adapt the hybrid technology to this new substrate; to show ,comparing the measured performances of a filter realised on fused silica and on this new substrate, that the latter is suitable for MICs in the wide band, but not in the narrow band; and to describe an application of this substrate in the 22–24 GHz band. Thus, after an investigation of the electrical parameters and of the costs of different substrates, Duroid was selected and compared with silica. This substrate is composed of a non‐woven glass microfibre reinforced by polytetrafluorethylene; its microwave quality is theoretically almost similar to that of the fused silica one but its cost is much lower. The adaptation of hybrid technology on this substrate, notably in order to use beam lead and die semiconductor components with thermocompression bonding as a connection method, involved the use of a copper foil laminated on Duroid. This paper describes the process that has been perfected: selective electroplating of gold on copper, compatibility of etching solutions of gold and copper, attachment and connection methods of semiconductors, substrate attachment in a package, etc. A comparison of the performances of a filter realised on fused silica and on Duroid gives the following conclusion: Duroid is suitable for wide band circuits, but not for narrow band circuits because of its instability under stress test temperatures (−20 to 80°). In this last case, silica will be preferred. A transmitter‐receiver in the 22–24 GHz band for radio links is described.