Body Grounding of RF Devices Using Indium Alloy 2 for Flight Applications

摘要

Trends in RF devices are towards miniaturization & adoption of more versatile devices. This trend results in the RFIC, MMIC version of the devices which are hermetically sealed in various metallic or plastic packages. The packages are to be mounted on the PCB to realize the complete circuit adhering to specific requirements. The body is gold plated which is attached to the gold plated pattern. Body grounding of RF circuits plays important role in circuit performance at microwave frequencies, as parasitic introduced due to improper grounding, leads to oscillations which renders in degraded performance. The process of body grounding and material selection is critical in device fabrication. The intermetallic bonds due to application of various materials, thermal budget and uniform grounding are the other criteria to be carefully considered. The new material requires proper handling, qualification and characterization to enable the process to be implemented in the flight hardware. The process is segregated into various steps such as detail study of material properties, baking and cleaning of PCB, tinning of leads, sequence of soldering & attachment, mounting of other components. This is followed by electrical testing and characterization to qualify the material for flight applications. In the present case we have qualified Indium alloy 2 which is having lower liquidus and solidus temperature compared to previously employed Indium alloy 7. VCO device is taken to qualify the process. The Indium alloy 2 (InPbAg) material is taken for this study and attached on RT-duriod substrate. The subsequent circuit is subjected to extensive qualification. Further complete electrical characterization, FTIR analysis, XRF and X-ray is carried out to qualify the process. The critical aspect is the intermixing of various materials which can result in the formation of inter-metallic bonds for which FTIR study performed along with XRF characterization. This article details the various process steps, attachment sequences, modelling, qualification plan and characterization for qualifying the process, further article proposed alternative material for body attachment having low temperature process compared to existing one without degradation of any electrical characteristics.