Radar technology has been developing towards greater flexibility in waveform, frequency range, and bandwidth. Progress in RF technologies has transitioned radar systems from low frequencies (L-band, 1-2 GHz) to high frequencies (X-band, 8-12 GHz). In addition, system design has been optimized such that lower cost components will make this high frequency technology affordable for military applications. A design for the X-band integrated downconverter module, which can perform in the presence of interference, is complete. Design is currently underway on the test vehicle for the downconverter. The test vehicle will have a significant number of the components from the bill of materials of the actual downconverter module and will be used to model reliability testing in parallel to the design and build of the actual module. The results from this testing will indicate whether there are areas for improvement in the module design.

The design of the X-band integrated downconverter test vehicle will focus on using readily available, low cost, commercial off-the-shelf (COTS) subsystems and components. The printed wiring board (PWB) design of the test vehicle will utilize mixed technologies of dielectrics and high-density interconnects. Polytetrafluoroethylene (PTFE) will be considered for RF components while flame retardant type 4 (FR-4) material and/or polyimide will be considered for non-RF application devices. Blind vias, buried vias, conventional through vias, and via-in-pad for fine pitch ball grid array (FPBGA) and chip scale packages will be integrated in the test vehicle design. RF paths will be located on the top surfaces while PTFE material and non-RF paths (low frequency and DC signals) will be either on the bottom or middle regions of the PWB using RF-4 material. Selection of materials and components will follow the guidelines spelled out by Restriction of Hazardous Substances (RoHS) regulations which prohibit cadmium (Cd), mercury (Hg), hexa-valent chromium (Cr6), polybrominated biphenyls (PBB), polybrominated diphenyl esters (PBDE), and lead (Pb).

The primary objective of the test vehicle design is to achieve a high density, high performance, and low cost assembly by optimization of miniaturized components and conventional surface mount technologies (SMT). The advantage with designing X-band integrated downconverters is that most of the RF and non-RF package types are widely available in both commercial and consumer supply chains. However, specifications for these components and devices must follow the strict J-STD-001 Class III requirements used in the defense industry.
The following issues will be addressed using the test vehicle.

• Low clearance tolerance for miniaturized devices and cleaning difficulties in these tight areas.
  
• Small solder joint integrity to be inspected to J-STD-001 Class III standard under X-Ray transmission imaging.
  
• Improvement with process engineering of miniaturized components being populated on the printed wiring boards.
  
• High precision solder paste application for miniaturized components.
• Compliance with RoHS regulations for all commercial components as well as consideration of pure Sn, NiPdAu, and SnAgCu balls on BGAs in manufacturing.

Module interface connectors and large case-grounded filters will be considered to ensure performance in this high technology RF application. The connectors will be edge-mounted with double-sided SMT-style components on the printed wiring board. Automation for chip placement will be used to reduce assembly cost as well as provide consistent manufacturing practices.

An examination of the manufacturing practices will be made by using virtual manufacturing simulation software tools for the test vehicle design. Bottlenecks can be identified and risk analysis can be performed to determine areas of optimization and improvement. Some of these issues will be examined and considered when builds of the test vehicles used for reliability testing are complete. Reliability testing and failure analysis on the test vehicles will be performed as well.

The X-band integrated downconverter test vehicle design will be examined and studied for any issues relating to manufacturing practices as well as product reliability in the field once actual
modules are being built.