Custom plastic ball grid array packages for microwave space applications up to 30 GHz

The realization of small size microwave packages for an assembly on a main board using a collective reflow soldering process is an interesting solution to reduce the lead-time and the cost of microwave space equipments with a building block approach. Custom plastic packages manufactured in-house have the advantage of offering flexibility in the design, even for small quantities. Compared to ceramic packages, there is no limitation in size because of a thermal expansion mismatch between the package and the main board, which is critical for the large temperature range that space telecom equipments have to sustain (-55°C to +100°C). The use of near hermetic encapsulation guaranties the reliability and life time of the packaged dice, and we show that satisfactory performance up to Ka band (30 GHz) can be obtained with BGA connections. This paper focuses on the results obtained for different layouts, both on the package side and on the main board, as well as different ball pitches and package sizes. The solder joints are observed using 3D X-ray computed tomography which gives accurate results to compare the different configurations. The issues related with the development of reliable plastic BGA packages for microwave space applications up to 30 GHz, including ball attachment and the assembly of the packages on the main board, have been successfully overcome. It paves the way for the implementation of next generation of space telecom equipments with a modular approach.