Quasi hermetic packaging for space application : from low level to high power applications
Monfraix, P.¹; Barbaste, R.¹; Drevon, C.¹; Mangenot, C.²; Marchand, L.²; Boetti, A.²; Dareys, S.³; Billot, M.³; Cazaux, J.L.^1
1Thales Alenia Space; ²ESA/ESTEC; ³CNES

Future satellite payload will exhibit higher functionalities (such as multi-spot beam coverage, re-configurability, on-board processing...) in higher frequencies (Ka, Q/V bands) compared to current telecom applications, mainly in Ku-band. For the packaging of the electronic equipment, from low to microwave frequencies, this drastic evolution is also in parallel with miniaturisation and cost-reduction.

For the design of a Focal Array Fed Reflector (FAFR) antenna for multimedia application in Ka-band, a major challenge was the design of a very large number of low noise amplifier (LNA) modules with both nominal and redundant paths. These modules had to be implemented within the focal array mesh (about 1.2λ=12mm @ 30GHz). This was reached with the introduction of new materials and technologies such as well-suited printed circuit board substrate, chip on board assembly and glob top encapsulation. THALES ALENIA SPACE - France (TAS-F) is involved on those new processes both for microwave and low frequency applications. Large investigations have resulted in the choice of epoxy based resins with silica fillers designed with ionic contents and out-gassing values in agreement with MIL standard and a "dam & fill" process to assume an accurate positioning of the dam.

The electrical characteristics of a LNA module in the [29GHz, 30GHz] frequency band is typically:
18dB gain
output return loss below -15dB without any isolator
noise figure below 3.3dB at ambient temperature
340mW power consumption
phase dispersion is below 15°pp
gain dispersion is below 1.5dBpp

All these results are reported on a batch of 18 LNA modules at EQM status manufactured and tested on the standard industrial facilities at TAS-F.

All these advanced technologies (including glob top encapsulation for microwave devices) have been tested according to environmental space requirement to evaluate their reliability. Thanks to this innovative packaging approach for space application, the integration achieved (72.4mm x 30.1mm, 31.6 grams for each LNA module) is four times lighter and half in volume compared to a standard fully hermetic solution.

In the frame of power applications, TAS-F has recently proposed different solutions to combine from 2 to 32 High Power Amplifiers (HPA) with very low combining losses in a compact volume by using rectangular waveguide interfaces. These new combining techniques require developing new technologies to reduce the size of the packaging. As the power devices should be embedded within the waveguide, standard hermetic packaging is not able to fulfil these tiny dimensions. As developed for FAFR LNA modules, the glob top encapsulation for power devices is a key solution to package the active devices. The main difference is on the dissipated power, now around 10-15W for each HPA device, that is to say around 2 orders of magnitude than LNA modules. This has an impact in the choice of the packaging architecture and on materials to select.

This paper will finally present : the design and the main electrical results obtained on the LNA modules developed on the frame of the FAFR multimedia antenna, a detailed description of the Chip on Board technology and glob top encapsulation developed for LNA module and the qualification status for space application, a brief overview of the 3D combining technique for high power applications and the related quasi hermetic packaging approach proposed.