The RF Converters market has recently significantly evolved: new programs show a great step in terms of linearity performances which induce higher heat dissipation. Requests for proposal (RFP) and programs have convinced THALES ALENIA SPACE to analyze the feasibility of "Thermal Enhancement".
The heat conductivity of AlSi material is 7 times higher than thermal conductivity of the Kovar. Our macro-hybrids are today manufactured using Kovar packages. The AlSi mass density is low and AlSi is machinable.
These considerations and recent requests from satellite operators pushed THALES ALENIA SPACE to evaluate this material to propose competitive solution at equipment level.
Preliminary tests on samples. These tests were performed on these tests vehicles types:
- Samples 1: bare samples dedicated to validate the plating. The experimental design concludes to the efficiency of the plating.
- Samples 2: validate the soldering of FeNi ring on AlSi frames RX analysis carried out after thermal cycles, confirms the absence of defects and the absence of evolution of small voids.
- Samples 3: validate the AuSn soldering of studs No deterioration of the soldering is visually observed after screwing of a nut on studs.
- Samples 4: validate the assembly of RF K100 feedthrough by AuSn soldering . The visual inspections allowed to confirm the integrity of 3 samples.
- Samples 5: samples for screwing tests We notice no degradation of the tappings in AlSi, even using high torque values.
- Samples 6: validate the AlSi fixation feet. The tests carried allowed to confirm the robustness of the AlSi points of fixation "ears". This option will be integrated on the designs of demonstrators.
Demonstrators Definition: Following these samples results, 2 types of representative demonstrators are defined to perform complete evaluation versus environmental conditions.
Version 1: Package (bottom and walls) in AlSi material, Fe Ni ring and kovar RF feed-through AuSn soldered.
Version 2: Bottom of package in AlSi material, kovar walls, kovar RF feed-through and kovar fixation feet AuSn soldered.
To present a product with higher thermal performances.
THALES ALENIA SPACE proposes here to design critical elements and models of RF Macro-hybrids packages using AlSi Material.
The brittleness and the high cost are the main drawbacks of AlSi. It is therefore mandatory to secure all the machining and assembly processes versus the space environmental conditions in terms of thermal and mechanical constraints.
The activities are organized in two phases:
Define the design of demonstrators using:
- Preliminary tests on step by step elementary process samples for each critical element to secure the design of demonstrators.
- Evaluation tests on representative demonstrators.
Fully Complete qualification phase on the Phase 1 best evaluated solution.
The results of the different tests performed within the framework of this phase 1, in particular on both demonstrator versions whose designs were defined thanks to the tests of the phase of evaluation, concluded:
- The contractual test files highlighted several defects on both demonstrators linked to multiple weaknesses not compatible with the commitment of a qualification phase (Phase 2). These defects are the consequences of the difficulties to obtain reliable models on the weak materials (AlSi, or glass). Our approach is empirical. A preliminary modelling activity is highly requested for large-dimension packages such as defined in this study registered in the products policy “RX and DOCON”. The sizes of the demonstrators were bigger than Kovar packages qualified up to day in TAS. We conclude that for future study on the AlSi material, smaller sizes package are recommended.
- This phase 1 allowed us to reinforce the design close to feedthroughs and to solve the non-compliance generating losses of hermeticity. All the connection assembly underwent the thermal stress successfully as shown by the good thermal tests results.