The International Multidisciplinary Artificial Gravity Project
- Paper number
IAC-04-G.3.01
- Author
Dr. Jancy C. McPhee, National Aeronautics and Space Administration (NASA)/Johnson Space Center/USRA, United States
- Year
2004
- Abstract
One of the most used component in the RF (Radio Frequency) transmissions devices mounted on satellite antennas are the ISP (Integrated System Package) modules. They are designed exploiting hybrid materials technology to improve their operative characteristics. In particular they are made up of a metallic carrier (KOVAR), a ceramic substrate (LTCC - Low Temperature Co-fired Ceramic ), a metallic frame (KOVAR) and a metallic cover (KOVAR). Inside ceramic substrate are allocated metallic circuits and vias to connect microelectronics components fixed on external surface of the substrate of RF transmission modules. Metallic cover is one of most delicate element of the package because it must provide to tightness of the assembly. The cover is welded to the frame by seam-welding technique. In order to assembly ceramic substrate and metallic frame a brazing process must be carried out. This brazing process introduces a residual stresses at the end of the welding process. These residual stresses induced by the thermal cycles could cause crack growth and eventually a component’s fracture during the operating life of the satellite. In order to foresee their criticality, qualification tests, base on MIL standard (MIL STD 883 G) are mandatory. This MIL procedure establishes that the package must be thermally cycled with five hundred cycles in the range of 223 K ≤ T ≤ 398 K. On account of this, thermal loads associated to thermal cycles, may cause fractures in ceramic substrate and the failure of electronic component. In this paper it will be proposed a numerical approach able to simulate all the brazing process and to evaluate numerically all the stresses inside the ISP module. Parametric studies on thermal loadings and on geometrical characteristics of the brazing subcomponents such as the metallic carrier, the ceramic substrate, the metallic frame and the metallic cover in order to evaluate maximum and critical stresses will be also presented. To perform such numerical analysis laboratory test such as DMA (Dynamic Mechanical Analysis) and TG/DTA (Thermogravimetry / Differential Thermal Analysis) have been carried out and detailed in the paper. The aim of these tests is to characterize the mechanical and thermal properties of all the material employed for the numerical (KOVAR, LTCC, Au-Sn) simulations. Finally a comparison between numerical analysis relevant to a broken ISP module will be presented in order to validate the used approach.
- Abstract document
- Manuscript document
IAC-04-G.3.01.pdf (🔒 authorized access only).
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