Residual stress brazing process induced in hybrid package for ISP applications

One of the most used components in the RF transmission devices mounted on satellite antennas are the ISP modules. They are designed by exploiting hybrid materials technology to improve their operative characteristics. In particular they are made up of a Metallic carrier, a ceramic substrate, a metallic frame and a metallic cover. Inside the ceramic substrate metallic circuits and vias they are allocated to connect microelectronic components fixed on the external surface of the substrate of RF transmission modules. Metallic cover is one of the most delicate elements of the package because it must provide for the 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 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 fracture during the operating life of the satellite. In order to foresee their criticality, qualification tests, based on MIL standard, are mandatory. This MIL procedure establishes that the package must be thermally cycled with 500 cycles in the range of 223 K <= 398 K. On account of this, thermal loads, associated to thermal cycles, may cause fractures in ceramic Substrate and the failure of electronic components. In this paper a numerical approach able to simulate all the brazing process and to evaluate numerically all the stresses inside the ISP module will be proposed. 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 tests such as DMA 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 simulations. Finally a comparison between numerical analysis relevant to a broken ISP module will be presented in order to validate the used approach. (C) 2009 Elsevier Ltd. All rights reserved.