Reliability of ceramic microwave packages for space applications

Packaging of microwave components and systems for space use is very challenging since high frequency, thermal and hermeticity aspects need to be considered. Furthermore, these packages have to be reliable under various environmental work conditions. Ball Grid Array (BGA) or Land Grid Array (LGA) packages are typically used for microwave applications. BGAs are better investigated in terms of reliability than LGAs. However, LGAs offer a lower profile than BGAs which might be advantageous with regard to mechanical shock and vibration. Prior to the reliability investigations of packages a screening test of silver, silver-palladium and silver- platinum thick film pastes was made to identify the optimum combination of pad metal and solder. The best thick film pastes with the highest shear forces before and after aging were DP6116 for SAC and DP6146 for SnPbAg. Three different sizes (5times7.5 mm2, 10times15 mm2, 14times20 mm2) of LTCC-LGA were investigated on reliability to determine the critical package size. Two different base board materials were included in the thermal cycling test between -40degC and 125degC (glued microwave PCB on an aluminium base plate and standard FR4). The aluminium board construction showed poor reliability of only 100 to maximal 300 cycles for both solders. FR4 boards offered a much better performance from 600 to over 1000 cycles.