The fatigue behaviour of joints between ceramic LTCC modules and printed circuit boards was investigated using thermal cycling tests at temperature intervals of 0°C - 100°C and -40°C - 125°C and analysis of the assemblies with scanning acoustic microscopy and SEM/EDS. Two types of printed circuit board, FR-4 and Hitachi Chemical MCL-E-679F, and variations in the via structure of the daisy-chain connections and structural rigidity were used in the assemblies. Rigid LTCC/FR-4 assemblies with long vias had mean fatigue lives of 335 cycles at -40 °C - 125°C and 3250 cycles at 0 -100°C, whereas more flexible LTCC / FR-4 combinations with short vias showed a mean fatigue cycle number of over 1400 at -40 °C - 125°C and no failures at 0 °C - 100°C. Rigid LTCC/Hitachi assemblies with long vias failed at 590 and 4440 cycles (mean values) at -40 °C - 125°C and 0 °C - 100°C, respectively. In the damaged joints, fatigue cracks propagated mainly in the LTCC ceramic and partly in the solder, but notable differences were observed in the crack origin and propagation directions between the assemblies. On the basis of these observations, three fracture modes were defined.
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