Flip-Chip Header for IR Detector Arrays Operating at Cryogenic Temperatures

The recent development of photovoltaic IR detectors made from thin films of IV-VI semiconductors, such as PbTe on BaF
2
substrates has necessitated the development of a new type of header. The most significant requirements were for face down mounting to permit illumination through the BaF
2
substrate and for Compatibility with the unusually large thermal expansion of the devices
\alpha
\approx
2 X 10
⁵
°K-l)when the devices are cycled in the' range of 300 to 77°K. The thermal expansion was successfully matched using a 4 structure that was predominately copper. The face down i mounting was obtained by flip-chip bonding to solder bumps i dammed by chromium on copper pads that were delineated ., from the foil component of a copper/copper sealing glass/ copper foil sandwich,