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 BaF2substrates has necessitated the development of a new type of header. The most significant requirements were for face down mounting to permit illumination through the BaF2substrate and for Compatibility with the unusually large thermal expansion of the devices 2 X 10⁵°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,