A fine pitch bump bonding process compatible with the manufacture of the pixel-HPD's for the LHCb RICH detector

A new approach to photo detection using pixel-HPD's has been adopted for the LHCb-RICH detector. These devices use a hybrid pixel detector inside an evacuated photo tube providing high-precision, low noise detection of Cherenkov radiation. The approach takes advantage of modern CMOS technology offering many advantages over more traditional techniques. These advantages include extremely high sensitivity, low noise and fast readout. A major technological challenge was the encapsulation of a hybrid pixel detector inside a photo detector tube. The fabrication of the HPD tube involves packaging of the pixel detector assembly onto a ceramic carrier to form the photo-anode and the subsequent bake out of the pixel anode under vacuum. Both processes involve high temperatures. A fine pitch solder bump-bonding technique, which is compatible with the manufacture of hybrid photo detectors, has been developed. The technology and the tests used for qualifying the new process for pixel-HPD production are described. More than 40 pixel detector assemblies have been produced with almost all showing <1% of missing pixels. A number of assemblies were baked out using temperature cycles identical to those used for pixel-HPD manufacture. None of the assemblies demonstrated any degradation. SEM photos clearly indicate the reliability of the process. 10 pixel-HPD tubes have been produced using this new bump-bonding process and those behave according to expectations. The pixel-HPD is the first of a new generation of photo detector tubes suitable for RICH and other visible photon sensing applications