Fine-pitch wafer bumping and assembly for high density detector systems

A number of high energy physics experiments will rely on pixilated detector arrays to track particles generated in a collision event. In addition, several medical imaging applications are using pixilated devices as the imaging elements. The pixels in these detectors are very small (50-100 mu m pitch) to provide adequate spatial resolution for particle tracking. Since the pixels and their electrical interconnections are arrayed over the entire area of the device, solder bumping is the natural choice for the integration of detector elements to readout and support electronics. The small pitch of the I /O presents new challenges to the bumping and assembly processes. The processes for fabricating bumps and assembling the detectors must have a high yield and be compatible with a high radiation, high vacuum, and low temperature operating environment to provide the necessary performance and operating lifetime. This paper presents an overview of MCNC Research & Development Institute's bumping and assembly processes and the results of our ongoing collaborations with Fermilab's BTeV and US-CMS detector groups and CERN's Medipix group for bumping and assembling pixel detector modules.