CERN Accelerating science

Article
Report number	physics/0510021
Title	Development of an Indium Bump Bond Process for Silicon Pixel Detectors at PSI
Author(s)	Brönnimann, C (PSI, Villigen) ; Glaus, F (PSI, Villigen) ; Gobrecht, J (PSI, Villigen) ; Heising, S (PSI, Villigen) ; Horisberger, M (PSI, Villigen) ; Horisberger, R P (PSI, Villigen) ; Kästli, H C (PSI, Villigen) ; Lehmann, J (PSI, Villigen) ; Rohe, T (PSI, Villigen) ; Streuli, S (Zurich, ETH)
Publication	2006
Imprint	4 Oct 2005
Number of pages	8
In:	Nucl. Instrum. Methods Phys. Res., A 565 (2006) 303-308
In:	International Workshop on Semiconductor Pixel Detectors for Particles and Imaging, Bonn, Germany, 5 - 8 Sep 2005, pp.303-308
DOI	10.1016/j.nima.2006.05.011
Subject category	Other Fields of Physics
Accelerator/Facility, Experiment	CERN LHC ; CMS
Abstract	The hybrid pixel detectors used in the high energy physics experiments currently under construction use a three dimensional connection technique, the so-called bump bonding. As the pitch below 100um, required in these applications, cannot be fullfilled with standard industrial processes (e.g. the IBM C4 process), an in-house bump bond process using reflown indium bumps was developed at PSI as part of the R&D for the CMS-pixel detector. The bump deposition on the sensor is performed in two subsequent lift-off steps. As the first photolithographic step a thin under bump metalization (UBM) is sputtered onto bump pads. It is wettable by indium and defines the diameter of the bump. The indium is evaporated via a second photolithographic step with larger openings and is reflown afterwards. The height of the balls is defined by the volume of the indium. On the readout chip only one photolithographic step is carried out to deposit the UBM and a thin indium layer for better adhesion. After mating both parts a second reflow is performed for self alignment and obtaining a high mechanical strength. For the placement of the chips a manual and an automatic machine was constructed. The former is very flexible in handling different chip and module geometries but has a limited throughput while the latter features a much higher grade of automatisation and is therefore much more suited for producing hundreds of modules with a well defined geometry. The reliability of this process was proven by the successful construction of the PILATUS detector. The construction of PILATUS 6M (60 modules) and the CMS pixel barrel (roughly 800 modules) will start in 2005.

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