Browsing by Author "Pöyry, Outi Irene"

In the upgraded CMS pixel detector (phase II upgrade), the pixel size will become smaller due to the higher occupancy caused by higher luminosity of the LHC. This means that also the bump bonds between the sensor and the read-out circuit will become smaller, which results in smaller gap between the sensor and the ROC. This will increase the probability for electrical sparking that might destroy the ROC, the sensor or both. Jaakko Härkönen has suggested using alumina passivation on the modules for sparking prevention. In this thesis it was studied whether bonding is applicable on a surface having an alumina passivation. It was also of interest, which parameters of the bonder make stronger bonds. Bonding was tested on metal pads with different layer thicknesses of alumina: 0 nm, 10 nm, 15 nm, 20 nm and 25 nm. The strengths of the bonds were tested using the bond pull test. The results indicate that wire-bonding on alumina does well in pull-strength tests, though the bonds are slightly weaker than on surfaces with no alumina. Increasing bonding force seems to weaken the bonds, increasing bonding power, on the other hand seems to make stronger bonds. The conclusion of this thesis is that alumina is a viable choice for passivation, since it does not seem to have a negative effect on the module wire bonding.