Junya Sasaki ; Hiroaki Aihara

2015
University of Tokyo Tokyo

Abstract: Belle II experiment is the upgrade of Belle experiment. Its purpose is to accumu- late the data of integrated luminosity 50 ab−1 for searching the phenomena beyond the Standard Model. The center of mass energy of Belle II is 10.58 GeV. That statistics is 50 times larger than that of Belle (1 ab−1). For launching Belle II, the upgrade of the detector and its read out system are now on progress. Silicon Vertex Detector (SVD) is one of the detectors in the Belle II, and SVD is composed of SVD “ladders”. We are now preparing for launching a mass production of SVD ladder. The main topic of this thesis is the method of the assembly of electrical working ladder. For achieving this, the way of the confirmation of the quality is necessary and detection of the problem not only during the assembly but also before and after the assembly is necessary. Electrical Quality Assurance (EQA) is one of the most important procedures for SVD ladder assembly. In our SVD, quality inspection for all components is implemented, but also step by step electrical quality inspection during is implemented. EQA must be the procedure so that we can trace the quality of SVD ladder or detect the problems in the assembly procedure. Whole EQA procedure is supported by one DAQ system, called APVDAQ, developed by High Energy PHYsics (HEPHY) in Austria. This system can measure noises and gains in all strips and these parameters are the key for completing EQA procedure effectively. There are mainly three steps in EQA, parts level EQA, assembly level EQA, and whole assembly level EQA. First in parts level EQA, we check the quality of all electrical components such as a read out chip, flexible circuit, and the sensor. Then bad or broken components are excluded by parts level EQA not to use it in a real SVD ladder assembly and only healthy components are used for a real ladder. If one electrical component doesn’t work well, of course SVD ladder cannot show its true performance so we must check the quality of all electrical components before the assembly. Second in assembly level EQA, electrical test is done during the assembly to confirm the quality of all electrical components or to detect the problems step by step; in the assembly procedure of SVD ladder, there are many procedures such as a wire-bonding, gluing, alignment of the sensor, and any other assembly procedures are so complicated that some problems are expected to be happen in one procedure. Especially, a wire-bond is so fragile that it is easily broken even by slight shock or by one assembly procedure. Although the number of a wire-bond is very huge, but we can check the condition of all wire-bonds in each wire-bonding procedure effectively by assembly level EQA; we check mainly each channel’s noise by electrical test with APVDAQ. The problem during the assembly must be detected by this procedure. Finally in whole assembly level EQA, a beta ray source test for an assembled ladder is implemented to check its performances; by this evaluation, we evaluate all channel’s signal to noise ratio to check whether all channels are working well, or how many channels are not working. To verify the constructed whole EQA procedure, we applied this procedure for the readable module assembly and we succeeded to detect the broken electrical components before the assembly. Also we succeeded to find out the problem of the broken line in a flexible circuit through that assembly procedure. Furthermore, we performed β-ray source test for an assembled readable module for evaluating its performances. As these procedures shown in above, its procedure allows us not only to trace the quality but also to detect the problems in each assembly procedure. In the SVD in Belle II, we demand a success rate of wire-bonding more than 99 percent. The EQA procedure which we constructed also enables us to achieve its severe requirement. We will see the whole procedure of the EQA, which promises the electrical quality of SVD ladder.

Note: Presented on 02 02 2015
Note: MSc