QART - the CERN facility for quality assurance
How would your detector perform in a very high magnetic field? Or at 60°C and high humidity? Will it work for 10 or more years? Answering these questions requires specialised and thorough testing. This can be done at the Quality Assurance and Reliability Testing Laboratory (QART) - a top-notch testing facility based at CERN, providing invaluable support for CERN projects. The QART lab has become a service in 2011, and invites all projects to use its equipment and expertise.
A portable high-sensitivity infra-red thermal imaging video camera (top left) is used to observe the thermal profile of a silicon strip sensor (top right). The thermal images taken before (bottom left) and after (bottom right) applying voltage to the device clearly show a hot spot developing on the sensor, indicating a serious defect. The infra-red camera is an example of the variety of sophisticated equipment in the QART lab available to CERN projects for the analysis of problems and environmental testing.
When developing the lab, the QART group selected the larger, more specialised and more expensive pieces of equipment that individual groups would not typically have. “Many projects develop quality assurance plans yet require extra resources or equipment to carry them out,” says Honma. “We can also help smaller projects that might not know how to build a comprehensive quality assurance plan, seeing them through the entire process - from creation to finished product.”
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A silicon tracking detector module prototype is fastened to the support head of the high-payload vibration tester (the white cylindrical device mounted on a red base). Several accelerometers measure the actual G-forces on the silicon sensors as a function of frequency. In the insert top right, the sharp peak of a strong vibrational resonance is observed close to 100Hz.
This small aperture laboratory electromagnet is capable of producing a 2T field - the same field strength as in the ATLAS solenoid magnet and about 50% of that in the CMS magnet. In this study, the risk of breakage of electronic micro-connections ('bond wires') used in a real circuit from an LHC experiment is analysed. A small alternating current passing through the wires in a very high magnetic field can lead to vibrations (see video). If this occurs at the resonant frequency of the bond wires, the metal fatigue caused by the vibrational motion can break the wires.
The strongest expertise the QART group can offer is in developing reliability tests based around the specific needs of a project. If a device needs to last a certain amount of time under very specific conditions, the QART group can devise a testing strategy to prove whether or not it can. This type of reliability testing is especially needed when the device needs to work flawlessly for a long time (10-20 years in the case of some LHC detectors) in a harsh environment with limited or no access for repair. Such testing can be performed in industry - but often at high cost and under test conditions which may not match the operating environment of the actual device.
The QART group has also carried out research to study potential issues that could affect experiments. “For example, we are investigating the effect that high magnetic fields have on micro-connection ('bond') wires used in many LHC detectors and electronics,” explains Honma. “These could break due to resonant oscillations (see video). Once developers are aware of the issue, it is an easy problem to fix.” The group is currently developing guidelines for these types of issues, getting the information out there before they cost time and resources.
If you would like assistance or advice in developing a quality assurance plan or a reliability testing programme, do not hesitate to contact the QART group, or visit the QART website for further information.
The QART facility is a free service run by PH/DT, and is operated and maintained by two full-time technical personnel. It is located in the Departmental Silicon Facility in Building 186, which also houses the wire bonding lab. Equipment at the QART facility is available for CERN projects to use or borrow free-of-charge. It includes a large-volume, rapid-cycling climatic chamber with humidity control, a small thermal cycling chamber, a portable infra-red thermal imaging video camera (Image 1), a vibration tester (Image 2), a high magnification stereo-microscope (320x) with video camera, a small aperture electromagnet with a magnetic field up to 2T (Image 3 and video), and a bond wire-pull tester. |
