Development of Wire Bonding Process and Reliability Evaluation for Gold coated Selenium

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For novel X-ray detectors, amorphous Selenium films are used on top of semiconductor substrates incombination with integrated circuits. Electrical connections to the Selenium layer are needed for operation.Typically, fine wires are used. The requirements for joining of the fine wires to the Selenium include lowtemperature (room temperature ideally), no organic adhesive reacting with Selenium, and small size as thejoints should not obstruct the X-ray images.Microelectronic wire bonding is the main technology to interconnect to integrated circuits. Existing lowtemperature processes of wire bonding are suggested for this project. Wire bonds have 100 % metallic natureand are very small but do not stick to all surfaces. To facilitate wire bonding, the Selenium is coated with a thinGold layer. However, as the Gold coating is thin and the Selenium layer quite soft, wire bonding often resultsin non-sticking failure. The bonds that stick might not be reliable in the long run.The development of a consistent low temperature wire bonding process and its reliability evaluation isproposed in this project to achieve the electrical connection of bonding wire to Gold coated Selenium. Thisprocess will allow the development of miniaturized and high resolution X-ray detectors with sufficient pixels.The project will adopt an improved design-of-experiment methods for the process development combined withreliability methods such as novel current stressing and real time resistance monitoring systems recentlydeveloped at the University of Waterloo. In contrast to other joining methods such as conductive adhesives andsoldering, a successfully developed low temperature wire bonding process to Selenium will maximize theperformance of the X-ray detector. The findings from the process development and reliability evaluation willadd to the knowledge on wire bonding technology in general.