The traditionally wired interfaces of many electronic systems are in many applications being replaced by wireless interfaces. Testing of electronic systems (both integrated circuits and printed circuit boards) still requires physical electrical contact through probe needles and/or sockets. This paper addresses the state-of-the-art, options, and hurdles-still-to-take of contactless testing, which would resolve many test challenges due to shrinking size and pitch of pads and pins and inaccessibility of advanced assembly techniques as System-in-Package (SiP) and 3D stacked ICs.Direct-contact probing is the standard way to test integrated circuit (IC) wafers via automatic test equipment (ATE). However, it entails high cost due to contact-point deformation and the need for repeated cleaning of probe needles. Wireless testing aims to replace probe needles with contactless circuits that link the wafer and ATE. The potential technologies for wireless testing include radio-frequency (RF), nearfield, and optical communication. We review these technologies and present the results of some simulation experiments to assess their efficiency and practicality.
IntroductionIC technology roughly doubles transistor density every two years, causing a steady increase in testing difficulty [1]. Wafer probing reduces overall testing costs by identifying known good dies prior to packaging. However, the frequent physical contacts (by means of touch-downs) between the ATE's probe needles and the wafer-undertest have some serious drawbacks. The probe needles and contact points suffer deformation, and debris accumulates that can affect test results. The debris can be removed by abrasive cleaning, but that can damage the probe needles [2]. In addition, the increasing use of components with multiple chips, such as 3D IC stacks employing through silicon via (TSV) technology, makes direct-contact probing extremely difficult. TSV tips are too fragile to be probed and conventional probe cards do not support variable contact-point locations.The limitations of direct-contact testing mainly derive from physical contact between the wafer and the ATE's probe needles. If we could replace this by wireless communication, the foregoing problems could be largely eliminated, and testing of TSV-based 3D ICs could be simplified. Wireless testing has some basic requirements of its own, however, including low power and small circuit size. To completely eliminate physical contact between a probe card and the device under test, power should be delivered by wireless technology or be generated on the wafer. The antennas and two-way communication circuits should not consume too much chip area nor affect the functionality of the original device. Therefore the power and size of the added components are severely restricted. The corresponding items on the ATE are much less restricted.Wireless testing has been proposed before [3,4], but little data has been published concerning the foregoing technology issues. However, useful insights can be gained from other communicatio...
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