Novel failure diagnostic methods for smart card systems

摘要

Currently smart cards with integrated silicon dies have found wide application for personal authorization, security identification and payment systems. As a consequence, the complexity of electronics is increasing, thus, specifically adapted failure analysis methods and work flows are required taking the peculiarities of smart card constructions with embedded chips as well as the used polymer materials into account. The aim of the paper is to present results of developing novel methods for non-destructive defect detection as well as for selective, artifact-poor target preparation routines specifically adapted for smart card systems. These methods allow fault localization and exposing defect areas for subsequent high resolution failure analysis within reliability investigations. As for non-destructive diagnostics, specific focus was given to the evaluation and application development of Lock-in thermography (LIT) as a method to detect thermally active failures such as increased contact resistivity, shorts or leakage currents. It could be shown that Lock-in thermography can be successfully applied for fault isolation of defects within the card and on the semiconductor surface. The LIT investigations were complemented by Scanning Acoustic Microscopy (SAM) in order to find delamination and chip cracks. New signal processing methods of ultrasonic microscopy resulted in a reliable detection of these mechanical damages. Scanning Acoustic Microscopy in the GHz frequency (GHz-SAM) domain was applied for investigations on chip level. Contact-induced mechanical damage just below the only few micrometer thick optically non-transparent passivation of the IC could be detected with high lateral resolution. However, for a detailed root cause analysis of the failures localized either by Lock-in thermography or Scanning Acoustic Microscopy, further adequate preparation routines are necessary to get direct access to the failure site. Within the study, a selective exposure of the semi- onductor chips from the composite laminate was achieved by laser ablation after optimizing laser frequencies and pulse widths as well as by adapted wet chemical procedures. Efficient cross section preparation was enabled by ion beam finish. A case study on how the methods can be applied for failure analysis of smart cards will be demonstrated.