Failure site isolation on passive RFID tags

Passive RFID tag typically consists of an inert carrier substrate, an antenna and a semiconductor chip. Qualification process of the passive RFID tags includes temperature cycling in high humidity conditions and damp heat storage tests. In order to pass qualification tests, a passive RFID tags needs to respond to queries by a tag reader. There was an unacceptable level of failures of passive RFID tags after exposure to cyclic testing (-40 to 70degC, 95%RH) and damp heat storage (85degC, 85%RH) tests. We performed an evaluation of the materials, manufacturing and assembly processes and qualification testing environment to create a set of possible failure sites with associated failure modes, mechanisms and causes. A physical analysis plan was created and executed to investigate these sites of interest on as-manufactured, exposed and failed passive RFID tags. The analysis included electrical resistance measurements, chemical decapsulation, cross-sectioning, focused ion beam etching (FIB), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis on cross-sections. Based on the analysis, we found damaged passivation layer and delamination between bump and die metallization. We also found instances of poor physical contact between the semiconductor bump and antenna. The analysis of these results led to implementation of several design and assembly process changes, which resulted in high degree of improvements in reliability and performance.