Abstract
Detecting failure in electrical connectivity at the component packaging level is a major expenditure of the industry’s failure analysis (FA) resources. These package failures can result from material/manufacturing excursions, stress tests, and/or customer returns. However, many of the methods employed currently (such as X-ray or crosssectioning) can fall short in terms of throughput time, or success rate. Moreover, many FA techniques can be destructive and therefore leave the sample useless for subsequent tests. On the other hand, time domain reflectometry (TDR) can be used as a component packaging level FA tool which meets the needs of quickly, precisely, and non-destructively locating electrical connectivity problems in signal traces. Once the failure location has been pin pointed, other FA methods (X-ray, cross-section, etc.) can be used more easily to determine why the failure occurred. Since TDR testing involves no physical preparation, the sample will be completely intact for subsequent tests. TDR uses a low voltage, low current, and very short rise time voltage pulse to determine the impedance of a signal trace as a function of time. With a waveform of trace impedance versus time, not only can the presence of a failure be detected, but the distance along the trace to the anomaly can also be quickly determined. This paper presents TDR as a useful tool for package level failure analysis labs. The paper proposes one set of solutions for enabling effective TDR analysis (e.g., TDR test fixturing), and discusses some TDR methodologies for detecting and locating anomalies. The methodologies will be illustrated using three example cases that reflect some commonly used packaging technologies: Flip-Chip Organic Land Grid Array (FC-OLGA), Flip-Chip Pin Grid Array (FC-PGA), and Plastic Land Grid Array (PLGA).
