Reliability monitoring of a separable land grid array using time domain reflectometry

A large separable land grid array package was assessed for interconnect degradation using a combination of event detector monitoring and time domain reflectometry (TDR) during temperature cycling. An interposer with a capacity of up to 7296 wire contacts was positioned between a printed circuit board and dummy device under compression. The time domain response of the package was monitored over 1400 cycles from -55°C to 125°C, over a frequency range of up to 10 GHz. TDR results indicate that the outermost set of contacts experienced measurable degradation, which was confirmed through a second independent and simultaneous measurement of the same circuit. The TDR response varied appreciably with temperature, necessitating the selective analysis of data obtained at room temperature, which was the temperature of calibration. Despite the observed changes in the TDR response, no failures were recorded by the event detector. This is the first publication known to describe the use of automated TDR monitoring during stress testing for reliability assessment of a commercial electronic package, and the first to monitor high frequency signal degradation of a separable land grid array during thermal cycling. The observations made during this study should enable future similar efforts to be conducted with greater efficiency and success.