Transmission line analysis is done in electrical failure analysis labs in order to find root causes that result in system level failures. After a fault is narrowed to a particular signal in a system, a Time Domain Reflectometer (TDR) can be used to analyze the physical transmission line associated with the signal. The transmission lines on smartphones often have inaccessible signal vias, few or no ground vias, probe points that are difficult to see, and short transmission lines. One solution that can alleviate these problems is to design a TDR Accessory Card. This paper discusses the processes involved in testing long and short transmission lines, providing the comparison between the expected and actual TDR measurement and the advantages and disadvantages of TDR, explaining four main points for using a TDR Accessory Card and two reasons for not using the TDR Accessory Card.

One issue that faces failure analysis at the system level is impedance mismatched transmission lines resulting from developers pushing the edge of trace layout recommendations. When transmission lines on printed circuit boards are routed in such a way as to allow for impedance mismatches, the effects can be unwanted on the signal that the line carries. Techniques can be used for discovering if capacitance, resistance, or split planes are creating the impedance mismatches that are resulting in the system level failure seen by the customer.

It is often difficult to find the root cause of motherboards that exhibit intermittent failures. This is due to irregularity and inconsistency. When failures occur at irregular intervals or symptoms are inconsistent, it poses challenges to effectively discovering root cause. This article presents strategies that can be used to analyze motherboards that involve failure irregularity, symptom inconsistency, or both. It also discusses the challenges faced in the analyses.

Series capacitors, under certain conditions, within high speed differential pair signals were found to have negative effects on mother board functions inside a personal computer (PC). It was noted in one case study that three conditions affected capacitors with this type of application: capacitor aging, DC offset voltage, and cold temperatures. These conditions led to the decrease in capacitance which then disabled the network connection inside the PC. It was concluded that a strategically chosen capacitor type alleviates these conditions. The capacitor type primarily depends on the dielectric material.

Failure analysis at the system level requires a well-defined process and methodology in order to drive quality improvements onto motherboards or other subsystems of a personal computer. This process needs to be structured around the type of failure mechanisms that an FA group desires to understand. This paper discusses a specific case study involving electrical overstress in a personal computer that impacted the motherboard of the system. The case study resulted in a solution to increase quality on motherboards in the context of electrical overstress prevention.