## 3 Defining Physics of Failure for Power Electronics
### The Test Platform
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**Physics of Failure (PoF) Model** & **Description** & **Applicability** \\ \hline Conductive Anodic Filament (CAF) Failure & Conductive Anodic Filament & Wall-to-wall distance between the plated copper filaments within a printed circuit board under an applied bias. CAF is influenced by electric field strength, temperature, humidity, laminate material, solder temperatures, and the presence of manufacturing defects. & Wall-to-wall distance between the plated through holes (PTHs) along the orthogonal axes, degree of overlap, and the frequency and type of qualification can be performed to assess CAF performance. \\ \hline Component Failure Mechanism Analysis & Benign environment makes wear-out a dominating influence on the lifetime of a component. & Lifetime predictions for ceramic and electrolytic capacitors can be made under the influence of temperature and voltage stress. \\ \hline Natural Frequency Analysis & Determines the resonant frequencies of the circuit card and component assembly, based on the structure defined and material properties assigned to each 3D element. & The natural frequency predictions can be used to determine how the board will respond to different types of shock and vibration loads. \\ \hline Harmonic and Random Vibrations & When subjected to vibration, the printed circuit board (PCB) experiences global and local changes to its shape and curvature. Strain is introduced into second-level solder joint. With repeated exposure, damage accumulates, leading to crack propagation and eventual failure of the solder joint. & The PCB strain during vibration is due to the solder or lead strains and therefore by calculating these at each modal a time to failure prediction can be made by converting the cycles to failure displacement equations. \\ \hline Mechanical Shock & The sudden application of single or multiple, but non-periodic, physical loads due to acceleration or deceleration that results in significant displacement or deformation. It affects the ductility of the solder and the fragility of the interconnect structure. & By utilizing implicit transient dynamic simulation, whereby a shock pulse is injected into PCB via the mounting, the resulting strains can be extracted through finite element analysis (FEA). \\ \hline Plated Through Holes (PTH) & PTH are stressed when the PCB experiences changes in temperature. Over time they are fatigued, and eventually fail with crack propagation. & Three step process involving a stress calculation, strain range calculation, and iterative lifetime determination can be applied for PTHs subjected to thermal cycling. \\ \hline Semiconductor Wear-out & Four wear-out electron-migration (EM), (b) time-dependent dielectric breakdown (TDDB), (c) bias temperature instability (BTI), and (d) hot carrier injection (HCI) dominate the semiconductor wear-out over its lifetime. & Semiconductor wear-out can be predicted using multiple methods depending on the availability of component-specific data. \\ \hline Thermal De-rating Analysis & Compares life cycle thermal events to the minimum and/or maximum rated operating and storage temperature of parts used in a selected PCB. & The rated temperature properties of each part to the temperature experienced by that part during each of the thermal profiles can be defined in the product life cycle. \\ \hline Thermal Mechanical Analysis & When a structure is held in place in two or more locations (such as PCB mount points) and the materials expand because of a temperature change, the structure necessarily bends, causing stresses throughout the structure. & Simulation of the structural deformation can be done using a Finite Element Analysis (FEA) model of a PCB and the temperature-dependent properties to determine the likelihood of solder joint failures for one or more temperatures. \\ \hline Solder Fatigue Analysis & Differences in the coefficient of thermal expansion (CTE), place the second-level solder joint under a shear load. & A proven methodology to assess the damage can help calculate time to failure using strain energy, which requires determining the applied force, the strain range, and then extrapolating cycles to failure from the derived strain energy. \\ \hline \hline \end{tabular}
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