Fatigue Prediction
Fatigue life equations relate the plastic strain amplitude of a material to the number of cycles required to reach failure. The application of manson-coffin strain-life is standard for evaluating the reliability of solder joints subjected to thermal cycling. It separates the total strain into elastic and plastic components to model low-cycle fatigue.
Designers use this relationship to estimate how many power-on cycles a device can withstand before the interconnections crack. Because plastic deformation dominates in the low-cycle regime, this model is more accurate than stress-based approaches for heavy thermal loads.
Material Constant
Empirical coefficients define the slope and intercept of the strain-cycle plot for specific alloys. Calculating the manson-coffin strain-life for lead-free solder requires data on ductility and the fatigue exponent. These values vary significantly between different formulations such as SAC305 and high-reliability bismuth alloys.
By plugging these constants into the power-law equation, the modeler predicts the point of crack initiation.
Lifecycle Validation
Reliability testing validates the mathematical projections through physical stress tests. If the manson-coffin strain-life estimate suggests a thousand-cycle life, the prototype must endure that load without losing continuity. This check confirms that the physical properties of the solder match the theoretical assumptions of the design.
