This paper demonstrates a combined approach of numerical analysis and experimental investigations to study the mechanical reliability of flip chip solder joints. The effect of various design parameters like bump geometry, "soft" and "hard" underfill, and used solder mask on the thermal fatigue life of solder joints is discussed. Since special attention has been directed towards Flip Chip on Board (FCOB) assemblies, constitutive properties of polymeric and solder materials are discussed in detail. The solder is modeled using a nonlinear constitutive law with time dependent (creep) and time independent plastic strains. Furthermore, material testing shows that the underfill and solder mask materials might be considered as linear viscoelastic with temperature time shift properties. Thermal mismatch between the materials assembled is often the main reason for thermally induced stresses. Thermal cycling (125 degrees C...-55 degrees C...125 degrees C) is therefore the load generally used in t he 3D non-linear finite element analysis. Calculation results of the solder bump deformation due to temperature changes are accompanied by experimental deformation analysis. The used MicroDAC method is based on algorithms of local object tracking in images obtained from electron scanning microscopy. The measured deformation fields were utilized for proper materials selection and processing, as well as for verification of finite element analysis

The speed ratio parameters of transmission are crucial factors that affect a vehicle’s power, economy, and comfort. Due to the complex working conditions, multiple working modes, and wide range of speed ratios of agricultural tractors, designing and optimizing speed ratio parameters in power-shift transmissions is a challenging task. This paper proposes a transmission speed ratio optimization method based on the life cycle speed utilization rate of general-purpose agricultural tractors. The speed ratio parameters are optimized and solved using the genetic algorithm, with multi-gear power-shift transmissions in agricultural tractors as the research subject. The optimization results and simulation analysis show that the optimized speed ratio has more and denser gears in the common operating speed range while ensuring the general-purpose agricultural tractors’ use requirements. Compared to commonly used geometric series speed ratios, tractors using the optimized speed ratio parameters in this paper can significantly improve fuel economy. Most importantly, this provides a practical method reference for optimizing speed ratios in multi-gear gearboxes with complex structures.