The Study Of Thermomechanical Behavior Of Conduction-Cooled High Power Semiconductor Laser Arrays

High-power semiconductor lasers are widely used in displaying,materials processing,pumping,medical treatment and national defense and military applications thanks to their excellent properties and reliability.Because of issues such as radiative recombination and absorption,a lot of energy is converted to heat with increase of the device power,leading to significant increase of junction temperature and high thermal stress owing to the coefficient of thermal expansion(CTE)mismatch between different materials.Heat and thermal stress is becoming a severe problem limiting the lifetime,stability and reliability of the lasers.In order to obtain more stable and reliable products for high-power applications,it is essential to study the thermo-mechanical behaviors of high-power laser devices and packaging comprehensively.The first chapter in this thesis summarized background and state-of-the-art of semiconductor lasers.In the second chapter,properties of the materials used in semiconductor chip and packages.Two kinds of packaging structure using In and AuSn solders are described in detail.In the third chapter,modeling and analysis of the semiconductor laser package using In solder is done by using analytical model and finite-element method.Firstly,based on the bimetallic theory and elastic mechanics model,a simplified analytical model of semiconductor laser package is established,including chip,solder layer and heat sink.The normal stress,shear stress and near-field nonlinear(smile)effect of the simplified model under the actual reflow conditions and working conditions are calculated.The theoretical relationship between the material properties,the process parameters and the thermodynamic parameters is obtained.Then,the finite element method is used to simulate the normal stress,shear stress,deformation and smile effect of the In-solder package structure during its reflow process and under operating condition.Then,the finite element simulation results and the analytical results are compared.The similarities and differences of the two results are analyzed.The influence of the residual stress and deformation on the thermodynamic behavior of the device under working conditions is discussed.Finally,the finite element model of AuSn solder encapsulation structure is also established,and its thermodynamic behavior parameters are simulated and compared with the thermodynamic behavior of In-solder package.The influence of different solder materials on the thermodynamics of device encapsulation is discussed and discussed.The chapter four discussed the mechanisms of the “smile” effect and the influences of temperature of heat sink on packages using In solder.The result shows that “smile” value increase with the temperature rising.Finally,the chapter five summarized this thesis with conclusions and perspectives.