Research On Thermal Stress Of Semiconductor Laser Chip Packagin

Diode laser has the advantages of wide wavelength range,direct modulation,high conversion efficiency,small size,and lightweight,can be widely used in industry,scientific research,military,and medical,etc.Most applications require the diode lasers to possess higher power.For single-chip diode lasers,the output power is greatly limited.Concentrating multiple emitters on a bar is a common method to achieve higher power.However,the Smile effect is a common problem in diode laser bar.Due to the mismatch of the thermal expansion coefficient in the packaging process,thermal stress will generate in the solidification process of solder,resulting in the spots of the laser not being in the same straight line.This phenomenon is known as the Smile effect.The Smile effect increases the difficulty of beam collimation,beam shaping,and beam combination,and has become one of the main factors that hinder the broader application of high-power diode lasers.Therefore,it is of great significance for the development of high-power diode laser to study the influencing factors of Smile effect and its reduction scheme.Therefore,this paper focuses on the packaging thermal stress of diode laser bar,the generation process of the Smile effect,and the reduction method of the Smile effect.The research is as follows:(1)Finite element method is used to simulate the packaging process of the high-power diode laser with micro-channel water-cooled packaging.The stress and deformation of the diode laser bar after P-side sintering and N-side sintering are simulated,respectively,and the generation and change of the thermal stress and Smile effect in the packaging process of diode laser are analyzed.(2)The influence factors of the Smile effect of diode laser are studied by combining finite element simulation and experiment.The influence factors of n-foil thickness,In solder thickness,WCu sub-heat sink package,and the introduction of external force on the Smile effect of diode laser are detailed investigated.The results indicate that the deformation of the diode laser bar decreases with the increase of n-foil thickness.In the experiment,a smaller Smile effect can be obtained in the diode laser when packaging with thicker In solder.WCu sub-heat sink packaging can reduce the thermal stress of diode lasers,but within certain limits of thickness,it will exacerbate the Smile effect.In the packaging process,introduce external force above the chip is an effective way to reduce the Smile effect of the diode laser.By optimizing these factors,the Smile effect of the diode laser can be reduced.(3)Aiming at the Smile effect,a new packaging structure is proposed,and the finite element method is used to simulate the structure.The thermal stress,Smile effect,and junction temperature during the packaging process of the model are calculated.The simulation results show that the structure of the new Cu sub-heat sink package can reduce the Smile effect of the diode laser and improve the device’s heat dissipation capacity.The experimental scheme is developed according to the simulation results.Moreover,the experiment verifies the positive effect of the Cu sub-heat sink package on the reduction of the Smile effect and increase of the heat dissipation in the diode laser.(4)The test method of the Smile effect and package thermal stress of the diode laser array are studied.In order to study the package thermal stress and deformation of the diode laser bar more effectively,the Smile test platform and space spectrum test platform are built.Based on the relationship between stress and wavelength variation of the diode laser,the magnitude and distribution of stress on diode laser chip are calculated.Meanwhile,the Smile effect has been characterized by means of mechanical contact probe scanning method and optical imaging method.