Research On The Solder Joint Formation Process And Multifield Coupling Reliability Of Complex Printed Circuit Boards

As a typical interconnection structure,solder joints are widely used in various fields such as automotive electronics,aerospace,medical equipment,and energy production due to their excellent conductivity,thermal conductivity,easy processing,and low-cost advantages.However,there are still many issues in the research on the formation process and reliability of solder joints under complex and harsh conditions.On the one hand,the continuous reduction of interconnection spacing and the diversification of encapsulation forms continually raise the requirements for the solder joint formation process.Currently,both domestically and internationally,research on the growth of intermetallic compounds during the solder joint formation process is relatively scarce.Additionally,there needs to be more systematic studies on the influence of different process parameters on the morphology of solder joints.On the other hand,with the gradual deterioration of application environments and the increase in unit power density of devices,issues such as solder joint cracking and interconnection failure under comprehensive stress environments are becoming increasingly severe.This significantly impacts the reliability of electronic devices.Currently,the application scope of reliability models for this issue is limited,and practical research methods for solder joints’ failure mechanisms and behaviours in complex and diverse environments still need to be improved.This paper addresses these issues from the perspectives of basic theory,microscopic molecular dynamics,and macroscopic experiments.It investigates the mutual diffusion behaviour of metal atoms during the solder joint interconnection process,the morphology of solder joints,and the generation and growth of intermetallic compounds.Combining simulation and experiments,the paper explores the failure mechanisms and behaviours of complex printed circuit board components under random vibration,high-low temperature cycling,electromigration,and the coupling effects of three environmental factors.The main research contents of the paper are as follows:1.Based on the theories of metal diffusion and reliability analysis,this study investigates the solder joint formation process,the growth of intermetallic compounds,failure behaviours and failure life models under complex and diverse environmental conditions.The paper first elucidates the factors influencing the quality of solder joints and the formation process and mechanism of intermetallic compound growth in typical coppertin systems.On this basis,four basic assumptions are proposed,and mathematical equations for the operation of metal mutual diffusion are derived.Subsequently,the analysis methods and mathematical models for random vibration,high-low temperature cycling,and electromigration are organized and selected.A life prediction model for solder joints under the coupling environment of vibration-temperature cycling-electromigration is constructed by integrating rapid life prediction methods and the linear damage accumulation theory for materials.2.Based on the principles of molecular dynamics,the diffusion behaviour at the interface of the copper-tin system has been simulated.Firstly,a simplified diffusion model for the copper-tin system interface is constructed,and appropriate potential functions and boundary conditions are determined.Next,the simulation is conducted on a classical solder material-solder pad system,investigating the evolution of system morphology,kinetic energy,potential energy,and time during the solder-wetting process.Simultaneously,the motion patterns of atoms of different types and positions are obtained,and parameters such as the mean square displacement,diffusion coefficient,and activation energy of copper atoms at different temperatures are calculated.The behaviour of tin atoms crossing the initial interface and the diffusion distance are analyzed.Finally,the evolution of the intermediate layer in the copper-tin system and the intrinsic connection between the growth of intermetallic compounds have been studied,providing a microscopic perspective on the morphological changes in solder joints and the formation process of intermetallic compounds.3.Experimental research has been conducted based on the reflow soldering process to study the evolution of solder joint morphology and the growth patterns of intermetallic compounds in single devices and printed circuit board components with different packaging forms under the influence of various processes and size parameters.Initially,the study investigates the impact of varying solder paste thicknesses,reflow profile settings,packaging forms,and solder pad surface treatments on the solder joint morphology of individual devices,as well as the patterns and thicknesses of intermetallic compounds.Subsequently,actual temperature curves during the reflow soldering process are collected for different positions on typical PCB components.Finally,the research summarizes the growth patterns of intermetallic compounds in terms of morphology and thickness to varying positions on distinct PCB components.The conclusions have significant implications for optimizing the reflow soldering process,enhancing solder joint consistency,and improving solder joint quality.4.Based on finite element simulation technology,the reliability of solder joint structures in printed circuit board components is analyzed under various application environments.A typical finite element model of the printed circuit board is established.Subsequently,employing the minimum energy method,the solder joint morphology of critical components is constructed.Finally,the failure locations of the printed circuit board are analyzed under four application environments: random vibration,high-low temperature cycling,electromigration,and the coupling of vibration-temperature cyclingelectromigration.Additionally,the solder joint failure life has been predicted in different application environments.The model and methods employed in this study contribute to rapidly identifying vulnerable locations in electronic components,effectively reducing experimental costs,and shortening the product development cycle.5.The accuracy of the finite element model and life prediction methods has been further validated based on relevant reliability experiments.Firstly,experimental specimens are designed and processed,and spectral analysis confirms the good interconnection of the initial structural solder joints.Subsequently,reliability tests are conducted,including airborne random vibration,high-low temperature cycling,electromigration,and the coupling of vibration-temperature cycling-electromigration.These tests are monitored according to the IPC-9701 A standard to obtain failure life data based on the daisy chain resistance and voltage monitoring.Finally,through solder ball staining and metallographic section experiments,the failure locations of solder joints in the printed circuit board components are determined,and the failure patterns of solder joints under different application environments are summarized.In addition,this study also investigates the growth patterns of intermetallic compounds between the cathode and anode in solder joints during the electromigration process.The experiments conducte not only fully verified the accuracy of the simulation but also contribute to the improvement and supplementation of the simulation work.