Mekanisk hållfasthet för lödfogar för kretskortskomponenter

Abstract

This thesis deals with the mechanical properties of solder joints used to fix components on circuit boards. The focus is on the inverter that is part of electric vehicle powertrains. The work is performed at Infimotion, a company specializing in electric powertrains. Today, there is a lack of data on the service life of solder joints under thermal and mechanical stress. The purpose of the project has been to analyze how different types of solder joints - THT (Through-hole technology), SMT (Surface mount technology) and BGA (Ball grid array) - are affected by vibrations and temperature changes. The work includes both theoretical calculations and simulations in FEM software to identify stress levels and identify potential causes of failure. The results obtained show that it is the thermal loads that cause the highest stresses in the solder joint, especially due to different thermal expansion coefficients of the material for solder joint, circuit board and component. It also appears that the solder joints that meet the requirements of the IPC-A-610 (Class 3) standard, exhibit a lower stress than those that do not meet the requirements. This indicates a better lifetime and reliability if the requirements of the standard are met. It can be concluded after the completion of the work that the thermal load is the most critical factor, and that combined loads (thermal + mechanical) exacerbate damage growth. As further work, it is suggested to do further calculations with more accurate mesh to find a result that converges. Also calculate more accurately on fatigue by calculating with varying thermal load and mechanical load together. Also perform tensile tests and thermal load to validate the simulation results