Advanced Evaluation Method For Solder Layer Degradation Based On Transient Thermal Impedance

Insulated Gate Bipolar Transistor(IGBT)is one of the basic components of converters and has grown to become an irreplaceable core component in many electrical devices,widely used in electric vehicles,high-speed railways,DC power transmission,ships and many other fields.The reliability of power device packaging is an important factor affecting the life of the device,power cycle is currently the most effective means of assessing the life of the device packaging,bonding line and solder is the weakest link in the device packaging,power cycle test standards are mostly used to determine the bonding line failure by 5%rise in saturation voltage drop,junction-to-case thermal resistance rise by 20%to determine the failure of solder.The junction-to-case thermal resistance includes the total thermal resistance of the chip,chip solder,DBC,system solder,substrate and other multi-layer materials.A large number of power cycle experimental data show that only the solder in each layer of the junction-to-case material shows signs of aging such as cracks and voids,while the chip,DBC,substrate and other materials have not aged.This paper proposes a new method for monitoring solder degradation based on transient thermal impedance curves,which can be used to extract the solder thermal resistance online during power cycle experiments and monitor the solder degradation of power devices in real time.The new method of online extraction of solder thermal resistance can provide more reliable basic reference data for device thermal design and lifetime prediction,which has important practical significance and broad application prospects.Firstly,this paper establishes the theoretical basis for accurate extraction of solder thermal resistance,analyses the thermal transient process of the solder layer after the application of heat source in the power cycle test,and proposes a method for the selection of the solder monitoring window,using the EasyPACK module as an example.The theoretical basis is laid.The new monitoring method was then extended to a power cycle testbed to monitor solder degradation.The EasyPACK module from INFINEON was chosen as the target for the study,and the feasibility of using this method to accurately extract the solder thermal resistance was verified through experiments.The same method is also used to monitor discrete devices and double-sided heat sink components to verify the effectiveness of the solder thermal resistance extraction method under different packaging structures.Finally,the feasibility of using the method to extract the solder thermal resistance and assess the solder ageing of the devices is further verified from the perspective of 3D heat transfer by establishing finite element simulation models of IGBTs of different voltage levels through 3D finite element simulation.The influence of the selection of the monitoring window on the extraction of the solder thermal resistance and the influence of the chip voltage level on the selection of the time window are analysed to ensure that the method can be applied to all power devices.