Prediction of the Fatigue Failure of Lead-Free Solders in New Power Electronic Components
Business: Electronic Motion Systems Ltd.
Result Areas: Increasing the product life cycles
Technology: Lead-free Solder Creep-Fatigue Simulation
Electronic Motion Systems (EMS) develop and manufacture control modules and systems for power conversion and electric motor drives for the automotive industry. Originally part of the large world-wide group International Rectifier, EMS was purchased by the employees and is now a Swansea based SME.
Due to environmental concerns, legislation has been introduced banning lead from solders and industry and research organisations worldwide have been working on converting to lead-free solders based on metals such as tin. This conversion process has been relatively rapid over the past decade, particularly in the European Union, however, the full impact on the electronics industry is still unknown as the reliability of lead-free solders is more difficult to predict due to the build-up of intermetallic layers. Certainly, new generations of lead-free solders are being developed on almost a yearly basis, and no single composition has been adopted world wide as standard. This has led to a lack of comprehensive thermo-mechanical data for lead-free solders.
EMS’s products require high standards of reliability at some of the highest power and thermal cycle ratings. Fatigue of solder joints in electronic assemblies arises from thermal expansion mismatch of various components (ceramic substrates, copper, solders etc), and this accumulates over the repetitive cycling over the lifetime of the package. Computational modelling can be used to accelerate design iterations, and optimise geometry of subcomponents and board layouts.
Using visco-plastic creep-fatigue models, ASTUTE has simulated thermal and power cycles on sub-components such as leads and on complete assembled modules. The computational power required has been significant with the 3D full board simulations taking over 10-15 days to run for only 10 cycles (failure can occur at many thousands of cycles).
However, the areas of predicted failure closely match those being seen in the testing of actual components, and in conjunction with metallographic analysis, has given an insight into the failure mechanisms of lead-free solders.
As a result of the work, EMS has been able to proceed with a cost-based down-selection of appropriate lead-free solders to be used in new products. Further work is planned where modelling is incorporated into a redesigned layout of the module which minimises the fatigue of solder joints in key areas.
Due to focus on Smart Specialisation, some of the expertise areas in the case studies might not be covered in the current ASTUTE 2020.