Thermo-mechanical characterisation and modelling of copper vias in high density printed circuit boards

High density interconnect printed circuit boards need to pass a temperature cycling tests in order to be accepted for specific space applications.  Due to thermal expansion mismatches, there are thermal stresses in the copper vias which may lead to mechanical fatigue fractures after some number of temperature cycling. It is the objective to optimise the material selection of the printed circuit board material and the design of the via to avoid fractures before the end of the qualification test. 
A method to design robust via structure is based on thermo-mechanical stress simulations using finite element modelling. Currently, the simulations comprise uniform materials for both the copper structures and the surrounding polyimide materials. The shortcoming of this approach is that the surrounding material is not uniform but a composite of polymer with fibres, and that copper structures are build up in different plating steps where the interfaces are the weak regions. It is the aim of the thesis to get more of these details in the model in order to better predict the stresses in the vias. With this improvement, the life time of the microvias will be more accurate and the simulations will allow to perform a virtual qualification of the space boards. 
The thesis will comprise following steps: 

• Literature study: available material models for polyimide polymer and fibres / Fatigue models of copper via’s / State-of-the-art of simulation of via structures
• Define characterisation tests to extract material behaviour for a specific space board 
• Create simulation models including all relevant microscopic details 
• Validation with available experimental thermal cycling tests and experiences
• Conclusion

Type of Project: Thesis; Combination of internship and thesis 

Master's degree: Master of Engineering Technology; Master of Science 

Duration: 6 months 

Master program: Mechanical Engineering; Materials Engineering 

Supervising scientist: for more information or application, please contact Bart Vandevelde (bart.vandevelde@imec.be)

Imec allowance will be provided for students studying at a non-Belgian university.