Surface mount technology (SMT) is a revolutionary change in the electronics industry. It enables electronics industries to progress towards becoming smaller, lighter, denser and cheaper components. The reliability of these components to coefficient of thermal expansion (CTE) mismatches, shock loading, and high temperature applications becomes critical to performance parameters. Defense electronics may often be subjected to high-g acceleration loads in addition to extremes of temperature, humidity and prolonged storage. Underfills provide excellent protection and survivability expectations under extreme thermos-mechanical loading, CTE mismatches, moisture. There is a dearth of computational tools to allow for the prediction of the initiation of damage and the progression of damage under high-g shock loads.  Defense electronics and military systems have longer lifetimes about 20-40 years and higher reliability requirements.  New packaging architectures, which often push the edge of the envelope in terms of miniaturization, cannot be compared with the state-of-art systems and lack decades of historical data to provide robust proof of their survivability.  Tools and techniques are needed to determine the failure envelopes for new component technologies for operation under high acceleration loads in current and next generation military systems.  In this paper, the interface fracture toughness of the PCB-UF interface has been studied under exposure to high temperature storage.  A three-point composite beam specimen has been used to study the interface fracture toughness.  The bi-material strips of PCB/Underfill were thermally aged for 30 days, 60 days,120 days and 150 days at temperatures ranging from 100°C to 150°C and then the sample specimens were subjected to quasi-static three-point bending to observe fracture parameters and to determine interfacial delamination of bi-material strips.  A 2D Digital Image Correlation (DIC) method was also employed to understand the Crack tip opening displacement (CTOD), crack initiation and the fracture toughness, CTOD were compared with the aging schedule and temperature. The experimental findings were fitted using linear regression to identify Crack opening displacement and to smooth out noise in the data set. Specimens were observed under a Scanning Electron Microscope to detect the microstructure changes due to thermal ageing. A FE model was developed with cohesive zone parameters to predict the crack propagation, delamination behavior and validate with experimental data.


Fe Modelling and Experimental Study of Crack Propagation at the Pcb/underfill Interface Due to Thermal Aging

Division / Sponsors: 
Electronic & Photonic Packaging Division (EPPD)

Paper Proceedings: https://asmedigitalcollection.asme.org/InterPACK/InterPACK2020/volume/84041

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