Interface Fracture Mechanics of Laminates and Its Application to Design of LSI Packages

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1.Delamination growth due to mechanical and thermal loadings is investigated for laminates consisting of two beams with different elastic and thermal properties.Two basic models, which are important for the fracture mechanics of interface of laminates, are analyzed.(1)The low velocity impact applied normal to the surface of laminated beam with an edge delamination is considered.The dynamical response of the beam is analyzed on the basis of the theory of transient vibration due to time varying externally applied force.The condition of the velocity of impacting bar is assumed as such that the velocity becomes constant after some short transient time.The magnitude of impacting force is then determined by making use of Laplace transform method.The bending moments near the edge of delamination are obtained in closed form, from which the energy release rate is calculated.Experiments are also conducted, which show that the predicted response of the beam agree well with the theory.(2)Delamination growth due to temperature gradient is analyzed for the beam with an internal delamination.It is shown that when the temperature gradient is below some critical value the model assuming the contact of the delaminated surfaces is effective and in this case energy release rate is identically zero.However, when the temperature gradient reaches some critical value, local delamination buckling occurs and energy release rate becomes no longer zero ; This implies that the delamination growth would occur only through the local delamination buckling.2.Numerical analyses based on FEM and experiments are made for delamination growth in large-scale integrated circuits(LSI)plastic packages.Using Kr 85 radioactive tracer techniques, initial sites of edge delaminations occurring during temperature cyclic tests in LSI plastic packages areidentified and the results are compared with analyses.