Mechanical stresses induced by the mismatch of coefficient of thermal expansion (CfE) among different materials are the major driving force of fracture failures in silicon dies of microelectronic packages. The stresses induced are concentrated at locations where diffe rent materials interfaced and geometrical singularities such as die comers and die edges. Stress analyses using finite element mechanical modeling demonstrated that the stresses close to the die comers are 30% -80% higher compared to the inner regions of the die. In addition, cracks inside the bulk mold compound and interfacial delamination on top of the die have been fowld due to these high stresses. DEP (Die Edge Protection) epoxy, a low-stress high CfE polymeric material, has been used to cover the comers and edges of the die to reduce stress levels with the objective of eradicating failures associated with these stress singularities. It acts as a buffering medium to mechanically shield the die comers and edges from being in direct contact to the high modulus molding compound materials. The DEP coating is achieved by dispensing the liquid DEP epoxy outside the wire bonded die area and allowing the epoxy to creep up along the die comers and edges. The DEP dispense process takes place after wire bonding. In the subsequent molding process step, areas coated with DEP will be shielded from the mold compowld. It was observed from experimental evaluations that the DEP coating managed to prevent die comers cracking and delamination. This paper examines the simulation of the DEP coating, and discusses the DEP process development required to implement such a scheme into high volume production.
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