Optical fiber sensors for studying drag forces of the molding flow in IC packaging

Using optical fiber sensors to study the drag force in molding flow is presented. This research have proved that this novel method can be used to study the drag force of the molding flow in IC packaging over a perfect elastic circular cylinder. The result of this study is found to be useful for characterizing the behavior of the wire sweep in encapsulation of semiconductor chips. An in-line fiber etalon (ILFE) as a sensor is designed, constructed, and implemented in the middle of the optical fiber for accurate strain measurement. This is done by first laying an optical fiber in the mid-plane of a simple rectangular mold cavity, and then measuring the strain at the mid-span of optical fiber subjected to the flow of homogeneous fluid. For a given flow field, several drag force models have been tried to calculate the drag force on the optical fiber, and the resulting strain of the optical fiber has been calculated by FEM and compared with the experimental results. From the comparison, a Takaisi's model to calculate the drag force exerted on the optical fiber by the flow of homogeneous fluid is modified according to the experimental data. Accordingly, the modified Takaisi's model for the drag force can be applied to study the wire sweep in the encapsulation of semiconductor chips. It is concluded that this measurement system can be used to verify the drag force model for a molding flow on a perfect elastic circular cylinder. Even more complex conditions in molding flow, the proposed sensing system can also be used to measure the axial strain accurately. In addition, the transient deformation of the optical fiber characterized by the ILFE sensor provides important information for developing the drag force model that can be used in IC packaging.