Flow Visualization of Solder Ball Arrangement for Underfill Encapsulation of Flip Chip

Abstract

The flip chip package has the advantages of low cost, low interface, and small volume in IC package. This study describes the analysis of underfill encapsulation between solder balls and microchip by experiment and 3D numerical simulation. The numerical simulation of underfill encapsulation is based on the concept of the control volume finite element method. The parameters of injection situation are used for central point, one line, L-line, and U-line injection types. The different processing parameters (solder ball arrangement, injection pressure, solder ball size, and injection situation) are used for underfill encapsulation. The results show that the free surface shape of the experiment is closer to that of the 3D numerical simulation on the plane flow situation for underfill encapsulation. The injection situation of L-line is the best underfill encapsulation of flip chip irrespective of the different arrangement of solder ball and size of the solder ball. The flow time has the biggest value for the different size of solder ball on an alternate arrangement of the solder ball. The flow time decreases as injection pressure increases. The free surface on the thickness direction is concave for the underfill process of the experiment. The contact angle of the free surface is the same for different injection pressures in underfill encapsulation. This situation indicates that the capillary effect dominates the flow situation in the underfill process.