Role of feed protocol in achieving chaotic mixing of highly filled flow systems during filling the empty cavity

Abstract

Chaotic mixing of highly filled viscous fluids is desired but hardly achieved in the electronic packaging industries. The demand for high reliability found in electronic package attracts more and more researchers to study the properties and distribution of binders and filler particles. These will affect properties such as coefficient of thermal expansion and stiffness. Both of these contribute strongly to reliability. The filler concentration, size distribution and spatial distribution must be examined in a structured manner to understand their effects on final properties. However, most studies deal with filler concentration and size distribution, while very few studies have tied the particle spatial distribution to the properties. It is not enough to just properly control the filler concentration and size distribution. The more uniform filler distribution, the more uniform are local properties, and this can be achieved by well-designed mixing processes.

Mixing is very important and in many cases the goodness of the mixing of fillers will affect or determine the properties of the products. In this thesis, the local properties of electronic package and their relations with filler particle distribution are quantified. For the first time, a new feed protocol that can generate chaotic mixing during filling cavity by implementing periodic and aperiodic filling process is presented. Instead of using single gate in the molding process, we have developed a two-gate feeding protocol. A numerical simulation experiment is conducted on a 2-D square cavity to examine the mixing of polymer fluid in low Reynolds number flows. Since there are a vast number of geometries in electronic packages, only cavities with 46 and 49 bumps, which can be treated as solder balls or leadframe, is investigated. Periodic and aperiodic feed protocols resulted in exponential growth of the distance between two adjacent particles, an indication of chaotic mixing. Entropic study shows that the global mixing has been improved 858% compared to single gate feeding. The improved properties and reliability could be foreseen in electronic package.