Underfill of flip chip on laminates: simulation and validation

Abstract

The flow characteristics of a number of underfills were evaluated with quartz dies of different patterns and pitches bonded on different substrate surfaces. Perimeter, mixed array, and full array patterns were tested. Observations on the flow front uniformity, streaking, voiding, and filler segregation were collected. The information was compared with the results predicted by a new simulation code, plastic integrated circuit encapsulationcomputer aided design (PLICE-CAD) under DARPA-funded development. The two-phase model of the combined resin and air takes into account geometrical factors such as bumps and die edges, together with boundary conditions in order to track accurately the propagation of the flow fronts. The two-phase flow field is based on the volume-of-fluid (VOF) methodology embedded in a general-purpose three-dimensional (3-D) flow solver. Index Terms-Capillary flow, filler settling, flip chip, flow simulation, flow streaking, full array pattern, mixed array pattern, organic laminates, peripheral pattern, quartz dies, underfill flow.

Three-dimensional simulation of underfill process in flip-chip encapsulation

“…Due to symmetry, only half of the device is shown. The right side in each sub-figure shows the observed melt-front reported by Nguyen et al [45]. The experimental results demonstrate that the encapsulant flows slower in the center region and faster in the edge region.…”

“…In this test, the driven force is underestimated in the solder region, and such that the encapsulant in this region flows slower than the observed results and the results predicted by our model. Furthermore, Nguyen et al [45] has pointed out that the encapsulant dispensed on one side of a die can flow along the outside edges fast to the adjacent edges, and then it will flow from the edges to the center in a direction parallel to the dispensing edge driven by the capillary action. During the encapsulation, the gap is filled up by two types of flows, i.e., the center flow and the edge flow, as shown in Fig.…”

Underfill process for two parallel plates and flip chip packaging

“…Power law constitutive equation and time independent velocity boundary conditions are applied in their simulations. Their model yields better predications compared with those of PLICE-CAD and the two-phase model used by Nguyen [12]. Young [13] has investigated the effect of viscosity on underfill flow in the flip chip encapsulation process using the analytical model.…”

Micro-PIV measurements of capillary underfill flows and effect of bump pitch on filling process

“…Wan et al (2009) also developed a numerical simulation method to predict the motion of flow front for non-Newtonian fluid. Nguyen et al (1999) tried to measure the flow front of capillary underfill using quartz dies. However, they did not present detailed flow fields when the meniscus passes through the solder bumps.…”