Study of Different Dispensing Patterns of No-Flow Underfill Using Numerical and Experimental Methods

Abstract

The conventional capillary underfill process has been a common practice in the industry, somehow the process is costly and time consuming. Thus, no-flow underfill process is developed to increase the effective lead time production since it integrates the simultaneous reflow and cure of the solder interconnect and underfill. This paper investigates the effect of different dispense patterns of no-flow underfill process by mean of numerical and experimental method. Finite volume method (FVM) was used for the three-dimensional simulation to simulate the compression flow of the no-flow underfill. Experiments were carried out to complement the simulation validity and the results from both studies have reached a good agreement. The findings show that of all three types of dispense patterns, the combined shape dispense pattern shows better chip filling capability. The dot pattern has the highest velocity and pressure distribution with values of 0.0172 m/s and 813 Pa, respectively. The high-pressure region is concentrated at the center of the chip and decreases out towards the edge. Low in pressure and velocity flow factor somehow lead to issue associated to possibility of incomplete filling or void formation. Dot dispense pattern shows less void formation since it produces high pressure underfill flow within the BGA. This paper provides reliable insight to the industry to choose the best dispense pattern of recently favorable no-flow underfill process.

Underfill Flow in Flip-Chip Encapsulation Process: A Review

“…For no-flow underfill, dot dispensing pattern gave the least void formation as compared to the cross pattern [60].…”

“…Subsequently, the FVM-based ANSYS FLUENT software was introduced and applied for the modeling of underfill flow in various Fig. 4 Overview on the experimental approaches in studying the underfill flow of flip-chip encapsulation process: (a) actual experiment using chip and underfill fluid of industrial standard [17,18,[24][25][26], (b) microparticle image velocimetry experiment using transparent imitated chips [27,28], (c) mold underfill experiment using scaled-up imitated chips [29], and (d) capillary underfill experiment using scaled-up imitated chips [20,30] types of underfill process including conventional capillary [20,30,39,47,[54][55][56][57], mold [37,38,40,55,58,59], pressurized [11], and no-flow [60]. FVM simulation gives various data on the underfill flow, filling time, and flow's dynamic and thermal distributions.…”