Topic: Study on a Formulated No Clean Flux for Fine-Pitch Flip Chip Package of Copper Pillar/ Micro-bump Interconnect.
Time: October 18, 10:00 am – 1:30 pm
Authors: Hsiang-Chuan Chen, Ya-Ching Chuang, Chia-Hao Chang, Watson Tseng
For several years, an approach to use fine-pitch flip chip package (<150um) with copper pillar/ micro-bump is for the realization of 2.5D/3D packages of higher density and performance enhancement. Generally, flux is widely used to clean the surfaces to be soldered for good wetting and form reliable joints. The upcoming concerns about fluxes are clean-ability for fine-pitch package, voiding and compatibility with underfill materials. There is a tradeoff between flux characteristics and soldering performance. Therefore, this paper will discuss in details about the applicability of a new no clean flux in fine-pitch flip chip interconnect from the point of view of flux formulations, including flux activity for wetting performance, rheological characterization for the study of behaviors during reflow process and the evaluation of compatibility with underfill. As a result, the flux with higher activity showed better wetting performance as well as good compatibility with underfill materials. Rheological properties of flux can be controlled by modifying the formulations to be applicable in dipping process, and keep stable during reflow process. In addition, long term reliability of thermal shock testing was determined. Hence, evaluation and selection of a suitable flux is very critical for a robust advanced package process.
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