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Introduction
Flux is used to clean the metal pad and to provide good wetting to the solder balls in the interconnection formation process in the flip chip package. Cross-linking reactions would occur during the reflow process and produce rosinous flux residues ([2] Baated et al. , 2010; [3] Beddingfield, 1997; [5] Hansen et al. , 2009). This by-product could be detrimental to the product performance. Thus, post-reflow flux residue cleaning is required. The findings of the cleaning efficiency of a new and environmental friendly water-based MPC® cleaning technology is reported here. This paper presents results on the flux residue formation due to different flux compositions and the efficiency of the cleaning technology in removing the ionic contaminations. Ion chromatograms that indicate the presence of ionic contaminants before and after the cleaning process are also presented. By using water-based chemical as cleaning agent, the ionic contamination levels are significantly reduced.
Background
2.1 Flip chip ball grid array package
Flip chip is one of the favorable integrated circuit packages that optimally increase the packaging density, which simultaneously increase the input/output of the device. The structure of the package consists of active silicon die with solder bumps, which is then flipped onto the substrates to form interconnections. In addition to solder bump alloys and pad metals, fluxes used during solder bump reflows are critical as well to form reliable flip chip interconnections.
High melting temperature solders are required to ensure reliable joints during control collapse chip connection (C4) attachment, wire bonding to carriers, and discrete components to modules. High reflow temperature would cause the flux residue to be more solid and harder to be cleaned in the subsequent processes. Corrosion-related failures at the bump interfaces due to reactive halides from flux residues could accelerate under high humidity conditions. It is important that flux residues formed under the chip and around the bumps during reflow have been sufficiently cleaned before proceeding to the subsequent processes.
2.2 Flux residue
Fluxes consist of rosin, activators and also solvent. The flux is activated when subjected to heat. After chip alignment, the assemblies are subjected to a reflow process in furnace with oxygen-free ambient and nitrogen-forming gas (5% H2 +95% N2 ). During this time, fluxing reactions such as...