Chip Scale Package & Flip Chip assembly using tacky flux

Application of solder paste by using stencil-printing process is a commonly used method for high volume electronics circuits manufacturing. This process has proved to be the fastest and most cost-efficient. Unfortunately this method has shown its limitation for components with pitch smaller than 300 micron. For these components an alterna-tive method is the tacky flux process. It takes place directly on the fine pitch component mounter equipped with flux-dipping unit.

The process stages can be described as follows:
1. Pick up component;
2. Dip component bumps in the flux unit;
3. Place component on the substrate.

The expectation is that this assembly process will allow handling of components with bump pitches down to 100 micron. Therefore it can be extremely interesting for assembly of Flip Chips with eutectic bumps. When FCs with eutectic bumps are placed in solder paste, the position of most components is corrected during reflow, due to the self-alignment of the liquid solder. Likewise, when components with eutectic bumps are placed in flux, the position of most of them is also corrected, due to self-alignment, but the placement accuracy requirements have not been fully investigated. This article presents the research findings with ref-erence to the relationship between placement accuracy and formation of solder joints for components with eutectic bumps placed in flux.

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