A majority of the package assembly facilities are using only DI water to remove flux residue from under flip-chip devices, prior to an underfill process. As the new technologies are being implemented, not only has DI water reached its limitations, but some cleaning chemistries are not able to perform adequately to remove ALL of the flux residues. Complete cleaning and removal of the flux residues under low profile components are critical to maintain the reliability of the integrated circuit. Therefore, the cleaning process must be carefully examined and optimized to obtain maximum performance for removing the flux residues. The total cleaning process can be broken down into two subsets:

  • Static Cleaning rate & Dynamic Cleaning rate

The Static Cleaning rate is ability of the cleaning chemistry to remove or dissolve the residue in the absence of temperature and pressure. The Dynamic Cleaning rate involves the kinetic forces and energy to remove the residue. This includes the Thermal energy and Impingement energy required to remove the flux residue. The sum of these two cleaning rates (Static and Dynamic cleaning rates) equal the Total Process Cleaning rate (see formula below). This paper will review cleaning problems brought about with the implementation of the latest technologies and explain how the cleaning process can be optimized to guarantee the reliability of the assemblies.
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