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IC Packaging Trends Causing Concerns in Complete Flux Removal
Keywords: Flip-chip, cleaning , solder flux
The complete cleaning and removal of flux / soil residues under low profile components (especially flip-chip devices) are becoming more critical, especially as the conductor spacings are decreasing and the power is increasing. If the residues are not completely removed, then the reliability of the circuit can be greatly affected. Packaging trends are pushing flip-chip bump pitch and sizes, and thus causing tighter and smaller spaces underneath the devices. A majority of flip-chip assemblers are using water soluble fluxes and they would typically use only DI water to remove the flux residues. Because of the tighter spaces and increased I/Os, the complete removal of these water soluble flux residues are becoming more difficult and all of the flux residue must be removed to ensure an acceptable bonding of the underfill material. To insure that all of the flux residues are being removed from under the package, cleaning chemistries must be used. The cleaning chemistries will lower the surface tension of the water and also increase the cleaning performance. But cleaning chemistries must also be match with the cleaning equipment. To completely remove flux residue under the IC packages, the dynamic energy of the cleaning equipment must also be studied, along with the cleaning chemistry. Additionally, both the cleaning chemistry and equipment must be matched up with the flux residue that is being removed. This paper will evaluate various cleaning chemistries and cleaning equipment that will provide the best cleaning performance for very low package stand-offs and tighter pitch devices, as well as the different flux residues and process parameters (such as: reflow profile, N2 vs Air, etc.) of the packages.
Rich Brooks, Regional Manager
Kyzen Corporation
Nashville, Tn

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