A study on the application of soldering flux on the solder balls of BGA packages

The growing demand for microelectronics packaging solutions with increased I/O density and smaller size has made BGA packages widespread used in modern microelectronic products. During the surface mount process of the BGA packages, dipping-chip is one of the commonly used methods to apply soldering flux on their solder balls to clean solder surface and prevent oxidation. In the dipping-chip method, flux is applied on solder balls by dipping the solder balls into a uniformly spread thin flux layer. The thickness of the flux layer used is equal to about half of the ball height, to make sure that the volume of flux applied is appropriate for effective soldering. In this method, accurately controlled flux layer thickness is obviously a prerequisite for achieving high quality and reliability of resulted soldering interconnection. However, little work has been published to investigate the controlling of flux layer thickness for surface mount of BGA packages. This paper studied the dependence of flux layer thickness on key parameters including flux type, printing speed, and printing height. The results showed that flux type and printing speed give negligible effect on the resulted flux layer thickness. The ratio between flux layer thickness and printing height increased from 60% to 75% with the printing height increasing from 38°m to 140°m.