Advanced Cleaning Fluid Design and Process for Cleaning Flip Chip Packages

With Flip Chip I/O increasing, reliability concerns move design engineers to study the beneficial properties of removing the flux residue before underfill. Cleaning flux residue under Flip Chip die requires advanced process design considerations in the form of mechanical impingement and the cleaning fluid. Improved mechanical designs and the introduction of water soluble flux allows processes that used DI-water only as the cleaning fluid. The problem is that as Flip Chip I/O increases, assemblers report that DI-water only will not adaquately clean certain package designs.

This paper introduces research and development of an engineered cleaning fluid with a surface tension in the low twenties that reduces the contact angle of the water droplet. The droplet size reduction improves wetting and penetration of the cleaning fuild under the flip chip die, while rendering no residue under the die.