Fluxless bump reflow using carboxylic acid

Abstract

We have established a new fluxless reflow technology and realized an organic solvent free wafer bump forming process. Some carboxylic acids have been used in order to reduce oxidized films on solder bumps of both eutectic and high lead tin types. We found that formic acid was most suitable for stripping of the oxidized films. To obtain good bump shape with this method, it is important to optimize the timing of supply of the acid to the vehicle, the maximum temperature, and the method used to reduce the formic acid on the vehicle. Bump shape, voids, shear strength, and the surface condition of the bumps have been researched with the vehicles obtained. The bumps which were formed by our new technology compare favourably to those formed by conventional reflow processing. The advantages of this technology are: (1) reduced material cost, e.g. flux and organic solvent; (2) environmentally friendly reflow process.