Dielectric studies of solder paste fluxes and applications to no-clean paste formulations

Ionic mobility is monitored using a 12.5-μm interdigitated electrode to monitor conductivity, loss factor, and permittivity of solder flux, solder vehicle, and solder residue. Maximum ionic mobility is achieved at the temperature for minimum viscosity (87°C) and other increases can be seen at the melting point of abietic acid. Ionic mobility is shown to be dependent on the amount of plasticizer in the resin material which is correlated to the material´s glass transition and viscosity. Differences in the particle size of metal particles in neat solder pastes have been correlated to the permittivity in this system. Measurements were made using a ceramic sensor with a 10-mil interdigitated electrode pattern. A linear relationship between particle size/relative surface area of the metal particles and permittivity has been observed. Flocculation has been observed by this method in pastes containing small particle size metal particles