Modified wetting balance set-up for the evaluation of lead-free solder / flux / metallization systems

This paper presents experimental investigations of wettability on lead-free solder/flux/solid metallization combinations obtained under nitrogen atmosphere. An adapted testing method is applied where fluxed samples are preheated. A commonly performed wetting balance testing method is explained in principle and the measurement system modifications as well as the adapted experimental procedures being performed are discussed in detail. Lead-free tin-silver alloy Sn₉₆ Ag and a copper doped Sn₉₆Ag_3.5Cu solder have been considered for testing in combination with five different widely employed FR4-metallization finishes and three Ag-based thick film conductor pastes. Selected solder bath temperatures cover the range from 240degC up to 260degC. One conventional RMA-type flux and two low solid no-clean fluxes have been provided for promoting the wetting tests. The effect of sample preheating varying within the range from 85degC to 115degC is investigated. Results are compared to conventional lead bearing material systems