Thin-film reaction with solder and its influence on stress have been investigated in Cr/Co/Au and Cr/Co/Au/Pb(Sn) structures. Results from X-ray analysis and RBS measurements reveal that without the Pb(Sn) layer the dominant reaction occurs by interdiffusion of Co and Cr followed by the reaction of Cr and Au. In contrast, the addition of the Pb(Sn) layer leads to a rapid dissolution of Au into Pb, which is followed by subsequent reaction of Co and Sn. In this reaction the intermetallic phases CoSn and CoSn2 are formed. These material reactions are correlated with measurements of the mechanical stresses of the multilayer structure during annealing which were carried out using a bending beam method. The overall reaction scheme of the multilayer structure and the individual reaction kinetics are discussed.