Model of the absorption variation during pulsed laser heating applied to welding of electronic Au/Ni-coated Cu-leadframes

Absorption is an essential mechanism during laser materials processing, affecting the process efficiency and reliability, but is studied little due to its complex nature. A mathematical model was developed to calculate the absorptivity and the resulting temperature field as a function of space and time during pulsed laser heating of a plane surface, based on modelling the temperature dependence of the absorptivity, here for Au/Ni-galvanized Cu-substrate as an electronic material. For this extremely reflecting case, the absorptivity can increase by a factor of seven during the process. Beside sensitivity analysis of process parameter variations, a process theory can be stated for a variety of effects like the absorption dependence on surface pollutions, diffusion of the coating during melting, acceleration of heating during melting, saturation when the melt exceeds the beam size and onset of evaporation, etc.