Microstructure of lead-free solder bumps using laser reflow soldering

Abstract

Compared with conventional reflow soldering using a furnace, laser reflow soldering brings advantages such as localized heating, rapid rise and fall in temperature, non-contact soldering and the fact that it is an easily automated process. In this study, to elucidate the characteristics of laser reflow soldering, we investigated the microstructures of a Sn-Ag-Cu solder bump and a Sn-Bi solder bump on a Cu pad after reflow and aging. In the as-soldered condition, we found obvious microstructural refinement and a thin intermetallic compound (IMC) layer at the interface for both the Sn-Ag-Cu solder bump and the Sn-Bi solder bump using laser reflow soldering. Also, during isothermal aging, the total thickness of the IMC layer increased, and a distinct second layer was observed at the interface between the Cu pad and the first layer, regardless of the soldering method. In particular, the growth of the IMC layer was faster in the case of the laser reflow soldering than in the case of the conventional reflow soldering.