Investigating the Fine Microstructure of Mn-doped SnAgCu Solder Alloys by Selective Electrochemical Etching

In our research the fine microstructure was compared between manganese-doped SnAgCuand traditional SAC305 (Sn96.5/Ag3/Cu0.5) solder alloys. The composition of the manganese-doped alloys was (Sn/Ag0.3/Cu0.7/Mn-x), where x is 0.1, 0.4, 0.7% wt%Solder bumps were prepared on FR4 testboards with reflow soldering technology. After the soldering, cross-sections of the samples were prepared and were investigated by Scanning Electron Microscopy. Backscattered Electrons detector was utilised and EDX (energy-dispersive Xray spectroscopy) analysis were performed. Samples were etched with selective electrochemical etching in order to reveal the fine microstructure of the samples prepared from the conventional and from manganese-doped SAC alloys. It was found that precipitates with relatively high Mn formed in the solder joint, which can influence the mechanical properties of the solder bulk. The manganese altered the formation of Cu-Sn intermetallic compounds, which were formed in very sharp, needle-like structures Additionally, particle-type Ag3 Sn intermetallic compounds readily formed next to the Mn precipitates; they are not distributed uniformly in the solder bulk at all.