The Effect of Reflow Time on Intermetallic Compound in Lead-Free Micro-Joining Joint

The growth behavior and the morphology of IMCs at the Sn-3.0Ag-0.5Cu/Cu interface were investigated firstly. Then the effect of reflow time on IMCs during reflow soldering was also studied in detail. The reflow time was 15s, 30s, 60s, 120s, 240s and 360s respectively. The scanning electron microscope (SEM) was utilized to observe the microstructure of solder joint and the alloy layer in interface of solder and Cu substrate. In order to survey component and distribution of IMCs, the X-ray energy dispersion spectrometer (EDS) was employed to do qualitative analysis and quantitative analysis of observed IMCs. The results show that, in all different reflow times, the obvious IMCs was observed at interface and the various morphology IMCs were also found in solder joint. With increasing of the reflow time, the morphology of IMCs changed gradually from long needle-like to scallop-like, and the quantity and the thickness of IMCs were always increasing. The effect of the reflow time on the serrated height of IMCs was not monotonous, that was from high to low then to high again, but the mean thickness of IMC layer was elevating at all times. In addition, it was observed that the great deal of kirkedall voiding existed at the interface between Cu substrate and Sn-Ag-Cn solder. The qualitative analysis and quantitative analysis by EDS show that there was a layer of Cu-Sn alloy in which the concentration of Cu lower from the Cu substrate to the solder. The study on the formation of IMC and voiding will also be discussed in the future