123697.fig.002a
(a)
123697.fig.002b
(b)
123697.fig.002c
(c)
123697.fig.002d
(d)
Figure 2: Solder wetting process: (a) SAC305 solder on the Cu substrate, (b) liquid solder spreading over the Cu substrate during soldering, (c) Cu diffuse in the liquid solder, and (d) Cu reacting with the liquid solder to form an intermetallic compound layer.