Method for controlling the formation of intermetallic compounds in solder joints

A method for controlling the formation of intermetallic compounds in solder joints, comprising:

• providing a substrate having a nickel-bearing pad;
• forming a SnAgCu solder on the nickel-bearing pad;
• and
• performing a reflow process to the SnAgCu solder and the nickel-bearing pad, so that the SnAgCu solder reacts with the nickel-bearing pad to form a soldering intermetallic compound, wherein if the SnAgCu solder has a copper concentration between 0.6 wt. % to 3.0 wt. % (including 0.6 wt. %), the soldering intermetallic compound includes a continuous (Cu1−xNix)6Sn5 layer, wherein if the copper concentration of the SnAgCu solder is between 0 wt. % to 0.4 wt. % (including 0.4 wt. %), the soldering intermetallic compound includes a continuos (Ni1−yCuy)3Sn4 layer and a non-continuous (Cu1−xNix)6Sn5 layer, and wherein if the copper concentration of the SnAgCu solder is between 0.4 wt. % to 0.6 wt. %, the soldering intermetallic compound includes the continuous (Cu1−xNix)6Sn5 layer and the continuous (Ni1−yCuy)3Sn4 layer.