| abstract |
A solder joint (200) has a first contact pad (114) and a second contact pad (124) of a first metal, preferably copper, facing each other across a gap. A coat (115 and 125, respectively) of a second metal, preferably nickel, covers each pad. A layer (201) of crystals of first intermetallic compounds, such as Ni3Sn4 and (Ni, Cu)3Sn4, covers the surface of each coat. Isolated crystals (202) of second intermetallic compounds, such as Cu6Sn5 and (Cu, Ni)6Sn5, different from the first intermetallic compounds, are dispersed on top of the layer of crystals of the first intermetallic compounds. A solder alloy (203) including a third metal, preferably tin, and the first metal fills the gap. The solder alloy may further include a fourth metal, preferably selected from a group of metals including silver, zinc, and indium. |