Formation of Ni3Sn4 at the boundary between Sn-Pb soldering layers and Au/Ni plated coatings

Ni3Sn4 formation should affect the reliability of soldering between package and printed circuit board. We have investigated the formation of the Ni3Sn4 at the boundary between Sn-Pb soldering layers and electro-, or electroless plated Au/Ni coatings. In the case of Sn-Pb solders, the shapes of Ni3Sn4 intermetallic compounds (IMC), which was formed at the boundary between the solder and Ni plated coatings, were shown to have many differences between them. We discovered that the shape of Ni3Sn4 would be controlled by p content of Ni-P plated coatings, the Pb content in the soldering layers, and the thickness of immersion Au plated coatings. Under the specific conditions, the shape of Ni3Sn4 using the electroless Au/Ni plating would become to be similar to the electroplated Au/Ni, then the reliability of solder joint could be higher.