Bonding Strength between Al–Wires and Ni–P Plated Lead Frames

Influences of surface roughness, hardness, surface cleanliness and phosphorous concentrations of Ni plated films on bonding strength have been investigated to clarify controlling factors for bonding between Al wires and Ni plated lead frames.It was found that surfaces of Ni plated films become smoother with higher additions of phosphorous above 9 mass%. Smoothness greatly enhances the shear strength of wire bonds. However, excessive oxidation of the surfaces of Ni plated films degrades bondability with Al wires. On the other hand, hardness of Ni plated films has hardly any effect on the bonding strength. The interface between Al wires and Ni–P plated films shows a high metallurgical stability during aging below 523 K up to 7200 ks. The oxidation and roughness of surfaces of Ni–P plated films should be kept at a minimum to maintain bondability with Al wires.