Influence of electroless PD plating film thickness on solder ball joint reliability

We investigated the influence of Pd film thickness in electroless nickel/electroless palladium/immersion gold (ENEPIG) plating on the intermetallic compound (IMC) growth and the solder joint reliability (SJR). We found that (Cu, Ni, Pd)
₃
Sn and (Cu, Ni, Pd)Sn
₄
IMCs were formed during the diffusion of Pd into the solder and two shapes of (Cu, Ni, Pd)
₆
Sn
₅
IMCs, which depend on the Pd plating film thickness, were formed at interface of Ni and solder. In the case of thin Pd plating films (0.1-0.2 μm), thin layers of (Cu, Ni, Pd)Sn
₄
IMCs were formed during the diffusion of Pd into the solder, and the shape of (Cu, Ni, Pd)6Sn5 IMCs was dendritic. On the other hand, in the case of thick Pd plating films (0.5-0.8 μm), thick (Cu, Ni, Pd)Sn
₄
IMCs were formed during the diffusion of Pd into the solder, and the shape of (Cu, Ni, Pd)6Sn5 IMCs was planar. We concluded that the thickness of (Cu, Ni, Pd)Sn4 IMCs affected the shape of (Cu, Ni, Pd)
₆
Sn
₅
and the SJR. The excellent SRJ is caused by the dendritic shape of (Cu, Ni, Pd)
₆
Sn
₅
IMCs and the poor SRJ is caused by the planar shape of (Cu, Ni, Pd)
₆
Sn
₅
IMCs.