We investigated the influence of Pd film thickness on the intermetallic compound (IMC) growth and the solder joint reliability (SJR) in electroless nickel/electroless palladium/immersion gold (ENEPIG) plating. With thin Pd plating films (0.1–0.2 μm), thin layers of (Cu, Ni, Pd)Sn₄ IMCs were formed during the diffusion of Pd into the solder, and the shape of the (Cu, Ni, Pd)₆Sn₅ IMCs was dendritic. On the other hand, with thick Pd plating films (0.5–0.8 μm), thick (Cu, Ni, Pd)Sn₄ IMCs were formed during the diffusion of Pd into the solder, and the shape of the (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)₆Sn₅ and the SJR. Excellent SRJ is associated with dendritic (Cu, Ni, Pd)₆Sn₅ IMCs and poor SRJ is associated with the planar shape of (Cu, Ni, Pd)₆Sn₅ IMCs.

A printed wiring board manufactured using the semi-additive method (SAP) was subjected to a constant voltage application test under constant temperature and humidity, and AC impedance measurement, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX) analysises were performed.

From the results of the AC impedance measurement, we found that the printed circuit board has three resistance components.

It is suggested that the resistance components are derived from the insulator of the printed wiring board, the surface state of the wiring, and the chemical reaction that occurs on the wiring.