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January 2017 • SMT Magazine 57 waves (1 min, 20 kHz) were applied to the Pd plated specimens to detect the low adhesion points. The surface of the Pd plated specimens before and after applying ultrasonic waves was observed using a scanning electron microscope (SEM). The cross section of these specimens was observed using a transmission electron micro- scope (TEM). Growth of IMCs depending on Pd Film Thickness The growth of the IMCs, corresponding to different Pd film thicknesses, was observed us- ing an SEM, and the composition of the IMCs was analyzed by energy dispersive X-ray spec- troscopy (EDX). Results and Discussion Results of High-Speed Solder Ball Shear Test The influence of electroless Pd film thick- ness on solder ball joint reliability was investi- gated. The results of the high-speed solder ball shear test are shown in Figures 4 and 5. Almost all the samples with electroless Ni/Au film (Fig- ure 4a) showed brittle fracture in each evaluated condition. The solder joint reliability with the electroless Pd film having a thickness of 0.01– 0.03 µm was higher than that with the electro- less Ni/Au films. In the case of electroless Pd films with thickness more than 0.3 µm, the per- centage of ductile fracture mode failures (Mode A) decreased with increasing number of reflow cycles and higher Pd film thickness. The reli- Figure 3: Classification of the fracture mode for solder ball shear test. (a) Mode A: Solder residual rate 100%; (b) Mode B: Solder residual rate 50~99%; (c) Mode C: Solder residual rate 10~49%; (d) Mode D: Solder residual rate 0~9%. Figure 4: Dependence of fracture modes on Pd thickness. Shear speed: (a) 20 mm/s, (b) 200 mm/s, (c) 500 mm/s. Figure 5: Dependence of fracture modes on Pd thickness. Shear speed: (a) 20 mm/s, (b) 200 mm/s, (c) 500 mm/s. SOLDER BALL JOINT RELIABILITY WITH ELECTROLESS NI/PD/AU PLATING