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January 2017 • SMT Magazine 61 SOLDER BALL JOINT RELIABILITY WITH ELECTROLESS NI/PD/AU PLATING The cross-sectional views of the IMCs for var- ious Pd thicknesses and reflow cycles are shown in Figure 13. In the case of 0.1 µm thick Pd film, the size of the dendrite layers of IMCs increased with increasing number reflow cycles. We con- sidered that the high adhesion at the dendrite layers of IMCs/solder interface resulted in an excellent joint after multiple reflow cycles. In the case of 0.5 µm thick Pd film, the IMC phase growth showed a more planar morphology after multiple reflow cycles. The poor adhesion at the plane IMCs/solder interface may be the reasons for the decrease in solder joint reliability. (2) Influence of Thermal Aging The level of reliability of the solder ball joint with a 0.1 µm thick electroless Pd film (Figure 4f) was better than that obtained with a 0.03 µm thick electroless Pd film (Figure 4d) after 1000 h of thermal aging. Therefore, the root cause of excellent solder joint reliability with a 0.1 µm thick electroless Pd film after thermal aging was investigated. The cross section and surface morphology of the IMCs after thermal aging were observed with 0.03 µm and 0.1 µm thick Pd films. The results are shown in Figure 14. The IMC phase growth after thermal ag- ing showed a more planar morphology than that after multiple reflow cycles. The IMC lay- ers with 0.1 µm thick Pd film were thinner than those observed in the joints with 0.03 µm thick Pd film. The composition of the IMCs with 0.03 Figure 11: Cross-section of IMCs depending on Pd thickness and reflow cycles. Figure 12: Cross-section and surface morphology of IMCs after reflow cycles with 0.1μm and 0.5 μm thick Pd films. Figure 13: Cross sectional models of the IMCs depending on Pd thickness and reflow cycles.