Figure 7

(a) Bending test and (b) scratch test on solder bumps of In–Sn, In–Sn–Bi, 0.6MWCNT/In–Sn–Bi composite, and 1.2MWCNT/In–Sn–Bi composite on the flexible PET substrate after reflow at 110 °C. The straight, opaque blue lines in (b) are the baselines of each scratching test, and the difference between the above line and the baseline indicates the degree of the average adhesion strength (shear force loaded) of the solder bumps on the PET substrate. Of the insets, (c) presents the low magnification SEM image of the 0.6MWCNT/In–Sn–Bi composite solder pads, (d) presents the SEM image of In–Sn conventional solder pads where contact with some regions is missing due to external bending forces, and (e) is an image of the bending tester used. The mechanical strength (particularly the resistance against bending and shear strength) of the composite solder pads (or bumps) was significantly improved by the MWCNT reinforcement as compared to the conventional solder pads (or bumps).