Boron Nitride Nanotubes Modified on a Lead-Free Solder Alloy for Microelectromechanical Packaging

In this study, we have investigated the role of boron nitride nanotubes (BNNTs) on the microstructural and interconnection reliability of a Sn–3.0 wt % Ag–0.5 wt % Cu (SAC305) lead-free solder alloy for microelectromechanical (MEMS) packaging. The BNNT was added in different fractions (0, 0.03, 0.1, 0.2, 0.4, and 0.6 wt %) to a SAC305 molten bath by manual mixing and melting to fabricate a BNNT-decorated SAC305 alloy (B-SAC). We evaluated the effects of BNNTs on the grain morphology, intermetallic compound (IMC) thickness, wetting, and spreading of the SAC305 matrix. The resultant B-SAC alloy was applied to join a 1608 chip to a flip-chip MEMS package, and the joint shear strength of the 1608 chip/Cu pad was studied. The results showed that the B-SAC alloy with 0.4 wt % BNNTs demonstrated finer grains and IMC thickness, a maximum spreading ratio (SR) of 94.08%, least zero-cross time of 0.5 s and surface tension of 224 mN/m, and the highest wetting force (6.95 mN) compared to the pristine SAC305 alloy due to the adsorption of BNNTs into the SAC305 matrix and increment in material fluidity. The joint shear strength of the 1608/Cu pad of the MEMS package also showed maximum improved shear strengthening and fracture energy in B-SAC alloys.