The effect of substrate surface roughness on the wettability of SAC237 (Sn 99.9%, Ag 0.3%, Cu 0.7%) with difference percentage of CNT on copper substrate was investigated. Solder paste of SAC 237 without CNT, 0.01% and 0.04% of CNT were reflowed at 270°C on different surface roughness of Cu substrate (abrasive number 240, 400, 600, 800). Contact angle of soldered samples measured by Infinite Focus Microscope (IFM). As a result, contact angle value of investigated solders range 7° to 20°. Contact angle obtained decreases with the increasing surface roughness of Cu substrate. This demonstrates that rougher substrate enhance the wettability of the solders. Addition of CNT also effects the wettability of investigated solders. Higher composition of CNT show better wettability.

Wettability of Pb-free soldered surface is one of the main solderability classifications. The aim of this study is to investigate the effect of various percentages of carbon nanotube (CNT) loading (0 -4%) on the wettability of solder paste SAC 237 and different substrates namely copper (Cu) and tin (Sn). The influence of surface roughness on the wetting behaviour was also studied. Both substrates were undergone a mechanical abrasion process by using four different grit sizes (P240 , P400, P600 and P800) before performing the reflow soldering process using a reflow oven at a temperature of 180°C for 13 minutes. The surface roughness of the substrates was characterized by using a profilometer. Meanwhile, wettability tests were performed by using the optical microscope. Both substrates have shown similar behaviour; the rougher surface gives better wettability compared to the smoother one. The wettability of SAC 237 is not significantly affected by the addition of various percentages of CNT. However, CNT loading in the solder paste has shown the different wetting behaviour for both substrates.