Characterization Of Indium Based Low Temperature Solder Alloy And The Effect On Surface Finish

The increased use of electronic devices has increased the usage of solder connections. Lead, the prime solder hitherto used, is hazardous to human health and the environment. Thus, replacing Sn-37Pb with a lead-free solder is one of the most important issues in the electronics industry. As such, the characteristics of In-Bi-Sn and In-Bi-Zn compared with that of the Sn-Ag-Cu solder alloy were studied. In the differential scanning calometry analysis, In-Bi-Sn and In-Bi-Zn system alloys presented a low melting temperature of 61.3 °C and 72.3 °C, respectively. Surface tension and contact angle of In-Bi-Sn and In-Bi-Zn lead-free solder alloys were measured on Cu substrate and different surface finishes at 100, 120 and 140 °C reflow. Sessile drop measurements showed that the contact angle depended on the reflow temperature. The contact angle gradually decreased from 30.76° to 17.25° as reflow temperature increased from 100 to 140 °C and for In-Bi-Sn and In-Bi-Zn solder alloy on Cu substrate, ranged from 58° to 7° after wetting on Ni/Cu substrate at the same reflow temperature range (100 to 140°C). Energy-dispersive X-ray analysis found two layers of intermetallic compound in the In-Bi-Sn solder alloy: Cu6Sn5 and Cu11In9 (scallop shaped) and Cu11In9 (brightly coloured) with Cu and Sn/Cu substrate. The IMC between the In-Bi-Zn solder alloy could be observed: Cu5Zn8 (continuous planar) and Cu11In9, a minor IMC layer with Cu and Sn/Cu substrate. However, only one type of IMC was formed between both solders (In-Bi- Sn and In-Bi-Zn) and Ni/Cu substrate, which was InNi2. As the reflow temperature increased, the shear strength of the In-Bi-Sn and In-Bi-Zn solder alloys on Cu, Ni/Cu and Sn/Cu joints improved due to reduced contact angle and larger spreading are

Experimental Investigations of Whisker Formation on Tin Platings

With the global transition to lead-free electronics, the electronic component market has seen an increase in the selection of pure tin and tin-rich alloys as lead-free component finishes. The adoption of tin-rich finishes has enhanced a reliability issue associated with the formation of electrically conductive whiskers, emanating from tin finished surface. A spontaneous growth of whisker may bridge adjacent conductors, leading to current leakage or electrical shorts. Whiskers tend to grow over many months. However, due to a lack of the factors accelerating whisker growth, prediction of whisker formation is extremely difficult. Therefore, the effective mitigation strategies are necessary, particularly for high-reliability applications, which require a long product operational life. The objective of this study is to investigate a method for characterizing whisker growth, which can further enable measuring the effectiveness of mitigation strategies. To achieve this objective, a set of experiments was conducted using matte and bright tin platings on copper, Alloy-42, and brass metal coupons. The plated coupons were subjected to high temperature exposures, including annealing (at 150ºC/one hour). Whisker growth on tin-plated samples was characterized using environmental scanning electron microscopy, in terms of the maximum whisker length, length distribution, and whisker density, at different time periods up to 24 months. The experimental results have shown different behaviors of whisker growth (length and density) between bright and matte tin, depending on the materials and exposure conditions. It was experimentally demonstrated that bright tin over brass could be considered a worst-case scenario for assessing the risks associated with tin whiskers. This work has further revealed that the current industry practice of testing for 3000 hours for monitoring the propensity of tin whiskers is insufficient to cover a saturation of whisker density and capture the temporal nature of whiskers. In order to overcome such insufficiencies, the use of time-based distribution data for whisker length and whisker density was proposed as an alternative method for characterizing whisker growth. With the application of this proposed method, the effect of annealing (150ºC/one hour) and its effect under the presence of electrical current were investigated for retarding whisker formation and growth on tin-plating