Contact Angles
The quality of a splice is strongly affected by the wettability of the solder used for the soldering. To study the wettability of selected solders to the surfaces of the coated conductors, a system has been established in our lab for measuring the contact angles of a molten solder droplet on a base-material using the so-called sessile drop method. A schematic of the system is shown in Figure 1. A measurement is normally carried out at a temperature 10 °C ~ 40 °C higher than the melting point (or liquidus) of the solder tested. The melting and spreading of the solder can be video taped. The images of the molten solder droplet are acquired by frame-grabber software and then analyzed for the evaluation of the wettability. A contact angle is measured at the triple line, which provides important information on the wettability of the solder on the coated conductor surface. The effects of flux usage and temperature on the wettability can also be studied. More information about the sessile drop test can be found in the book Wettability at High Temperatures, which was edited by N. Eustathopoulos et al and published by Pergamon in 1999. For selected 2G wires, contact angles for some of the solders are listed in Table 1 below with specified fluxes and testing temperatures. Figure 2 shows some of the images of the solder droplets from which the contact angles were measured.
Figure 1. Schematic of the contact angle measurement system. 1 - computer, 2 – TV, 3 – video camera, 4 – camera lens, 5 – heater, 6 – light diffuser, 7 – backlight source, 8 – substrate, 9 – solder droplet, 10 – thermocouple.
Table 1 Contact angles of selected solders on 2G wires.
|
2G Wire |
Solder |
Flux |
Testing T (°C) |
Contact Angle (°) |
|
344B |
52In48Sn |
Alpha 260HF |
~165 |
14.7±5.6 |
|
344B |
52In48Sn |
Kester 135 |
~165 |
32.5±4.1 |
|
344B |
100In |
Alpha 260HF |
~165 |
18.9±2.9 |
|
344B |
100In |
Kester 135 |
~165 |
37.5±3.3 |
|
344B |
67Bi33In |
Alpha 260HF |
~150 |
24.8±5.1 |
|
344B |
67Bi33In |
Kester 135 |
~150 |
40.1±6.6 |
|
SCS4050 |
60Sn40Pb |
Kester SP-44 |
~200 |
21.1±6.9 |
|
SCS4050 |
100In |
Kester SP-44 |
~195 |
27.6±5.6 |
Figure 2. Examples of solder droplet images of solders on the surfaces of selected coated conductors.