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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

14.75.6

344B

52In48Sn

Kester 135

~165

32.54.1

344B

100In

Alpha 260HF

~165

18.92.9

344B

100In

Kester 135

~165

37.53.3

344B

67Bi33In

Alpha 260HF

~150

24.85.1

344B

67Bi33In

Kester 135

~150

40.16.6

SCS4050

60Sn40Pb

Kester SP-44

~200

21.16.9

SCS4050

100In

Kester SP-44

~195

27.65.6

 

 

 

Figure 2. Examples of solder droplet images of solders on the surfaces of selected coated conductors.

 

 

 

 

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