There are different ways to test the solderability of solders to the coated conductor surfaces. In our lab, we have established a set-up to study the solderability of various solders using a standard qualitative testing method, IPC/ECA J-STD-002C. More information about this standard can be found at the IPC website. While the test is normally used to verify that the solderability of electrical component leads and terminations meets the requirements established by the standard, it can be easily carried out to compare the solderability of different solders to the 2G wires. In the test, a solder pool is kept at a temperature about 30 °C ~ 50 °C higher than the melting point of the solder. This setting of the testing temperature is different from what exactly required by the standard but closer to the condition for soldering coated conductor tapes. The coated conductor tape is immersed into the molten solder and then slowly withdrawn out of the solder pool. After the solidification of the solder, the surface morphology is observed under an optical microscope and the solderability is evaluated and compared according to specific criteria. Shown in the figure below are some of the surface optical microscopic graphs of the solderability test samples. The width of each image is such that it exactly covers the width of the tape which is about 4 mm.
a. 52In48Sn/Kester135/344B b. 52In48Sn/260HF/344B
c. 100In/Kester135/344B d. 100In/260HF/344B
e. 67Bi33In /Kester135/344B f. 67Bi33In /260HF/344B
g. 100In/SP44/SCS4050 h. 60Sn40Pb/SP44/SCS4050
Figure 1. Surface optical microscopic graphs of the solderability test samples.