Evaluation of Joint Resistance Between Bi-2223/Ag Superconducting Tapes
We fabricated Bi-2223/Ag jointed tape and evaluated its current carrying capacity and joint resistance at 77.3 K as a function of the contact length. The tapes were jointed by the conventional resistive joint method with 40Pb-60Sn solder as an insert material and their joint resistance was measured by two different techniques, i.e., the standard four-probe and field decay methods. It was observed that the current carrying capacity and joint resistance were significantly dependent on the contact length. As the contact length increased, the current carrying capacity improved and increased to the level of critical current in the unjoined tape at the contact length of 5 cm. On the other hand, the joint resistance linearly decreased as the contact length increased. In addition, the joint resistances measured by the two methods were similar to each other (7.3times10-9 Omega~8.0times10-9 Omega), indicating that the standard four-probe method maintained a moderate degree of accuracy at the level of resistance of 10-9 Omega
Voltage-current property of two HTS tapes connected by ordinary Sn-Pb solder
Abstract The V – I property of two HTS tapes connected by ordinary Sn–Pb solder has been studied both numerically and experimentally. Two basic joint structures: “shake hand” and “pray hand” with different overlapped length are studied. By means of a Finite Element Analysis package ANSYS, not only the entire V – I curve from 0 to 2 I c can be obtained but also the detail of current distribution along the HTS tape can be simulated. The numerical approach is based on a 2D electric field analysis, where the conductivity of the HTS material is simulated in terms of a power law E – J relation. The simulated results are compared with the experimental data obtained from the commonly used four-probe method. We found that from the energy dissipation point of view, the “pray hand” structure is more appropriate for use in the high current region.
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.