Mechanical and electrical properties of joints between stranded Ag-plated Cu conductors and Ag-plated Kovar interconnectors are crucial for the reliability and energy efficiency of space solar arrays. Parallel gap resistance welding (PGRW) is a conventional approach for fabricating the welds. However, the PGRW involves two critical issues, namely underheated wire-interconnector interfaces and overheated wires, which narrowed the weld lobe and resulted in unsatisfying joint properties. In this study, an indirect resistance spot welding (IRSW) with a redesigned electrode system was developed to address the issues. By the IRSW, 80% enlargement in the weld lobe and 18% reduction in joint resistance were achieved. The two processes regarding interfacial microstructure and thermal behaviors were comparatively investigated to understand the fundamental mechanism behind the advancements. Compared with the PGRW, the IRSW elevated the temperature history at the wire-interconnector interface, which reinforced the interfacial bonding by transforming the sold-state diffusion bonding to brazing. The IRSW decreased the temperature of the upper wires while uniformizing the temperature among the multi-layered wires (e.g. the peak temperature gap between the upper and low wires was narrowed from 118℃ to 15℃), which inhibited the formation of high-resistivity Ag-Cu solid solution. The process also reduced the temperature at the heat-affected zone of wires, which suppressed the softening. The key to achieving high-quality micro welds between Ag-plated Cu conductors and Ag-plated Kovar interconnectors was to obtain brazing-based interface bonding while suppressing alloy behavior through uniformized electric and thermal fields.

中文翻译：

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重新设计的电极系统对绞合导体与互连器电阻微焊接界面微观结构和热行为的影响

绞合镀银铜导体和镀银可伐互连器之间接头的机械和电气性能对于空间太阳能电池阵列的可靠性和能源效率至关重要。平行间隙电阻焊 (PGRW) 是制造焊缝的传统方法。然而，PGRW 涉及两个关键问题，即电线互连接口过热和电线过热，这会导致焊缝变窄并导致接头性能不令人满意。在本研究中，开发了一种具有重新设计的电极系统的间接电阻点焊（IRSW）来解决这些问题。通过IRSW，焊缝扩大了80%，接头电阻降低了18%。对界面微观结构和热行为的两个过程进行了比较研究，以了解这些进步背后的基本机制。与PGRW相比，IRSW提高了导线-互连器界面处的温度历史，从而通过将固态扩散键合转变为钎焊来增强界面键合。IRSW降低了上层导线的温度，同时使多层导线之间的温度均匀化（例如上下层导线之间的峰值温度差距从118℃缩小到15℃），从而抑制了高电阻率Ag的形成-Cu固溶体。该工艺还降低了线材热影响区的温度，从而抑制了软化。在镀银铜导体和镀银可伐互连器之间实现高质量微焊接的关键是获得基于钎焊的界面结合，同时通过均匀的电场和热场抑制合金行为。