The laser impulse metal bonding (LIMBO) process is a novel laser spot welding process to form a weld joint between a massive interconnector and thin metallization on a thermally sensitive substrate. As for the LIMBO process, the gap between joining partners in overlap configuration allows energetic separation of the melting and joining processes, whereas the underlying joining partner is only thermally stressed during the welding process. The LIMBO process shows, therefore, potential to substitute the ultrasonic wire bonding and the soldering process for joining interconnectors on metallized substrates such as direct bonded copper or PCB. Due to a separation between joining partners, the LIMBO process is divided into three stages that are achieved with temporal pulse modulation. The initial stage prepares a melt pool on an upper joining partner which penetrates through the material. After achieving a local melt pool through the upper joining partner, the temporal intensity modulation of the laser beam is initialized for the second stage. The enhanced laser beam intensity on the melt pool surface vaporizes the melt surface rapidly and induces a recoil metal plume. Hence, the recoil metal plume pressure accelerates the melt toward the underlying joining partner. After the contact, further energy input is required for the last stage to melt the underlying joining partner and subsequently to form a weld. Therefore, the laser beam intensity is once again temporally modulated to lower the intensity value. In this paper, the LIMBO process is extended with a further stage which combines spatial and temporal pulse modulation. From the outgoing position from the last stage of the LIMBO process, the laser beam is spatially modulated to perform a circular movement around the weld joint. Therefore, the spatial pulse modulation allows us to overcome the limitation of the spot welding process. In combination with temporal pulse modulation during the circular movement, the weld joint is expanded continuously. During the extended stage, the accessed heat is also considered, so the thermal threshold of the sensitive substrate is not exceeded. In addition, the overlap pulsed welding process is applied with the extended LIMBO process to achieve a linear weld joint area.

中文翻译：

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激光脉冲金属键合工艺的空间和时间脉冲组合调制技术的发展

激光脉冲金属键合（LIMBO）工艺是一种新颖的激光点焊工艺，用于在大型互连器和热敏基板上的薄金属化层之间形成焊接接头。对于LIMBO工艺，搭接结构中的连接伙伴之间的间隙允许熔化和连接过程进行有力的分离，而下面的连接伙伴仅在焊接过程中受到热应力。因此，LIMBO工艺显示出替代超声波引线键合和焊接工艺的潜力，该工艺可以将互连器连接到金属化基板（例如直接键合铜或PCB）上。由于连接伙伴之间的分离，LIMBO过程分为三个阶段，这三个阶段可通过时间脉冲调制实现。初始阶段在上连接伙伴上准备熔池，该熔池穿透材料。通过上连接伙伴达到局部熔池后，在第二阶段初始化激光束的时间强度调制。熔池表面上增强的激光束强度使熔体表面快速蒸发，并产生反冲金属羽流。因此，后坐金属羽流压力使熔体朝着下方的连接伙伴加速。接触后，最后一步需要进一步的能量输入，以熔化下面的连接伙伴并随后形成焊缝。因此，再次临时调制激光束强度以降低强度值。在本文中，将LIMBO过程扩展到一个进一步的阶段，该阶段结合了空间和时间脉冲调制。从LIMBO过程的最后阶段的出射位置开始，对激光束进行空间调制，以在焊缝周围进行圆周运动。因此，空间脉冲调制使我们能够克服点焊工艺的局限性。结合圆周运动期间的瞬时脉冲调制，焊缝不断扩展。在扩展阶段，还会考虑访问的热量，因此不会超过敏感基板的热阈值。此外，重叠脉冲焊接工艺与扩展的LIMBO工艺一起使用，以实现线性焊接接头区域。空间脉冲调制使我们能够克服点焊过程的局限性。结合圆周运动期间的瞬时脉冲调制，焊缝不断扩展。在扩展阶段，还会考虑访问的热量，因此不会超过敏感基板的热阈值。此外，重叠脉冲焊接工艺与扩展的LIMBO工艺一起使用，以实现线性焊接接头区域。空间脉冲调制使我们能够克服点焊过程的局限性。结合圆周运动期间的瞬时脉冲调制，焊缝不断扩展。在扩展阶段，还会考虑访问的热量，因此不会超过敏感基板的热阈值。此外，重叠脉冲焊接工艺与扩展的LIMBO工艺一起使用，以实现线性焊接接头区域。