Wire-bonding technology is the most commonly used chip interconnection technology in microelectronic packaging. Metal bonding wire is the key material for wire bonding and plays an important role in the reliability of electronic devices. In recent years, palladium-plated copper (PdCu) bonding wire has been widely used because of its low cost, good electrical and thermal conductivity, the fact that it is not easy to oxidize, and its high reliability. Therefore, it is necessary to review its research progress. In this paper, the preparation and application of palladium-plated copper bonding wire are reviewed. Firstly, the preparation methods of electroplating, electroless plating, and direct plating are introduced. Secondly, the factors affecting the distribution of Pd in free air balls and bonding interfaces, the effect of Pd on the formation and growth of intermetallic compounds in PdCu wire, stitch bond, and reliability of PdCu wire are summarized and analyzed in the application process. Finally, its development prospect is prospected. Hopefully, this review can help readers to have a comprehensive understanding of the preparation and application of palladium-plated copper bonding wires, and can accelerate the promotion of its application in more fields in the future.

In this paper, three Pd-coated Cu (PCC) wires with different Pd-layer thicknesses were used to make bonding samples, and the influence of Pd-layer thickness on the reliability of bonded points before and after a high-temperature storage test was studied. The results show that smaller bonding pressure and ultrasonic power lead to insufficient plastic deformation of the ball-bonded point, which also leads to small contact area with the pad and low bonding strength. Excessive bonding pressure and ultrasonic power will lead to ‘scratch’ on the surface of the pad and large-scale Ag spatter. The wedge-bonded point has a narrowed width when the bonding pressure and ultrasonic power are too small, and the tail edge will be cocked, resulting in false bonding and low strength. When the bonding pressure or ultrasonic power is too large, it will cause stress concentration, and the pad will appear as an ‘internal injury’, which will improve the failure probability; a high-temperature environment can make Cu-Ag intermetallic compounds (IMCs) grow and improve the bonding strength. With the extension of high-temperature storage time, the shear force of Pd100 gradually reaches the peak and then decreases, due to Kirkendall pores caused by excessive growth of IMCs, while the shear force of Pd120 continued to increase due to the slow growth rate of IMCs. In the high-temperature storage test, the thicker the Pd layer of the bonding wire, the higher the bonding strength; in the cold/hot cycle test, the sample with the largest Pd-layer thickness has the lowest failure rate. The thicker the Pd layer, the stronger its ability to resist changes in the external environment, and the higher its stability and reliability.

Federated heavy hitter analytics enables service providers to better understand the preferences of cross-party users by analyzing the most frequent items. As with federated learning, it faces challenges of privacy concerns, statistical heterogeneity, and expensive communication. Local differential privacy (LDP), as the de facto standard for privacy-preserving data collection, solves the privacy challenge by letting each user perturb her data locally and report the sanitized version. However, in federated settings, applying LDP complicates the other two challenges, due to the deteriorated utility by the injected LDP noise or increasing communication/computation costs by perturbation mechanism. To tackle these problems, we propose a novel target-aligning prefix tree mechanism satisfying ε-LDP, for federated heavy hitter analytics. In particular, we propose an adaptive extension strategy to address the inconsistencies between covering necessary prefixes and estimating heavy hitters within a party to enhance the utility. We also present a consensus-based pruning strategy that utilizes noisy prior knowledge from other parties to further align the inconsistency between finding heavy hitters in each party and providing reasonable frequency information to identify the global ones. To the best of our knowledge, our study is the first solution to the federated heavy hitter analytics in a cross-party setting while satisfying the stringent ε-LDP. Comprehensive experiments on both real-world and synthetic datasets confirm the effectiveness of our proposed mechanism.

The full-discretization method introduced by Ding has high computational efficiency without loss of any numerical precision regardless of low and high radial depth of cut for the stability analysis of ordinary milling operation in time domain. Contrast to ordinary milling, it exists the separation phenomenon between each cutter tooth and the workpiece in feed ultrasonic milling operation. So before analyzing the system stability by the full-discretization method, the contact state between the cutter tooth and the workpiece should be made clear. In this paper, the trajectory method is proposed by the authors to judge the contact state between the cutter tooth and the workpiece. The stability analysis is developed for separated feed ultrasonic and ordinary end milling operations by the above methods and is validated via time domain simulations and experiments for both operations. The analyses show excellent agreement with both the time domain simulations and the experiments. Further, several end milling experiments were conducted that demonstrate the result ultrasonic vibration in feed direction can suppress chatter in machining operations.