Surface Engineering and Applied Electrochemistry最新文献

Wire bonding remains a primary method for assembling integrated circuits and micromodules due to its high process automation and versatility across manufacturing technological options, as well as the geometric dimensions of the products. Significant progress has been made in the development of interconnection methods in integrated electronic devices, mitigating the complexity of these operations and notable successes towards their full automation. Various processes such as thermocompression bonding, ultrasonic (US) bonding, and thermo-ultrasonic bonding during the assembly of integrated circuits and micromodules are extensively examined. The characteristics of automatic equipment for bonding, along with the peculiarities of the tools employed, are provided for comprehensive understanding. In ultrasonic bonding, mechanical vibrations of ultrasonic frequency are introduced into the contact zone, resulting in the plastic deformation of the wire lead and the removal of oxide films, thereby creating atomically clean juvenile surfaces. This process intensifies the formation of active centers during the bond formation without significant wire deformation or substantial heating. Thermo-ultrasonic bonding involves the combined action of ultrasonic energy, tool loading force, and heating temperature up to 200–220°C. This combination enhances the reproducibility of bond quality and eliminates sensitivity to variations in the properties of the materials being bonded, leading to more consistent and reliable results.

This chapter explores the evolving trends in contemporary electronic module designs and assembly technologies. The enhancement of computer technology and digital communication tools, coupled with the escalation in the operational speed of the elemental base, hinges directly on the reduction of signal transmission length between logical elements, i.e., the constructive delay of the transmitted signal. Interconnection technology, crucial for bridging the microcosm of semiconductor chips with the external world of electronic devices, emerges as pivotal for producing viable products. We provide a comprehensive classification and discussion of assembly connection designs, employing methods involving direct material contact under the influence of pressure, heat, and physical impact in various combinations. Intermediate materials such as solder, microwires, and conductive adhesives are utilized in these processes. Special emphasis is placed on surface mounting of electronic components, COB assembly technology, Flip Chip, BGA, and the assembly of multichip electronic modules.

This chapter delineates detailed methods and tools for the visual inspection of soldered joints. It enumerates the primary types of defects and the capabilities of automatic visual and electrical inspection for their detection and highlights the use of automatic equipment for thermographic, acoustic, and X-ray inspection of soldered and microsoldered joints. The methodology for monitoring transient electrical resistance in contact connections is also examined. For automatic electrical inspection of connections, systems equipped with flying probes are used. These systems supply power and receive signals from the inspected connection on the board or component, automatically verifying functionality. The criteria for assessing the strength of soldered joints include the magnitude of the pull-off force, the durability of the joints under alternating loads, and vibration resistance. Destructive testing is employed to ascertain the mechanical and physico-mechanical properties of soldered joints. In metallographic inspection, the diffusion zone between the solder and the base metal is identified, and the quality of the soldered joint is assessed based on its width. Typical defects of soldered joints and their causes are considered.

The chapter elucidates the assortment of inter-block mounting contact connections and their corresponding implementations: crimping wires with terminals, employing elastic connections facilitated by conductive rubber, and embedding connectors onto flat cables. The integration of multilayer printed circuit boards, configured as junction panels housing robust ground and power circuits made with metal-capacitive layers, has presented considerable challenges for technologists during assembly. The massive ground and power layers act as proficient heat sinks during soldering and reflow processes, leading to the migration of heat towards these layers and consequently causing unsoldered holes. To address this issue, soldered connections have been supplanted by nonsoldered “Press-Fit” types, achieved through the application of special bulging on the contact pin, inducing elastic deformation upon insertion into the metallized hole of the board. This transition necessitates an exploration of various “Press-Fit” connections, the mechanism underlying the establishment of a nonremovable connection between the pin and the metallized hole, as well as the requisite equipment for executing this process.

The physical models of primary and secondary ultrasonic effects in liquid media are described, offering a comprehensive understanding of these phenomena. The mechanisms underlying oxide film removal and the enhancement of solder wetting on materials under the action of ultrasonic vibrations are thoroughly explored. In particular, the formation of soldered joints with nonmetallic materials in an ultrasonic field is elucidated, highlighting the activation of diffusion and chemical interaction of solder components with materials. Detailed insights into modern technological equipment and tools utilized in ultrasonic processes are provided, shedding light on their capabilities and functionalities. Furthermore, the impact of ultrasonic process parameters on the properties of contact joints is examined, offering valuable guidance for optimizing process conditions. Ultrasonic technology emerges as an environmentally friendly solution, often referred to as “green” technology, as it obviates the need for fluxes and the subsequent removal process, as well as eliminates the use of lead-containing solders. The widespread adoption of ultrasonic soldering and metallization processes is observed in Western Europe and the United States, underscoring their significance and utility in modern manufacturing practices.

The concept of solderability is rigorously defined, accompanied by the proposal of quantitative criteria for its assessment. A comprehensive categorization of solderable materials into three distinct groups—namely, easily solderable, moderately solderable, and unsolderable—is proposed based on solderability parameters. Practical recommendations are given for the effective deployment of solderability testing methodologies across a spectrum of materials and electronic components. Detailed expositions are offered on the methods employed in the evaluation of solderability, encompassing solder immersion, measurement of solder spreading area, and assessment of capillary penetration into gaps. Schematic representations of these evaluation techniques, alongside descriptions of the requisite apparatus for their implementation, are presented. Furthermore, tabulated data on the solder spreading factors for diverse categories of chemical and electroplated coatings, including hot tinning, are given. Prolonged storage may lead to the formation of oxide films on the surface of coatings, thereby deteriorating solderability. To enhance the quality of electroplated coatings, it is recommended to employ periodic currents in nonstationary electrolysis modes during the deposition of electroplated coatings.

This chapter discusses the design features of metal-glass and metal-ceramic packages for integrated circuits and microblocks, focusing on their hermetic sealing processes through soldering and welding. Modeling performed using the ANSYS Mechanical environment has revealed significant internal stress at the boundary of the lead in metal-ceramic assemblies with molybdenum metallization. To address this, the study proposes modifying the assembly design by incorporating bevels during metallization formation, which promotes a more uniform distribution of the resulting stress. For vacuum-tight joints with Kovar, parts must undergo annealing to decrease internal stress, and soldering should occur at a temperature only 20–30°C above the melting point of the solder. Before soldering, Kovar parts should be nickel-plated with a coating thickness of 10–15 µm and subsequently annealed at 950°C. To prevent the liquid phase from penetrating along the grain boundaries of Kovar, the use of gold or copper-germanium solders is recommended.

The operation of mounting chips into packages is the most critical in the technological assembly of electronic products, pivotal for ensuring precise chip positioning, robust mechanical connection, reliable electrical contact, and efficient heat dissipation. Whether accomplished through soldering with eutectic alloys or low-melting-point solders, or via bonding onto a conductive composition, chip mounting must adhere to stringent criteria: high joint strength under thermal cycling and mechanical loads, low electrical and thermal resistance, minimal mechanical stress on the chip, and the absence of contaminants. To elucidate the thermal dynamics and mechanical stress involved, a thermal model of a power transistor with a soldered chip on a chip holder is explored. This model facilitates the determination of thermal resistance and maximum mechanical stress in the chip post-cooling. Automated technological equipment for chip mounting by vibration and ultrasonic soldering is presented, as well as the peculiarities of mounting transistor chips in D-Pak and Super-D2Pak casings, and in power electronics modules. Transitioning towards mounting with rigidly organized leads necessitates the operation of forming a matrix structure of solder leads. This operation is executed through various methods, including induction heating, laser irradiation, and others, to ensure optimal performance and reliability.

The issues of selecting the frequency and power of high-frequency heating in soldering electronic modules and device enclosures are thoroughly examined. High-frequency electromagnetic energy is explored for its efficient non-contact heating capabilities, enabling rapid heating to soldering temperatures through the induction of eddy currents in the metal components and solder. Compared to convective heat sources, high-frequency heating can achieve heating rates up to 10 times faster, with the heating zone precisely localized within the area defined by the inductor design. Methods and device schematics for high-frequency soldering processes are provided, alongside descriptions of the technological equipment and fixtures utilized in these processes. Transistor generators operating at medium (66 kHz) and high frequencies (440 and 1760 kHz) have gained widespread adoption for high-frequency heating applications. To enhance the quality of solder joints and increase product yield, computer-controlled thermal profiles are essential for high-frequency soldering processes. The advantages of high-frequency heating, including locality, simplicity of design, high environmental cleanliness, and the ability to leverage electromagnetic forces for improving solder flow, make it an optimal choice for surface mounting of electronic modules. Induction devices constructed on magnetic cores are also viable for soldering power contacts, connectors, and wires to printed circuit boards, coaxial cables, and sealing metal-glass housings of integrated circuits. These applications highlight the versatility and efficacy of high-frequency heating techniques in modern electronic assembly processes.

In this chapter, we comprehensively discuss the primary varieties of solders and fluxes utilized in the fabrication of electrical connections within electronic modules. Particular emphasis is placed on the challenges associated with the use of lead-free soldering materials. A potential resolution to these challenges involves the modification of solder compositions, potentially transitioning towards nanoscale architectures. A promising avenue of exploration lies in the utilization of water-based fluxes and flux gels. Water-based fluxes containing surfactant additives offer notable advantages, particularly in their application via spray mechanisms. They exhibit robust stability and mitigate thermal shock occurrences during soldering operations. Furthermore, we delve into the characteristics of solder pastes employed in the surface mounting of electronic modules, elucidating their application methodologies, operational considerations, and optimal storage practices. Additionally, we provide a comprehensive overview of conductive adhesives utilized in the formation of contact connections. The chapter also examines the primary types of mounting microwires employed in ultrasonic and thermosonic microwelding processes, alongside outlining the role of protective liquids in the cleaning of connections.