With the advancement of technology, electronic, electrical, and digital products have become increasingly sophisticated and are gaining popularity worldwide. Any component included in the products covered by this field may involve soldering processes—ranging from large PCB board components to tiny crystal oscillator elements. The vast majority of these soldering operations need to be completed at temperatures below 300°C.
Currently, both chip-level packaging (IC packaging) in the electronics industry and board-level assembly extensively employ tin-based alloys as soldering fillers to complete device encapsulation and board assembly. For example, in flip-chip technology, the solder directly bonds the chip to the substrate; in electronic assembly manufacturing, solder is used to weld components onto circuit boards.
Soldering processes include wave soldering and reflow soldering. In wave soldering, the soldering process is carried out by bringing the surface of a continuously flowing wave of molten solder into contact with the soldering surfaces of a PCB that has components inserted into it. In reflow soldering, solder paste or soldering clips are pre-placed between the PCB pads; after heating, the components are joined to the PCB as the solder paste or soldering clips melt.
Laser soldering is a brazing method that uses a laser as the heat source to melt solder, thereby achieving a tight fit between the workpieces.
Compared to traditional soldering processes, this method features rapid heating, low heat input and minimal thermal impact; precise control over the welding position; automated welding process; accurate control of solder quantity, ensuring high consistency in solder joints; significantly reduced exposure of operators to volatile substances during soldering; non-contact heating; and suitability for welding parts with complex structures.
Laser soldering uses a laser as the primary heat source to melt and solidify solder material, achieving the desired effects of joining, conducting electricity, and reinforcing the connection. Based on the state of the solder material, it can be categorized into three main forms: solder wire filling, solder paste filling, and solder ball filling.
Laser soldering application with tin wire filling
Wire-feeding laser welding is a major form of laser soldering. The wire-feeding mechanism is used in conjunction with an automated workbench and employs modular control to achieve automatic wire feeding and laser beam emission for welding. This method features a compact structure and the ability to perform operations in a single step. Compared to other soldering methods, its distinct advantage lies in the fact that it allows for one-time clamping of materials and automatic completion of the welding process, making it highly versatile.
The primary application areas include soldering of PCB circuit boards, optical components, acoustic components, semiconductor cooling components, and other electronic components. Figure 1 shows a laser wire-feed soldering product; as you can see, the solder joints are well-filled and exhibit excellent wetting on the pads.
Solder Paste Filling Laser Soldering Application
Laser soldering with solder paste is typically used for reinforcing components or pre-applying solder, such as reinforcing the edges and corners of shielding covers by melting solder paste at high temperatures, or melting solder onto magnetic head contacts.
It is also suitable for soldering conductive circuits and delivers excellent results when soldering flexible circuit boards—for example, plastic antenna mounts. Since these components do not involve complex circuitry, soldering with solder paste often achieves very good outcomes. For precision, miniature components, solder paste filling soldering fully demonstrates its advantages.
Due to the relatively uniform heating of solder paste and its relatively small equivalent diameter, precise control of tiny solder-dot volumes is achievable using advanced dispensing equipment. As a result, the solder paste is less likely to splash, ensuring excellent soldering performance.
Due to the highly concentrated laser energy, solder paste can experience uneven heating, leading to cracking and spattering. The splashed solder beads are prone to causing short circuits. Therefore, the quality of solder paste must be extremely high; anti-splash solder paste can be used to prevent such spattering.
Solder Ball Filling Laser Soldering Application
Laser solder ball welding is a soldering method in which solder balls are placed into solder ball nozzles, then melted by laser heating and allowed to fall onto the solder pads, where they wet and bond with the pads.
Tin balls are small, pure tin particles that are uniformly dispersed. After being melted by laser heating, they do not cause spattering. Once solidified, they have a full and smooth surface, eliminating the need for subsequent cleaning or surface treatment processes on the solder pads.
Using this welding method, it is possible to achieve excellent soldering results when welding small pads and enameled wires.
Challenges in the Application of Laser Soldering Technology
Traditional soldering techniques—including wave soldering, reflow soldering, and manual soldering with a soldering iron—can address most soldering challenges. Laser soldering can gradually replace these conventional methods. However, for soldering technologies such as surface-mount soldering (primarily reflow soldering), laser soldering technology is currently not yet suitable. Moreover, certain inherent characteristics of lasers themselves make laser soldering processes more complex. Specifically, these complexities can be summarized as follows:
1) For precision and fine soldering with tin, it is difficult to accurately position and clamp the workpieces, and both prototype fabrication and mass production pose challenges.
2) The high energy density of lasers can easily cause damage to workpieces, especially in soldering PCB boards. If the substrate and metal layer structure are poorly designed, the boards are highly prone to burning, resulting in a high defect rate and significantly increased costs—costs that customers simply cannot accept.
3) The highly concentrated energy of the laser easily causes solder paste to splash, which can readily lead to short circuits during PCB soldering and result in product scrap.
4) For flexible wire materials, clamping and positioning consistency is poor, resulting in significant variations in weld bead fullness and appearance.
5) Precision soldering often requires wire-fed solder addition; it is difficult to automate wire feeding for solder wires with a diameter of 0.4 mm or less.
Overview of the Laser Soldering Market for Tin Alloys
Laser soldering has seen varying degrees of development both domestically and internationally. Despite years of progress, however, it still hasn't achieved a significant breakthrough or expanded its applications—this is undeniably a weak point in soldering technology.
However, market demand is constantly evolving—driven not only by vertical growth in quantity but also by the continuous expansion of horizontal application areas, with a primary focus on soldering processes for components related to electronic and digital products.
Covers the tin-soldering process requirements for components across various industries, including automotive electronics, optical components, acoustic components, semiconductor cooling devices, security products, LED lighting, precision connectors, disk storage components, and more.
In terms of the customer base, demand for soldering processes related to components derived from Apple’s products is dominant. Consequently, upstream suppliers in the industry chain have also begun actively seeking laser soldering solutions. Overall, laser soldering is poised for remarkable, explosive growth and will likely develop into a sizable market—both now and well into the future.
In the current context of a weakening global economy, Apple stands out as a shining star. Its substantial market share in digital electronics and its massive, large-scale global procurement have driven business growth for a host of companies—primarily those specializing in electronic components. Soldering is an indispensable step in their manufacturing processes.
Urgent need for breakthroughs in manufacturing processes
Companies, including suppliers to Apple, face challenging process issues during mass production due to the cutting-edge and high-end designs of their products, and urgently need to make improvements and refinements.
A very typical example is the storage component industry. The magnetic head is an extremely precise storage component with exceptionally high process requirements. The data cable for magnetic heads typically consists of flexible PCBs that are mounted onto a steel housing. At one end, an array of tiny soldering points must be pre-tinned. The minuscule amount of solder required can only be applied and inspected under a microscope, and the quality of the soldering itself is subject to extremely stringent standards.
The traditional welding method is manual welding, which places extremely high demands on the skill level of operators. The scarcity and mobility of labor resources introduce significant uncertainty into production. Moreover, it’s impossible to quantify process standards—there are no process parameters, and the post-weld quality relies entirely on the operator’s subjective sensory judgment. Therefore, there is an urgent need for new welding technologies to overcome these technical barriers.
Process upgrade and scalability requirements
Laser soldering enables the quantification of process parameters, improves yield rates, reduces costs, and ensures standardized production operations.
As labor costs rise in the Chinese market and skilled talent becomes increasingly scarce, the demand for manual labor in the traditional soldering field is gradually shifting toward mechanized operations. Laser soldering will break through the limitations of conventional techniques and set new industry standards. Judging from the current soldering samples provided by our customers, the widespread adoption of laser soldering is an inevitable trend.
Conclusion
Because laser soldering offers advantages that traditional soldering simply cannot match, it is bound to find even wider applications in the field of electronic interconnects and holds tremendous market potential.
