» PCB & ASSEMBLY Using
» PCB & ASSEMBLY Using laser as a power source Selective soldering with light The laser is a phenomenon (normally designated as a technology) that was discovered more than a century ago, but only actually deployed since the beginning of the 1960s. In less than 50 years, it became the basis for multiple applications, which are nowadays highly sophisticated, and will be further developed in the coming years. Monochromatic and collimated Laser beam from the vertical – Component damaging I mplementing the appropriate materials and provisions that take advantage of determinate laws of physics, it is possible to produce what is normally called a “laser beam”, which is substantially a light or a well-defined electromagnetic wave. Source: Seica S.p.A. However, this is not a common electromagnetic wave, but rather radiation which has the capability to create a “coherent” flow, in terms of space as well as time. Two important properties are the result of this capability: • The first is being “monochromatic”, therefore characterized by a limited set of wavelengths which, depending on the type of materials used, can range from infrared to ultraviolet. • The second is being “collimated”, therefore composed of a set of parallel and unidirectional sub elements. In particular, the latter of these two properties, collimation, enables the laser to convey energy with a density (energy/surface) much higher than a standard light source. In other words, a laser can be considered as a source of energy which can be conveyed to a target (very small and defined areas) without making contact (contactless). Choosing the appropriate wavelength of the laser source allows to optimize the laser beam according to the process and the materials involved, in order to Source: Seica S.p.A. Angled laser beam 38 EPP Europe » 04|2021
achieve the best transmission and power absorption by the target. From the output of the source, the laser beam can be conveyed via optical fibers, or through a system of fixed or movable mirrors driven by galvanometers, in order to deflect the beam where necessary. A fundamental component of a laser system are the optics, whose task it is to focus the laser spot in the desired manner and shape. PCBA assembly technologies Over the course of the last decades, the evolution of electronic component and electronic board assembly technologies has seen a gradual decrease of Through Hole Technology (THT) components, that is those having leads that are inserted through a hole in the printed circuit, in favor of surface mounted components (SMD). The advantages of SMD technology are widely noted, but they are not relevant in the context of this article. It is a fact that, even though the complete elimination of THT technology was predicted, it never happened. Anybody who assembles electronic boards is aware that, to different extents, it will be necessary to face the problem of mounting and soldering some THT components onto boards (sometimes only connectors). Above all, it has to be done quickly (especially for high-volume productions) and accurately, making sure not to damage what is already on the board. Ensuring the quality of the product is also important, which until that moment, has been involved in less critical, high-yield assembly processes. Recently it has become common that products are designed and engineered to include one or more electronic boards, which are placed in plastic or resin casings (composite casting). In this case, the junction between the electronics and composite item is often done with metal mounting tabs, which ensure the connection between the parts, and are soldered in the same way as the THT leads. These linking elements often have significant crosssections, since they carry high-intensity current. Laser and selective soldering for electronics The challenges faced in electronic board manufacturing are becoming increasingly difficult. First of all, volumes, which can reach high numbers in some industries, can impel incessant cycle times. There are also the quality targets, that require not only high process yields, but also the production of a final product able to withstand mechanical, thermal and electrical stresses over a long-life cycle. In addition, there are layout, weight and design requirements which mandate that the electronics be inserted into Existing potential damages also with inclined laser On the left, the principle of the so-called “Standard approach”, on the right, the innovative approach of the FireFly Next complex positions and containers, which standard soldering systems have poor ability to handle. Finally, to withstand the impact of all these technological challenges while reducing costs, it becomes strategic to adopt machinery and production technologies with a high level of automation. In this scenario, it is easy to conclude that laser has some intrinsic characteristics that make it a very interesting technology to use as the basis for a selective soldering system to be deployed in the finishing phase of PCBA. In particular, there are some fundamental considerations: • No contact on the solder joint is required. • The agility to easily access boards with accessibility issues and problems caused by the close proximity of adjacent components. Alberto Ghirelli Pre-Sales & Product Development, Seica Strambino. Source: Seica S.p.A. Source: Seica S.p.A. Source: Seica S.p.A. EPP Europe » 04|2021 39
