In this regard, it is irrelevant whether a fully automatic or a manual printer is used. “The first inaccuracies can be created already during the printing of the solder paste, and they can only be corrected to a limited extent during the subsequent processes,” as Anton Hacklinger, Managing Director of High Q Electronic Service GmbH from Munich, points out. As a result, according to Hacklinger, it is even more important to set the printing process as accurately as possible already at the start of the production, since up to 64% of all faults are caused in the first work step of the manufacture of electronic modules.
Especially the development of SPI systems in the past few years has made it evident that electronics manufacturers focus increasingly on the optimization of the printing process. “High Q specializes in the manufacture of prototypes and of small and medium-sized series. Due to the large number of product changes required, our manufacture is not organised as inline production. An SPI would represent an additional work step that would extend the production time. For this reason, we have opted for a different step,” Hacklinger explains.
The considerations behind this decision were rather simple: The more efficient and precise the stencil, the less inaccuracies will be produced and the less rework will be caused. Hacklinger has calculated that approx. 1% of the material costs of an electronic module are caused by the printing stencil. However, if a stencil is used that is too old or of poor quality, this will in turn have a direct impact on the rework costs. As a result, the costs of the rework could amount to up to 25% of the total costs.
“Unfortunately, it is still a fact that a large number of faults experienced in SMT manufacture can be attributed to faulty soldered joints caused during solder paste printing,” Thomas Lehmann, Head of CAD/CAM Customer Support at Christian Koenen GmbH, points out. To prevent such type of faults, High Q Electronic Service GmbH chose Christian Koenen as their supplier. “Already at an early stage, we made the decision to work together with Christian Koenen GmbH. This cooperation has existed for 10 years now,“ Hacklinger confirms, because from the beginning, the Munich-based circuit board assembly service provider looked for a supplier with that a close exchange on how to minimize rework would be possible.
“Thanks to our continuous ongoing development, our customers obtain clear added value: The increase of the production output through the reduction of failure rates during printing as well as a significantly increased stencil performance speak for themselves,” Christian Koenen, President of Christian Koenen GmbH, explains. Already the solder paste printing involves more than twenty parameters that have an impact on the quality and the performance of the entire electronics manufacture. In this regard, it does not matter whether the manufacture is designed as inline or cellular production. For this reason, an adapted stencil layout in conjunction with optimal release properties in the printer are vital for the production process.
In 2008, Christian Koenen GmbH opened its in-house laboratory for research and development, the Application Center. The technical facilities provide the customers with the option of outsourcing the research and development work for improving the printing processes. In addition, the Application Center can be used to gather vital information, thus continuously developing and improving the stencils. All customers can benefit from the gained expertise all around the printing process. “Process advice is important to us, particularly for complex printed circuit board designs since, particularly in these cases, the expertise of the supplier is vital to ensure that we can start a fault-free manufacturing process”, Hacklinger explains.
A wide variety of components and the combination of large and small designs result in high variance in opening sizes for solder paste stencils. In some cases, different stencil thicknesses might be necessary to account for the special paste requirement and the different components. This is precisely where the analysis of critical points to be considered when defining the right stencil begins.
Especially complex modules with an extensive component spectrum place high demands on the design and execution of the manufacturing process. In this context, it is very important to make the right decisions during planning to ensure a perfect production. This begins with the tolerances of the printed circuit board, a stable opening layout of the print stencil, the correct solder paste selection, and ends only with the manufactured flawless product.
The solder paste deposits pose particular challenges for very small components. Here, a discrepancy exists between the actually required paste amount of the soldered connection and the reproducible printability of small solder paste amounts. The generally applicable rule is: The openings in the stencil should be dimensioned as large as possible and, at the same time, as small as necessary, since large apertures are easier to print. Consequently, the different calculations in respect of the filling behaviour of the stencil openings in the printing process as well as the release properties of the paste, and also the selection of the right paste class must be completed beforehand to decide on the optimal manufacture of the stencil.
In the process, the experts of Christian Koenen GmbH adjust the printing process based on the customer parameters and the used materials because the combination of solder paste and printer accounts for the majority of inaccuracies experienced in electronics manufacture. Various parameters play a role in this regard, including the print quality of the solder paste, the used hardware, the printing parameters, the know-how of the machine operator and the production environment. Other common fault sources include, for example, printed circuit boards of poor quality, PCB distortion outside the tolerances, too narrow layouts due to the continuing miniaturization as well as the final componentry mix to be placed on the printed circuit board.
In this context, a wide range of diverse options must be considered, such as the production of different material strengths within the printing plate (stepped stencil) or defined surface processes, such as CK electropolishing, plasma coating and the design of the squeegee side. “Here, the quality and condition of the printed circuit board also play a vital role, such as for example the solder resist height above the pad, filled vias and their planarity, PCB distortions, marking print, etc.,” Lehman says.
In this area, Christian Koenen GmbH cooperates very closely with the customers and, most importantly, can present the options to the customers and test the finished stencils in the company’s own Application Center. Necessary measurements, for instance distortion measurement, as well as an assessment of the inline printer capability including SPI can also be performed. Every deposit can be measured and evaluated in 3D.
Particularly the release properties during detaching and separating of the printed circuit board from the stencil have a decisive influence on the quality of the solder deposit. During laser cutting of the stencil, melting residues are formed on the stencil surface and the inner walls of the openings. “These material changes are the cause of unclean deposits in many applications, particularly in the fine pitch area,” Lehmann explains. Various surface processes reduce these effects significantly. However, the release properties can also be optimized through special forms that have been adapted to the corresponding components and processes. “Here, the machine operators also have a major role to play. The squeegee pressure and the printing speed of the printer must be set correctly. Equally, the stencils must be cleaned thoroughly. If these points are not observed, all prior efforts are useless,” Lehmann adds. Hacklinger agrees: “Without well trained, experienced staff, even the best stencil in the world is of no value to me. Particularly in cellular manufacture, the contribution of the staff is vital. But for us small EMS companies, it is equally important that suppliers have the expertise to support us with the optimization of our processes.”
Christian Koenen GmbH
Good is not good enough – this motto has become the company’s philosophy. The company Christian Koenen GmbH is the technology leader in the manufacture of precision tools for technical printing.
In the air-conditioned production, stencils for SMD, wafer and LTCC technology as well as PumpPrint™ stencils are manufactured. The entire value added chain, from the selection of the material through to the traceability of the manufacturing processes, are available for the optimal manufacture of the precision tool stencil.
Christian Koenen GmbH sees itself as a technology company that advises and assists its customers and supports them during the optimization of the processes. The in-house precision tool stencil promotes technological progress.
High Q Electronic Service GmbH
Being an owner-managed EMS service provider, High Q Electronic Service GmbH is the technology partner for electronics production in the heart of Munich. Greatest care and precision as well as the highest quality and reliability are consistently implemented during the development, production and testing of electronic products.
High Q Electronic Service advises its customers in their efforts to design a series product, and produces electronics from the prototypes through to readiness for series production.
The products manufactured by High Q Electronic Service are used worldwide, for example in wireless communication systems, high-frequency power amplifiers or in digital telemetry systems.