Continuous wave or selective?

Having started in the bath and bedroom of the family home almost 35 years ago, VOIGT electronic is a modern EMS service provider today with great passion and know-how for electronics manufacturing. The product spectrum ranges from components for biogas systems to medical technology. By investing in a VERSAFLOW ONE from Ersa which was introduced in 2021, VOIGT have now modernized their THT production and created additional capacities.

No, the foundation of VOIGT electronic GmbH on April 1, 1989 was not an April Fool’s joke, but the starting signal of a success story the kind of which is more commonly known from the USA. However, the origin of this story lies in the former GDR – in the city of Erfurt to be precise. After a marathon of nine months with the authorities, Matthias Voigt finally held the business license in his hands and started his company to produce printed circuit boards.

From the beginnings in the living rooms of the parents’ house with self-made production equipment – for example, a converted hanging file cabinet was used to expose the photoresist for the printed circuit board – VOIGT electronic developed into a modern EMS service provider that is passionate about electronics. The company has never specialized in one industry but has remained broadly positioned until today. The family-owned business manufactures components for measuring instruments, communication, and industrial electronics – as well as for railroad and traffic technology, which is used worldwide. The secret of success: VOIGT live for electronics. This means that they put themselves in the customer’s shoes to understand and optimally manufacture his product. If necessary, products are optimized in terms of production technology and top quality is ensured. Of course, these processes happen in close cooperation with the customer.

With the advent of SMD technology in the 1980s, the development in electronics has changed rapidly. Mixed assembly with THT components and SMDs on both sides is increasing steadily and has become state of the art. The classic soldering process for thru-hole components is the wave process.

However, VOIGT has now reached certain limits with this process. The portfolio includes products that are well-suited for wave soldering, for example assemblies with a large share of THTs on four-layer printed circuit boards. These are mainly long-running products that have been manufactured for many years. Nevertheless, many new customer projects are ill-suited for the wave soldering process – here, VOIGT is dealing with electronic assemblies for measurement technology or test systems, consisting of multilayers with up to 16 or 18 layers assembled with a large variance of bottom-terminated components. This means that all connections are located on the underside of the board. The Erfurt-based company also has many small production lots in its order book: in addition to batches of up to 1,000 units, it also produces prototypes and lots of 20 to 25 assemblies per series. Up to twelve product changes per day have to be handled. VOIGT therefore started a project to evaluate and replace the existing wave soldering system. Here, it was also a matter of assessing whether wave soldering still fitted the product spectrum or if it could possibly be replaced by a selective soldering process.

The advantages of the selective soldering process are, on the one hand, the elimination of solder masks. During wave soldering, these solder masks protect SMD components located on the underside of the PCB from being re-melted and washed away in the solder wave. They are needed even for very small production lots. They must be made specifically for each product and are, of course, a time and cost factor. It is a constant balancing act – if you order too few masks, waiting times occur because the masks are not cleaned quickly enough after a soldering process and it takes too long until they are ready to be used again. You also don’t want to have too many masks for cost reasons.

Another advantage is the flexibility in the selective soldering process: The individual components of a board can be soldered with their individual parameters, whereas with wave soldering one is forced to make compromises. Heating and wetting time in the solder wave can only be set for the entire assembly. Consequently, it is necessary to find the best average value in order to protect sensitive components and still achieve sufficient wetting of the component pins with high heat requirements so that a reliable solder connection is produced. Moreover, since the printed circuit board is only wetted with flux and solder in the spots where the connections to be soldered are located, there is less residue on the board in the selective soldering process. This significantly reduces the cleaning effort and has a positive effect on economic efficiency.

The respective advantages of wave or selective soldering processes are to be found in the amount of THT components in the assemblies to be processed. For mixed assemblies with SMD and THT components, the classic wave soldering system has an advantage if the SMDs are only on the top side of the PCB. In this case, the wave soldering process is very economical because no solder masks are required for processing. If, on the other hand, the underside of the PCB is also fitted with SMDs, with a low proportion of THT components at the same time, selective soldering has an advantage. The economic efficiency is significantly higher simply because solder masks are no longer required.

“Of course, quality is a decisive criterion. But in this case, output was almost more of a priority for us. At the end of the day, I have to produce a certain number of assemblies, otherwise I won’t make my delivery times,” production manager Frank Koppetsch describes the requirements. “In addition, we are currently experiencing a growth boost,” adds Managing Director Sabine Voigt. “The new soldering system should make our production future-proof and provide a backup for further growth.”