Innovative and resource-saving processes
Stannol has successfully completed an EU-funded project on tin recycling. Together with four partners, the project investigated how already used solder paste can be recycled using new, resource-saving processes – without sacrificing quality.
Other cross-thematic focal points also included the determination of the CO2 emissions generated and the creation of a sustainable return concept for used solder pastes. In addition, the project investigated how a transparent supply chain can be ensured using blockchain technology. Stannol led the twelve-month project. The company was supported by MTM Ruhrzinn GmbH, the Fraunhofer Institute for Applied Information Technology (FIT), the Fraunhofer Institute for Environmental, Safety and Energy Technology (UMSICHT) and bpc specialties GmbH. The project was funded by the EU through the European Regional Development Fund (REACT-EU).
Recycling tin – why?
Tin is one of the raw materials with the lowest reserves. Moreover, the primary extraction of the metal is accompanied by enormous environmental destruction. At the same time, however, tin is one of the strategic technology raw materials – it is indispensable for the manufacture of electronic products. The problem is that Germany's recycling rates for tin are far below the international average. Sustainable recycling processes would ensure that many problems do not arise in the first place.
Reuse and tin recycling is complex
The effort required to return tin waste to the production process is enormous. According to the German Federal Institute for Geosciences and Natural Resources, tin-based solders from the electronics industry are therefore reused "only to a small extent", and at best only recycled proportionally. In the case of chemical products, for example solder pastes and flux-filled solder wires, there is almost no reuse at all because the combination of metal and chemicals makes the process unattractive from an economic point of view. In addition, there has been a lack of company-based research into the value of secondary raw materials – especially to address reservations around their quality. "This is exactly where we wanted to start with our project," explains Ingo Lomp, Head of Innovation at Stannol. "The aim was to conduct holistic research into how metal powder that has already been produced can be optimally processed for reuse without any loss of quality in order to produce a solder paste from pure secondary materials – including sustainable process engineering, practical recycling processes, transparent supply chains and a verifiable CO2 assessment of the new process."
Isolate solder powder
One of the main tasks in the project was the purification of solder powder with an expired shelf life or from solder paste that had already been used. The technical challenge here was to separate the solder powder from the flux contained in the solder paste in such a way that the recovered powder does not differ in quality from newly produced solder powder. At the same time, the process had to be as energy-saving as possible. Here, Stannol's research and development department worked with different physical separation processes. "The challenges of the project were to develop a universal process that would make it possible to reliably purify solder pastes from a wide range of manufacturers while keeping energy consumption and environmental impact for the purification process low," explains Dr. Sven Mönninghoff, Head of Research and Development at Stannol.
Scientifically proven: Secondary tin has the same quality as primary tin
As part of the project, Stannol also commissioned an external study at the University of Rostock under the direction of Prof. Dr.-Ing. habil. Mathias Nowottnick, in which solder samples made of primary and secondary tin were comparatively examined. The aim was to prove scientifically that primary and secondary tin do not differ in purity and quality.
The result of the analysis: crystallographic examination on the prepared microsections of the samples revealed no visible differences between the two variants. A chemical etching process made the individual crystals and grain boundaries in the tin samples clearly visible – no impurities could be detected along the grain boundaries in either the primary or secondary tin.
Scanning electron microscope and EDX
The purity of the tin samples was also analysed qualitatively by scanning electron microscopy and by energy dispersive X-ray spectroscopy (EDX) using mapping scans and quantitatively by point analysis with stoichiometric evaluation. The results of these analytical methods also show a high purity of the samples of both tin variants.
Thermal analysis
In the thermal analysis, only minor differences in the order of <0.5 K were found between secondary and primary tin. The slightly higher melting point of the secondary tin is a little closer to the theoretical literature value of the melting temperature for the pure tin. Therefore, together with a lower standard deviation of the measured melting temperature values for the secondary tin compared to the primary tin, it can be concluded that the secondary tin is of high quality and purity. "With these results, we can clearly prove that secondary tin is not qualitatively different from primary tin. We hope that we can thus finally dispel prejudices that prevail in the electronics industry against this valuable recycling raw material," emphasises Ingo Lomp, Head of Innovation at Stannol.
Recycling concept for tin waste
Within the project, MTM Ruhrzinn GmbH has taken on the task of developing an innovative recycling concept for tin waste in order to prepare it for reuse. To be able to produce a product with the lowest possible conversion losses that is not only more sustainable than the one previously used but also digitally traceable, the various alloys and grain sizes must first be cleanly separated from one another. Here, samples were taken from both newly produced and opened and partially used solder paste containers and examined. The difficulty: Not only the solder pastes are offered in different containers such as cans, cartridges or syringes in different sizes and with different designations of the contents. Solder paste waste is also returned in different ways – sometimes in the original container, scraped out in buckets or in large cans. Often, different pastes, manufacturers and alloys are also mixed together.
Dan Mutschler, Managing Director of MTM Ruhrzinn GmbH, explains: "Classifying and separating the respective pastes according to alloy and grain size for subsequent homogeneous reuse, as well as classifying the fluxes they contain for reprocessing, was the biggest challenge. Assembling the correct mono-fractions for reprocessing from various mixed batches required intensive thinking in terms of product specifications, as otherwise reusability after reprocessing would not be given." However, the trials around the purification process clearly showed that it is possible to separate raw materials from flux and original packaging using solder pastes as an example.
Data for the Blockchain
In addition, MTM Ruhrzinn determined the data on the contents of the containers, which can be used as the basis for a demonstrator via blockchain for reasons of traceability. In order to ensure transparent, but at the same time data protection-compliant traceability of the raw material chain, a new database also had to be developed, which the blockchain accesses. The collected data and information on different materials and their ingredients are sufficient to be presented in a blockchain demonstrator. This also enables the creation of a digital CO2 certificate that guarantees the traceability of the materials.
Survey on tin recycling in companies
As part of a study, companies were also asked about their reservations regarding the recycling of tin. The various questionnaires revealed that the majority of decision-makers, especially in the tin waste sector, do not see the need to consider a more sustainable use of materials in production. Dan Mutschler: "The results of our study have shown that there is a great need for clarification here. It must become clear to decision-makers in companies that recycled material not only has the same quality as primary material, but must absolutely gain in importance for reasons of sustainability."
Blockchain for more transparency
The Fraunhofer Institute for Applied Information Technology (FIT), under the direction of Prof. Wolfgang Prinz, was responsible for using blockchain technology to ensure supply chain transparency and to work out how this can support the circular economy. After researching existing IT concepts and blockchain solutions, an in-depth analysis was conducted to determine which smart contract functionality is best suited for tracing the supply chain and certifying a product. A solution adapted to the requirements was then developed. "At the beginning, it was particularly important to bring all partners to the same level of knowledge regarding blockchain technology. This was the only way to design the system together. Limited access to reliable information was also a challenge in the project," explains Martin Unkel from the Fraunhofer FIT Institute. As a result, a prototypical decentralised web application (dApp) for a transparent circular economy could be presented. "For the future, it is of central importance that the willingness of recycling companies to make their processes around the preparation for the reuse of raw materials more transparent, increases," the expert emphasises.
Greenhouse gas emissions significantly minimised
Within the framework of the project, the experts of the Fraunhofer Institute for Environmental, Safety and Energy Technology (UMSICHT) considered the environmental impact of the newly developed processes for the recovery of solder powder in comparison to the environmental impact of primary tin. The evaluation parameter for this was the emission of greenhouse gases measured in CO2 equivalents. The challenge: The environmental indicators are often confidential and are not published by the companies – if they even know them themselves. In addition, the data on primary tin varies greatly, as it was determined at different times (between 10 and 20 years) and in different regions. "One must keep in mind with this topic that there is no "correct" value for the greenhouse gas emission of a substance, but that it depends on the environmental conditions, for example, the type of tin mining, the type of electricity generation or the length of the transport routes," explains Jan Blömer from Fraunhofer UMSICHT. However, it can be clearly proven that the carbon footprint can be significantly minimised with the help of the new processing methods: While theCO2 footprint value of solder paste made from primary tin is around 38.5 kg-CO2-eq, it only measures around 3.3 kg-CO2-eq with the new reprocessing methods.
Mechanical reprocessing
bpc specialties GmbH had the task of designing a system capable of processing used solder paste by machine. For this purpose, the developed separation process had to be taken up technically and a machine had to be designed on this basis. The important thing here is that the solder powder must be separated as completely as possible from the flux in the system – with a purity of the solder spheres of over 99.9 percent. The particles must also not be mechanically damaged in the process. Other requirements: The machine should be intuitive to operate, ergonomic as well as space-saving. Ease of operation is also essential, so that no additional specialist personnel have to be employed.
Conclusion of the project
The duration of one year is too short for such an extensive project to produce conclusive results. For this reason, intensive research will continue in the respective areas in the future. "We are very satisfied with the results so far. In the course of the project, it has been demonstrated that it is possible to obtain high-quality material using new, environmentally friendly processes in order to reduce environmentally harmful emissions and save resources," emphasises Ingo Lomp.
More information on the project is available at metallpasten-recycling.de.
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