Since 2021, one-hour virtual meetings of the Research Association 3-D MID e.V. have been held at three-monthly intervals. The dates are announced on the homepage, on LinkedIn and in newsletters. Participation is open to all interested parties and free of charge. Two presentations from the industrial sector on products, processes and methods of quality assurance or from research form the content of this format. A mid-double-digit number of participants regularly attend the events to learn about developments, research results and trends.
At the 10th MID Day, two lectures from the areas of material and process development were on the program. The first lecture, entitled: “3D functional integration: from microwave sintering to agricultural systems of the future,” was presented by Prof. Dr. Christian Dreyer. He heads the Polymer Materials and Composites PYCO division at the Fraunhofer Institute IAP – one of the six research areas. The Fraunhofer Institute PYCO, together with the Chair of Manufacturing Automation and Production Systems (FAPS) at FAU Erlangen-Nuremberg, is working on the AiF project MikSin (Sintering of printed conductive structures by energy input using microwave irradiation).
In the project MikSin, energy input by means of irradiation of the semi-finished products with microwaves is being investigated. By inducing eddy currents in the conductive structures through an external electromagnetic field, they can be selectively heated and subsequently sintered. In this way, the range of functionalizable materials in particular can be extended to include temperature-sensitive and at the same time weakly polar substrates: These remain largely unaffected by the microwaves and experience heating at most locally in the immediate vicinity of the conductor paths to be sintered.
Substrates of different materials such as thermoplastics or (fiber-reinforced) duromers, among others, can be functionalized by applying conductive structures using various printing processes such as inkjet, piezo jet or aerosol printing technology, using these structures as conductive tracks for controlling integrated electronic components or as heating elements. For the final adjustment of the conductivity of the printed structures, a sintering process of the printed conductive inks downstream of printing is required, which is usually performed in conventional ovens by applying heat directly to the printed semi-finished products.
In the project MikSin, the energy input is investigated by irradiating the semi-finished products with microwaves. By inducing eddy currents in the conductive structures through an external electromagnetic field, they can be selectively heated and subsequently sintered. In this way, the range of functionalizable materials in particular can be extended to include temperature-sensitive and at the same time weakly polar substrates: These remain largely unaffected by the microwaves and experience heating at most locally in the immediate vicinity of the conductor paths to be sintered.
Fig. 1: Heated armrest demonstrator from the passenger car sector; Source: Fraunhofer PYCO
Fig. 1: shows three development stages of the demonstrator of an armrest from the passenger car sector. In the upper area, the CAD representation of the armrest is presented, in the middle the heating layout with silver feed line (green) and carbon heating lines (red) and in the lower area the implementation of the layout of the feed lines with silver paste on an APCB substrate.
Samples of the material APCB substrate in the form of an armrest and a piezo printer, as shown in Fig. 3, were used to fabricate the demonstrator. Two conductive inks (Loctite ECI 8001 and Loctide EDAG 418 SS) were processed for comparison.
Fig. 2: Experimental setup piezo printer; Source: Fraunhofer PYCO
A patented continuous microwave system from Fraunhofer PYCO was used for the sintering process using microwaves. As shown in a comparison with a heterogeneous oven, this system delivers more precise results and is therefore ideally suited for the production of temperature-sensitive printed MID assemblies.
Fig. 3: Images of samples with different magnifications: Furnace sintering top row a) and b) and microwave sintering bottom row c) and d); Source: Fraunhofer PYCO
As can be seen from the lighter coloration in Fig. 3 d, the conductive silver layer was little changed, which indicates a gentler treatment by microwave sintering. Prof. Dreyer concluded by explaining the application of microwave sintering in future products, for example in the illumination of cultivation containers for vertical farming.
In the second presentation, Mr. Niklas Piechulek from the Chair of FAPS at FAU Erlangen-Nuremberg presented his results from the research project:” Efficient cabin through digital networking of technologies and systems (EFFEKT)”, funded by the German Federal Ministry of Economics and Climate Protection. The challenge in this research project was to test polymer materials from the avionics industry with incorporated additives for laser direct structuring. The aim was to produce a demonstrator with mechatronic integration. A plastic part with a purely load-bearing function was provided with an electronic function. A passenger service unit (PSU) was selected as a suitable plastic part. A compound approved for aerospace applications was selected for the part and various activators from LPKF, Keeling & Walker and Merck were added at a percentage of 1 – 5 %. A filament was then obtained from the polymer compound, which was used to produce demonstrator parts in a 3D printer. Because of the comparability to real parts, a complex interconnection was designed, which was applied to the parts with an LPKF laser. Subsequently, the part was metallized with reagents from Rohm and Haas at the chair. Fig. 5 shows the CAD design of the demonstrator with the complex filigree interconnection. As a result, it can be stated that a functioning process chain exists for the manufacture of such assemblies. However, there is still some potential for optimization along the process chain, which must be worked out consecutively in further research projects. The characteristic advantages of MID technology, such as design freedom, functional expansion and material savings, have also been demonstrated in this application.