Molded interconnect devices
As molded interconnect devices ( MID ), English for injection molded circuit carrier , injection molded plastic components with applied special processes are metallic conductor tracks designated to serve as a circuit carrier for electronic or mechatronic components.
Major applications for the MID technology are the automotive industry , the industrial automation , the medical technology , the home appliance industry, the telecommunication technology , the measurement and analysis technology and the air and space travel . The market volume of MID technology is subject to constant growth.
Advantages of MID technology
The advantages of MID technology lie in the improved freedom of design and environmental compatibility , as well as in a rationalization potential with regard to the manufacturing process of the end product.
The improved freedom of design and the integration of electrical and mechanical functions in an injection molded part can lead to miniaturization of the assembly. In addition, new functions can be implemented and any shape can be designed.
The potential for rationalization lies in the reduction of the number of parts (material savings) and the shortening of the process chains . Furthermore, by reducing the assembly steps, the reliability can be increased.
By using MID technology, the material mix of a combination of circuit board and mechanical component (conventional solution), which usually consists of many materials, can be replaced by a metallized plastic part (MID). MIDs are made from recyclable thermoplastics and are less critical for disposal than conventional printed circuit boards. In contrast, the base material for a printed circuit board is generally a hard-to-dispose and non-recyclable thermoset .
MID manufacturing process
MIDs can be manufactured in a wide variety of ways. The most important processes for applying the conductor tracks as well as transmitting or shielding surfaces are two-component injection molding, hot stamping, mask exposure, laser structuring and back injection molding. A basic distinction is made between subtractively structuring and additively metallizing processes.
Two-component injection molding
With two-component injection molding, the workpiece is manufactured in two injection molding stages ( two shot molding ). One plastic forms the base body, another can be metallized and forms the conductor track layout. There are two common methods, the PCK and the SKW method.
In the PCK process (PCK = Printed Circuit Board Kollmorgen ), a metallizable, non-electrically conductive plastic is used for one shot. The other shot is made with a non-metallizable plastic. Depending on the variant, the later conductive areas (variant a) or the later non-conductive areas (variant b) are filled.
The SKW process (SKW = Sankyo Kasei Wiring Board ) essentially corresponds to the PCK process variant b, but it uses a further process step between the two injection molding stages: the later conductive, still exposed structural part is already superficially germinated, i.e. with a catalyst (e.g. palladium).
After the second shot, the MID base part has its final shape and the corresponding metals are applied to the metallizable plastic in the following steps. Depending on the process, the surface of the metallizable plastic must first be activated (this is not necessary with the SKW process). Metal is electroplated onto this surface . For this purpose, a thin copper layer is first chemically deposited and then galvanically reinforced.
MID hot stamping
The hot stamping process is also a fully additive manufacturing process, which, however, requires very few work steps. It has only a limited three-dimensionality and only simple shapes can be produced.
The injection-molded part, which already has the final geometric shape, is placed in an embossing press. A surface-modified metal foil is simultaneously punched with the embossing tool and bonded to the molded part using pressure and heat. The stamping foils are provided with an adhesive layer or have a black oxide coating that ensures adhesion.
Hot stamping has only a few work steps and requires little investment in the systems.
Laser MID process
In the laser -MID process, a distinction is made between laser direct structuring (additive) and subtractive laser structuring:
Laser direct structuring (LDS)
Laser direct structuring (LDS), also known as the LDS process, was invented from 1997 to 2002 at the Ostwestfalen-Lippe University of Applied Sciences in Lemgo and developed as part of a research cooperation with the company LPKF , patented by the inventors and initially licensed exclusively to LPKF . In 2002 the patents for the LDS process were transferred to LPKF.
The LDS process uses a thermoplastic material doped with a (non-conductive) laser-activated metal compound as a plastic additive. The basic component is manufactured using one-component injection molding, with almost no limitation in terms of 3D design freedom. A laser beam now writes the later conductor tracks on the plastic. Where the laser beam hits this plastic, the plastic matrix is superficially broken down into volatile fission products, i.e. slightly removed. At the same time, metal nuclei are split off from the additive and are very finely distributed in the rough surface. These metal particles catalyze the subsequent chemical-reductive copper metallization. Layers of copper, nickel or a gold finish can then be applied to this by electroplating. See also plastic plating .
The LDS process achieves full three-dimensionality in a spherical sphere with the appropriate laser beam guidance. It is highly flexible: for a changed course of the conductor tracks, only new control data have to be transmitted to the laser unit. Various functional components can thus be created from a basic component. The finest conductor tracks with a width of <100 µm are possible. Then why can even integrated circuits with the flip chip are placed.
Any body can be coated and structured with a special lacquer doped with LDS additive. So if a component z. B. in a 3D printer made of plastics unsuitable for laser structuring and coated with the LDS lacquer, the laser direct structuring can still be done. The components created in this way are used for. B. as a functional model or prototype.
Subtractive laser structuring
With subtractive laser structuring, the entire component surface is metallized and then etch resist is applied. With the help of the laser, the etching resist is structured and the exposed copper layer is etched away.
Mask exposure process
The process corresponds to the conventional photochemical manufacturing process for printed circuit boards . After the plastic part has been injection molded and the surface has been activated, a chemical base metallization with a thin copper layer takes place over the entire surface . A photoresist is applied to this.
Exposure to ultraviolet occurs through a curved photomask. The exposed photoresist is developed and removed and in the next step the exposed conductor track geometry is galvanically reinforced up to the desired layer thickness. After removing the remaining photoresist, the base metallization is etched away.
The mask exposure method requires many process steps and is not very flexible. It is only 3D capable to a limited extent, but the finest conductor track widths are possible as with conventional circuit boards.
Foil back injection
In the case of back injection molding, a separately produced, single or multi-layer flexible conductor pattern film is inserted into an injection molding tool and back-molded with suitable plastics.
Foil back injection allows the structuring process to be carried out prior to injection molding. It has few process steps and any plastic material can be used.
Direct ladder writing
The main advantages of the direct process are chemical and mask-free production and high flexibility; Individual copies can also be produced inexpensively by changing the path control. Two of the methods are mentioned below by way of example.
Flamecon
In the so-called Flamecon process, copper is melted and sprayed onto the carrier material with compressed air or protective gas. In order to improve the structure sharpness and edges, an adhesion promoter is applied beforehand in a structured manner so that the material only adheres there. The component pre-structured with primer can allegedly also be pulled through a metal melt in order to apply the conductor tracks.
In terms of substrates and structuring, the process is an optimized thermal spray process similar to flame spraying and allows conductor widths> 1 mm and layer thicknesses.
Plasmadust
The so-called plasmadust process uses a non-thermal plasma at normal pressure, together with very fine metal powder (100 nm to 20 µm). Compared to conventional plasma spraying , the plasma temperature is so low that thermoplastics can be coated. The surface is activated by the plasma, which means that the layers adhere well.
Research association 3-D MID
The research association for spatial electronic assemblies 3-D MID e. V. was founded in 1993 in Erlangen . The aim of the research association is to promote and further develop MID technology. For this purpose, projects for community research are carried out, the exchange of experiences among the members promoted and the implementation of the new technical possibilities stimulated through appropriate public relations work. A particular concern is the support of small and medium-sized companies. With 65 member companies and 34 research institutes, it is the largest industrial research association in the field of 3D-MID technology worldwide.
literature
- J. Franke (Ed.): Spatial electronic assemblies (3D-MID): materials, manufacture, assembly and applications for injection-molded circuit carriers. Hanser, Munich 2013.
- Electronics. Special edition spatial electronic assemblies. WEKA Verlag, 2011.
- J. Franke, J. Gausemeier, C. Goth, R. Dumitrescu: MID study 2011 market and technology analysis. Paderborn 2011.
- H. Wißbrock: Laser direct structuring of plastics - a new process in the mirror of introduced MID technologies. In: plastics. 11, (2002), Vol. 92, pp. 101-105.
- G. Naundorf, H. Wißbrock: Conductor structures and processes for their production. Patent WO 2003005784, 2001.
Web links
- www.3d-mid.de - Official website of the 3-D MID research association
Individual evidence
- ↑ Irene Fassi, David Shipley: "Micro-Manufacturing Technologies and Their Applications"; Springer-Verlag 2017; 295 pages; P. 181f
- ↑ https://www.plasticsportal.net/wa/plasticsEU~de_DE/function/conversions:/publish/common/upload/technical_journals/electronics_and_mechatronics/Laser_Direkt_Strukturierung_von_MID_Bauteilen.pdf Reinhard Stranskyßler, Nils-Heininger, Wolfgang Boiler Directly on the component "; Journal PLASTVERARBEITER, Volume 56 (2005), No. 4, pp. 62f