Full title of project outline: Spatially optimised manufacture of a power module using stereolithographic multi-material fabrication of ceramic 3D substrates with embedded conductive structures [MultiPower]
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For the implementation of classic power electronic structures (inverters, high-power LEDs), the heat sinks and metal-ceramic substrates used are manufactured separately from each other in long process chains and brought together by a subsequent joining process (bonding, soldering, sintering). Additive manufacturing processes offer solutions for shortening the process chain. Power electronic structures are usually produced by a sequence of different processes, for example PBF-LB/C formerly SLS (selective laser sintering) to realise the ceramic structures and PBF-LB/M formerly -SLM (selective laser melting) to realise the metallic structures.
A similar two-stage approach was pursued in the completed AiF project “Active Power”, in which ceramic 3D substrates with greater design freedom were additively manufactured for the first time and subsequently functionalised by dispensing active solder.
Additive multi-material processes, which allow the simultaneous processing of several materials within one layer and thus a further reduction of the required process steps and an increase in design freedom, are therefore of great interest for the one-step production of metal-ceramic composites and are hardly used at the current state of research. In principle, flexible layer thicknesses in multilayer design and high functional integration in the substrate body, excellent heat dissipation and geometrically optimised conductor path guidance with regard to (gate and load current path) inductances can be realised by co-processing metal and ceramics.
The suitability of a new type of stereolithographic multi-material system (VPP, Vat Photopolymerization), which enables the simultaneous processing of metallic and ceramic materials (metal-ceramic substrates) or slurries for the construction of power electronic modules, is therefore to be tested in the intended project. Furthermore, the VPP process is to be combined with the use of piezo jet (PJ) printing to apply conductive structures on the outside of the manufactured module in order to connect additional circuit elements, e.g. resistors and temperature sensors. Due to the greater flexibility on 3D surfaces and finer structures, PJ printing is an ideal complement to the VPP process.
Within the project, the materials used, such as conductive and ceramic VPP slurries and PJ inks/pastes, are first optimised with regard to their compatibility (adhesion, wetting) in order to subsequently identify suitable process parameter windows for VPP and PJ. This includes the design and layout of a suitable circuit layout, the selection of the ceramic track combination and the development of a conductive slurry. To set up a chemical bond between metal and ceramic, the conductive track material must be matched to the ceramic base body.
In summary, a functional, power-electronic module with an integrated cooling structure, integrated conductive tracks in multilayer design and external functionalisation is constructed as a technology demonstrator and characterised in terms of thermal and electrical performance and compared with alternative assembly and manufacturing concepts. The mechatronic qualification and the optimisation of the geometric design to reduce voltage peaks and power losses are carried out iteratively.
Figure 1: Design draft – Innovative structure (side view) with embedded conductive structures and spatial optimisation; Source: wbk Institute for Production Science, FAPS Institute for Factory Automation and Production Systems
The aim of the research project is the spatially optimised manufacture of a power electronic module with embedded conductive structures in a ceramic housing by means of additive manufacturing in order to optimise heat dissipation, minimise gate-path losses and increase component integration and functional density. The following scientific sub-goals are being pursued:
- Development of a conductive slip material after the sintering process for multi-material manufacturing with ceramics with chemical bonding by titanium additives.
- Process stability of the multi-material production as well as the subsequent sintering process
- Process stability of PJ on 3D surfaces of AlN and Al2O3 produced by VPP
- Optimisation of thermomechanical loads through targeted design adaptation
Benefits and economic significance for SMEs
The production of metal-ceramic substrates for power electronics using conventional processes is inflexible, and each design change is investment-intensive due to the necessary tooling and process adjustments. Innovations in the packaging sector are therefore slowed down and can usually only be realised economically by large companies with a high output. The envisaged research project lays the foundation for highly flexible power electronics manufacturing, based on VPP and PJ, with a minimum of supplier parts and necessary production facilities. This will pave the way for SMEs to build customised power electronics and shorten development loops, thanks to in-house systems or service providers for additive manufacturing.