The recent research in wide-bandgap (WBG) power electronic semiconductors has produced a wide variety of device and combinational topologies, such as HFETS, MOSHFETS, and the Cascode Pair. Each variation needs to be tested with certain package criteria (e.g. high voltage SiC devices up to 15kV, high current GaN devices up to 300A, or unprecedented high frequencies). Having a common package is costly and cannot provide an investigation of optimized performance. Hence, use of a rapid prototyping method to print power electronic packages and modules is needed. Also, the continual move to higher frequencies will require greater integration of packaging into the end application, as is presently done with point-of-load converters. The future modules will take on more functional integration, including more mechanical features, which further supports use of printed fabrication technologies. It is not reasonable to assume that a complete module can be directly printed, though most would be; some assembly is required. This paper discusses partitioning of a module process, and identifying key elements that can be combined for optimum power package production.
To select the best process, or combination, for rapid-prototype printing of power modules current, Additive Manufacturing (AM) methods are evaluated, such as Stereolithography (SLA), Selective Laser sintering (SLS), and Fused Deposition Manufacturing (FDM). Several modules were fabricated to demonstrate mechanical resolutions in the packaging. A thermoplastic printer, specifically the MakerBot, which is a high end consumer 3D printer, produces packages with 100 micron resolution. The Acrylonitrile butadiene styrene (ABS) build object can have surface texture enhancement with post chemical treatment, such as an acetone vapor bath. Today, this is finding a home and proving useful in low volume rapid prototyping in small electronics companies. The ABS plastics are typically rated for <105°C applications. Another printed module to be reported uses a high-end commercial machine with <20 microns in resolution (Stratasys Objet) using standard UV curable polymers. This provides a slightly higher temperature range with greater mechanical integrity. Materials for >250°C that use both UV and thermal sintering are available, but not evaluated in this paper.
Functional integration can include electrical, mechanical, and thermal appendages and sub-systems. Electrical sub-systems, such as gate drivers and sensors, can impact process partitioning, by requiring “low power” circuit fabrication processes integrated with those for high power. This paper demonstrates a printed polymer substrate process for functional integration of a signal-circuit. Since nearly all AM processes were developed initially for mechanical systems, many processed materials have not been electrically characterized, though the basic material compositions may have suitable electrical characteristics. This paper categorizes several materials for their potential suitability for power packaging. The evaluation is based on the electrical, mechanical, and thermal parameters, along with precision, surface texture (affecting electric field contours) and process times. Cost and performance will be of main concern.
