Bringing SiC to the Masses

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Microchip has recently launched its MB and MC ranges of 1200V mSiC power MOSFETs, and also integrated them into in advanced BZPACK packaging in a number of configurations. Previously, the company had introduced MA mSiC products in 700V, 1,200V, 1,700V and 3,300V to provide the highest reliability. The two newer ranges are intended to offer a balance between performance, reliability and cost that will cater for a much wider range of use cases.

One of the selling points that Microchip often claims for its power products, is that the company’s manufacturing process and packaging technology deliver devices that are very robust and have less need for derating, and therefore designers can use more cost effective solutions that are closer to the specified voltages than those from other manufacturers. It is no different here, as while the MB and MC ranges may not offer quite the same robustness of the company’s MA range, they are still designed to be very rugged. To prove that fact, and give easy access to customers, the company has, for the first time, published quality testing figures on its website for easy download.

Nitesh Satheesh, Product Line Manager, High Power Solutions Group, at Microchip explains, “historically, we've not had reliability documents publicly available for our customers to use, but we started to get so many requests that it was becoming a gating issue for our products. We have a whole suite of tests that we perform, not just in the die, but also on the package. We have HTRB, HDGB, HB, HV-H3TRB to show the robustness of the die, and we test thermal shock, mechanical shock, and vibration stresses on the package. We also perform power cycling at a very elevated ΔTj to allow our customers to easily extrapolate for lifetime.”

He continued “the MA family is a planar-based technology with excellent RDS(on) over temperature performance. Its die size is naturally larger, so to bring costs down, it was reduced, and that brings certain trade-offs that had to be balanced. However, we did attempt to keep the RDS(on) over temperature performance as stable as possible for the new devices. The MA family has a 1.6X RDS(on) range between room temperature and high temperature, and that figure has gone up to 1.8x with the MB and MC families. So that is slightly worse, however, some of the trench platforms that our competitors offer can range from 2X to 2.5X, meaning that the MB and MC families are still very competitive, and systems don’t need to be over-designed by using a device with a very aggressive RDS(on). A customer may get by with a 12mΩ Microchip device, but need an 8mΩ one from our competitor to balance out temperature variations.”

The two new families are differentiated by the inclusion of a gate resistor in the MB devices. Members of the MC family are intended to be discrete devices, and the MB devices will mainly be used in modules, and the integrated gate resistor facilitates paralleling for that role. Instead of the 20V gate voltage found in the MA series, the MB and MC devices have an 18V gate voltage, which can comfortably operate at 15V, where Satheesh estimates is the sweet spot for the industry at the moment. The new devices also feature improved switching losses. The reliability and robustness of the new devices allows them to exceed the requirements necessary to meet High Humidity High Voltage High Temperature Reverse Bias (HV‑H3TRB) standards, being tested for as long as 3,000 hours, instead of the 1,000 hours mandated by the standard. The two other areas of performance that Satheesh points out as notable features of the new MOSFETs are their short circuit withstand of up to 3μs and the fact that they are avalanche rated. The former figure is critical to applications such as motor drives and the latter for use in situations where repetitive high energy bursts are found, such as in e-fuses and hot-swap applications.

The new BZPACK modules with MB series dies come in two variants, BZ1, and BZ2, which is a larger package. Each has a choice of topologies, including half bridge, full bridge, PIM/CIB and three phase bridge. This is the first time that Microchip has used BZPACK for SiC designs, and also one of the first times for the industry. The company has previously used BZPACK for silicon designs for applications like low-cost motor drives. Modifying the pack to operate with SiC technology provides advantages, such as the body diode being integrated into the SiC MOSFET, unlike with IGBTs, which need two separate dies. Microchip is also currently working on an IGBT and hybrid BZPACK options for key customers.

As an example of practical BZPACK designs, Satheesh talks about the 4mΩ half bridge, “when we started development, 8mΩ was the standard, but some customers wanted more current and more power from the package. That was actually a surprise as the package is pin limited. Squeezing additional pins closer together could have run into issues with clearance. But, we managed to keep them separate and cool enough to make it work with a 4mΩ module, which is rated at 200A continuous and 400A peak. The modules come with a choice of a pre-applied thermal interface to save customers a manufacturing process step, and without. There are also options for a base plate or without, for lighter designs, as well as a choice between low-cost aluminum oxide, and high performance aluminum nitride. These options ensure that mSiC modules can be used in a wide variety of applications, including e-mobility, although the devices are not certified for use inside vehicles so far, robotics, motor drives, solar systems, data centers, and HVAC systems.”

https://www.microchip.com/en-us/products/power-management/silicon-carbide/modules