Advances in substrate technology have led to the development of power modules optimized for automotive BLDC applications

By Matthew Tyler

As we all know, people are increasingly concerned about the state of the environment and the impact of carbon emissions on the global ecosystem. In addition, the increasing demand for oil in emerging economies means that the consumption of oil reserves is accelerated (according to the International Energy Agency, the current annual oil shipment volume is 35 billion barrels), and the uncertainty of long-term oil supply has increased. Therefore, automakers face considerable challenges. They need to develop more fuel-efficient models to ensure that they continue to comply with international regulations, while surpassing their competitors and providing car buyers with lower driving costs and more environmentally friendly vehicles.

One of the key ways to address this growing problem, and comply with the stringent regulations that are now in place, is to reduce the mechanical load on traditional petroleum engines. Another approach is to reduce the overall weight of the vehicle, so that less energy (fuel) is required to provide the same driving experience. Both approaches benefit from moving from traditional mechanical systems to systems that are primarily powered by electricity. In addition to electric power steering systems, electric coolant and oil pumps are common examples of moving to this electronic design approach. In addition, the need to further optimize traditional implementations of automotive electric motors, such as side mirror adjustment, seat positioning, climate control, and window opening/closing, is further driving innovation in electric mechanical design.

Currently, both brushed DC motors and brushless DC motors (BLDC) are used in automotive applications. However, BLDC is rapidly increasing in popularity, as it has many features that make it attractive to automotive engineers, chief among them being

• Compared with DC motors, BLDC motors have a higher degree of control and support variable speed operation (higher energy efficiency).

• BLDC motors are typically more compact than DC motors for comparable output power, saving valuable space (which is increasingly limited in modern automotive designs due to, for example, the inclusion of a greater number of wiring harnesses).

• Since BLDC motors do not require brushes or commutators, there are no sparking or noise issues.

• BLDC motors are less susceptible to wear and tear (a problem with DC motors), meaning they last longer, reducing repair or replacement costs.

Therefore, it is clearly very advantageous to install BLDC motors in automotive systems. However, they require more advanced drive electronics than DC. In many cases, discrete solutions are used to drive BLDC motors, involving a large number of off-the-shelf parts covering power, control, protection and thermal management activities. Typically, 13 to 16 discrete components need to be specified and installed. However, as commercial and technical pressures are greater than ever, this discrete approach is beginning to be considered outdated. It relies on too many components to be purchased, installed and tested, which may not be feasible in the future. In addition, this approach is not space-efficient and especially not cost-effective.

Power modules using highly integrated structures offer a more attractive alternative for the automotive industry. This can reduce component count, improve space utilization, and improve reliability (because there are fewer components that may fail), and also solve the problem of inconvenient installation of discrete devices. In addition, this approach requires fewer engineering resources to be allocated to the task, shortens the design cycle, and reduces the required investment. The emerging new generation of power modules with higher integration and more innovative packaging technology (including the use of thermally conductive metal substrates) is the key to further development of BLDC motor control.

Direct bond copper (DBC) substrate structures are driving the development of more advanced power modules, offering numerous operational and logistical advantages over discrete deployments or traditional power module solutions. Essentially, a DBC substrate consists of an insulating ceramic with excellent thermal conductivity. This ceramic layer is bypassed on either side by a highly conductive copper layer. The outer copper plate is covered with a coating, while the inner copper layer serves as the basis for a printed circuit structure. Components are soldered directly to the DBC. Interconnect bond wires connect the wafer and the printed circuit structure, or connect different components within the module, greatly reducing the physical footprint of the system, thereby reducing the size and weight of the final solution.

DBC还可以显着缩短电源系统的热路径，而不影响电气绝缘。这使得电源模块可以显著降低物料单成本，加快开发速度，改进热性能。，这种技术还支持实施比以前提及的替代方法的尺寸小很多的布局。因此，可以显着提高功率密度。它也无需电源模块和散热器之间额外的绝缘，为工程团队提供了更大的设计灵活性。卓越的热性能还意味着可以为电机驱动系统指定更小的散热器，进一步减轻了重量、节省了空间和降低了总系统成本。

In response to the growing demand for more sophisticated and higher performance power modules, ON Semiconductor is at the forefront of DBC power module design for automotive motor control. The company has launched the STK984-190E, a 30 A/40 V rated MOSFET power module that is highly optimized for automotive 3-phase BLDC motor drive applications. It includes 6 MOSFET devices in a 3-phase bridge configuration, and an additional MOSFET provides a reverse battery protection switch mechanism. The module uses a dual in-line package (DIP) with a size of only 29.6mm x 18.2mm x 4.3mm, which is much smaller than any similar product on the market.

Since all MOSFETs in the STK984-190-E are AECQ101 qualified, the module is able to cope with the harsh conditions of automotive applications. It is highly optimized for embedding into 12V automotive applications, including pumps, fans and wipers, and supports an operating temperature range of 40°C to 150°C. The STK984-190E can be used with ON Semiconductor's LV8907UW sensorless motor controller IC (combined with a LIN transceiver for in-vehicle networks) to provide a complete reference design for automotive BLDC motor control.

Figure 1: Illustration of the ON Semiconductor STK984-190E used in an automotive fan system for climate control

Figure 2: STK984-190E power module and LV8907UW motor controller IC for climate control fan; a) bottom view; b) top view

Adopting a more integrated strategy will improve the energy efficiency of 3-phase BLDC motor drives while making the entire system more compact, lighter and more reliable than before. The high power density levels achieved by modules (such as the power module just described in detail) mean that only half the board space and half the number of components of traditional discrete solutions are required - the size reduction will have a significant impact on the development of automotive electronics going forward. Therefore, these very advanced metal substrate modules will enable engineers to continuously improve the fuel economy and space utilization expected by the automotive industry.