Choosing Your Power Workhorse: Maxi Brick vs. Mini Brick IGBT Modules in High-Power Applications

In the world of high-power electronics, standardization is not just a matter of convenience; it’s a cornerstone of reliability, supply chain resilience, and system design efficiency. For decades, the “brick” style IGBT module has been the undisputed workhorse for applications ranging from industrial motor drives to renewable energy inverters. These industry-standard packages offer a robust, field-proven solution that engineers trust. Within this family, the Mini Brick and Maxi Brick represent two of the most common footprints, each tailored for specific power ranges and application demands. Choosing between them is a critical design decision that impacts thermal performance, power density, cost, and overall system reliability.

This article provides a deep dive into the characteristics of Maxi and Mini Brick standard packages, comparing their technical specifications, exploring their ideal application scenarios, and offering practical guidance for engineers making this crucial selection.

Understanding the Anatomy of a “Brick” IGBT Module

Before comparing Maxi and Mini Bricks, it’s essential to understand what makes this package style so enduring. A standard brick module is a marvel of electromechanical engineering, designed to handle immense electrical and thermal stress while providing straightforward integration.

The core components include:

• Copper Baseplate: A thick, flat copper plate forms the foundation of the module. Its primary role is to act as a highly efficient heat spreader, drawing thermal energy away from the semiconductor chips and transferring it to an external heatsink. Its mechanical rigidity is crucial for mounting.
• Direct Bonded Copper (DBC) Substrate: This is a ceramic substrate (typically Alumina, AlN, or Si3N4) with copper layers bonded to both sides. It provides excellent electrical isolation between the live semiconductor chips and the grounded baseplate while offering a low thermal resistance path. The top copper layer is etched to form the circuit traces.
• Semiconductor Chips: IGBT and Freewheeling Diode (FWD) chips are soldered onto the top copper layer of the DBC. These are the active components that perform the high-power switching.
• Wire Bonds: Thick aluminum wires connect the semiconductor chips to each other and to the power terminals, engineered to handle high currents and thermal cycling.
• Terminals and Housing: A robust plastic housing encases the internal components, providing mechanical protection and defining the electrical terminals (gate, emitter, collector). The screw-down power terminals and smaller control pins are standardized for position and size, facilitating easy busbar and gate driver connections.

The success of the brick package lies in this robust, thermally efficient, and standardized construction, which has been refined over generations of power modules. For a comprehensive overview of modern IGBT module technologies, see this guide on IGBT Modules.

Core Comparison: Maxi Brick vs. Mini Brick

While sharing the same fundamental design philosophy, Maxi and Mini Bricks are dimensionally and electrically distinct. The choice between them is primarily driven by the application’s power level, cooling capacity, and space constraints.

Here is a detailed comparison of their key characteristics:

Parameter	Mini Brick	Maxi Brick (and variants)
Typical Footprint	~107.5 mm x 45 mm	~107.5 mm x 62 mm
Typical Voltage Classes	600V, 1200V, 1700V	1200V, 1700V
Typical Current Range (per module)	50A to 250A (at 1200V)	200A to 600A (at 1200V)
Internal Configuration	Half-bridge (2-in-1), Single Switch (1-in-1)	Half-bridge (2-in-1), Single Switch (1-in-1)
Thermal Resistance (Rth(j-c))	Higher (less efficient heat transfer)	Lower (more efficient heat transfer due to larger baseplate)
Stray Inductance	Relatively low, suitable for moderate switching speeds	Slightly higher due to larger internal layout, but optimized for lower frequencies
Primary Application Area	Mid-power inverters (20-100 kVA), small to medium motor drives, UPS systems, welding machines.	High-power inverters (100 kVA+), large industrial motor drives, renewable energy converters, railway traction.
Cost Consideration	More cost-effective for lower power levels.	Higher unit cost, but often more economical at the system level for very high power due to fewer required parallel units.

Application Scenarios: Where Each Brick Shines

Theory and tables are useful, but real-world engineering problems best illustrate the trade-offs. Let’s explore two common design scenarios.

Scenario 1: Mid-Power Uninterruptible Power Supply (UPS)

Problem: An engineering team is designing a three-phase, 75 kVA commercial Uninterruptible Power Supply (UPS). The key design goals are high reliability, reasonable power density, and a streamlined manufacturing process. The inverter switching frequency is set at 8 kHz.

Solution: The team selects three 1200V / 200A Mini Brick IGBT modules, one for each phase of the inverter.

• Why Mini Brick? At this power level, a 200A Mini Brick provides sufficient current handling capability with a manageable thermal load. The smaller 45mm width allows for a more compact overall inverter layout, contributing to better power density. The standardized footprint simplifies PCB and busbar design, and multiple-sourcing from different manufacturers is straightforward, de-risking the supply chain.

Result: The final design meets the power requirements in a compact and cost-effective enclosure. The thermal dissipation per module is well within the limits of a standard forced-air cooled heatsink. The well-understood characteristics of the Mini Brick package simplify thermal simulation and reliability predictions, leading to a faster time-to-market.

Scenario 2: Heavy-Duty Industrial Motor Drive

Problem: A system integrator is building a robust variable frequency drive (VFD) for a 400 kW induction motor used in a rock crusher application. The environment is harsh, with high ambient temperatures, vibration, and severe load cycling. Extreme reliability and tolerance to overload conditions are paramount. The switching frequency is low, around 2-4 kHz, to minimize switching losses.

Solution: The design engineer opts for Maxi Brick modules. Specifically, they use three 1200V / 600A Maxi Bricks in a half-bridge configuration, paralleling two modules per phase leg is not required at this power level but the Maxi Brick is chosen for its ruggedness and thermal margin.

• Why Maxi Brick? The significantly larger baseplate of the Maxi Brick provides a lower thermal resistance, which is critical for dissipating the high conduction losses associated with the 400 kW load. This superior thermal performance translates directly into lower junction temperatures and, therefore, higher reliability and longer power cycling lifetime. The mechanical robustness and large screw terminals are better suited to handle the vibration and high-current busbars required in such heavy-duty applications. While paralleling smaller modules is an option, using a single, higher-rated Maxi Brick simplifies the gate drive and busbar layout, reducing the risk of current-sharing imbalances. For more insights into industrial motor control, Mitsubishi Electric offers valuable resources on their motion control solutions.

Result: The VFD operates reliably under demanding conditions. The lower operating temperature of the IGBT chips, thanks to the Maxi Brick’s efficiency, provides a significant safety margin against overloads and extends the service life of the drive, minimizing costly downtime for the end-user.

Practical Selection Guide and Engineering Tips

When selecting between Mini and Maxi Bricks, consider the following checklist:

1. Calculate Total Losses: First, estimate the total power dissipation (conduction and switching losses) for your target current, voltage, and switching frequency. This is the primary factor determining your cooling requirements.
2. Evaluate Thermal Performance: Use the module’s datasheet Rth(j-c) value to calculate the junction temperature. A Maxi Brick’s lower Rth(j-c) will result in a lower junction temperature for the same power loss, providing more thermal headroom. Aim to keep the maximum operating junction temperature well below the datasheet limit (e.g., Tj < 125°C for a 150°C rated device) to ensure long-term reliability.
3. Consider Paralleling Strategy: For very high power, you may need to connect modules in parallel. Using fewer, higher-current Maxi Bricks can simplify the busbar design and gate drive circuitry compared to paralleling many Mini Bricks. However, careful layout is still critical to ensure good current sharing. For expert guidance, refer to application notes like this one on demystifying IGBT paralleling.
4. Analyze Mechanical and Layout Constraints: Does your enclosure have space for the wider 62mm Maxi Brick footprint? The choice will dictate the heatsink size, busbar layout, and overall system dimensions. The larger terminals on a Maxi Brick may be necessary for the thick cables or busbars used in very high-current systems.
5. Factor in the Supply Chain: Both packages are widely available from multiple vendors like Infineon, Mitsubishi, Semikron, and Fuji Electric. However, for very specific voltage/current ratings, availability might differ. Confirming a stable supply chain with second-source options is a prudent step.

Conclusion: The Right Brick for the Right Job

The choice between Maxi Brick and Mini Brick IGBT modules is a classic engineering trade-off between power capability, thermal performance, size, and cost. There is no single “best” package; the optimal choice is entirely dependent on the application’s specific requirements.

To summarize the key decision factors:

• Choose Mini Brick for:
  • Mid-power applications (approx. 20-100 kVA).
  • Designs where power density and a compact footprint are critical.
  • Cost-sensitive projects at lower power levels.
  • Applications like commercial UPS, solar string inverters, and small-to-medium industrial drives.
• Choose Maxi Brick for:
  • High-power applications (100 kVA and above).
  • Systems where thermal margin, ruggedness, and ultimate reliability are the top priorities.
  • Low-frequency, high-current applications like large motor drives, central solar inverters, and industrial heating.
  • Designs that benefit from simplified high-current busbar connections.

By carefully analyzing the power requirements, thermal constraints, and mechanical layout of your system, you can confidently select the right power workhorse, ensuring your design is not only functional but also robust, reliable, and efficient for years to come.