Cooling for High-Performance Modules, Both Small and Large
High temperatures in electronic components significantly reduce their service life and affect the reliability of individual parts. Efficient thermal management keeps electronic components within the manufacturer-specified temperature range and prevents operational failures, including complete component destruction. This affects all areas of cooling in electronic building blocks, including power electronics.
Today’s power electronics are a subfield of electrical engineering and largely involve steering, converting, or shifting electrical energy. Power electronics systems, such as power inverters, power supply units, motor control systems, or EV charging units, generate significantly more heat during operation. Electrical resistance generates this thermal waste heat, for example, in semiconductors, transformers, converters, throttles, conductive paths, and passive elements. Heat loss depends directly on switching frequency, load current, voltage level, and the cooling method for each component.
Without appropriate measures to dissipate waste heat, operational components will inevitably overheat, resulting in serious consequences. Efficient, well-designed thermal management ensures that operating temperatures remain within specified limits. Targeted heat dissipation through suitable cooling concepts is a critical aspect of electronic design and a standard part of every power electronics design. Cooling solutions that work well and suit the application increase reliability, extend service life, and enable higher power densities in electronic components and systems.
Thermal dissipation in small form factors
Mini-fan cooling
Power dissipation in high-performance electronic components built onto circuit boards is so common today, and at such volume, that purely passive cooling methods using classical aluminum heatsinks are no longer adequate. High-volume, high-performance heatsinks exist; however, because of their size and weight, they are often a poor choice for attaching to circuit boards.
The LAM series mini-fan units shown in Figure 1 are small, compact, high-performance, and specially designed to remove large volumes of heat in a small space. Mini-fan units can be built into the circuit boards themselves or mounted on them, which can greatly benefit the user.
An above-mounted axial fan motor directs air over tube-shaped extruded aluminum sections with specially shaped internal heat-exchange structures in finned form, allowing high volumes of heat to be dissipated. The internal heat-exchange structure handles the rest, creating a homogeneous heat distribution across the entire aluminum section. The assembly and geometry of these internal heat-exchange surfaces are calibrated to the specific characteristics of each fan, such as dynamic pressure and air volume.
The basic structure of each cross-section consists of a wraparound rectangular base frame, which also serves as the mounting base for the semiconductor. The back of this base is equipped with the fin structure, which absorbs heat from the component and transfers it into the internal airflow of the cell structure. The upstream fan, positioned in front of the base section, forces the heat building up in the fin channel out and away from the unit.
Semiconductors are mounted to the fan unit either using CNC-machined threaded inserts or via a clip assembly with specially designed snap-in transistor-retaining springs. These springs use integrated groove geometry to ensure secure, quick anchoring of the component to the semiconductor surface.
Liquid heatsinks
If the goal is an even greater increase in heat dissipation on the circuit board, high-performance liquid heatsinks are an efficient way to cool smaller power modules (Figure 2).
These are specially conceived, developed, and available for use on circuit boards. The different types of liquid heatsink models are made of stainless steel so that no corrosion protection is needed when using water as the cooling medium. The liquid heatsink in Figure 2 measures 40 × 10 × 30 mm (L × W × H) and can dissipate ~670 W, with a temperature differential from water input to water output of 10°C and a normal operating pressure of 3 bar.
The liquid heatsinks are attached to the circuit using pressed-in soldering pins on the underside, forming a secure, stable joint with the circuit board, for example, via reflow soldering. The special liquid heatsinks for the circuit board are manufactured via 3D printing and have an internal heat-exchange structure optimized by AI.
Each assembly side has its own cooling circuit, separating the two sides of the heatsink and generating very low flow-pressure losses. The result for the user is dual-sided component mounting on a single liquid heatsink. Alternative power semiconductor packaging, for example, in a TO package or a multiwatt system-in-package form factor, is mounted the same way as described for the fan-cooled units: using an integrated groove geometry and THFU-series snap-in transistor-retaining springs to secure the components in place.
The two-sided semiconductor assembly areas are also finely sanded and very uniform, with low surface roughness. Beyond the standard models, Fischer Elektronik also offers custom design options, materials, and features tailored to specific client requirements.
Thermal dissipation in larger form factors
Fan-cooled systems
For cooling very large power modules—for example, different IGBT performance classes—users must, in practice, rely on fan-cooled systems. These systems consist of large hollow-fin sections paired with fan motors mounted at the air inlet. High-performance fan aggregates using radial fan motors (Figure 3) can achieve airflow rates of up to 1,400 m3/h, resulting in a minimal thermal resistance of just under 0.015 K/W.
In a radial fan motor, air is drawn in laterally through the fan-blade geometry, redirected 90°, and then expelled as a high-volume, high-pressure stream into the heat-exchange structure of the hollow-fin section. High-performance fan aggregates driven by radial fan motors can be considerably larger than those using other fan types, which generally don’t tolerate high pressure as well.
To ensure proper assembly of the power module onto the base section, base plates made of durable materials are used. These serve two purposes: promoting even heat distribution within the fan aggregate and providing a solid anchoring point for the power module across different types of mounting threads. Manufacturer-specified surface tolerances for the assembly, particularly with respect to diagonal flex and longitudinal torsion, can readily be corrected through a machining process such as CNC milling.
A closer look at the standard tolerance fields in a power module’s datasheet quickly shows that the manufacturer-recommended surface smoothness of <0.02 mm typically cannot be achieved without additional mechanical adjustment. For this reason, along with the complexity and precision required, all semiconductor assembly surfaces on Fischer Elektronik’s fan aggregates are precision-milled to standard dimensions and further protected from damage with protective wrapping.
Larger liquid heatsinks
For cooling applications in which power modules can’t accommodate high-performance fan aggregates due to large installation-space requirements, high weight, or high noise levels from fan motors, compact liquid heatsinks (Figure 4) offer an efficient alternative.
Liquid heatsinks paired with water as the cooling medium perform very reliably. This is evident in water’s specific heat capacity: At 4.182 kJ/kg·K, water’s cooling capacity is about 4× that of air, which is why liquid cooling significantly outperforms other cooling approaches.
Fischer Elektronik’s liquid heatsinks are made entirely of aluminum, including the internal, 3D honeycomb structure that serves as the heat-exchange surface. For this reason, a water-glycol mixture should be used as the cooling medium rather than pure water. The individual aluminum sections are bonded to the internal heat-exchange structure to form the side pieces and semiconductor mounting surfaces, providing optimal heat transfer from the component being cooled into the continuously flowing liquid. Both the liquid heatsink construction and the precisely milled semiconductor mounting surfaces allow flexible component placement with minimal thermal transfer resistance.
Different liquid heatsink types can use different connection technologies and, depending on their base construction, be implemented as I-flow or U-flow models. High manufacturing quality minimizes leakage concerns for the user, as proven sealing procedures, coupling systems, and hose systems represent the current state of reliable technology in this area.
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