science

Power electronic substrate

Power electronic substrate is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Power electronic substrate rather than just read about it. In short: The role of the substrate in power electronics is to provide the interconnections to form an electric circuit (like a printed circuit board), and to cool the components. Compared to materials and techniques used in lower power microelectronics, these substrates must carry higher currents and provide a higher voltage isolation (up to several thousand volts).

Key takeaways

Power electronic substrate belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Power electronic substrate to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Power electronic substrate from memory before moving on to harder problems.

Reference excerpt

The role of the substrate in power electronics is to provide the interconnections to form an electric circuit (like a printed circuit board), and to cool the components. Compared to materials and techniques used in lower power microelectronics, these substrates must carry higher currents and provide a higher voltage isolation (up to several thousand volts). They also must operate over a wide temperature range (up to 150 or 200 °C).

Direct Bonded Copper (DBC) substrate

DBC substrates are commonly used in power modules, because of their very good thermal conductivity. They are composed of a ceramic material tile with a sheet of copper bonded to one or both sides by a high-temperature oxidation process (the copper and substrate are heated to a carefully controlled temperature in an atmosphere of nitrogen containing about 30 ppm of oxygen; under these conditions, a copper-oxygen eutectic forms which bonds successfully both to copper and the oxides used as substrates). The top copper layer can be preformed prior to firing or chemically etched using printed circuit board technology to form an electrical circuit, while the bottom copper layer is usually kept plain. The substrate is attached to a heat spreader by soldering the bottom copper layer to it. A related technique uses a seed layer, photoimaging, and then additional copper plating to allow for fine lines (as small as 50 micrometres) and through-vias to connect front and back sides. This can be combined with polymer-based circuits to create high density substrates that eliminate the need for direct connection of power devices to heat sinks. One of the main advantages of the DBC vs other power electronic substrates is their low coefficient of thermal expansion, which is close to that of silicon (compared to pure copper). This ensures good thermal cycling performances (up to 50,000 cycles). The DBC substrates also have excellent electrical insulation and good heat spreading characteristics. Ceramic material used in DBC include:

Alumina (Al2O3), commonly used because of its low cost. It is however not a really good thermal conductor (24-28 W/mK) and is brittle. Aluminium nitride (AlN), which is more expensive, but has far better thermal performance (> 150 W/mK). Silicon nitride (SiN) (90 W/mK) HPS (Alumina w/ 9% ZrO2 doped) (26 W/mK) Beryllium oxide (BeO), which has good thermal performance, but is often avoided because of its toxicity when the powder is ingested or inhaled.

Active Metal Brazed (AMB) substrate AMB consists of a metal foil soldered to the ceramic baseplate using solder paste and high temperature (800 °C – 1000 °C) under vacuum. Although AMB is electrically very similar to DBC, it is typically suited for small production lots due to the unique process requirements.

Insulated Metal substrate (IMS)

IMS consists of a metal baseplate (aluminium is commonly used because of its low cost and density) covered by a thin layer of dielectric (usually an epoxy-based layer) and a layer of copper (35 μm to more than 200 μm thick). The FR-4-based dielectric is usually thin (about 100 μm) because it has poor thermal conductivity compared to the ceramics used in DBC substrates. Due to its structure, the IMS is a single-sided substrate, i.e. it can only accommodate components on the copper side. In most applications, the baseplate is attached to a heatsink to provide cooling, usually using thermal grease and screws. Some IMS substrates are available with a copper baseplate for better thermal performances. Compared to a classical printed circuit board, the IMS provides a better heat dissipation. It is one of the simplest ways to provide efficient cooling to surface mount components.

Other substrates When the power devices are attached to a proper heatsink, there is no need for a thermally efficient substrate. Classical printed circuit board (PCB) material can be used (this method is typically used with through-hole technology components). This is also true for low-power applications (from some milliwatts to some watts), as the PCB can be thermally enhanced by using thermal vias or wide tracks to improve convection. An advantage of this method is that multilayer PCB allows design of complex circuits, whereas DBC and IMS are mostly single-sided technologies. Flexible substrates can be used for low-power applications. As they are built using Kapton as a dielectric, they can withstand high temperatures and high voltages. Their intrinsic flexibility makes them resistant to thermal cycling damage. Ceramic substrates (thick film technology) can also be used in some applications (such as automotive) where reliability is of highest importance. Compared to DCBs, thick film technology offers a higher degree of design freedom but may be less cost-efficient. The thermal performances of IMS, DBC and thick film substrate are evaluated in Thermal analysis of high-power modules Van Godbold, C., Sankaran, V.A. and Hudgins, J.L., IEEE Transactions on Power Electronics, Vol. 12, N° 1, Jan 1997, pages 3–11, ISSN 0885-8993 [4] (restricted access)

References

Illustrations

Worked examples

Example 1 — a first encounter with Power electronic substrate

Start with the simplest possible case. Write down what Power electronic substrate claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Power electronic substrate before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Power electronic substrate ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Power electronic substrate

In research: Power electronic substrate appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Power electronic substrate in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Power electronic substrate is common in secondary-school and first-year university syllabi. It links to neighbouring topics Power electronics, so understanding it makes those chapters shorter.
In everyday life: Look for Power electronic substrate outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Power electronic substrate in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Power electronic substrate means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Power electronic substrate out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Power electronic substrate in simple terms?

Why does Power electronic substrate matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Power electronic substrate?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Power electronic substrate.