The role of the substrates in Power electronics is twofold: to provide the interconnections to form an electric circuit (like a Printed Circuit Board), and a convenient way to cool the components. Compared to the techniques used in microelectronics, these substrates must carry higher currents, and provide a higher isolation voltage (up to several thousand volts). They also must operate over a wide temperature range (up to 150 or 200°C). Look up substrate in Wiktionary, the free dictionary. ... Power electronics is the technology associated with the efficient conversion, control and conditioning of electric power by static means from its available input form into the desired electrical output form. ... Close-up photo of one side of a motherboard PCB, showing conductive traces, vias and solder points for through-hole components on the opposite side. ...

Direct Bond Copper substrate

Structure of a Direct Bonded Copper Substrate (top) and an Insulated Metal Substrate (bottom).

Direct Bond Copper substrates are commonly used in power modules, because of their very good thermal performance. They are composed of a ceramic tile (commonly alumina) with a sheet of copper bonded to both sides by a high temperature oxidation process. The top copper layer is 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. Aluminium oxide (or aluminum oxide) (Al2O3) is a chemical compound of aluminium and oxygen. ... General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance metallic brown Atomic mass 63. ... Close-up photo of one side of a motherboard PCB, showing conductive traces, vias and solder points for through-hole components on the opposite side. ...

Ceramic material used in DBC include:

• Alumina (Al₂O₃) which is widely used because of its low cost. It is however not a really good thermal conductor and is relatively brittle.
• Aluminium nitride (AlN), which is more expensive, but has far better thermal performance.
• Beryllium oxide (BeO) has good thermal performance, but is often avoided because of its toxicity when the powder is ingested or inhaled.

One of the main advantages of the DBC substrates is their low coefficient of thermal expansion, which is relatively close to that of silicon (compared to pure copper). This ensures relatively good thermal cycling performances^[1]. Aluminium oxide (or aluminum oxide) (Al2O3) is a chemical compound of aluminium and oxygen. ... Aluminium nitride (AlN) is an extremely wide bandgap semiconductor material which has potential application for deep ultraviolet optoelectronics. ... Beryllium oxide (BeO) is a white crystalline oxide. ... During heat transfer, the energy that is stored in the intermolecular bonds between atoms changes. ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance dark gray, bluish tinge Atomic mass 28. ...

Insulated Metal Substrate

Insulated Metal Substrate (IMS) is constituted by 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. General Name, Symbol, Number aluminium, Al, 13 Chemical series poor metals Group, Period, Block 13, 3, p Appearance silvery Atomic mass 26. ... A dielectric, or electrical insulator, is a substance that is highly resistant to the flow of electric current and has a relative permittivity greater than unity. ... FR-4, an abbreviation for Flame Resistant 4, is a type of material used for making a printed circuit board (PCB). ...

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. Silicone thermal compound Metal (silver) thermal compound Metal Thermal Grease Small CPU Imperfections Thermal grease (also called thermal compound or thermal paste) is a substance used to help the conduction of heat between two (usually metal) surfaces. ...

Compared to classical Printed circuit board, the IMS provides a better heat dissipation. It is one of the simplest way to provide efficient cooling to surface mount components^[2] . Surface-mount components on a keydrives circuit board Surface mount technology (SMT) is a method for constructing electronic circuits in which the components are mounted directly onto the surface of printed circuit boards (PCBs). ...

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 multi-layer PCB allows design of complex circuits, whereas DBC and IMS are mostly single-sided technologies ^[3]

• Flexible substrates can be used for relatively low power applications. As they are built using Kapton as a dielectric, they can whistand high temperature and high voltages. Their intrinsic flexibility makes them resistant to Thermal cycling.

• Ceramic substrates (thick film technology) can also be used in some applications (such as automotive) where reliability is more important than good power dissipation ^[4].

A large copper heatsink. ... Close-up photo of one side of a motherboard PCB, showing conductive traces, vias and solder points for through-hole components on the opposite side. ... A through-hole component, also spelled thru-hole, is an Electronic component that has pins designed to be inserted into holes and soldered to pads on a printed board. ... Convection is the transfer of heat by currents within a fluid. ... Olympus Stylus camera with skins removed, showing flex circuit assembly. ... Kapton is a polyimide film developed by DuPont which can remain stable in a wide range of temperatures, from -269°C to 400°C. Kapton is used in, among other things, flexible printed circuits and spacesuits. ...

References

1. ^ Source: Curamik, manufacturer of DBC [1]
2. ^ Source: The bergquist company [2]
3. ^ Thermal Management in High-Density Power Converters , Martin März, International Conference on Industrial Technology ICIT'03 Maribor, Slovenia, December 10 - 12, 2003 [3] (pdf document, last accessed 6/5/06)
4. ^ Quick presentation of several applications and features of the thick film substrates [4]

• 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 [5] (restricted access)