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).
Structure of a direct bonded copper substrate (top) and an insulated metal substrate (bottom).
DBC substrates are commonly used in power modules, because of their very good thermal conductivity.[1] 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.[2]
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).[3] The DBC substrates also have excellent electrical insulation and good heat spreading characteristics.[4]
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.[5]
Aluminium nitride (AlN), which is more expensive, but has far better thermal performance (> 150 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) substrateedit
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)edit
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.[6][7]
Other substratesedit
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.[8]
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.[9] 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)
^Source: Liu, Xingsheng (February 2001). "Processing and Reliability Assessment of Solder Joint Interconnection for Power Chips". Virginia Tech Dissertation [1]
^Source: Liu, Xingsheng (February 2001). "Processing and Reliability Assessment of Solder Joint Interconnection for Power Chips". Virginia Tech Dissertation [2]
^Source: The Bergquist company 8 February 2006 at the Wayback Machine
^Source: AI Technology, Inc 28 September 2007 at the Wayback Machine
^Thermal Management in High-Density Power Converters , Martin März, International Conference on Industrial Technology ICIT'03 Maribor, Slovenia, 10–12 December 2003 (PDF). Archived from the original (PDF) on 13 June 2007. Retrieved 6 May 2006.{{cite web}}: CS1 maint: archived copy as title (link) (pdf document, last accessed 6/5/06)
^Quick presentation of several applications and features of the thick film substrates
January 01, 1970
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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 Contents 1 Direct Bonded Copper DBC substrate 2 Active Metal Brazed AMB substrate 3 Insulated Metal substrate IMS 4 Other substrates 5 ReferencesDirect Bonded Copper DBC substrate edit nbsp Structure of a direct bonded copper substrate top and an insulated metal substrate bottom DBC substrates are commonly used in power modules because of their very good thermal conductivity 1 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 2 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 3 The DBC substrates also have excellent electrical insulation and good heat spreading characteristics 4 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 5 Aluminium nitride AlN which is more expensive but has far better thermal performance gt 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 editAMB 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 editIMS 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 mm to more than 200 mm thick The FR 4 based dielectric is usually thin about 100 mm 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 6 7 Other substrates editWhen 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 8 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 9 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 edit Rogers DBC Datasheets PDF Source Hytel Group manufacturer of copper on ceramic substrates Archived 22 February 1999 at the Wayback Machine Source Curamik manufacturer of DBC Source Liu Xingsheng February 2001 Processing and Reliability Assessment of Solder Joint Interconnection for Power Chips Virginia Tech Dissertation 1 Source Liu Xingsheng February 2001 Processing and Reliability Assessment of Solder Joint Interconnection for Power Chips Virginia Tech Dissertation 2 Source The Bergquist company Archived 8 February 2006 at the Wayback Machine Source AI Technology Inc Archived 28 September 2007 at the Wayback Machine Thermal Management in High Density Power Converters Martin Marz International Conference on Industrial Technology ICIT 03 Maribor Slovenia 10 12 December 2003 Archived copy PDF Archived from the original PDF on 13 June 2007 Retrieved 6 May 2006 a href Template Cite web html title Template Cite web cite web a CS1 maint archived copy as title link pdf document last accessed 6 5 06 Quick presentation of several applications and features of the thick film substrates 3 Retrieved from https en wikipedia org w index php title Power electronic substrate amp oldid 1190233114 Insulated metal substrate, wikipedia, wiki, book, books, library,
