Frequently Asked Power Electronics Questions

Jul 01, 2020

Reliability

Olivier´s Twist is typically utilized for deeper discussions over specific topics within the power electronics community. Our goal is to provide guidance and information on the most applicable substrates for your current or future application. However, in this edition we would like to answer a few frequently asked questions to benefit those new to the power electronics community and a refresher training for those experienced in the industry as well.

What do the abbreviations DBC and AMB stand for?

DBC stands for Direct Bonded Copper and AMB stands for Active Metal Brazing. Both acronyms refer to joining technologies to attach relatively thick copper sheets, of typically 0.2 mm and more, on flat ceramic tiles. These technologies are used for the production of metallized ceramic substrates.

What are metallized ceramic substrates used for?

Metallized ceramic substrates are required to carry and interconnect multiple power semiconductor devices to form an electronic assembly known as a power module or multichip package.

What is the main difference between DBC and AMB?

AMB requires an active metal to braze copper on ceramics, however no additional material is needed to join copper and ceramics with DBC technology.

Which kind of ceramics can be used for DBC and AMB?

DBC technology only works with oxide ceramics such as alumina (Al2O3) and zirconia doped alumina (also known as HPS). Non-oxide ceramics will have to be oxidized before they can be bonded to copper with the DBC technology. This is possible for aluminum nitride (AlN) which can be produced either as DBC or AMB substrates in contrast to silicon nitride (Si3N4) which is available as an AMB substrate only.

Does AMB work with oxide ceramics too?

Yes, it does. However, DBC is the established technology to join thick copper with oxide ceramics because it is satisfactory and less expensive than AMB.

What are the most important ceramic properties to consider when designing a new substrate?

Ceramics are chemically inert and resistant to corrosion, humidity and temperature, which is often the reason ceramics are preferred in contrast to organic dielectrics that can degrade in applications with corrosive environments. Electrical, thermal and mechanical properties are equally important considerations when designing a new substrate. Dielectric strength is critical to fulfill the requirements regarding isolation; and set by the standards, norms and regulations for the targeted application. A low thermal conductivity would negatively impact the heat conduction from the chips to the ambient. The bending strength and fracture toughness play a significant role to improve the substrate’s lifetime when it is exposed to thermomechanical stress.

How do I select the right substrate for my application?

First, you should understand how much heat needs to be dissipated from the power semiconductor devices in your application. Depending on the chip and ambient temperatures you can then calculate the required thermal resistance of your substrate. However, not every combination of copper and ceramic is possible to achieve the required thermal resistance. On one hand, isolation voltage defines the minimum ceramic thickness. On the other hand, the copper to ceramic thickness ratio has a strong influence on the reliability. Finally, there are only a limited number of standard combinations which are already available.

Are DBC and AMB substrates suitable for high voltage applications?

DBC substrates are very popular for applications with an operating voltage up to 1.7 kV. For higher operating voltages a thick ceramic layer is necessary in order to fulfill the requirements regarding isolation. AlN is often selected because its high thermal conductivity compensates for the increase in thickness. Moreover, resistance against partial discharge is particularly important for such applications. Therefore, in this regard AMB is better than DBC technology, unless voids in the interface between copper and ceramic can be eliminated.

What are the standard combinations?

Please refer to our design rules to check the standard combinations. The most recent edition of our design rules can be found in the Design Support Hub accessible by the link below.

www.rogerscorp.com/designhub

Are DBC and AMB substrates available with copper metallization on both sides only?

DBC and AMB substrates can also be produced with copper metallization on only one side but these substrates are not standard material combinations because the resulting substrates’ flatness are critical for many applications.

Which options for surface plating and surface treatments are possible?

Bare copper surface, nickel, gold and silver plating are possible. Additionally, substrate roughness can be reduced upon request. Such information should be included in the drawing or in a technical specification.

What are the minimum and maximum possible size for DBC and AMB substrates?

DBC and AMB substrates cannot be bigger than 5” x 7” (127 mm x 178 mm) which is the maximum usable area on our ceramic panels. Any substrate larger than 15 mm x 15 mm can be produced and delivered according to our design rules. Upon request smaller substrates are possible but they are likely to be more expensive as they require additional laser cutting, complex handling and packaging and added care during the production and final inspection.

Which substrates shapes are possible?

A rectangular shape is the least expensive to produce and the most common. Other shapes are possible but are likely to generate additional production costs.

In which format can DBC and AMB substrates be delivered?

DBC and AMB substrates are usually delivered as single pieces. However for mass production, panels containing multiple single piece substrates are also available. In this case the single pieces usually have a rectangular shape and will be separated by the customer after delivery. In addition, single pieces can be pre-cut by means of laser technology for an easier separation.

How are the substrates arranged on the panel?

All substrates are arranged in the same direction and aligned next to each other to achieve the best possible utilization of the total surface area. However, other arrangements are possible on request.

How long can DBC and AMB substrates be stored?

Under conditions of 22°C +/- 5°C, substrates can be stored in an air atmosphere before opening the sealed tray packaging or in a pure nitrogen atmosphere after opening the sealed tray packaging; for a maximum of 12 months as indicated on the tray label. On a production floor, the substrates should be processed within 24 hours after opening the sealed tray packaging.

What information is required for a quote?

For an initial quote we do not necessarily need a drawing. Preliminary information such as substrate length and width, type of ceramic, ceramic thickness, copper thickness on front and back sides, surface finish and the required quantity are sufficient to complete the first quote.

Which drawing format is required for production?

DXF and DWG files are required. Gerber files can be accepted, if DXF or DWG files are not available.

How do I make sure that the drawing is compliant with the design rules?

Our team will check your drawing and will provide a counter proposal if the drawing does not comply with the design rules.

What is the minimum order quantity?

For samples, the minimum order quantity is ten master cards. For mass production, the minimum order value is 2.000€ for each item.

Do you have any questions or require some information about our substrates? Please contact us, if you need any assistance.

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