Metallized Ceramic Substrates for the New Decade

Jan 27, 2020

Reliability

Direct Bonded Copper (DBC) and Active Metal Brazed (AMB) substrates have been available for the last four decades. Together they have made a large contribution to the market adoption and penetration of power modules. Rogers Corporation is at the forefront of research and development with its curamik® product portfolio. With the welcoming of the new decade, the question arises which substrate innovations are required to face the challenges associated with a new generation of power modules. Let’s imagine what could be the next technology leap for substrates.

New ceramic materials

Alumina (Al2O3), aluminum nitride (AlN) and silicon nitride (Si3N4) are the most popular advanced ceramic materials for the production of DBC and AMB substrates. Advanced ceramic materials have a good dielectric strength, a high melting temperature and are highly resistant to chemicals. Consequently, they can be used as an insulator for a wide range of applications in power electronics, despite harsh conditions. However, their thermal and mechanical properties – though they are good enough for state-of-the-art power modules - are limiting factors to achieve a better heat dissipation and eventually maintain or improve the module's lifetime with increased power density. New developments in the field of ceramic materials are required to reach an unprecedented level of thermal and mechanical performance that has the potential to change the game. Rogers' Power Electronics Solutions (PES) team is currently exploring various options with its long term and strategic suppliers.

Thicker copper layers

Copper is well-established as a material for metallization on ceramic substrates due to its superior electrical and thermal conductivity. The ever-growing power density, current carrying capability and reliability requirements are positive characteristics leading to its widespread use in the market. In addition, copper is readily available, relatively inexpensive and not likely to disappear anytime soon.

Typically, copper thickness ranges from 127 µm up to 800 µm. However, module makers are pushing the limits of semiconductor and packaging technologies to further increase the output power in existing or even smaller footprints. This eventually leads to the development of substrates with layers of copper thicker than 1 mm. Because of its isotropic characteristic, wet chemical etching becomes inadequate for patterning thick copper layers, as it results in wide trenches between conductor tracks while customers require narrow trenches to reduce the footprint of their modules. Instead, specialized structuring technologies have to be developed to achieve narrow gaps, straight sidewalls and negligible undercut.

Novel and more complex structures

DBC and AMB substrates are currently available in simplistic single layer structures and most often in a rectangular shape. More design freedom is required to assemble small and fast switching semiconductor devices in a compact form factor. Chip embedding and double side cooling are recent developments highlighting the need for more complex structures. Cavities in copper metallization and small copper protuberances are examples of structures to facilitate new die attach techniques. Although, this requires specialized copper patterning and structuring technologies.

A multilayer structure is another approach that was demonstrated to be effective in a study conducted by the Fraunhofer institute. Interconnection between layers is the key technology and foundation for multilayer structure. This structure has the advantage of combining a short thermal path from the chip back side to the ambient and a low inductive connection to the gate, source and drain contacts of each switching cell.

Integration

If you consider a broad view Rogers is aiming to deliver solutions that truly relieve the pains and maximize the gains in the power electronics value chain; integration has the potential to do that.

Heat dissipation, reliability and costs can be improved through a smart combination of substrates, base plate and heat sink in only one component because less assembly steps and joining layers are required for the benefit of the module maker and end user. Parasitic inductance in the gate and commutation loops can be significantly reduced, due to integrated connections between substrates and rigid busbars or flexible printed circuit boards. Even passive components such as capacitors or entire cooling systems can be integrated onto substrates.

But integration often requires a paradigm shift. A higher level of integration comes along with higher risks, as scrap costs become more significant for the same production yield loss. Besides, not any kind of integration makes sense and a thorough analysis of the process and value chain is indispensable to define the best strategy.

As a manufacturer of metallized ceramic substrates with a strong commitment to serve the power electronics community, Rogers is continuously investing in marketing, research and development to understand the market requirements, explore potential solutions and foster innovation. If you have any questions, would like to share your future substrates needs or discuss the various options currently under development, please contact us. Our Rogers' PES team is available to become your development partner.

The information herein is for reference only. Neither the author nor Rogers Corporation makes any warranties as to its contents.