Direct Bond Copper (DBC) technology, which involves bonding copper foil directly to ceramic substrates, has been widely adopted for various microelectronic applications. It utilizes copper foil instead of pastes or expensive sputtered metallization, providing excellent electrical and thermal properties. Initially designed for high-power circuits, advancements in the DBC process have expanded its applications to fine-line and high-frequency circuits.

The DBC process involves using oxidized copper foil, such as oxygen-free or tough-pitch copper, which is placed on an oxide ceramic substrate like alumina or beryllium oxide. The foil and substrate are then subjected to high temperatures in a specialized belt furnace with a controlled thermal profile. The elevated temperature causes the copper oxide to form a liquidus cuprous oxide matrix, chemically bonding to the ceramic surface. The resulting bond exhibits exceptional strength, exceeding 24,000 PSI sometimes, particularly with alumina and beryllium oxide surfaces.

However, how does the blistering formed during the process?

During the bonding process, excess gas is released as the cupric oxide on the copper surface converts to cuprous oxide. To prevent gas entrapment and the formation of blisters, the copper foil is often pre-etched with parallel grooves. These grooves facilitate gas dissipation but can lead to other challenges like chemical entrapment, ceramic staining, and undercutting in fine-line circuits. Modern techniques aim to control oxide thickness, eliminating the need for grooves and addressing these issues.

Thorough Surface Cleaning and proper surface activation can also reduce the amount of blistering being formed: Implement a rigorous cleaning process to ensure the removal of any contaminants or debris from both the copper and ceramic surfaces before bonding. Use appropriate surface activation techniques, such as plasma cleaning or chemical treatments, to promote strong bonding and minimize bubble formation.

Even temperature distribution: Inconsistent temperature distribution within the furnace can result in inconsistent bonding quality of DBC products. Uneven temperature can lead to overheating in some areas and insufficient temperature in others, affecting the stability and consistency of the bonding process. This can result in variations in bonding strength and potential cracks and damage due to thermal stress.

Stable atmosphere control and oxygen content: The atmosphere control and oxygen content within the furnace have a significant impact on the quality of DBC products. If the atmosphere control is unstable, such as having high oxygen content, it can lead to oxidation of the copper surface, compromising the reliability and electrical performance of the bonding. Maintaining the appropriate atmosphere and stable oxygen content can minimize occurrences of oxidation and contamination, thereby enhancing the quality of DBC products.

Fortunately, the use of a quality-designed belt furnace can effectively address the challenges of uneven temperature distribution and unstable atmosphere control in DBC production:

To address uneven temperature distribution and unstable atmosphere control, a quality-designed belt furnace can provide solutions. Our Hengli furnace ensures a high level of temperature uniformity with an across belt temperature uniformity of ±1°C and a an across section temperature uniformity of ±1.5°C. The heating zone and dwell zone are regulated by a closed-loop negative feedback system with a control accuracy of ±5ppm, ensuring precise and stable temperatures. Additionally, for applications requiring a fully nitrogen environment, we can achieve oxygen content levels lower than 2PPM, creating optimal conditions for production.