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Mitsubishi Materials Corporation ("MMC") has developed a new product of the high-performance oxygen-free copper MOFC (Mitsubishi Oxygen-Free Copper) series, expanding the lineup. The newly developed MOFC-GC (Grain Control) is a new oxygen-free copper (*1) that is extremely resistant to the crystal grain coarsening during heat treatment.

With the electrification of automobiles and the spread of renewable energy, materials and components for electronic devices are required to have high electrical conductivity and high heat dissipation performance to handle large currents. As a result, demand for oxygen-free copper, which has excellent electrical and thermal conductivity, is rapidly expanding. In power modules (*2) used for power control and conversion in xEVs, etc., materials such as AMB substrates (*3) are used to dissipate heat generated from semiconductor elements, and many of them use oxygen-free copper for the circuit layer (see Figure 1).
Manufacturing AMB substrates requires brazing of ceramics and oxygen-free copper. However, conventional oxygen-free copper has problems that cause quality variation and affect the performance of AMB substrates, such as coarsening of the copper crystal grains and formation of non-uniform structures due to heat treatment in the brazing process.

For this reason, oxygen-free copper, from which AMB substrates are composed, is required to have characteristics that inhibit coarsening of the crystal grains even when heated (crystal grain growth inhibition performance). Materials with advanced crystal grain growth inhibition performance that resist coarsening of the crystal grains over a wide range of temperatures are especially required in recent years in order to accommodate various brazing conditions.
In response to this demand, MMC has successfully developed the oxygen-free copper MOFC-GC, which achieves a fine and uniform crystal structure with very little variation in crystal grain size even after heat treatment, by making full use of its high quality oxygen-free copper production technology nurtured over many years, as well as its proprietary material design and patented technology (see Figure 2).




Figure 2: Crystal structure image comparison between newly developed MOFC-GC
and conventional oxygen-free copper (*)
(*) Optical micrograph of each copper circuit layer surface of AMB substrate (prototype) fabricated using the same brazing conditions with the only difference being the copper circuit materials in order to compare the crystal structures
(Click the picture to see the enlarged image)

It has been confirmed that MOFC-GC stably maintains a fine and uniform crystal structure even when heated to 1000℃ (see Figure 3), which was not possible even with conventional improved oxygen-free copper, and inhibits crystal grain coarsening to an extremely high level.
In addition, as well as having advanced crystal grain growth inhibition performance, it also shows high electrical and thermal conductivity (*4), contributing to improved quality and more stable processes for various electronic components and modules.

MOFC-GC can be provided in a wide range of thickness from 0.3 mm to 1.2 mm. The following benefits can be expected from using it as the material for the circuit layer of ceramic substrates such as AMB substrates.

• Improved optical recognizability
• Reduced surface roughness (improved smoothness and reduced variation)
• Improved plating appearance
• Improved ultrasonic image inspection quality of the brazing boundary between the copper circuit layer and the ceramic
• Stabilized substrate warpage
• Improved thermal cycle reliability
• Resolves the problem of insufficient wire bonding strength (when using small diameter wires, etc.)
• Reduced variation in semiconductor device soldering and sintered material bonding

MMC Group has established Our Commitment as "For people, society and the earth, circulating resources for a sustainable future." We will continue to create new materials and supply one-of-a-kind highly functional materials and products to strive toward realizing Our Commitment.

(*1)

Copper with a purity of 99.96% or more with an extremely low oxygen (oxide, etc.) content. An application for the registration of MOFC-GC has been filed to the Copper Development Association (CDA).

(*2)

A power module is a module used for power control and conversion in xEVs, etc. that combines multiple power semiconductors (IGBTs, MOSFETs, etc.), drive circuits, protection circuits, etc. in a single package.

(*3)

AMB stands for active metal brazing. An AMB substrate, or active metal brazed substrate, is an electronic component (ceramic substrate) composed of a copper plate (circuit layer) and ceramic (insulating layer) such as alumina (Al₂O₃), aluminum nitride (AlN), and silicon nitride (Si₃N₄) brazed with brazing filler metal containing active metals.
Compared to a ceramic substrate composed of a copper plate directly bonded with ceramic, which is generally called a DCB (direct copper bonded) substrate, it is highly reliable for temperature cycle tests, etc.

(*4)

Comparable to those of oxygen-free copper C10200, which has the highest electrical conductivity (101%IACS) and thermal conductivity (391 W/m∙K) of all copper materials.

(*5)

Results of observation after annealing a single copper plate in an air atmosphere at a heating rate of 10℃/min and holding time of 1 hr.

[Related Release]

September 27, 2021
Development of "MOFC-HR" (HR: Heat Resistance)
Oxygen-Free Copper with the World's Highest Standard in Strength and Heat Resistance
URL: https://www.mmc.co.jp/corporate/en/news/2021/news20211001a.html

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