Why Are Large-Size Single-Crystal Diamond Heat Sinks Manufactured Using a Mosaic Assembly Process?

In the packaging design of 5G RF power amplifiers, automotive VCSEL radars, high-performance AI chips, and high-power industrial lasers, large-area single-crystal diamond heat sinks measuring 35 mm or larger are an essential requirement. Most procurement and thermal design engineers ask the same question: Why do 25×25 mm single-crystal heat sinks on the market tend to use a mosaic assembly structure? This is not due to a simplification of manufacturing processes, but rather because of unavoidable physical limitations in MPCVD single-crystal growth; the mosaic approach is currently the only industrial solution that balances high quality with mass-production feasibility.

1. Limitations Imposed by the Uniform Temperature Zone in the Plasma Field

In mainstream 2450 MHz mass-production MPCVD systems, the microwave plasma is spherical. Only a very small central region within the chamber can maintain uniform and stable temperature, hydrocarbon gas flow, and plasma density. Only within this region can single-crystal diamond with low nitrogen content, no twins, and no polycrystalline regions be grown. If the seed crystal’s edge length exceeds 12 mm, the crystal edges fall within the region of plasma non-uniformity. The temperature gradient continues to widen, resulting in the growth of extensive polycrystalline layers and dislocation defects, causing a direct drop in local thermal conductivity of more than 30%. Even when using 915 MHz ultra-large-chamber equipment, the total cost of the system, energy consumption, and O&M costs increase by 8–10 times, with a yield rate of less than 10%, making industrial-scale batch production unfeasible.

2. Risk of Stress Cracking in Large-Area Crystal Growth

Diamond has an extremely low coefficient of thermal expansion. During the growth of a single large-size single crystal, a persistent temperature difference exists between the center and the edges of the crystal, causing massive internal growth stresses to accumulate. When the single crystal exceeds 25 mm in size, these stresses increase exponentially, making it highly prone to developing microscopic internal cracks invisible to the naked eye after cooling; under thermal cycling conditions in high-power devices, the entire single crystal may shatter, resulting in complete device failure. The mosaic process divides large crystals into multiple 10–12 mm standard, high-quality seed crystals, allowing the stress in each individual crystal to be controlled and eliminating the risk of hidden cracks at the source.

Many customers hold the misconception that assembly will compromise a heat sink’s thermal conductivity. In fact, a mature, precision mosaic assembly process fully preserves the core thermal dissipation advantages of single-crystal diamond, meeting the demands of high-end precision thermal management applications.

1. The overall thermal conductivity is excellent. The core heat dissipation areas of the heat sink consist entirely of high-purity single-crystal structures. The bonding interfaces undergo precise growth control, resulting in extremely low residual stress and preventing the formation of thermal barrier layers. The thermal conductivity of the entire substrate can be stably maintained at 1800–2000 W/m·K, which is essentially on par with that of a single, monolithic crystal and far exceeds that of traditional heat dissipation materials such as copper and silver.

2. Flatness and uniformity meet specifications. Through precise crystal orientation calibration, uniform thickness arrangement, and step-wise buffer growth, the large-size substrate achieved after joining exhibits high flatness and uniform thickness. After subsequent grinding and polishing, it can meet the large-area bonding requirements of chips and laser devices, ensuring gap-free bonding and effectively reducing interfacial thermal resistance.

3. They offer greater structural stability. The mosaic interfaces effectively block crack propagation. Compared to large, monolithic single crystals, which are highly brittle, mosaic-assembled heat sinks exhibit superior resistance to deformation and thermal shock, making them suitable for long-term operation under harsh conditions involving high power and extreme temperature cycling.

As a manufacturer with an in-house developed MPCVD full industrial chain, we are capable of mass-producing mosaic single-crystal heat sinks in sizes ranging from 35 to 100 mm. We offer customization options such as crystal orientation, ultra-thin reduction, and double-sided nano-polishing to provide a one-stop single-crystal diamond solution for the thermal management of high-power devices. If you have requirements for large-size single crystals, please feel free to consult our professional team.