Recently, researchers reported a boron nitride-based all-ceramic composite (ceramic matrix composite, CMC) that can be thermoformed into a complex structure. This thermoformable material is not only electrically insulating, but also exhibits excellent mechanical strength and thermal conductivity at room temperature. Electronic product heat sinks made of this material are lighter in weight than traditional metal heat sinks and will not interfere with radio frequency signals. This material is used in thermal management systems for high-density electronics, or could change the design and construction of next-generation electronics. According to the authors, their discovery actually arose from an unexpected failure of an experiment.
The researchers previously undertook an industrial project related to hypersonic materials to test a ceramic material. They heated the material with a blowtorch, but an accident happened while loading a sample of the material into the fixture and the material fell out. Generally, when ceramic materials are subjected to large thermal shock and mechanical load, they tend to crack or even explode. However, when the author picked it up, it was found to be intact, only altered in shape. This discovery surprised them, and after repeated tests several times, they found that the deformation can be easily controlled.
The machining process is divided into five steps. First, hexagonal boron nitride (hBN) particles, as the core component of the CMC material, are added to the photoresist and deposited on the substrate. Next, the slurry is fabricated into a thin film, and the shear force can enhance the in-plane orientation of hBN and improve the intralayer alignment. Subsequently, it is cured using ultraviolet light. During the gradient heating and sintering process, part of hBN was uniformly oxidized to B2O3.
Interestingly, when this CMC material is heated above 450 °C, boron oxide (B2O3) will melt, making the material exhibit viscosity and plasticity again, by applying sufficient heat (500~700 °C), pressure and molding time (>10 min), the thermoforming of structural parts can be realized. In addition to being easy to process, the CMC material has high thermal conductivity, with a thermal conductivity of 3.52 ± 0.67 W mK-1 in the vertical plane.
In order to explore the application of CMC materials in actual heat dissipation, the researchers thermoformed an all-ceramic heat sink in a 500 °C oven and mounted it on a printed circuit board. The thickness of the radiator is only 0.68 mm, compared with the parallel fin aluminum radiator of the group, it needs 9.07 mm of space to complete the installation. During operation, the maximum temperature of the all-ceramic heat sink is 52.9 °C, which is better than that of the aluminum heat sink (56.8 °C maximum temperature).
The material, which is less than a millimeter thick, can be molded into the right shape to replace the thick aluminum heatsinks in phones, pulling heat away from the device, and the ceramic material won't interfere with the radio frequency signals of phones and other systems. If this material is used in the thermal management system of electronic products, it may change the design and construction of next-generation electronic products.
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Reference
- Thermoformable Boron Nitride Based All-Ceramics.
Jason E. Bice, Echo St. Germain, Samuel J. Wohlever, Grace Goddard, Randall M. Erb.
