Composite body having high thermal conductivity and method of making the composite body

A method of forming a composite article, comprising:

• preparing a mixture of ceramic particles and an organic polymer, wherein the ceramic particles comprise at least 90 vol % hBN particles based on the total volume of the ceramic particles, an amount of the hBN particles ranges from 40 vol % to 90 vol % based on a total volume of the mixture, the hBN particles have an average particle size (D50) of at least 1 micron and not greater than 100 microns, the hBN particles comprise a multi-modal particle distribution, wherein the particle size distribution of the hBN particles includes a first peak having a first peak maximum and a second peak having a second peak maximum, and an intensity ratio of the first peak maximum to the second peak maximum at least 2:1 and not greater than 10:1, and a distance between the first peak maximum and the second peak maximum is at least 20 microns and not greater than 70 microns, and an average aspect ratio of length to thickness of the hBN particles is not greater than 200;
• applying a layer of the mixture to a mold or a support;
• conducting an alignment procedure of the hBN particles;
• and
• solidifying and/or curing the organic polymer to form a composite body, wherein an in-plane thermal conductivity of the composite body is at least 13.5 W/mK.