Analysis and Discussion on the Classification of Thermal Conductive Silicone (Sheets) Products

Thermally conductive silicone (films) are widely used in various electronic products and electrical equipment on the contact surface between heat-generating components and heat dissipation facilities. They act as a heat transfer medium and provide shock absorption. This type of silicone material offers excellent thermal conductivity for heat-generating electronic components. Examples include: transistors, CPU assemblies, thermistors, temperature sensors, automotive electronic components, car refrigerators, power modules, and printer heads. Because thermally conductive silicone and thermally conductive silicone sheets vary in their state and composition, they are subject to different customs codes. The following are some case studies to illustrate how thermally conductive silicone and thermally conductive silicone sheets should be classified: Case Study 1: Thermally Conductive Film Product Description: The thermally conductive film is a mixture of silicone resin, boron nitride (or aluminum oxide), and glass fiber. The silicone resin content is 20%–30%, the boron nitride or aluminum oxide content is 65%–75%, and the glass fiber (for reinforcement) content is approximately 5%. Application Method: Cut it into small pieces and adhere it to the surface of the electronic product or electronic component. This product's excellent thermal conductivity effectively dissipates heat generated during electronic product operation, preventing damage from overheating. Classification Approach: This product is actually a thermally conductive silicone sheet. It's a thermally conductive medium material synthesized through a special process using silicone as the base material and adding various auxiliary materials such as metal oxides. It comes in sheet form and is cut into small pieces as needed before being adhered to the surface of electronic products or components. The material is relatively soft, has good compressibility, good thermal conductivity and insulation properties, and a wide adjustable thickness range. It can be stretched and deformed under external force, and it doesn't easily return to its original shape after the force is removed. Based on the product's characteristics, it does not meet the requirements of Chapter 39, Note 1 of the Customs Tariff regarding "plastics," as its function is heat conduction and dissipation, not as an adhesive or glue. It also does not conform to the description of heading 35.06 in the Customs Tariff and its Notes. Therefore, it is recommended that this product be classified under Customs Tariff heading 3824.9999 as an unlisted chemical. Case Study 2: Thermally Conductive Silicone Sheets Product Description: Thermally conductive silicone sheets are made of over 70% polysiloxane, mixed with alumina, aluminum nitride, boron nitride, and ferrite. They are molded into sheets with a thickness of 0.152 mm under external force. After molding, the shape remains unchanged even when the external force is removed. After import, they are cut into smaller pieces as needed. Used as thermally conductive insulators for semiconductors, and as press-fit materials for thermistors and temperature sensors. These are versatile sheet-like conductive gel materials with high compliance and high heat resistance. They easily adhere and bond to components of most shapes and sizes, including protruding and recessed areas, and their flexibility is ideal for filling air gaps and uneven surfaces. Classification Approach: The main component of this product is polysiloxane under heading 39.10. Since plastics under headings 39.01 to 39.14 can contain plasticizers, stabilizers, fillers (such as wood flour, cellulose, textile fibers, minerals, starch), and other substances primarily intended to impart special physical properties to the finished product, the other components in this product-alumina, aluminum nitride, boron nitride, and ferrite-are materials added to the polysiloxane to impart special physical properties. Alumina can make silicone thermally conductive, thus preventing electrical fires; thermal conductivity is a special property. Therefore, this product conforms to Chapter 39, Note 1 of the Customs Tariff, and is classified under tariff heading 3920.9990 for sheet materials made by compression molding. Through Case 2, we can further derive two other products: (1) After the product in Case 2 is made into a sheet (width exceeding 20 cm), if one side is coated with adhesive for easy attachment to electronic devices, a release liner is attached. According to the description of heading 39.19 and its subheadings, "including all adhesive flat materials other than floor coverings and wall coverings of heading 39.18, whether in rolls or not...", it is recommended that such products be classified under tariff heading 3919.9090 as self-adhesive plastic sheets, films, etc. (2) If glass fiber is added as reinforcement to the product in Case 2, and the rest of the processing is exactly the same, according to the description of heading 39.21 and its subheadings, "this heading includes plastic sheets, films, films, foils and strips other than those of headings 39.18, 39.19, 39.20 or Chapter 54, i.e., only foamed plastic products and products reinforced, laminated, supported or composed in a similar manner with other materials," then the product should be classified as a plastic sheet, film, etc. reinforced with glass fiber material and classified under tariff heading 3921.9090. Of course, if a plastic product has been shaped into a specific form for use in machinery or equipment during production, it should be classified according to the classification principles for electromechanical product parts. The above are merely personal opinions; any inaccuracies are welcome for criticism and correction.