The country of origin of micro controller integrated circuits

N352821 September 22, 2025 OT:RR:NC:N2:209 CATEGORY: Origin Sa Ung Kim SEIN Customs & Auditing Corp 138, Seoun-ro, Seocho-gu Seoul 06619 South Korea RE: The country of origin of micro controller integrated circuits Dear Mr. Kim: In your letter dated August 25, 2025, you requested a country of origin ruling on micro controller integrated circuit chips on behalf of your client, Nuvoton Technology Corp. The item concerned is a microcontroller integrated circuit chip (Product No: KM1M7AF52NXW, Product Name: Micro Controller, Model Name: MOS Microcomputer IC). This item is designed for optimal power electronics control, featuring high processing performance and low power consumption. In use, the micro controller is mounted on the micro-inverter module on the back of a solar panel. It precisely controls the operation of the DC/DC converter and DC/AC inverter using Pulse Width Modulation signals. It also continuously monitors the voltage and current of the battery and the grid via an Analog-to-Digital Converter. Furthermore, it serves a communication role, exchanging data with the PLC Controller & Circuit through Universal Asynchronous Receiver/Transceiver communication. The manufacture of the micro controller takes place in several countries and the manufacturing steps are as follows: Wafer Production - The wafer may be manufactured within various countries - (i.e. Japan, USA, Singapore, Taiwan, etc.) The manufacturing process includes: Ingot Manufacturing - High-purity polycrystalline silicon is filled into a quartz crucible. The polycrystalline silicon is melted at a high temperature and grown into a single-crystal silicon ingot. Wafer Slicing-After smoothing the surface of the ingot, it is cut into blocks. The ingot blocks are then sliced into individual wafers. Wafer Surface Polishing - After polishing the edge of the cut wafers, the wafer surface is smoothed and planarized. They are then packaged and exported to Singapore for the subsequent process. Front-end manufacturing - The actual micro controller die are created on the wafer during the front-end manufacturing process that takes place in Singapore. The front-end manufacturing process includes: Film Deposition - The wafer is placed in a high-temperature oxidation furnace (1000-1200) to form a silicon oxide film on its surface. Resist Coating - A thin layer of photoresist (a photosensitive film) is applied to the wafer. Exposure - Align the photomask with the wafer, and then shine light from above to print the pattern onto the wafer. Development - Using a developer solution removes the photoresist in the exposed areas, which reveals the silicon oxide layer underneath. Etching - Using a corrosive solution (etchant) or an active gas in a plasma state, the exposed silicon oxide layer is scraped away to reveal the silicon surface of the wafer. Resist Stripping - Stripping away the unwanted photoresist. Impurity Doping - Using ion implantation, impurities (boron, phosphorus, etc.) are injected into the silicon surface from which the silicon oxide layer has been removed. Metallization - After repeating above steps, holes are created to connect the devices and circuits. Then, a thin metal film (aluminum or copper) is formed on the wafer surface using a sputtering technique to electrically connect the devices and circuits. The wafers are then packaged and exported to Japan for probe testing Probe Test - Testing conducted in Japan includes: Once the front-end process is complete, every chip on the finished wafer undergoes individual electrical testing. This is done by making contact with a probe to apply an electrical current, then checking if the chip's functions are working properly according to pre-set standards. Afterward, the wafers are exported to China for the back-end process. Back-end Manufacturing - The finished die are packaged in China during the back-end manufacturing process. The back-end manufacturing process includes: Chip Cleaning - The surfaces of the sliced chips imported from Japan are re-cleaned to remove any residue or contaminants. Dicing of wafer into individual chips. Die Bond - The selected chips are attached to the die pad of the lead frame using silver epoxy (die attach material). Wire Bond - Using gold or aluminum bonding wire, the chip's electrode pads are connected to the lead frame pins. Molding - The wire-bonded component is encased in epoxy resin to protect the chip and bonding wires from external environmental damage. Post-Mold Curing - The molded package is baked at a controlled temperature to fully cure the resin. Marking - For identification and tracking, brand names, product types, and lot numbers are laser-engraved onto the package surface. Tie Bar Cutting - Using a mold according to the product design drawing, the tie bars between the leads are removed. Cutting & Bending - Using a stamping mold according to the product design, the package is cut and bent into individual units. FT Test - Using a handler and tester, a 100% electrical test is performed to detect defects from the diffusion process. Automated Optical Inspection(AOI) - Using an AOI machine, the electrical final product is inspected for marking accuracy, foreign substances, and lead shape defects. Visual Inspection - Perform a manual inspection for visual defects on the package body and leads, such as scratches, cracks, or contamination. Packing - Using automated packaging equipment, the final product is vacuum-sealed and packaged. The packaged item is then exported to South Korea for firmware programming. ROM Writing - In Korea, firmware is downloaded to the micro controller integrated circuits. This process includes: ROM Writing - Using a ROM writer, the imported item's firmware code is converted into an electrical signal and permanently written to the MCU's internal memory. Packaging - The ROM-written products are packaged in anti-static plastic to prevent chip damage and electrostatic discharge. They are then placed in boxes and finally exported to the United States. The electrical design and functionality are fully established during the front-end process. The back-end process performed in China and the “ROM Writing” that takes place in Korea does not impart any electrical design or functionality nor does it change the predetermined end use that was established in Singapore. When determining the country of origin, the substantial transformation analysis is applicable. See, e.g., Headquarters Ruling Letter (“HQ”) H301619, dated November 6, 2018. The test for determining whether a substantial transformation will occur is whether an article emerges from a process with a new name, character, or use different from that possessed by the article prior to processing. See Texas Instruments Inc. v. United States, 681 F.2d 778 (C.C.P.A. 1982). This determination is based on the totality of the evidence. See National Hand Tool Corp. v. United States, 16 C.I.T. 308 (1992), aff’d, 989 F.2d 1201 (Fed. Cir. 1993). Based upon the facts presented it is the opinion of this office that the front-end processing that takes place in Singapore, imparts the essence to the micro controller chip. In this instance, the front-end processing, is a complex process of forming circuits on a wafer which transforms the non-functional wafer into a wafer containing numerous semi-conductor integrated circuit die with a predetermined end use. This process constitutes a substantial transformation that gives the product a new name, character, and use. The micro controller chips do not undergo a substantial transformation as a result of the back-end processing within China, nor the firmware download that takes place in Korea. The products identity and predetermined end use is retained. The country of origin for marking purposes will be Singapore at time of importation into the United States. The holding set forth above applies only to the specific factual situation and merchandise description as identified in the ruling request. This position is clearly set forth in Title 19, Code of Federal Regulations (CFR), Section 177.9(b)(1). This section states that a ruling letter is issued on the assumption that all of the information furnished in the ruling letter, whether directly, by reference, or by implication, is accurate and complete in every material respect. In the event that the facts are modified in any way, or if the goods do not conform to these facts at time of importation, you should bring this to the attention of U.S. Customs and Border Protection (CBP) and submit a request for a new ruling in accordance with 19 CFR 177.2. Additionally, we note that the material facts described in the foregoing ruling may be subject to periodic verification by CBP. This ruling is being issued under the provisions of Part 177 of the Customs and Border Protection Regulations (19 C.F.R. 177). A copy of the ruling or the control number indicated above should be provided with the entry documents filed at the time this merchandise is imported. If you have any questions regarding the ruling, please contact National Import Specialist Steven Pollichino at steven.pollichino@cbp.dhs.gov. Sincerely, (for) Denise Faingar Designated Official Performing the Duties of the Division Director National Commodity Specialist Division