Copper is a versatile metal used in a wide range of applications due to its excellent thermal and electrical conductivity, corrosion resistance, and attractive appearance. From printed circuit boards to decorative ornaments, copper is an essential material for many industries. However, shaping copper into intricate designs and patterns can be challenging using traditional machining techniques such as cutting, drilling, or milling. Chemical etching copper offers a cost-effective and precise alternative to these methods, allowing manufacturers to produce high-quality copper parts with complex geometries.
What is Chemical Etching Copper?
Chemical etching, also known as photochemical machining or photoetching, is a subtractive manufacturing process that uses chemical reactions to selectively remove material from a metal sheet. The process involves four main steps: preparing the copper sheet, applying a photosensitive resist, exposing the resist to light, and etching the copper with a chemical solution. Each step requires careful control of the parameters to achieve the desired precision, surface finish, and repeatability.
Preparing the Copper Sheet
Before the etching process can begin, the copper sheet must be cleaned and degreased to remove any contaminants that may interfere with the adhesion of the photosensitive resist. Typically, the sheet is first cut to the desired size and shape using shears or a guillotine cutter. Then, it undergoes a series of cleaning steps, such as solvent cleaning, alkaline cleaning, and acid pickling, to remove dirt, oil, oxide layers, and other impurities from the surface. This step is critical to ensure that the resist adheres uniformly and firmly to the copper and that the subsequent etching process produces a high-quality part.
Applying the Photosensitive Resist
The next step is to apply a photosensitive resist to the copper sheet. The resist is a thin layer of polymer or other organic material that is sensitive to light and can be selectively exposed and developed to create a patterned mask for the etching process. There are two main types of resist: positive and negative. Positive resist is sensitive to UV light and becomes more soluble in a developer solution after exposure, whereas negative resist is sensitive to visible light and becomes less soluble in a developer solution after exposure.
To apply the resist, the copper sheet is coated with a liquid or dry film resist using a roller or laminator. The resist is then cured by baking or UV exposure to crosslink the polymer chains and increase its resistance to the etchant. The thickness of the resist can vary depending on the desired feature size, aspect ratio, and undercutting tolerance. Thicker resist can withstand longer etching times and produce deeper features but may also cause more lateral undercutting and less accurate feature placement.
Exposing the Resist
After the resist is applied and cured, the next step is to expose it to a patterned light source. This can be achieved using a photomask, which is a transparent film or glass plate with a patterned opaque layer that blocks the light in certain areas. The photomask is placed in contact with the resist-coated copper sheet, and a UV or visible light source is used to illuminate the pattern through the mask. The resist in the illuminated areas undergoes a chemical change that alters its solubility in the developer solution. This allows the unexposed resist to remain intact while the exposed resist is selectively removed by the developer, leaving behind a patterned mask that exposes the underlying copper.
Etching the Copper
The final step in the chemical etching process is to etch the exposed copper using a chemical solution, such as ferric chloride, cupric chloride, or ammonium persulfate. The etchant reacts with the copper and dissolves it in the exposed areas, leaving behind the patterned copper part.