What is Metal Etching and Etching Process?

Etching is a technique used to treat the surface of objects through chemical reactions involving strong acids, mechanical polishing, or electrochemical electrolysis. Beyond enhancing aesthetics, etching also increases the added value of objects. This technique finds applications ranging from traditional metalworking to high-tech semiconductor manufacturing.

What is Metal Etching?

Metal etching is a technology that removes metal materials through chemical reactions or physical impacts. It can be divided into wet etching and dry etching. Metal etching involves a series of chemical etching processes. Different etching agents have varying corrosive properties and strengths for different metals.

Also known as photochemical etching, metal etching involves exposing, plating, developing, and removing the protective film in the etching area after contact with chemical solutions to achieve dissolution, corrosion, bump formation, or hollowing. Initially used for manufacturing engraved printing plates from copper and zinc, it is widely applied to reduce the weight of instrument panels or to process thin nameplates. With continuous improvements in technology and equipment, etching techniques are now utilized in aerospace, machinery, chemical industries, and semiconductor manufacturing processes to produce precision metal etched products for electronic thin parts.

Types of Etching Techniques

Wet Etching: Wet etching involves immersing the wafer in an appropriate chemical solution or spraying the chemical solution onto the wafer to quench it. The etching is achieved through the chemical reaction between the solution and the material being etched, removing atoms from the film’s surface. During wet etching, reactants in the solution diffuse through the stagnant boundary layer, reach the wafer surface, undergo a chemical reaction, and produce various products. These products, either liquid or gas, then diffuse through the boundary layer and dissolve into the main solution. Wet etching affects both vertical and horizontal directions.

Dry Etching: Dry etching typically includes plasma etching or chemical etching. Based on the etching effect, it involves the physical impact of ions in plasma, chemical reactions of active radicals, surface atoms of the device (wafer), or a combination of both, including:

• Physical Etching: Sputter etching, ion beam etching.
• Chemical Etching: Plasma etching.
• Physicochemical Etching: Reactive ion etching (RIE).

Dry etching is an anisotropic process with good directionality but poorer selectivity compared to wet etching. In plasma etching, the plasma is a partially dissociated gas where molecules are dissociated into electrons, ions, and other chemically active species. The main advantage of dry etching is its “anisotropic etching.” However, the selectivity of (radical) dry etching is lower than that of wet etching because the etching mechanism is physical interaction, where ion impacts can remove both the etching film and the photoresist mask.

Etching Process

The etching process varies depending on the type of metal, but generally follows these steps: metal etching plate → cleaning and degreasing → water washing → drying → coating or screen printing ink → drying → exposure → development → water washing and drying → etching → film removal → drying → inspection → finished product packaging.

1. Cleaning Process Before Metal Etching: Cleaning before etching stainless steel or other metals is crucial for removing dirt, dust, grease, etc., from the material’s surface. It ensures good adhesion of the subsequent film or screen-printed ink. Therefore, grease and oxide films on the metal surface must be thoroughly removed.
2. Applying Dry Film or Screen Printing Photosensitive Layer: Depending on the product’s material, thickness, and precise width of the pattern, dry film or wet film screen printing is used. The etching treatment time required for the product pattern should be considered, and a thicker or thinner photosensitive layer can be applied for better coverage and clarity.
3. Drying: After the film or screen printing ink is applied, the photosensitive layer must be thoroughly dried to prepare for exposure, ensuring the surface is clean and free of adhesions or impurities.
4. Exposure: This critical step in metal etching determines the energy needed based on the product’s material thickness and precision, reflecting the technical capabilities of the etching processing enterprise.
5. Development: The exposed photosensitive layer on the metal etching plate hardens, and the unwanted parts of the pattern are revealed. This step ensures the final dimensions meet the requirements by thoroughly removing the unnecessary photosensitive layer.
6. Etching Process: In this step, a chemical solution etches the prepared product. Parameters such as concentration, temperature, pressure, and speed of the etching solution determine the final metal etching service and product’s quality.
7. Film Removal: After etching, the photosensitive layer remaining on the product’s surface must be removed. Since the photosensitive layer is acidic, it is usually removed by neutralizing with acid and alkali, followed by water and ultrasonic cleaning.
8. Inspection: The final product undergoes inspection and packaging to confirm it meets the specifications.

Considerations in the Etching Process

• Reducing Lateral Corrosion and Enhancing Edge Definition:
  The longer the printed board is in the etching solution, the more severe the lateral etching. Severe undercutting affects the precision of printed lines and may prevent the creation of fine lines. Reducing undercutting and edges increases the etching coefficient, maintaining fine lines closer to the original image size.
• Improving Consistency in Etching Rates Between Boards:
  Consistent etching rates yield uniform etched boards. Selecting an easily regenerable, compensable etching solution with a controllable etching rate is crucial. Techniques and equipment should provide constant operating conditions and automatic control of various solution parameters, such as copper content, pH value, solution concentration, temperature, and flow uniformity.
• Enhancing Uniformity Across the Board’s Surface:
  The uniformity of the etching liquid’s flow rate across the board surface determines the consistency of etching between the upper and lower sides of the board. Adjusting the spray pressure of the nozzles addresses this inconsistency. A spray system with oscillating nozzles can further improve uniformity by varying spray pressure between the center and edges of the board.

Advantages of Etching Processes

• Maintaining Material Properties:
  The etching process does not alter the material’s properties, stress, hardness, tensile strength, yield strength, or ductility. Etching is performed in a mist state, leaving no significant surface pressure.
• No Burrs:
  The process involves no pressing force, eliminating issues such as curling, chipping, or pressure points.
• Compatibility with Subsequent Processes:
  Products can be personalized through stamping, plating, bonding, electrophoresis, or blackening.
• Adaptability to Miniaturization and Diversification:
  The process is suitable for small-scale and diverse productions, offering short cycles and low costs.

Applications of Etching

• Consumer Electronics
• Filtration and Separation Technologies
• Aerospace
• Medical Devices
• Precision Machinery
• Automotive
• High-end Craftsmanship

Talk to BE-CU Prototypes’ Metal etching experts.

Whether you need aluminum cnc machining or precision metal etching service in China, our experts are ready to help. Start with your free project review today, or chat with one of our project managers here.Be-Cu provides the highest standard of  parts prototype manufacturing service for all your needs. Contact us today to know more about what we offer!

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