Chemical etching, also referred to as photochemical machining (PCM) or acid etching, is the process of removing a material from a substrate using chemicals to obtain complex designs, precision parts, or fine details. Such a process finds its industrial applications in aerospace, electronics, manufacturing, and automotive industries to produce highly accurate components.
Correct material selection for chemical etching is very significant to make the process successful and economical. The choice of material will influence the etch rate, accuracy, quality of surface, and overall cost of production. This blog will walk you through the selection of materials for chemical etching and what aspects should be considered to achieve optimal results.
Know about Chemical Etching
In order to actually pick a material, you would first of all have to understand how chemical etching works. In chemical etching, the raw material is usually in a form of sheet or foil, and before etching, it will be cleaned off of any surface contaminants. A photoresist is then applied on top of the material, exposing it to a patterned mask by UV light, which makes the desired areas completely nonexposed.
Etching: The areas exposed are chemically etched using an acid or alkaline solution, thus removing the unwanted material to create the desired pattern or shape.
Resist Removal: The photoresist is removed, and thus leaves only the etched product.
The choice of material for this process is heavily reliant on a number of factors including the chemical compatibility, thickness, and end-use of the part.
Factors to Consider When Choosing Materials for Chemical Etching
1. Material Compatibility with the Etchant
One of the most critical factors when it comes to the choice of material is the reaction that the material undergoes when exposed to the etchant in the chemical etching process. Each material is different with regard to the type of etchant that may be necessary. This mainly comprises acid-based or alkaline solutions.
- Acid Etching: Some common acids that can be applied to etching contain ferric chloride, nitric acid, and hydrochloric acid. All these etchants can be successfully applied for materials such as copper, stainless steel, brass, and aluminum.
- Alkali Etching: Sodium and potassium hydroxide are alkali etchant materials. These etchants work very well for the above materials, in particular aluminum and its alloys. Selection of material must provide better etch economically without degrading or unfavorable reaction with the chosen etchant. Depending on the precision or surface finish to be achieved, there might be a requirement for different etchants on the material.
- Example: If you are etching stainless steel, ferric chloride can be used because it comes clean and nontoxic with a proper finish that will not ruin the integrity of the structural material.
2. Material Thickness
- The other crucial consideration when making a choice for material in chemical etching is the thickness of the material. Thicker material is expected to take up a longer time or stronger etchants to achieve the critical depth of etching, thus increasing costs and time in production. Etching thin materials tends to be easier and faster, but it may warp easily or is damaged during etching.
- The thickness chosen depends also on the final application of the part. Thin foils will be very appropriate for making electronic components, whereas a structural component in aerospace or in the automotive industry would probably require thicker materials.
- Example: For high precision electronic components, a 0.01 mm thin copper foil might be perfect for producing intricate circuits in just minutes. On the other hand, thicker stainless steel sheets at 1-2 mm are used in medical devices to produce long-lasting and anti-rust robust components.
3. Desired Precision and Complexity
- The part to be produced is of much complexity; therefore, a suitable material needs to be chosen because chemical etching is very efficient to make fine detailed designs. For example, some materials can be etched far more precisely than others.
- Metals such as copper, brass and stainless steel: are the most common metals that will provide fine details and can well be etched.
- Materials such as aluminum: can be etched but are usually hard to work with as they are chemically reactive and so limit the amount of detail that is possible.
- If the patterns to be made on your project are intricate, fine holes, or complex, you’ll need a material with good precision etching support.
- Example: stainless steel is significantly favored by aerospace and medical equipment industries because it allows for high precision even in complex part with intricate patterns and thin walls.
4. Material’s Mechanical Properties
Another point which is very important to be taken into consideration is the mechanical property of the material. Depending on the final utilization of the etched part, the material will require a specific quality that may include strength, flexibility, hardness, or resistance to environmental influences, which includes corrosion.
- Strength and Longevity: Any time the application requires strength and endurance, like in automobile and airframe parts, the material will be stainless steel or titanium because of its strength.
- Flexibility: For flexible parts such as springs or diaphragms, many opt to use copper, brass, and phosphor bronze. Corrosion Resistance: Materials including stainless steel, nickel, and titanium prove excellent for the parts if exposed to harsh conditions or chemicals.
- Example: The Part in the medical device industry can be made of stainless steel because its corrosion resistance is good along with biocompatibility. Such parts can withstand the harsh sterilization processes and the conditions in which they may have to survive.
5. Cost of Material
Material cost is another significant variable in any manufacturing process, and chemical etching is no different. Though materials such as titanium or nickel provide outstanding properties, they are costlier than, say, copper or brass. So, one needs to provide appropriate material performance coupled with cost considerations for the project to stay within budget.
Example: Copper is relatively inexpensive material that performs well in many applications of chemical etching, and quite particularly in electronics. For high-end aerospace-type applications where significant life form durability and performance are critical however, the added investment in something like titanium might be justified.
6. Surface Finish Requirements
Surface finish of the etched part often proves to be a critical consideration in material choice, particularly with products that find their way into aerospace, medical devices, and electronics applications that require an extremely smooth, high-quality finish.
Materials etch quite differently and sometimes rather cleanly. In this manner, etching can serve to provide a higher quality surface than another due to whether it is rougher or smoother to work with. Stainless steels tend to etch to very high-quality surfaces; aluminum etches rather noisily and for most applications requires post-processing.
Example: In the electronics industry, a non-turbid and smooth surface is required to ensure electrical connectivity. Copper or brass materials are suitable for producing finishes of high quality to meet these requirements.
Chemical Etching Materials
That’s having considered the considerations above, let’s now look at some of the most common materials that are used in chemical etching together with some applications:
1. Stainless Steel
- Properties: High strength, corrosion resistance, excellent surface finish.
- Applications: Aerospace, medical devices, automotive, and industrial parts.
- Etchant: Ferric chloride.
- Advantages: Stainless steel is one of the most adopted materials in chemical etching. In fact, this material exhibits strength, with a great resistance to corrosion and precision capabilities.
2. Copper
- Properties: Good electrical conductivity, flexible, easy to etch.
- Applications: Electronics, circuits, connectors, and gaskets.
- Etchant: Ferric chloride.
- Advantages: copper is ideal for electronic components because it has excellent conductivity and affordability.
3. Brass
- Properties: Good electrical conductivity, easy to etch, and affordable.
- Applications: Decorative, connectors, electrical components.Etchant: Ferric chloride.
- Advantages: Brass is employed for easy etching and cost-effectiveness in applications in which mechanical performance combined with electrical performance are required.
4. Titanium
- Properties: It has a high strength-to-weight ratio, lightweight, resistant to corrosion, and biocompatible.
- Applications: Aerospace, medical devices, industrial components.
- Etchant: Hydrofluoric acid
- Advantages: It is more expensive, but titanium is highly valued for its strength-to-weight ratio and resistance to corrosion.
5. Aluminum
- Properties: Lightweight, corrosion resistant, cheaper
- Applications: Aerospace, automotive, electronics
- Etchant: Sodium hydroxide.
- Advantages: It is light weight and relatively low-cost; however it presents a challenging etching task compared to some other material.
Conclusion
The right choice of material makes chemical etching. Thus, not only the compatibility of the etchant for the material but also the thickness, precision, mechanical properties, and cost need to be considered.
Whether you are manufacturing medical devices, electronics, aerospace components, or anything else, knowing how different materials behave will give you the edge to optimize your chemical etching process and make really quality parts at precision and efficiency.
