Within the engineering industry, precision, reliability, and efficiency are not just goals to aim for – they are the foundation on which innovative solutions and advanced technologies are built. Within this industry, one technique has been steadily revolutionizing manufacturing processes photochemical etching.
Straddling the line between chemistry and engineering, this method offers a unique blend of accuracy and versatility, proving to be a game-changer in the fabrication of metal components with intricate details.
Emerging as a cornerstone in subtractive manufacturing, Photochemical Etching, also known as chemical etching or photo etching, has demonstrated its adaptability and utility across a myriad of industries, from the microscopic circuits in electronics to the robust components in aerospace.
The technique’s ability to marry fine-detail accuracy with material integrity has positioned it as an invaluable tool in the engineer’s arsenal, unlocking new possibilities in design and application. It’s the meticulousness of this process that facilitates the birth of components that are not only functional but also embody the pinnacle of engineering precision.
As we delve deeper into an era defined by rapid technological advancements and a growing emphasis on sustainable practices, Photochemical Etching stands at the forefront, a silent harbinger of innovation and environmental consciousness.
The technique’s environmentally friendly nature, coupled with its capacity for cost-effective production, resonates with the modern ethos of sustainable development. In essence, Photochemical Etching is not just shaping the present landscape of engineering; it is actively sculpting the future, setting new benchmarks for quality, precision, and responsible manufacturing.
What is Photochemical Etching?
Photochemical etching, alternatively known as chemical etching or photo etching, stands as a notable technique in subtractive manufacturing, using chemical etchants to selectively remove metal.
It is a chemical milling process used to fabricate sheet metal components using a photoresist and etchants to corrosively machine away selected areas.
This process emerged in the 1960s as an offshoot of the printed circuit board industry. Photo etching can produce highly complex parts with very fine detail accurately and economically.
This process can offer economical alternatives to stamping, punching, laser or water jet cutting, or wire electrical discharge machining (EDM) for thin gauge precision parts. The tooling is inexpensive and quickly produced.
This makes the process useful for prototyping and allows for easy changes in mass production. It maintains dimensional tolerances and does not create burrs or sharp edges. It can make a part in hours after receiving the drawing.
PCM can be used on virtually any commercially available metal or alloy, of any hardness. It is limited to materials with a thickness of 0.0005 to 0.080 in (0.013 to 2.032 mm). Metals include aluminum, brass, copper, inconel, manganese, nickel, silver, steel, stainless steel, zinc, and titanium.
Photochemical machining is a form of photo engraving, and a similar process in microfabrication is called photolithography.
How Does Photo Etching Work?
The process starts by printing the shape of the part onto optically clear and dimensionally stable photographic film. The “phototool” consists of two sheets of this film showing negative images of the parts (meaning that the area that will become the parts is clear and all the areas to be etched are black). The two sheets are optically and mechanically registered to form the top and bottom halves of the tool.
The metal sheets are cut to size, cleaned and then laminated on both sides with a UV-sensitive photoresist. The coated metal is placed between the two sheets of the phototool and a vacuum is drawn to ensure intimate contact between the phototool and the metal plate.
The plate is then exposed in UV light that allows the areas of resist that are in the clear sections of the film to be hardened. After exposure, the plate is “developed”, washing away the unexposed resist and leaving the areas to be etched unprotected.
The etching line is a multi-chambered machine that has driven-wheel conveyors to move the plates and arrays of spray nozzles above and below the plates. The etchant is typically an aqueous solution of acid, frequently ferric chloride, that is heated and directed under pressure to both sides of the plate.
The etchant reacts with the unprotected metal essentially corroding it away quickly. After neutralizing and rinsing, the remaining resist is removed, and the sheet of parts is cleaned and dried.
Advantages Of Photochemical Etching
Photochemical etching utilizes a mylar film with silver-based ink as the tool to transfer the image. The general cost for an engineered tool for the photochemical etching process is approximately $400. The tooling can also be generated or revised/re-generated in 1-2 business days.
In comparison, a traditional stamping or tooling-based manufacturing method could be several thousand dollars and have a significant lead time from start to first application.
Preserved Metal Properties
Unlike traditional mechanical fabricating, photochemical etching produces no jagged corners or abrasions and preserves the physical properties of the metal. This machining process does not affect the metal hardness, grain structure, or ductility because no mechanical forces are applied to the metal.
Because the process does not include heating the part, there are no heat-affected zones as with other traditional fabrication methods.
With photochemical etching, you can make several changes to parts during the prototype development process, and the designer or manufacturer can change the dimensions utilizing low-cost tooling. A single tool can also be used to create multiple styles of a potential design.
The photochemical machining process has the ability to produce burr-free products. Finished etched features like holes and separated edges will be smooth, rounded, and burr-free.
Replicability Of Design
Photochemical etching allows patterns to be replicated several times on a panel, which enables lower costs while maintaining design accuracy.
Recessing Of Material Thickness
Commonly referred to as “Half Etch”, photochemical etching allows the material to be removed from only one side of the sheet. This allows for multiple depths throughout the designed part. This could be used as text identification, bend lines for post-processing, recessed pocks, or general surface finishing and roughness.
Application Of Photochemical Etching
These include all electronic components, sensors, RF shields, semiconductors, electrical contacts, and so forth. A popular electronic component that is produced by photochemical etching are computer processors. Production at this scale is virtually impossible for mechanical machining processes.
The aerospace industry relies on sophisticated detection systems using flat spring contacts and precision-designed fuel cells. Most of these components are made from aluminum and titanium, which are lighter than steel, copper, or brass.
Weight and space are critical aspects of aircraft and spacecraft construction. The precision tolerance possible with photochemical etching as well as its ability to use any type of metal make it the ideal process for producing aerospace components.
The fact that photochemical etching can produce high precision and customizable part designs, is the reason it is so widely used in the aerospace industry. Thicknesses below 0.0005″ to 0.062″ can easily be done through photochemical etching while being impractical for the conventional stamping process.
Gaskets and Seals
Photochemical etching is preferred for this application due to its burr and residual stress-free products. Also, for custom gaskets, this process does not require high investment cost for fabricating hard tools.
Fine Filters and Screens
Due to its microscale production capability, photochemical etching is preferred than blanking, piercing, or stamping.
Photochemical etching is also used for jewelry and decorative purposes due to the ease of creating complex designs. As long as the artwork can be printed into a photo tool, it can be produced by this process.