Photochemical machining, also known as photochemical (also spelled photo chemical) etching, is a type of chemical machining, which is process used to chemically remove unwanted material from a surface. Photochemical machining first emerged in the 1960s as a byproduct of the printed circuit board industry. Photochemical machining embarks on this industrial etching process using a combination of acidic chemicals and exact light exposure in order to create small and complex parts and products.
Almost any metal or metal alloy of thicknesses between 0.0005 inches (1.3 mm) and 0.080 inches (2.032 mm) can be machined using this process. Some of the metals most commonly photochemically etched include: steel, stainless steel, aluminum, inconel, copper, nickel, brass, manganese, silver, titanium and zinc. Photochemical machining is very popular for use in manufacturing the precision components used in the electronic and hardware industries as well as the jewelry industry. Parts and products that are commonly perfected using photochemical machining include: EMI shields, RFI shields, sensors, screens and meshes, pressure membranes, fuel cell components, battery grids, flexible heating elements, heat sinks, apertures and masks, springs, washers, metal gaskets, metal seals, retainers, semiconductor leadframes, encoders and jewelry. It is also very useful during prototyping. Because it so efficient, precise and affordable, it is often employed in place of similar metal machining processes such as electrical discharge machining, stamping, water jet cutting, punching and laser cutting.
Photochemical machining begins with the creation of a phototool, which is made up of the negative images of the desired parts, printed onto two sheets of dimensionally stable and optically clear photographic film. Once the phototool has been designed and printed, two metal sheets are prepped for etching. To accomplish this, manufacturers first thoroughly clean them, then they laminate them on both sides with a UV sensitive photoresist. The photoresist many be applied using either the wet dip method or the roller method. Using the wet dip method, manufacturers dip the metal into a liquid film and then harden the film by baking the metal. Using the roller method, manufacturers send the metal sheets through rollers, which apply the laminate on both sides. Either way, once they are completely cleaned and coated in photoresist, the metal sheets are positioned in between the two halves of the phototool. Once there, they are placed in a vacuum environment, which guarantees that the phototool and the metal plates are closely touching, and they are then exposed to highly focused high intensity UV light. This exposure transfers the image imprinted on the phototool to transfer onto the laminated surface of the metal. At the same time, the UV light exposure causes the areas of resist in the clear sections of the film to harden. After this, the metal is developed, meaning that the portions of the resist that were unexposed and unhardened are washed away. Left exposed are areas to be etched by an etchant. At this point, the preparations are complete and the metal may be etched. For this to happen, manufacturers place the metal sheet on a conveyor that takes it through an etching machine. This etching machine contains several different spray nozzles positioned above and below the conveyor. As the sheet moves along the conveyor, the nozzles spray it with a pressurized and heated acidic solution. Most often, this solution, which is the etchant, is ferric chloride. When the etchant comes in contact with the metal sheet, it chemically reacts and rapidly erodes everything that is not protected by the laminate. What remains are the metal forms that will go on to serve as parts. To finish the process, the remaining lamination is removed and the parts are neutralized, rinsed and dried.
Photochemical machining is a highly useful process that allows for precision etching of complex and intricate patterns and designs that could not be accomplished as easily, as well or, in some cases, at all by other machining methods. It is incredibly cost effective, especially when compared to similar machining and etching processes, which generally rack up much higher tooling costs and maintenance costs, and it is also incredibly time efficient. What’s more, because it does not engage in mechanical cutting, when performed correctly, photochemical machining leaves no sharp edges, no burrs and no imperfections. It also does not alter the physical properties of the metal it acts upon. To find out whether or not photochemical machining may add value to your production application, reach out to an experienced machining expert with whom you can share your specifications and requirements.
Photochemical Machining - Great Lakes Engineering, Inc.
Photochemical Machining - Lancaster Metals Science Corporation
Photochemical Machining - Lancaster Metals Science Corporation
Photochemical Machining: Metal Etching Using Photo-Reactive Maskant
Metal Etching is an umbrella term that encompasses numbers of technologies, including photochemical machining, micro-fabrication, and electro etching. If observed closely, all these processes employ the same principle to etch metal surfaces or other materials using corrosive or acidic chemicals. However, over time, they have evolved into specialized processes applied for particular components that range from glasses to chips to springs.
Here, in this article, discuss photochemical machining, which is also known as photochemical etching. During this chemical milling process, sheet metal components are machined or fabricated using etchants—materials that by the corrosive action remove material, and photo resist, a light-sensitive material. The process has its origin in photography when it was used to print photographs or for photo engraving on metal surfaces. However, the modern process emerged in the sixth decade of the 20th century; it came from the printed circuit board industry and evolved as its own industry.
Reasons for the rise of photochemical etching:
- Photo-etched parts can be highly complex and can be produced economically in comparison to other alternatives.
- Detailing achieved by etching is unparalleled across a variety of applications
- Tolling involved is not very expensive and is produced easily and quickly
- Process does not result in sharp edges or burrs
- Parts can be fabricated in hours versus days or weeks
- All alloys or metal with varying strength can be etched
Because of all these advantages, photo etching has become an economical alternative to other industrial processes like punching, laser and water jet cutting, stamping, and electrical discharge machining. However, it has limitations, too, as sheet-metal thickness should be between 0.013 to 2.032 mm.
Applications of Photochemical Etching
Photochemical machining is used for making a vast variety of manufacturing components, from meshes and fine filters to screens and battery grids, to fuel cell components and semiconductor motors.
Equipment Used for Photochemical Etching
During the etching process, a modern spray-etching machine is typically employed, which has a conveyor belt on which work pieces or metal sheets travel. On the belt, the parts are carried horizontally to a rigid poly vinyl chloride chamber. In the chamber, hot etchant is sprayed on the parts from a cache of nozzles installed around the track.
All the machines are designed to achieve a highly productive etch rate since work pieces are sprayed perpendicularly.
Etchants Used During the Process
Typically, aqueous ferric chloride is used as an etchant in the majority of photo-chemical etching for a number of reasons:
- Aqueous ferric chloride is readily available and is inexpensive.
- The solution is versatile; it can attack and dissolve metals and alloys easily.
- Ferric chloride is environment friendly and has low toxicity in comparison to other alternatives.
- The recycling, filtering and replenishment of ferric chloride is easy.
However, ferric nitrate is also used when non-standard materials like silver and molybdenum need to be etched.
Monitoring of Etching
During the etching process, the chemistry of etchants is important, therefore, onsite laboratory facilities are common. Etching professionals manage the production chemistry by monitoring and adjusting the chemistry.