A Fascinating Non-Conventional Metal Fabricating Option
Photo etching, also known as photochemical machining or chemical milling, is a fascinating process that lies at the intersection of science and art. It's a technique used in various industries, from aerospace to electronics, to create intricate metal parts with remarkable precision. In this blog post, we'll delve into the science behind photo etching, exploring the chemical processes that make this technique possible.
The Basics of Photo Etching:
Photo etching involves selectively removing material from a metal sheet using chemical processes.
Imaging
It begins with a photoresist-coated metal sheet, typically made of materials like stainless steel, copper, or aluminum. A design or pattern is then transferred onto the photoresist using a photographic process. Exposing the coated metal sheet to UV light through a photo mask hardens the exposed areas of the photoresist.
Developing
The unexposed areas of resist remain soluble. The unexposed resist is "developed" by spraying it with an alkaline solution between 9 and 11 pH that washes the uncured material away, leaving bare metal.. This creates a stencil-like pattern on the metal surface, protecting certain areas from chemical attack in the subsequent etching step.
Etching
Once the photoresist pattern is developed, the metal sheet undergoes chemical etching. Conveyorized etching systems spray the etching solution onto both side of the plates using oscillating spray bars. The speed of the conveyors is determined by the thickness of the metal. The etchant removes material from the exposed metal surface, effectively "corroding" away the unwanted portions while leaving the protected areas untouched.
The chemical reaction between the etchant and the metal is a critical aspect of the process. The choice of etchant, its concentration, temperature, spray pressure and other factors influence the rate and uniformity of material removal. Ferric chloride etching solution is widely used for stainless, nickel and copper alloys, Ferric nitrate will etch silver and molybdenum. Aluminum will etch in both acids and bases.
Consistency and Control are Critical
Controlled etching is essential for achieving precise and consistent results in photo etching. Factors such as etchant composition, temperature, pressure, and etching time must be carefully controlled to ensure uniform material removal across the metal sheet.
Temperature control is particularly crucial, as variations can affect the etchant's reaction rate and the quality of the etched features. About 300 gallons of etching solution are in circulation in a double chamber etching machine. Thermal probes constantly react to changes in temperature, calling for the heaters or chilled coolant to maintain 122 +/- 3 deg F.
In addition to spray bar pressure and conveyor speed, other sensors and probes are paying attention to the condition of the etching solution, calling for "regeneration" by adding oxidizing agents and hydrochloric acid to restore the solution's "oxygen reduction potential."
Finishing the Process
Once the desired etching is completed, the metal sheet is "stripped" thoroughly in a caustic solution to remove the photoresist and rinsed in deionized water. After inspection of the etched parts, there may be other operations, such as: forming, plating, heat treating, etc., that we have a network of suppliers to provide.
Photo etching is a sophisticated manufacturing technique that relies on precise control of chemical processes to create intricate metal parts. Understanding the science behind photo etching, from photoresist patterning to controlled etching, is essential for achieving high-quality results. By mastering these chemical processes, manufacturers can unlock the full potential of photo etching in various industries, from aerospace and electronics to medical devices and beyond.
