This is a crucial process in many manufacturing industries. It usually involves the fabrication of metal elements through chemistry and precision photolithography. The process is also known as chemical machining, metal-etching, photo-etching, and chemical milling.
It consists of several essential steps and each step depends on the previous step. This means that every individual step is a vitally important prerequisite to the next step. Different companies may use a different photochemical machining process. Some use very proprietary and unique methods to arrive at the final product but the fundamental operations are regarded the same.
This method is known widely as viable for working metal and although it is a growing industry, it is gaining a lot of recognition and experience globally. The following are the steps used throughout the process.
1. Designing / Engineering
This involves creating, designing or engineering the photo tool which is used to profile the part. This is done when a new part is ordered by a customer who provides the original dimensions either using a CAD file that contains detailed and accurate measurements or by drawing. Professional tooling engineers then reconstruct the part in a complete form, changing the measurements so as to suit the unique requirements of the PCM process. Here, materials are cut into manageable sizes which are free from any kind of tabbing during the next processes.
2. Cleaning / Metal Preparation
After cutting into certain sheet sizes that are more manageable, the elements are cleaned using chemicals in order to get rid of unwanted substances such as dust, foreign debris, grease, and etcetera. This allows the photoresist to cling or attach to the metal sheet making it ready for the step that follows.
3. Material Coating / Coating Operation
This is a very significant process. It is done immediately after cleaning to prevent the surface of the metal sheet from being oxidized or contaminated. A dry-film-photoresist coat is preferred in this step because it can easily be removed, and is more controllable. The entire step is done using a hot-roll-lamination system and takes place in an environment that is yellow in color and safe from light.
4. Imaging /Exposing / Printing
During this step, the image of the photo-tool material is moved to the prepared metal-sheet. This is done by activating the-sensitive-polymer in the photoresist film. The sheet is then sandwiched between two photo-tool-elements. This takes place in a vacuum-frame which makes it intimately in contact while ensuring there is neither gaps nor air bubbles between the metal and photo-tool. A strong UV light is then exposed to the panel which prints the photo-tool element onto the sheet.
5. Developing Step
This step is a must for all the coated and exposed materials. Chemical solutions are sprayed to the panel to remove the uncured, unhardened, and unexposed photoresist. Various factors are strictly monitored and controlled. These include temperature, spray pressure and distribution, PH, and dwell time. The remaining material is cured and coated and it is which should continue with the following process – Etching.
This is where there is a total erosion of materials which are not secured by the resist using various etchants like ferric nitrate (for silver and molybdenum materials), cupric chloride (for non-ferrous alloys materials), iodine-based etchant (for gold and its alloys materials), ferric chloride (for ferrous alloys such as Kovar, stainless steel, and etcetera) and other types of etchants. At the end of this step, all sheets are completely etched and rinsed and the measurements accurately maintained. This is done carefully while calibrating the speed of the conveyor.
7. Stripping Step
During the process of etching, some photoresist materials may remain on the metal sheets. This step completely removes these materials by stripping them off using chemicals such as sodium hydroxide solution. Once this is done, city water is used to clean the sheets, and then de-ionized water is used to rinse them. There is then a total inspection of the materials using quality control methods before the sheets are ready for secondary operations such as welding, plating, soldering, and etcetera. Otherwise, they are packed ready for shipment.
8. Final Step: Quality control and Shipment
Once everything has been done, the materials are inspected clearly by the FAI (First-Article-Inspection) before release. Dimensions are verified and once approved by the respective inspection agencies, they are packed keenly in a manner that they are not damaged when being distributed to the relevant customers. Various containers are created during packing such as labeling/bar coding, individual bagging, wooden crates (for large parts), waffle packaging, and among others. These steps are what most manufacturing industries use during the photochemical machining processes.