Etching processing is a common process in metalworking operations, which generally uses a strong acid solution to corrode the metal surface. A common etching solution is ferric chloride.
What is etching technology? Simply put, etching is to block the parts you want to keep, expose the parts to be corroded, and then immerse them in a corrosive solution (like a "corrosion bubble bath").
Its process flow is briefly described as: Incoming Material Pretreatment → Drying → Coating → Baking → Exposure → Development → Full Inspection and Touch-up Painting → Etching → Stripping → Full Inspection and Packaging.
1. Introduction to the Etching Process Flow
The etching process flow varies with the type of metal, but the general procedures are as follows:
Metal Etching Plate → Degreasing → Water Washing → Etching → Water Washing → Drying → Screen Printing → Drying → Water Immersion for 2～3min → Etching Patterns and Texts → Water Washing → Ink Removal → Water Washing → Pickling → Water Washing → Electropolishing → Water Washing → Dyeing or Electroplating → Water Washing → Hot Water Washing → Drying → Soft Cloth Polishing (Buffing) → Spraying Transparent Paint → Drying → Inspection → Finished Product Packaging.
Pretreatment Before Etching
All processes before metal etching are pretreatment, which is a key process to ensure good adhesion between the screen printing ink and the metal surface. Therefore, it is necessary to thoroughly remove oil stains and oxide films on the metal etching surface. The degreasing plan should be determined according to the oil stain condition of the workpiece. It is best to perform electrolytic degreasing before screen printing to ensure the degreasing effect. For removing oxide films, the best etching solution should be selected according to the type of metal and the thickness of the film to ensure the surface is clean. Drying is required before screen printing; if there is moisture, it will also affect the adhesion of the ink, and even affect the effect of subsequent pattern etching or cause distortion, affecting the decorative effect.
Screen Printing
For screen printing, a screen printing plate with standard patterns should be made according to the printing needs. During the decoration process, screen printing mainly plays a protective role, and the number of times of applying photosensitive adhesive should be increased to make a thicker screen, so as to achieve good covering performance and high clarity of the etched patterns. Under the action of light, the adhesive film on the plate surface undergoes a photochemical reaction, making the photosensitive part cross-linked into a water-insoluble adhesive film. However, since the photosensitive part melts with water, the screen gaps are exposed. Therefore, the screen plate coated with adhesive film is engraved with a mesh pattern consistent with the black-and-white positive film.
Fix the screen printing plate with patterns on the screen printing machine, use alkali-soluble acid-resistant ink to print the required patterns on the metal plate, and after drying, etching can be carried out.
Post-treatment After Etching
After etching, the screen printing ink must be removed. General acid-resistant inks are easily soluble in alkali. Immerse the etched plate in a sodium hydroxide solution of 40～60g/L at a temperature of 50～80℃ for several minutes to remove the ink. After removal, if high brightness is required, polishing can be performed, followed by dyeing. After dyeing, to prevent discoloration and increase wear resistance and corrosion resistance, a transparent varnish can be sprayed. For some metals that have good corrosion resistance and do not need dyeing, transparent varnish may not be applied, depending on actual needs.
2. Process Requirements for Copper Alloy Etching
1> Copper alloy etching process: Pretreatment * Anti-corrosion layer production → Hanging → Etching * Flowing water washing * Photochemical treatment → Automatic water washing, inspection, anti-corrosion layer → Drying, unloading * Inspection * Packaging.
2> The requirements for the main processes are as follows.
① Pretreatment
Carry out in accordance with the pretreatment process specifications for copper and its alloys.
② Anti-corrosion Layer Production
The scribing method shall be carried out in accordance with the scribing process specifications; the photosensitive method shall be carried out in accordance with the photosensitive process specifications; the screen printing method shall be carried out in accordance with the screen printing process specifications; the laser lithography method shall be carried out in accordance with the laser lithography process specifications.
③ Hanging
Select an appropriate hanging method according to the different etching methods.
The hanging should be firm to ensure that the workpieces do not adhere to or collide with each other.
The hanging position should be appropriate to avoid air bubbles during chemical treatment as much as possible and ensure uniform etching.
If a transmission-type etching equipment is used for etching, hanging is not required, but appropriate tooling should be adopted to prevent the workpiece from shifting during spraying, which will affect the etching process.
④ Etching
Alkaline etching of pure copper shall be carried out in accordance with Table 4-16, and acid etching of copper and copper alloys shall be carried out in accordance with Table 4-17.
For vertically etched workpieces, the upper and lower positions should be swapped regularly. During the etching process, attention should be paid to checking the change of etching depth. When the etching reaches about 80% of the depth, the workpiece should be taken out to measure the depth, and then the remaining etching time should be determined.
For step and pattern etching with low depth, the time can be determined according to the pre-process test.
For vertically etched workpieces, the upper and lower positions should be swapped regularly. During the etching process, attention should be paid to checking the change of etching depth. When the etching reaches about 80% of the depth, the workpiece should be taken out to measure the depth, and then the remaining etching time should be determined.
For step and pattern etching with low depth, the time can be determined according to the pre-process test.
Inspection
This step mainly checks whether the etching depth and the effect of the etched surface meet the process requirements, and checks whether there is any abnormality in the anti-corrosion layer.
Removal of Anti-corrosion Layer
The anti-corrosion layer made by screen printing, photosensitive or laser lithography can be cleaned with organic solvent and 5% sodium hydroxide solution; the anti-corrosion layer made by scribing can be directly peeled off. For workpieces with small thickness, attention should be paid to preventing workpiece deformation during peeling.
Drying
Dry in a drying oven (room) at 60℃～80℃.
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Written by
CoolingThermal Engineering TeamCoolingThermal is an automation equipment manufacturer based in Kunshan, China, specializing in heat pipe and vapor chamber production equipment since 2017. Our engineering team designs, builds, and commissions complete production lines covering forming, degassing, welding, testing, and assembly processes. The technical content on this blog is written by the same team that develops the equipment — based on real production experience, not secondary research.
