Introduction
It is an important part of the PCB manufacturing method, as some of the copper is removed from the PCB’s surface to reveal the desired pattern on the circuit board. Which Chemical Is Used For PCB Etching process, all copper is removed except the circuit pattern protected by the tin plating. As a result, the tin plating is eliminated, and the copper is cleaned. The PCB etching process is complex and safety measures are important to prevent injuries. There are multiple techniques for etching, and all these techniques and methods will be discussed elaborately in this comprehensive guide.
What Is PCB Etching?
In this process, we eliminate unwanted copper from the circuit board to get the required circuit pattern. This process focuses on the removal of substrate copper from PCB. The hardened copper is more easily etched as compared to the electroplated copper. The alkaline etching process aims to react potent chemical acids or strong alkalis with the copper surface of the printed circuit board, it erodes the extra copper while preserving the (Cu) layer of the circuit through electric tin plating.
The various types of chemicals used
This etching process has a specific etching rate. It is non-foaming and can be applied through spraying.
150 MG Copper Etchant:
This is a tested etchant. It is specifically engineered for copper etching in the production of PCBs. It is used during large-scale manufacturing. The chemicals have selected compounds in small proportions that make them suitable for both spray and immersion.
Nickel Cleanser:
It is an aqueous solution of acidic chemicals. It is used to restore the solderability of the PCB. Rough material can be eliminated by dipping the PCB for 15-20 seconds at room temperature. Immersion time is shortened when the solution is heated to 74°C. After treatment, the PCB is fully cleaned through hot water spray.
Solder Remover:
It is used for removing tin and lead from the PCBs. It has been a highly cost-effective material that is beneficial for cleansing.
Resist cleanser:
It is a concentrated solution. It has no organic solvents. It can be used in dipping containers and spraying machines.
Anti-foamer:
It has no silicon and is called an anti-foamer. It is used to conveyorize spraying materials. It controls excessive foaming across a wide range of temperatures.
6109 Lacquer:
It is a fast-drying resinous system that is designed to protect printed circuit boards and other electronic components from the oxidation process. It protects the solderability of metallic surfaces. It leaves a resin coating. It is fully compatible with almost all rosin-based fluxes.
In addition to cleaners, there are other chemicals used in the PCB development process that are required to be mentioned:
Enhancer:
During the assembly process, the printed circuit boards can have some damage. The enhancer helps in maintaining the PCB’s functionality during development. It plays an important role in neutralizing, brightening, and restoring the balance of developer parts.
PCB Cleansing Materials:
Cleansers are used in the development of the PCB. They are applied to maintain resistance against etching cracks due to acidic solvents.
Foam-resisting material:
They are used to mitigate the foam generated by other chemicals that are utilized in the process. They are extensively used during the production stages.
How does our PCB etching machine work?
Different types of PCB etching machines are available in the market, using lasers or plasma to end unrequired materials from the PCB; some of the machines also use ammonium edge solutions for etching. In the etching process of the PCB manufacturing process, the PCB is placed on a conveyor belt in the Alkali Etching Machine. When the machine is activated, the conveyor belt moves and places the PCB inside the machine. In the machine, the PCB is sprayed with ammonium edge solution, eliminating all the copper areas that are not protected by tin, leading to clean fiberglass with some traces of copper protected by tin coating.
What elements are used in the Printed Circuit Board etching process?
First of all, it is necessary to get information about the tools and components that are required for the task of etching. The following are the tools used for etching:
Copper (Cu) Boards
Copper-clad boards
They are important for PCB production, consisting of flat sheets made up of fiber and composite materials with a thin copper layer along the sides. There are different thickness types in copper boards. The copper layer thickness may also be different.
Etching solution
Etching solutions
It is the chemical agent that has a major role in removing undesirable copper from the PCB. Two frequently used etching solutions are FeCl3 and (NH4)2S2O8. Ferric chloride is preferred among hobbyists for small-scale manufacturing and ammonium persulfate is frequently used for larger-scale production.
Protective gear
There are many health hazards associated with etching solutions. It is mandatory to costume protective gear to protect the skin and eyes. It is recommended to use protective equipment like, safety glasses and gloves as well.
Etching Container
Etching Container
An etching Container is used to dip the PCB in it with the etching solution. It can also be utilized with the etching solution to dip the copper board in it.
Water for Washing
Water for Washing
When the etching process is complete, it is a must to rinse the board with water to end any residual etching solution. Cleaning the board with water makes it easier to start the further processes on it. A clean board makes a powerful circuit as impurities are removed from it. So, it is important to have a water source for rinsing the board.
Developing solution
Developing solution
In case, if a photoresist method is used, a developing solution is required to eliminate the visible photoresist from PCB later in the exposure process.
Laser printer
Inkjet printer
The laser printer is also used for drawing an initial circuit on the board. Sometimes, the toner process is also used for printing the circuit. A laser printer is also used for printing the design on the paper.
Heat source
Flexible PCB heater
A heat source is also used for transmitting the toner to the copper board. A laminator is used as a heat source for aiding in the transfer of toner to the copper board.
Stages for PCB etching Process
Step 1: Start the etching process by designing the circuit board. Important note: Make sure to move it to the other side. So that the PCB diagram is oriented.
Step 2: Print the required structure of PCB through a printer.
Step 3: Prepare the copper surface. This can be achieved by roughening the surface to increase the adhesion to easily handle the solutions.
Step 4: Clean up the surface of the PCB by wiping it with a mixture of water and alcohol. Then dry it up.
Step 5: Place the printed sheet on the prepared PCB surface.
Step 6: Slide the surface by a laminator multiple times until the plate is heated.
Step 7: Dip it in a cold bath until the sheet starts to float.
Step 8: PCB is placed in the solution inside the PCB etching tank. It is agitated until the unnecessary copper is completely removed.
Step 9: Wash the PCB in a water bath. Then dry it and wipe the ink from the PCB.
Step 10: Now, your PCB board is prepared. The holes are required to be drilled.
Step 11: A thorough inspection of the PCB is performed to ensure the accuracy of the circuit pattern and to identify any defects or issues.
Step 12: A layer of solder mask is applied at the end. It is an optional step. This layer provides insulation and protection to the copper traces.
What are the different methods for PCB etching?
Various methods for PCB etching are used for manufacturing semiconductors. This process selectively removes the copper from the surface that is covering the film. Etching methods are divided into wet etching and dry etching.
Wet Etching
Wet PCB etching is a very simple process. In this procedure, the etching materials are dipped in a chemical solution to remove the surplus copper. Three primary factors are responsible for impacting the etching rate:
- The concentration of the etching chemical.
- The temperature of the etching solution.
- Agitating or stirring the etching solution.
Wet etching is performed in two different ways:
- Alkaline etching.
- Acidic etching.
Ferric Chloride and Cupric Chloride are used for acidic etching
Acidic etching is used for etching the inner layer of PCB. It is compatible with a photoresist that protects the required components needed in the PCB circuit design.
Chemical solvents used in the Acidic Etching process are:
- Cupric Chloride etchant
- Ferric Chloride etchant
Alkaline Chemicals: chloride copper (CuCl2 Castle, 2H2O) + hydrochloride (HCl) + hydrogen peroxide (H2O2) + water (H2O)
The entire process is carried out inside a high-pressure spray chamber. A PCB is thoroughly exposed to an etchant spray in this chamber. All the unwanted copper is removed from the board during this process.
Manufacturers use special chemical solvents for the alkaline etching process. These solvents include the following:
- Cupric Chloride etchant.
- Ferric Chloride etchant.
Dry Etching
Dry etching is an important method for etching the sub-micron-sized devices. It utilizes plasma to etch thin films. This technique is dependent on plasma to react with the surface of the film, leading to direct bombardment on the target film. The anisotropic nature of dry etching is its special feature.
Plasma Etching
Plasma etching is considered the most common use of plasma. In plasma etching, a very powerful and highly reactive substance is generated from O2 or a gas having fluorine. This gas is bombarded on the sample surface leading to a quick reaction. As a result, the copper on the surface breaks down into smaller molecules that are removed through the vacuum system.
Laser Etching
The PCB laser etching process uses computer-controlled equipment. In this technique, a high-power laser is utilized to make circuit prints on the PCB’s substrate. Unwanted copper traces are completely evaporated or peeled away from the PCB. It is used to create uniform etching on large plates.
Laser Etching
What Factors Determine the Quality of Etchants?
The special parameters that are used to check the quality of the etching agent ensure the smooth operation of the etching process.
Baume
Baume is also known as Be. Its amount tells about the molarity of the etching agent. It is dependent on the solution’s density. High Baume levels typically lead to increased etchant molarity and higher etching rates.
Temperature
Usually, higher temperature accelerates the etching rate of the etching agent. However, limitation arises due to the materials used in the etching machine which are made up of plastic. Manufacturers utilize balanced temperature settings to achieve successful etching. Typically, the allowed temperature range for etching is between 500 and 550 degrees Celsius.
Redox potential (ORP)
Manufacturers measure the redox potential of the etching agent to check its effectiveness. The redox potential tells about the relative conductivity of the etching agent measured in millivolts. It clarifies the correlation between copper ions, ferrous ions, and iron ions. During the etching process, the chemical solution transforms into a ferrous/copperite state.
Chemical additives (free acids)
Various manufacturers use chemical additives to increase the etching rate of the etching agent. HCl is frequently used as a chemical additive with FeCL3 and CuCl2 etchants. When HCl is introduced in the etching solution, it acts as a chlorine source leading to the creation of metal chloride. As a result, these etchants effectively retain the dissolved metal.
PH
The pH level of the etching agent is very important for the etching process. PH level is measured to ensure effective alkaline etching. The ideal PH level of the etching solution falls in the range of 7.9 to 8.1. PH levels play a vital role in the context of acid etching, it should be balanced for best etching results.
Safety Protections during PCB Etching
Etching can be very dangerous if suitable safety measures are not followed. Some crucial safety guidelines to follow while doing PCB etching:
- Always use gloves, safety glasses, and masks while managing chemicals.
- Perform PCB etching in a well-examined environment.
- Prevent the contact of etching chemicals with the skin.
- Follow proper disposal procedures to get rid of hazardous etching chemicals.
Developments in PCB etching
Technological advancements have increased the effectiveness of the PCB etching method. Advanced technology has resulted in good accuracy, precision, and cost-efficiency. Innovations in PCB etching are laser printing and plasma etching. These interesting methods lead to quick production cycles and output rates.
Conclusion
The etching process plays a vital role in the process of PCB production. It is an excellent procedure for the cost-effective manufacture of circuit boards. Special materials and tools, methods, and techniques are utilized for the PCB etching. It is necessary to follow safety measures while handling the chemicals and equipment used for etching.
Frequently Asked Questions
Why do we do PCB etching?
We do this to remove the selective part of copper from the PCB to achieve the desired electrical connections and circuits.
Describe some methods used in PCB etching.
There are several methods used for PCB etching like photoresist technique and the toner Process.
What components are required for PCB etching?
We need a copper board, an etching solution, a developer solution, and an inkjet printer with transfer paper to perform the toner transfer technique. We also require safety equipment including gloves and glasses.
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