Comparing PCB Etching Techniques

Etching is the process of removing copper elements from the board to pave a conductive path for electricity flow. PCB etching is one of the most important elements of the PCB manufacturing process. Manufacturers must prepare a design, transfer it, apply the etching solution, clean it, and perform a finishing process to etch PCB for an electrical device.Although it sounds straightforward, the PCB etching process is quite complex and precision is vital. Without the proper knowledge of what is PCB etching and its standards, manufacturers may find themselves struggling with various approaches during the process. This blog will cover every aspect of PCB etching, including the steps for the process, real-world examples, and types of etching.

What is PCB Etching?

PCB etching refers to the task of eliminating unwanted copper from the board surface. Manufacturers can create desired circuit patterns only with the removal of unwanted copper traces through PCB etching. It is one of the most crucial steps after the PCB fabrication process.

Before starting with PCB etching, a process called photolithography is conducted to transfer the desired blueprint of the board. With the help of this layout, unwanted copper elements are traced out and removed. This is just the tip of the iceberg. There are many other techniques for the PCB etching process like chemical etching, laser etching, etc. See how PCBs are manufactured in JLCPCB factory.

How to Etch PCB - Step-by-Step Guide:

Considering the importance, PCB etching goes through a series of well-structured steps. Etching a PCB through wet etching process requires taking the following steps:

Design the PCB:

Create the layout using software like EAGLE, KiCad, or EasyEDA. Print the design in reverse onto a transparency sheet for transfer. Verify that the PCB pad sizes and orientations match the component's PCB design constraints.

Transfer the Design:

Clean the PCB thoroughly to remove any dirt, oil, or other contaminants. Align the design with the copper board. Apply sufficient heat and pressure to ensure that the ink sticks to the copper surface firmly. After the heating process, cool it down to peel off the transfer paper. Now, only the design will remain stuck to the copper surface.

Choosing Etching Solution:

Etching solutions like ferric chloride, ammonium persulfate, or vinegar and hydrogen peroxide are easily available in the market. Choose any one of them depending upon the PCB quantity and accessibility.

Monitor the etching process:

Immerse the board in the solution and stir it. Keep an eye on the PCB as it etches. The amount of time it takes for the etching to be completed depends on the type of etchant, the PCB thickness, and the temperature of the solution.

Rinse and Clean the PCB:

Once the etching is complete, rinse the PCB thoroughly with water to remove any remaining etchant solution. Consider using a soft brush to scrub and remove any leftover copper from the surface. After cleaning, dry it with a clean cloth.

Perform an inspection:

Inspect the PCB to ensure that the circuit pattern is accurate and that there are no defects or problems.

Finishing Process

To protect the copper traces from oxidation, a thin tin layer is applied to the surface. Additionally, a solder mask is used to prevent solder from bridging between adjacent traces, offering insulation and added protection for the copper. Finally, silkscreen printing is performed to label the board with details like the registration number, brand name, and other identifiers. While not mandatory, these steps enhance durability and functionality.

PCB Etching Best Practices

• Surface Preparation: Ensure the PCB surface is thoroughly cleaned to remove contaminants for optimal etching results.

• Quality Materials: Use high-quality copper-clad laminates to achieve better precision and durability.

• Safety Measures: Equip personnel with safety gear, including gloves and protective eyewear, to handle chemicals safely.

• Prevent Over-Etching: Promptly remove the board from the solution as soon as unwanted copper is eliminated to avoid over-etching.

• Neutralize for Disposal: Mix the used etching solution with a neutralizing agent like baking soda to ensure safe disposal.

Types of PCB Etching Techniques:

There are many etching methods and choosing the right one is critical for the purpose. Always keep in mind that PCB etching is not an area of guesswork. Here is the proper breakdown of the PCB Etching techniques:

Wet Etching Process:

The wet etching process uses a solution that dissolves unwanted copper using chemical reactions. It uses two types of chemicals: acidic chemicals and alkaline chemicals.

Acidic Etching:

In the acidic PCB etching process, the used etchants are Ferric Chloride (FeCl3) and Cupric Chloride (CuCl2). The acidic method is usually used to etch off the inner layers of a rigid PCB. Of the two solutions, cupric chloride (CuCl2) is most common because it accurately etches off smaller features and provides a constant etch rate and continuous regeneration. Cupric chloride in combination with sodium chloride (NaCl) is one of the methods to obtain the maximum etching rate.

The acidic etching is more accurate and cheaper than the alkaline one. The acidic method is used for the inner layers because the acid doesn’t react with the photoresist and doesn’t damage the required part. Furthermore, this method has the smallest undercuts, which are the portion of the copper removed under the photoresist. However, acidic etching can be a lengthy process and it’s much more time consuming than alkaline etching. As a result, it’s not always suitable for large quantities of PCBs.

Alkaline Etching:

Alkaline etching is chemically removing the undesired copper layer, it is a suitable method to etch off outer layer circuit patterns. The alkaline etchant is the cupric chloride with ammonia composition which is a strong oxidizing agent and reacts with and dissolves the metal copper.  Alkaline etching is an incredibly fast and cost-effective way of etching a PCB. However, the process must also be closely controlled. This is because the solvent can damage the board if left for a long period of time.

To make the process as quick, efficient and accurate as possible, alkaline etching is usually carried out in a conveyorised, high-pressure spray chamber. During the etching process, the point at which the etching of the unwanted copper is complete is called the breakpoint and further steps can be performed after that.

Dry Etching:

Dry PCB etching utilizes gas or plasma as an etchant to remove undesired substrate materials. Plasma activates chemical reactions between base and surface atoms of the laminate and causes the unwanted copper to dissolve. Unlike wet etching, dry etching avoids the use of chemicals through which enormous hazardous chemical waste is generated. At the same time, it reduces the risk of water contamination.

Laser Etching:

The laser etching process allows for the use of precise, computer-controlled hardware. During the process, a high-powered laser carves out trace lines on the PCB’s substrate. These unwanted copper traces either evaporate entirely or are flaked off the PCB. Compared with other wet PCB etching techniques, laser etching greatly reduces the number of steps, thereby diminishing production costs as well as production time. It also eliminates the need for any inks, acids or toxic chemicals to be used.  However, it can be hard to etch evenly on large boards. On top of this, laser etching processes are very expensive.

Plasma Etching:

The process was created as a way to help reduce liquid waste disposal in manufacturing and achieve selectivities that were difficult to obtain with wet chemistry. It is a selective etching reacting with chemically active free radicals. It also includes directing the high-speed stream of plasma of a proper gas mixture at the etched material. Compared with wet etching methods, plasma etching is clean. Plasma PCB etching can perform controlled and precise etching on a very small scale. This special process also reduces the occurrence of polluted vias and solvent absorption.

However, although it has its advantages, plasma etching is incredibly costly. As a result, unless you’re etching in vast quantities regularly, it’s likely to be much more expensive than a wet etching method.

Difference Between Wet Etching and Dry Etching

As the process of PCB etching gets complex, manufacturers try out more methods to simplify the procedure. Manufacturers continually refine PCB etching processes to achieve efficiency and precision. Here's a comparison of the two primary methods:

1. Meaning:

• Wet Etching: Involves immersing the PCB in a chemical solution, like ferric chloride, to dissolve unwanted copper.
• Dry Etching: Uses gases or plasma in a vacuum chamber to selectively remove copper without chemicals.

2. Procedure:

• Wet Etching: Relies on a chemical reaction to remove exposed copper, ideal for single-sided boards.
• Dry Etching: Employs reactive gases, offering directional precision for complex patterns.

3. Cost:

• Wet Etching: More economical but involves handling hazardous chemicals.
• Dry Etching: Cleaner and safer but requires specialized, costly equipment.

4. Precision:

• Wet Etching: Dissolves material in all directions, limiting precision.
• Dry Etching: Provides high accuracy by removing copper in a single direction, suitable for advanced designs.

Each method serves specific design and budget needs, offering flexibility in PCB production.

Conclusion:

PCB etching is a cornerstone of manufacturing, enabling the creation of precise circuit patterns essential for electronic devices. From initial design to the final finishing process, each step demands meticulous attention and adherence to best practices to ensure quality. This process demands designing, creating a substrate, printing layers, removing copper, drilling, plating, and much more. And you can’t forget the etching process, which makes all of this possible.

Now you know all there is to know about the long PCB etching process and how the perfect etching is achieved. With diverse etching methods like wet, dry, laser, and plasma, manufacturers can tailor techniques based on budget and design complexity. You also know how there are multiple ways to complete the etching process, such as with chemical etching, plasma etching, or laser etching. Either way, you can rest assured your electronics will function properly.