Printed circuit boards are necessary for multiple devices and equipment, including electronics. PCBs are also core features of smart devices that’s why they should have high-quality manufacturing. Etching is an important step in the PC Board Fabrication process. It is used to remove unwanted copper from the board and create the desired circuit patterns. This process is also known as photolithography, and it requires a special etching solution and a masking material to accurately etch the board. In this article, we will discuss the etching process in PCB manufacturing in more detail.
Understanding PCB Etching
Etching is the process of removing unwanted copper from the printed circuit board by using a chemical etching solution. The etching solution comes up with different compositions like it can be a mixture of hydrochloric acid (HCl) and ferric chloride (FeCl3). But, there are also other solutions that we will discuss here.
PCB manufacturers apply the etching solution to the board through a stencil, which has a masking material such as photo-resist. This masking material blocks the etching solution from reaching the desired copper traces and protecting them from the etching process.
Etching Process in PCB Manufacturing
Manufacturers use an etching process to create the desired copper traces on the PCB. During this process, they apply a resist material to the board. Such a resist material can either be a photo-resist or a dry film resist. The resist material is then exposed to ultraviolet light, which causes the resist material to harden. This hardened resist material prevents the etching solution from reaching the desired copper traces. The etching solution is then applied to the board, which removes the unwanted copper and leaves the desired copper traces intact.
Advantages of PCB Etching
Etching is an efficient and cost-effective method of creating the desired copper traces on the Printed Circuit Board. It is also very accurate, as it can create very fine details on the board. In addition, etching is a quick process and does not require a lot of manual labor.
Etching is a precise process, which allows for finer lines and more accurate features than other methods. This makes it an ideal choice for complex designs and high-density PCBs.
You can use etching to create a variety of features, including traces, vias, micro-vias, and blind and buried vias.
Etching is one of the most cost-effective methods for PCB manufacturing, as it requires it does not involve much production costs.
Etching produces less waste than other methods, as it uses a minimal amount of material to create the desired features.
Etching is a fast method of producing PCBs, as you can complete the entire process in a matter of hours.
Etching provides improved thermal performance compared to other methods, as there is less material to absorb and dissipate heat.
Etching produces reliable boards with better electrical properties and higher levels of performance.
However, the above benefits depend on the type of solution and the etching technique you are using.
Types Of Etching Techniques
PCB manufacturers use two major techniques to etch or remove unwanted conductive material, such as wet and dry etching. Let’s discuss them in detail.
What Is Wet Etching?
The wet etching technique involves a chemical solution and it is popular among manufacturers as it works fast. It involves different chemicals which vary from each other in terms of properties, such as solvent concentration, ambient, and gripping. Wet etching is further divided into soluble or alkaline etching and acidic etching.
Etching Using Alkaline: It involves a solvent to remove the extra surface material from the board. It needs care as you have to check that the chemical has the right specification. Leaving the chemical on the board for longer can damage it, so watch the duration.
You should also consider other things during alkaline etching, like the quantity of the material to be etched, the spritz, and the nature of the layer. You can have an excellent etching by considering these elements. It involves different solvents, including chloride copper, hydrogen peroxide, water, and hydrochloride. It works fast which makes it an expensive process.
Etching Using Acid: As the name shows it involves acid, however, the main purpose of this method is to etch the inner layer. It is ideal for a rigid circuit board and costs less than alkaline etching. Manufacturers use either ferric chloride or citric chloride for acidic etching. However, it is a time-consuming process compared to others.
What Is Dry Etching In PCB?
The dry etching of circuit boards involves machines for removing copper and its residues. You can also call it plasma etching according to experts. Dry etching is not as hectic as wet etching, and it is suitable for the high-volume production of circuit boards. You don’t need a lot of effort while removing the waste material as it goes to the airspace, giving you a clean surface to work with.
Popular Etching Solutions
You have to choose an etching solution carefully because it’s often poisonous as its vapors can damage the metallic parts in a PCB. Below, we will discuss some safe solutions in this regard.
Sodium Persulfate: It is a combination of acid and water, and its clear color helps monitor etching during the entire process. Though it is more costly than other solutions, it is compatible with the resist tool. Remember that sodium persulfate is combustible which makes it toxic to the surroundings.
Ferric Chloride: It is a combative solution that can remove a tough material during etching. Ferric chloride is cost-effective and its rustic tone covers the etched residue. It has a blotting property and blots the parts that it touches.
Cupric Chloride: It is also known as inanimate copper chloride and has a dusty yellow tone. Cupric chloride is not combustible and can damage aluminum due to its acidic effect. When you heat it in a fire, it will produce gas, like hydrogen chloride. It helps have hydrogen peroxide during depletion.
Ammonium Persulphate: You can use ammonium persulphate in a tin-resistant method as it helps have visibility. Moreover, it is not very combative and involves high temperatures. It creates toxic vapors and can turn into nitrogen and sulfur during metal decaying which causes ignition.
Benefits of High-Quality Etching
Different devices involve different etching techniques, such as smart devices involving reactive ion and additive methods. Similarly, the same technique is applied to the computer motherboards’ etching. This method got popular due to the Apple Company, and the latest devices need high-end etching as they are multilayered. The applications with thin copper need high-quality etching, including reactive ions and additives.
The mSAP process helps develop compact motherboards for smartphones that helps engineers insert a large battery with a longer life. Today’s PCB design have small traces, like up to 30 microns, which might reach 10 microns in the future.
Other than smartphones, high-quality etching is getting essential for medical equipment and devices, automotive, wearable, and aerospace industries. It can help manufacturers use a six-layer PCB having single or double lamination. Right now, the 10-layer HDI PCB having 4 cycles of lamination is in practice.
HDI PCBs are used in aerospace and military applications that involve fine lines, firm pinouts, and small vias. Such applications also involve PCB stack-ups just like smartphones, and manufacturers try to reduce the layer counts and the number of laminates by adding the layers through mSAP and SAP techniques where subtractive etching goes well.
High-quality etching is also essential for wearable as they are thin, lightweight, and flexible. Printed circuit boards used in medical plants have 20-micron traces with a double-sided design having gold conductors that provide biocompatibility.
Frequently Asked Questions
Why is PCB Etching Important?
PCB etching is essential as it removes unwanted copper from the board and creates the desired circuit patterns.
What Are Popular Etching Techniques?
PCB manufacturers use two major techniques to etch or remove unwanted conductive material, such as wet and dry etching.
Which Solutions Help In Etching?
Some common PCB etching solutions are Sodium Persulfate, Ferric Chloride, Cupric Chloride, and Ammonium Persulphate.
What Is High-Quality Etching?
The latest devices are compact and delicate and need high-quality etching in PCB. HDI PCBs used in aerospace and military applications that involve fine lines, and firm pinouts, need high-quality etching.
Etching is an important step in the PCB manufacturing process. PCB manufacturers use etching to remove unwanted copper from the board and create the desired circuit patterns. This process is also known as photolithography, and it requires a special etching solution and a masking material to accurately etch the board.
Etching is an efficient and cost-effective method of creating the desired copper traces on the PCB, and it is also very accurate and quick. Various solutions and etching techniques are there in the PCB market.
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