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Everything You Need to Know About PCB Desmearing

Updated: Aug 17, 2023


Plasma desmearing is a process step that is typically utilized in the printed circuit boards (PCBs) manufacturing process.


A PCB is composed of different layers, which can either contain copper routes, which are the current conductors to link the different components of the PCB and make the desired electrical circuit, or other insulating materials like epoxy resins which avoid shorts between the different copper traces.


Once the different layers have been manufactured, they are aligned and stacked. Holes are drilled in the PCB to allow electrical connections between the different layers.


After drilling, the PCB undergoes a metallization process in which copper is deposited in the holes to make the electrical connection between the PCB layers.


Since the drilling operation uses drill bits that spin at high speed, it can cause the epoxy layers to melt or degrade at the hole surface, leaving a smear of non-conductive material that will reduce the quality and performance of the metallization layer deposited in the hole.


This problem can be solved with plasma desmearing, but what exactly is plasma desmearing, and how does it work?


In this article, we'll take a closer look at this process and explore the two types of descum. We'll also discuss whether plasma descum is right for you and point you in the direction of experts who can help you make informed decisions for your project.


What Is Plasma Desmearing?

After the PCBs have undergone the drilling step, they are introduced into a vacuum plasma desmearing system. In this system, a mix of process gases is used based on the smear material composition.


Gases that are normally used in this process are Oxygen (O2), Hydrogen (H2), Argon (Ar), or even fluorinated gases like Sulfur Hexafluoride (SF6) and Tetrafluoromethane (CF4).


The process gases are turned into an aggressive plasma with the help of an energy source like an RF generator.


How Does Plasma Descum Work?

When the PCBs are in the plasma environment, the plasma active species will chemically and physically react with the smear breaking it into small molecules.


Since the process is performed at low pressure (~1 mbar), these by-products produced from the chemical reaction between the plasma and the smear can evaporate from the surface and be removed by the vacuum system.


This process is highly effective as, by choosing the correct process gases, the etching of the smear can be selective for the smear only, leaving the copper traces untouched and assuring high uniformity of the results.


The 2 Types of Desmearing Processes

There are two types of desmearing and both have a slightly different process.


1. Chemical Desmearing

This process was used at the beginning of PCBs manufacturing, and it is still used today. Instead of using plasma to remove the smear, chemical solutions are used.


Pros

  • Efficient and Reliable: Chemical desmearing methods are efficient and have been reliably used in the industry for many years.

  • Accessible: The required chemicals for this process are relatively easy to source.

  • Broad Material Compatibility: Chemical desmearing works with a variety of materials used in PCBs.


Cons

  • Environmental Impact: Chemical desmearing involves hazardous chemicals, which need careful disposal to mitigate environmental harm.

  • Safety Concerns: Handling and disposing of the chemicals can pose safety risks to workers.

  • Potential Damage: Overexposure to chemicals can damage the base material of the PCB

2. Plasma Desmearing

Plasma desmearing uses a plasma reactant to remove the smear from the PCBs, as explained above.


Pros

  • Selective and Uniform: Plasma desmearing is highly selective and offers uniform treatment. It can precisely desmear without damaging the underlying material.

  • Environmentally Friendly: This process does not involve the use of hazardous chemicals, reducing the environmental impact.

  • Better for High-Density Interconnect (HDI): Plasma desmearing is better for HDI boards with smaller holes that chemicals may have difficulty penetrating.


Cons

  • Costly: The equipment needed for plasma desmearing is expensive, which can lead to higher manufacturing costs.

  • Complexity: The process is more complex and requires a higher degree of control over various parameters compared to chemical desmearing.

  • Requires Specialized Knowledge: Proper operation of the equipment requires specific training and knowledge, making it potentially more challenging to implement.

Is Plasma Desmearing Right for You?

If you are seeking more information regarding plasma desmearing, then the expert team at SCI Plasma are the right folks to speak with. SCI Plasma knows all the ins and outs of plasma desmearing, among other processes that you might consider for your needs. By reaching out to them, you'll be able to tap into a wealth of knowledge and experience that will set you on the path to success.


With their guidance, you'll be able to pick the optimal technique for your project, ensuring that your devices come out looking and performing their absolute best. And because you'll be working with such knowledgeable specialists, you can rest easy knowing that you're making informed decisions that will set you up for success.


In conclusion, plasma desmearing is a process used in the manufacturing of circuit boards. It ensures that the smear on the PCB holes is removed, which is crucial for maintaining strong and efficient connections on the board.


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