What is Selective Gold Plating & What’s The Reason for the Isolation?

When someone or something is isolated, it is because the person or something didn’t align with the traditional standards of association. When it comes to the design and production of Printed Circuit Boards (PCBs), a similar concept is used. That concept is what is known as selective gold plating.

In this article, you will learn how it makes all the difference in the circuit board design process. You will also find out some of the reasons for the isolation.

Circuit Board Plating – The Background

The plating process is the background to the selective process of plating gold on a PCB. So, what does plating mean?

Simply put, plating a PCB means the protection or coverage of a surface from corrosion or exposure to adverse weather conditions. To this end, you want to use the selective gold plating technique to protect the surface and components on the surface of a circuit board.

What is Selective Electroplating Technique?

Selective gold plating is known by other names, such as selective electroplating technique gold plating and hard gold plating. It is so-called because of the use of the electroplating process. A little definition of this process will suffice.

Ideally, there are two methods or processes to plating a PCB. These are the electroplating and electroless plating processes. For the electroplating, it has to do with the use of (electric currents) or electricity. This involves the dissolution of metal cations, that, in turn, form a thin metal coating on the submerged object. The electroplating process also leads to a change in the object or surface’s properties. To that end, we are looking at the improved durability, corrosion resistance and friction reduction on the PCB.

On the other hand, the electroless plating technique doesn’t require the use of electric currents or electricity. Rather, the immersion of the object in a liquid bath is used. This process is called auto-catalytic chemical reaction.

Understanding the Selective Plating Process

The selective plating process entails the itemization of a specific part, surface or component in a Printed Circuit Board (PCB). This selectiveness or specified plating process is done as a way of protecting specific parts more than the others are protected.

This brings us to an important question – why are some PCB parts plated and the others are not?

The Scope of Selective Electroplating

The scope refers to the targeted areas, places or parts that are usually prioritized when using the selective gold plating process. The following are usually the priorities:

  • It is used to remove the spots, dents or design errors noticed on those parts. In essence, the selective gold plating is an ideal technique for repairing and refurbishing the damaged areas of a PCB.
  • The selective gold plating is also used to bolster the protection of the most important parts or components on a PCB.

The Application of Selective Electroplating

The electroplating technique for selective gold plating is very important and has a lot to do with the application process. A wide range of options are available for you to choose from, including brush plating.

In this section, we talk more about the different processes or techniques that can be used to achieve the selective gold plating for PCBs. But before going into details, let us look at how these processes can be applied to the specific areas in the circuit board.

First, the electroplating process, which the selective gold plating uses, is to be well-positioned. This ideally involves the use of the following:

  • Cathode: this refers to the component or PCB part to be plated.
  • Anode: this refers to the metal to be applied.

Now, the application process starts with the use of electrodes for the purpose of creating a thin metal coating on the specific PCB part. To this end, the following processes are usually followed:

  • An electrolyte bath is to be made. It normally comprises metal salts, which are responsible for increasing electric current flows.
  • Both the anode and cathode are to be added or immersed in this electrolyte bath.
  • Electric current is now to be added to the anode. Doing this leads to the oxidation of the metal atoms. It also leads to the dissolution of the same into electrolyte solution.
  • On the other hand, the cathode (the part to be plated), will attract the metal ions. The plating process starts when the ions stick to the object (the cathode).
  • At the end of the process, you will realize a change in the mechanical, chemical and physical properties of the cathode.
  • To this end, you can say that you have subjected and completed the PCB parts’ selective gold plating process.

The Selective Gold Plating Methods

Now, let us talk about some of the different ways that the selective gold plating technique can be used to improve the chemical, physical and mechanical properties of the PCB parts.

1. Brush Plating

This is one of the common selective gold plating processes and it is because of the selective process actualized due to the manual process. Ideally, brush plating entails the electrode technique that prevents the immersion of all the PCB parts in the electrolyte solution.

The following summarizes how the brush plating process works:

  • “Brush” Formation: the brush in this instance refers to the stainless steel or a chemically-reactive anode. Graphite is an example of such anode. Now, this anode or metal or stainless steel is to be wrapped in an absorbent material or a piece of cloth. Cotton is usually used.
  • Brush Saturation: the second step is to saturate or immerse the brush/anode in the plating solution.
  • Solution Application: with the anode now dipped in the solution, the next step is to apply it to the localized area or specific part in the PCB. This area is usually the negatively-charged part in the PCB.

Here are some of the top benefits of using the brush plating gold plating method:

  • It is a manualized selective gold plating process that typically involves movements between the anode (the metal or stainless steel to be applied) and the part (the cathode or PCB component where the anode is to be applied).
  • Brush plating selectively helps to facilitate the real-time repair and refurbishment of the damaged parts in the PCB.
  • It is a highly-effective process that helps to stick the application of the plating solution to the limited area on the PCB. This ensures excellent protection or masking of those parts.
  • The brush plating method is one of the selective gold plating methods that work best for the PCB baths that don’t usually fit into liquid bath or plating solution.
  • It requires less power and might not require a need for the use of mask.
  • Using the brush selective gold plating process is an excellent way to cut down on the need for high-volume chemicals.
  • Due to the manual and convenient process, you can do brush plating of a PCB part in any environment.
  • For the best results, consider using brush plating for either the PCB parts with smaller areas or for the repair and refurbishment of the low-volume projects.

2. Reel Linkage Selective Plating Process

This is also called the reel-to-reel method of selective plating. As the name might have suggested, it has to do with the usage of “reels,” which, in this instance, refer to the following:

  • The masking of the specific parts or localized areas for selective gold plating. A continuous strip of rubber is often used to do this – covering the parts that wouldn’t be plated.
  • Plating can then be done or carried out on the selected copper foil portion.

Here are some few points to note about the reel linkage selective gold plating process:

  • The process can either be manualized or automated.
  • It is best to use it if you are working on a huge volume or number of circuit board parts. Even at that, batch welding should be used to facilitate the process and save costs.
  • The commonly-plated parts are the contact pins and pins for the following: flexible PCBs, connectors, transistors and Integrated Circuits (ICs).

On the flipside, using the reel linkage selective gold plating process comes with some downsides, such as:

  • It is not one of the most-flexible plating processes for PCB parts.
  • Changing over and making relevant setups between the runs is not always easy.

How Traditional Selective (Brush) Gold Plating Compares to Immersion Plating

The difference between the traditional selective gold plating and immersion gold or ENIG is that the former allows the electroplating of the nickel coating, followed by the application of the gold plating on the specific circuit board pads or parts. On the contrary, immersion plating or Electroless Nickel Immersion Gold (ENIG) doesn’t use electric current, which means that the nickel coating has to be deposited before the gold coating can be applied to the PCB pads and other localized areas with chemical reactions.

Final Thoughts: Where Can Selective Gold Plating be Applied or Used?

You can use selective plating microbiology across different manufacturing and industrial applications. The process has been found useful in the electronics, defense, dentistry and aeronautics industries. It can also be used in the architecture and medical industries.

For the best results, the following metals should be used when making a selective gold plating: gold, nickel, palladium, cadmium, silver, copper, chromium, zinc, and tin.

Always consult a professional selective gold plating to help you through the process. We’ve laid the groundwork for you. Don’t hesitate to contact us when you are ready to selectively apply gold on your PCB pads.

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