FPC Board Gold Plating: The Ultimate Guide

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Oakley Mae

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Most electronic devices in the industry today use FPC board gold plating.

This method involves depositing a thin layer of gold on another material surface. 

Surprisingly, while gold is known for its shiny appearance and beauty, it contains several functional purposes and properties that make it ideal for use in electronics.

Generally, gold plating improves the FPC board’s electrical performance and reduces cases of corrosion.

Also, it improves the FPC material strength and durability. 

Please keep reading for more information on gold plating, including its uses, types, pros, and cons. Let’s get started. 

Table of Contents

What Is FPC Board Gold Plating

A blue gold-plated microchip PCB

(A blue gold-plated microchip PCB)

Gold plating involves having gold plates on other metal surfaces to enhance conductivity.

Also, it helps eliminate PCB corrosion cases on the vulnerable copper layer.

To implement this process, you create a gold plating solution with many gold ions.

Gold ions involve a gold atom without at least a single electron. 

The process is possible through electro-deposition, connecting gold to the anode.

Generally, the anode represents the positively charged electrode in the circuit.

Moreover, we connect the substrate to the cathode, which is the negatively charged circuit electrode.

Afterward, we immerse the two pieces into an electrolytic solution and apply a DC to the anode. 

Therefore, the gold atoms will oxidize and dissolve in the solution.

Consequently, these dissolved ions get reduced and deposited at the cathode substrate.

Surprisingly, the process creates a thin, uniform gold layer on the FPC substrate. 

Why Use Gold On FPC Boards?

Gold-plated computer memory connectors

(Gold-plated computer memory connectors)

We employ gold on flexible circuit boards over other options for the following reasons: 

  • Efficient electrical conductor: Gold is among the best conductors of electricity and thus works well when used on circuit boards. 
  • No corrosion: Other alternatives like copper and silver still conduct electricity effectively but rusts easily. Therefore, such metals will affect PCB efficiency. Besides gold being non-corrosive, it also eliminates cases of corrosion for the layer under it. 
  • High heat resistance: Gold has a high heat resistance that helps eliminate fire hazards.
  • Reusable: With gold, you can easily melt and reuse it anytime you see fit. 
  • Flexible: Flexible circuit boards are electronics’ present and future. Not all surface finishes you use on FPC boards will support the flexibility. Fortunately, it will still keep the material highly flexible and efficient. 

Gold Plating Steps

A functional, flexible PCB

(A functional, flexible PCB)

The first step to gold plating is purchasing a reliable gold plating kit.

This kit will have a liquid gold solution, a plating brush, and an electrical supply.

However, depending on the type of material you wish to plate, you might require extra accessories and solutions. 

But generally, follow the following steps:

  • Preparation: First, ensure the surface you seek to plate has no dirt. We recommend sandblasting, polishing, stripping, and tumbling for most circuit boards. 
  • Cleansing and rinsing: After surface preparation, expose it to ultrasonic cleaning, electro-cleaning, or steaming. This deeper cleansing step guarantees your flexible PCB is ready for the following stages. Afterward, rinse with water to remove any residue. 
  • Strike layer: Apply a nickel buffer layer to the surface you wish to plate. Generally, it improves the bonding between the substrate and the plating material. 
  • Additional rinsing: After you have added the strike layer, rinse the board again. 
  • Base coating: Add a coating layer to the base material. We usually have multiple layers (gold, nickel, and copper) on a single substrate. 
  • Final coating: Submerge the board into a plating solution to attract gold ions. Surprisingly, this process should happen under controlled voltage and temperature. Furthermore, different metal types require unique voltages and temperatures. 
  • After finishing the final coating process, rinse the board and allow it to dry. 

Gold Plating Baths

A red gold-plated PCB

(A red gold-plated PCB)

You’ll come across three gold plating bath options: 

  • Alkaline: This non-cyanide solution gets gold ions from sodium gold sulfite. The PH range for this solution is between 9 to 13. Surprisingly, the solution limits base metal co-deposition and produces a bright and hard deposit. Moreover, you can improve conductivity by incorporating complex agents. 
  • Acid: These baths produce top-quality pure gold deposits at a low PH between 3 to 6. Surprisingly, the deposits are sometimes 99.999% pure gold. And although it encourages alloy formation, you can eliminate such cases using a complexing agent. 
  • Neutral: These baths don’t have free cyanide and are mostly used for ceramic and plastic substrates. Also, they have a PH of 6-8. 

Are There Differences Between FPC Gold Plating and Immersion Gold?

Yes! There are many differences between immersion gold and gold plating, although they achieve the same purpose.

For example, the main difference is that immersion gold involves soft gold, while gold plating involves hard gold.

Check out the other differences below: 

  • The two have different structures with gold plating using a thinner gold thickness than immersion gold. 
  • Gold plating is more challenging to weld and causes welding problems. 
  • Immersion gold is designed with a denser crystal structure making it more difficult to oxidize than gold plating. 
  • Immersion gold is designed with only nickel on the pad, thus making it difficult to produce a gold wire short circuit. On the other hand, gold plating is prone to gold wire short circuits. 
  • Immersion gold has a better service life and flatness than gold plating. 

Pros of FPC Board Gold Plating

Gold plating presents the following benefits:

  • First, gold plating offers excellent corrosion protection. Unlike other metals, gold is not prone to oxidation which is responsible for rust and corrosion.
  • Second, gold plating provides increased electrical conductivity.
  • Third, increased durability thanks to the material’s resistance against wear and tear.
  • Also, gold plating is a straightforward process.
  • Gold plating provides high heat resistance, allowing high-temperature applications up to 125 degrees Celsius. 
  • Furthermore, gold plating provides a decorative appearance. Who doesn’t know that gold is the most precious and elegant material in the world? 
  • The process provides stronger flexible circuit board structures. 
  • Finally, gold is non-magnetic and therefore supports different applications without electromagnetic interference. 

Cons of FPC Board Gold Plating

Apart from the above pros, gold plating has some downsides worth noting. 

  • One of the downsides of gold plating is tarnishing which happens after some years of use. Therefore, you’ll have to polish the surface regularly to keep the shine. 
  • The process is costly since it uses gold, one of the most expensive materials we know. 
  • Gold-plated surfaces are less resistant to water. 

FAQ

What is the lifespan of gold plating?

A gold-plated FPC has an average lifespan of 2 years.

After two years, expect the gold finish to start tarnishing and wearing down.

However, the period could go beyond 2 years with proper care after plating.

And even when the PCB starts to tarnish, you can re-plate it. 

Is gold plating good?

Yes! Gold plating is a good thing. First, it makes a flexible circuit board surface solderable.

Also, it covers the underlying copper layer, thus preventing cases of corrosion and rust.

Furthermore, it gives your circuit board a decorative and elegant appearance. 

What type of gold is in circuit boards?

All circuit board applications require a 99.9% gold purity for the best performance.

Surprisingly, there are different gold finish types to consider and include: 

  • Electroless nickel immersion gold is the most popular option, usually about 1-3 micro-inches. 
  • Electroless nickel electroless palladium immersion gold adds palladium to the alloy. 
  • Finally, we have gold fingers. 

Conclusion

Flexible circuit boards are designed with vulnerable copper layers that might corrode if left uncovered.

Therefore, there is a need for gold plating, which involves depositing a thin gold layer over the PCB surface.

Fortunately, the gold plating process is very straightforward, as highlighted above. 

Generally, the process has several benefits, including excellent corrosion prevention, increased electrical conductivity, and high durability.

Moreover, it guarantees high heat resistance and provides stronger structures.