Most of the electronics we use in our daily lives contain at least a little bit of gold. While this precious metal is widely known for its beautiful, shiny appearance, it also has quite a few functional purposes that make it a sought-after material in a variety of industries.
The electronics sector, though, is the main consumer of gold today. Even though that gold is rarely seen, it plays a critical role in keeping the components of your devices functioning properly over time. Electronic parts aren’t typically made entirely of gold because of the material’s cost. More often, manufacturers use electroplating to apply a thin layer of gold over the main material that comprises the component.
Frequently used in combination with nickel plating, the thin layer of gold protects the component from corrosion, heat, wear and helps ensure a reliable electrical connection. At Sharretts Plating Company, 99% of our gold plating work serves the electronics industry. Over the last eight decades, we’ve perfected our gold plating, also called Au plating, processes and offer both electroplating and immersion plating.
In the rest of this article, we’ll look in more detail at the processes, benefits and uses of gold plating for electronics and electrical components.
What Is Gold Plating?
At SPC, we’ve developed and applied many gold plating processes. We use electro-deposition, which is commonly known as electroplating and uses an electric current to apply the coating. We also use immersion plating, which doesn’t use electricity.
To plate an item with electro-deposition, we connect the gold to the anode, the positively charged electrode, of an electrical circuit. We also connect the substrate, the material that we’ll be plating, to the cathode, which is the negatively charged electrode. We then immerse both pieces in an electrolytic solution.
Then, we apply a DC current to the anode. This oxidizes the metal atoms in the gold and dissolves them into the solution. The dissolved ions are reduced at the cathode, and they then deposit onto the substrate.
Types of Gold Plating Baths
There are three basic types of gold plating baths:
- Alkaline: An alkaline bath is a non-cyanide solution that uses sodium gold sulfite as the source of the gold ions. It has a pH level ranging from 9.0 to 13.0. Alkaline solutions produce a hard and bright deposit and reduce the co-deposition of base metals. Adding complexing agents can improve conductivity.
- Acid: Acid baths, which have a low pH of 3.0 to 6.0, produce exceptionally pure gold deposits. In fact, these deposits can be up to 99.999% pure. Acid gold baths allow for the formation of alloys with base metals, but you can also prevent this with complexing agents.
- Neutral: Neutral baths, which have a pH between 6.0 and 8.0, are typically used for plastic or ceramic substrates because they don’t contain free cyanide, which can damage these more delicate materials.
Reel-to-Reel Gold Electroplating
We most frequently use reel-to-reel electroplating, also known as continuous electroplating, when applying gold to a material. We use this method to plate reels of raw material before they get shaped into electronic components. It can coat strips of manufactured parts.
We load the reels onto our equipment and feed it through our electroplating processes before re-reeling it. Reel-to-reel plating can cover an entire substrate or be used more precisely to plate specific parts.
Gold Rack Electroplating
At SPC, we also build our own racking equipment, which allows us to meet the precise requirements of our clients’ projects. Rack plating is ideal for fragile components or larger, more complex projects. However, it can be difficult to create a uniform deposit, and discoloration may appear where the item attaches to the rack.
The process involves hanging the substrate on a rack that uses hooks to apply the electrical current and hold the items in place. Once everything is properly attached, we lower the rack into the electrolytic bath, depositing the plating material.
Gold Barrel Electroplating
Barrel electroplating is useful for quickly and economically applying a uniform coating to a substrate. This method is less precise than other methods, and works best when the entire surface of an item needs to be plated. It’s also not ideal for large or fragile components, as the piece may be too large for the barrel or become damaged during the plating process.
In this method, we place the component to be plated in a barrel that contains the plating bath, as well as bars that provide the electrical contact. Machinery rotates the substrate in the barrel while electrical current is applied, resulting in a complete and uniform deposit.
Gold Immersion Plating
For some applications, we use immersion plating, which doesn’t involve an electrical current. We dip the substrate into an electrolyte solution with gold ions, which causes the dissolution of ions from the substrate material. This releases electrons, allowing the gold ions to deposit onto the substrate. The gold ions replace the ions of the less noble metal, which typically results in a thin coating that has similar properties to electroplated gold.
Properties of Gold Plating
While gold’s aesthetic appeal does contribute to its value, in the electronics industry, its functionality is what makes it such a prized material. Gold has several physical properties that lend themselves perfectly to use in electronic components. Manufacturers typically apply gold plating to connection points within electronic devices because it improves conductivity and protects the component, which helps that reliable connection last longer.
These properties include:
- Corrosion Resistance: One of gold plating’s most valuable attributes is its ability to resistant the corrosion that affects so many other metals. Gold is among the least reactive of all metals and won’t react with oxygen and rust like other metals do. Gold may tarnish slightly, but this isn’t damaging and can be removed by polishing. Resistance to corrosion is critical for electrical components because oxidation may cause a less reliable electrical connection. Its non-corrosive capabilities enable it to retain the smooth surface that’s needed for a strong connection.
- Expanded Connection Area: Gold is also highly ductile and malleable. This means it can stretch out into thin wire and will deform when placed under pressure, allowing it to spread out and cover more surface area. This creates a larger connection area, which leads to more reliable connectivity. Even with repeated use, gold’s flexibility helps electronic devices to continue to function correctly.
- Protection From Heat: Au plating is suitable for applications that involve high temperatures and will protect other materials from damage caused by heat. Gold has a melting point of 1943 degrees Fahrenheit, or 1062 degrees Celsius. It conducts heat well, in addition to electricity, and will continue to function appropriately even under intense temperatures. This makes it a useful for electronics that may become hot when used. For applications likely to involve frequent and intense heat, making the plating layer thicker will increase its resistance to heat.
- Reflectivity: Gold’s reflective properties make it ideal for use in components such as semiconductor parts, including reflector rings and reflector arrays. Gold reflects higher amounts of UV radiation below 0.35 µm than other metals do. It also reflects infrared radiation with wavelengths above 0.7 µm, which helps keep electronics cool. These reflective properties have made gold plating an integral part of spacecraft and satellite design.
- Resistance to Wear: Applying a gold plating to a piece of equipment can help it last longer, as the coating will protect the component itself from wearing away. Gold isn’t susceptible to fretting degradation, which wears away material due to repeated low amplitude relative motion. This can lead to corrosion, and then resistance. Because gold doesn’t corrode, it won’t become damaged due to fretting, protecting the layer beneath it. Gold is resistant to wear, so your plating will last a substantial amount of time. Like anything, it will eventually wear off naturally, buy when it does, you can easily re-plate the piece of equipment.
Use Cases for Gold Plating in Electronics
You can find gold in all sorts of electronics including smartphones, laptops and desktop computers. One ton of smartphones, or about 10,000 phones, contains approximately 10 troy ounces of gold, which is equal to around three fifths of a pound. From 200 laptops, you could get about five troy ounces of gold, which is worth roughly $8000.
Gold’s ability to improve and sustain electrical connectivity makes it ideal for all types of applications in electronics. Manufacturers can apply it to any place that must facilitate an electrical connection to improve its reliability. You can find Au plating on the outside of devices, such as on electrical connectors. Most of the gold in electronics, however, is located inside the devices in the circuit boards.
Electronics companies use gold plating to enhance the conductivity of the circuit board and protect it from corrosion. Keeping a reliable connection within the circuit board is crucial to the reliable operation of any device.
Semiconductor components, such as top chucks, reflector rings and reflector arrays, are another area where gold plating is especially useful. Semiconductors, such as transistors, chips and other control parts, are partially conductive and may use plating to make a device more electrically efficiently. It also helps to protect these vital components from outside elements.
Because semiconductor chips are so small and fragile, the electroplating used for them varies slightly from the standard procedures. The chip must be handled carefully to avoid breaking any of the tiny wires inside, which would cause a faulty component. Even dust particles getting into the chip can result in a malfunction.
Because of this, the room where semiconductor plating takes place must have 0.01% of the amount of dust normally in outside air. The electrolytic bath must also be thoroughly filtered to remove any dust or other small particles.
In fact, in all electronics plating procedures, it’s necessary to prepare the substrate surface adequately to prevent the deposition of ionic and nonionic residue. These residues can reduce conductivity and even prevent the metal coating from adhering properly. Although the process of removing these residues required using hazardous organic solvents in the past, today we use eco-friendly, high-pressure water systems to prepare the surfaces of electronics for electroplating.
The Benefits of Underlayers for Gold Plating
As useful as gold is, it’s even more useful when combined with other metals. A layer of nickel is often placed on a substrate directly under the gold plating layer. This underlayer provides several benefits:
- It acts as an extra layer of protection against corrosion that may creep in through pores located in thin areas of the gold plating. It also helps prevent existing corrosion from spreading.
- It prevents other metals, such as zinc and copper, from diffusing into the gold where they may oxidize.
- It adds to the thickness of the plating. Because gold is relatively expensive, adding a thicker underlayer can reduce costs while still allowing access to the benefits of gold. This extra thickness also increases the plating’s overall durability.
Another common way to increase durability is to add a small amount of cobalt or nickel directly to the gold. This substance is referred to as hard gold — it’s relatively common and highly durable. Pure gold is often called soft gold.
Gold plating doesn’t need to be thick to be effective. In most cases, the gold should be as thin as possible without comprising any of its useful properties. For most connector manufacturing uses, a 0.8 micron layer of gold over a 1.3 micron layer of nickel should provide enough durability. Based on the application, however, you may need to vary the thickness of the plating.
The needs of your project will also determine whether you should choose hard gold or soft gold. For applications where durability is the most important aspect, hard gold is the best option. If you want a malleable coating, or if durability isn’t a priority, soft gold may be the right choice.
Choosing Gold for Electrical Component Plating
When it comes to metal plating for electronics, gold is an ideal choice. It offers the resistance to corrosion, wear and heat, as well as the enhanced conductivity vital to properly functioning electronic equipment.
When you work with the plating experts at SPC, we’ll assess your project’s needs and help you choose the right materials and plating methods for the job. With eight decades of plating experience, we have the skills and knowledge to reliably achieve an effective result, even for unusual projects. To get started, contact us or request a free quote through our website today.