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What is Hard Gold in PCB?
Hard gold in PCB is one of the key options for PCB plating, also called nickel gold electroplating. Plating gold involves adding a layer of gold over a nickel coat barrier via electroplating.
Plating gold has two options, including soft gold and hard gold plating. Smooth gold plating involves using pure gold as your layer. Contrarily, hard gold involves mixing other elements to make the gold harder.
You can undoubtedly use hard gold plating in applications that require friction force. Some of these applications include keypads and gold fingers.
Hard gold is pretty durable and handles work under harsh conditions. However, it’s not easy to solder hard gold. Plus, getting one can be expensive.
So, it’s best to avoid using hard gold in solderable areas. But you can use them to make metal contacts or for high-wear areas on your PCB.
Properties of Gold-Plated Circuit Boards
In truth, gold offers excellent mechanical, thermal, and electrical features likewise gold-plated PCBs. So, let’s take a closer look at the properties.
Immune to Corrosion
Gold won’t go down quickly if there’s a risk of corrosion from chemicals or rust. Indeed, it’s completely immune to corrosion and won’t react to chemicals or rust.
Although it may have a slight tarnish, it won’t corrode. Hence, the gold-plated circuits are ideal for preventing oxidation.
Wider Connection Area
It’s easy to manipulate gold under high pressure. Hence, you can even stretch it out into thin wires. For this reason, you can cover more connection areas with a gold-plated circuit board.
High Durability
Gold-plated circuit boards can operate for extended periods because of their immense durability. They won’t wear out quickly, no matter how long or hard you use them.
These gold-plated boards have excellent resistance. Interestingly, you can use the coating on these circuit boards to shield your components. Also, you don’t have to worry about fretting degradation.
Infrared Reflection
Gold-plated boards have surplus UV radiation, allowing them to reflect infrared radiation. Hence, these circuits are always in excellent condition and are the go-to for spacecraft and satellite designs.
Heat Immunity
Do you work with high-temperature applications? If yes, you’re lucky because gold-plated PCBs can handle the heat. Not only are they resistant to heat, but they also protect other components. Since gold is a great electrical conductor, these circuit boards can also prevent overheating. In other words, gold-plated circuits will work effectively, regardless of the temperature.
Factors to Consider When Plating Gold
Porosity
It would help if you considered this factor because the process of plating gold is porous. Also, there’s a relationship between the gold’s coating thickness and porosity.
So, your circuit would experience low porosity when it’s beyond 0.76 μm. Conversely, if it’s below 0.36 μm, you’ll have a rapid increase in porosity.
Wear
Two factors determine the lifespan of any plated surface. The first is hardness, and the second is friction.
Additionally, if you apply more friction, your circuit’s surface life will reduce quickly. However, gold-plated courses are immune to wear and tear.
Nickel Underlayer
Nickel is essential when you’re platting gold on your board. But, in truth, It’s like a heavy wooden door preventing gold and copper from diffusing.
Nickel closes substrates and pores to reduce pin-hole correction. Also, its underlayers have intricate layers beyond their metal platings.
Why Use Gold Rather than Silver and Copper in PCB Fabrication
There are several reasons why we use gold over silver and copper. First, gold offers unbeatable properties that make it easier to apply surface finishing.
It’s also great for several applications and offers more durability than other PCB fabrication materials.
Undeniably, circuits made with copper, aluminum, or iron would suffer from corrosion and be a waste pile in a few years.
But that’s not the case with gold-plated circuits. You’ll also need a nickel layer to prevent the gold from reacting with the PCB copper.
Silver is the only material that comes close and is an excellent alternative to gold, but its durability level is comparably lower.
Copper is also great for its electrical conductivity but is more susceptible to corrosion.
PCB Immersion Gold Circuit Board
The immersion gold process adds a thin layer of gold to your circuit’s coating. These gold layers aren’t thick and can increase the shelf life of new courses.
Immersion gold also works in PCB fabrication but not electrolytic gold plating. It’s not as thick and adhesive as regular electroplated gold.
Additionally, you can find gold-plated layers in connector shrapnels and component pads. Even mobile phone circuit boards usually have gold plating.
PCB Immersion Silver Circuit Board
As mentioned earlier, immersion silver is a cheaper alternative for users who can’t afford immersion gold. Also, it has excellent connectivity, contact, and flatness properties. Plus, immersion silver can work in several applications.
These applications include communication products, computer peripherals, and automobile applications. While immersion silver has electrical properties comparable to gold, it’s not as durable. But it’s a great way to cut costs when necessary.
PCB Copper Clad Laminate (CCL)
Copper Laminate
Copper-clad laminate is the primary PCB fabrication material you find anywhere. It’s the standard for most PCB manufacturers, helping electronic circuits interconnect.
No doubt, it’s not as expensive as immersive gold and not as durable. However, it is superior in electrical conductivity and can directly manufacture printed electronic components.
Immersion Gold vs. Gold Plating: What is the difference?
Immersion gold and gold plating are different ways of using gold as a surface finish. While one is hard and puts up a lot of resistance, the other is soft and more flexible.
Let’s look at the differences between these two surface finish types.
Gold Thickness
Immersion gold boards offer more thickness than gold-plated boards. Undoubtedly, immersion gold boards also have deeper colors. In contrast, gold-plated boards have the color of nickel.
Different Crystal Structures
Since immersion gold is softer and more flexible, you’ll have no problem soldering. Its crystal structure allows you to control the stress and create bonding products.
Contrarily, Gold plating is not easy to solder, and you may encounter several problems.
Additionally, immersion gold boards have a denser crystal structure than gold-plating boards. So they can’t produce oxidation quickly.
Nickel Usage
You need to apply nickel coating on your circuits before gold plating. Otherwise, the gold would react with the PCB copper and damage your circuit. On the other hand, immersion gold only needs nickel for its pad.
Flatness and Service Life
Immersion gold boards offer better service life and flatness compared to gold-plated boards.
Gold used in PCB Manufacturing
There are different ways to use gold as a surface finish. This section will look at three common ways to use gold in PCB manufacturing.
Also, designers love to use soft gold in PCB manufacturing. Why? Because It’s easy to manage and process at 1 to 3 micro-inches.
ENIG
ENIG stands for Electroless nickel immersion gold, one of the first to use gold as a surface finish. Luckily, you can use this method to get excellent oxidation resistance.
You’ll also have a flat gold layer, which helps to solve some assembly processing challenges.
ENEPIG
The only difference between ENEPIG and ENIG is that it includes palladium. However, after the introduction of ENIG, designers witnessed several problems, including the famous black pad and non-wetting.
ENEPIG (electroless nickel electroless palladium immersion gold) attempted to fix these problems by mixing palladium into the nickel layer beneath the gold layer.
However, it only added more cost to an already expensive method.
Golden Fingers
Golden fingers brought a whole new spectrum entirely. They usually include connectors you can plug into motherboards or other connected devices.
However, the type of connection you’re making determines the method of gold you’re utilizing.
An immersion surface will be an excellent option if you make a one-time connection.
But if you’re inserting and removing a card repeatedly, the golden fingers should have a gold-plated surface.
Final Words
Gold surface finishing can make your circuits more durable and resistant to several defects. Also, it can help increase performance and effectiveness.
There are different ways to use gold in PCB manufacturing, including immersion gold and gold plating.
Remember that you need to understand the characteristics of hard and soft gold before choosing one for your design.
So, do you want to build a gold PCB? Don’t hesitate to contact us.
