Hard Gold PCBs

Hard gold PCBs are coated with a Nickel under layer that serves as an excellent substrate for copper and provides mechanical support. The Nickel layer also inhibits creep corrosion and pore degradation.

The co-deposited elements in hard gold electrodeposits like cobalt and nickel oxidize at soldering temperatures, which reduces the quality of the solder joint. For high temperature applications, soft gold is preferred.

Corrosion Resistance

Gold has a natural corrosion resistance and can protect components from highly corrosive environments, such as those that contain sulfur or chlorine gases. This makes it an excellent choice for use in electrical devices, which are often exposed to these conditions. Other metals, like copper or nickel, can be more susceptible to these environments and may corrode over time, making them less reliable.

The corrosive properties of hard gold are related to the size of its grain, which is determined by hard gold the electrolytic plating process used. When the grain is too large, it can create cracks in the coating and allow pollutants to penetrate the base metal. A smaller grain size, however, can produce a smooth surface that resists corrosion.

Other factors, like the item’s intended environment, also contribute to its corrosive resistance. For example, dental work placed in the mouth has different corrosive requirements than a computer chip that will be placed in a power supply.

Hard gold is plated over a barrier coat of nickel, which helps improve its oxidation resistance and reduce contact resistance. This type of finish is typically applied to high-wear areas, such as edge connector fingers and keypads, but can be plated over the entire PCB. It isn’t suitable for soldering, however, because the layer of nickel underneath it oxidizes at high temperatures.

Wear Resistance

Unlike soft gold, hard gold provides superior wear resistance. Its abrasion resistance is greater than that of nickel and copper, and it has an excellent coefficient of friction.

This makes it suitable for applications that require regular sliding wear or make/break switching events. This type of finish also offers longer lifecycles based on the thickness of the deposit; thicker deposits can withstand more cycles before degradation.

The nickel underplate used prior to both hard and soft gold plating acts as a diffusion barrier. This prevents solid-state metallic diffusion between the copper base metal and alloying elements, such as zinc from brass, which could weaken the gold deposit over time.

As mentioned above, hard gold contains non-noble metals such as nickel and cobalt. These elements oxidize at soldering temperatures, which can reduce the strength of the solder joint. For delicate joining applications like ultrasonic wire bonding and thermosonic bonding, ENIG is recommended instead of hard gold.

Additionally, hard gold’s finer grain structure gives it a bright appearance. This is why it’s frequently chosen for applications that require cosmetically acceptable gold contacts, such as visible interconnect applications. As a result, this finish is the choice for high-quality PCBs that require both durable, high-performance contact surfaces and a beautiful appearance. HASL is another option for these types of boards, but it doesn’t offer the same level of corrosion resistance or wear resistance as hard gold.

Electrical Conductivity

In most PCB applications, the electrical conductivity of gold is a key determinant in choosing a plating type. Silver, for example, tarnishes and becomes less effective as an electrical conductor due to its interaction with oxygen in air, creating hard oxides that are electrically insulating. Gold is non-reactive and does not tarnishe, making it a more suitable material for electrical contact.

The hardness of hard gold plating can be a drawback in certain circumstances. Hard gold is more prone to scratching than soft or ENIG gold, which makes it less suitable for sensitive joining applications like ultrasonic wire bonding or thermosonic welding.

To improve the durability of Hard Gold PCB Supplier hard gold, a nickel underplate can be added. This reduces the load on a contact surface and enhances durability, while also improving the ductility of the gold layer.

Some hard gold electrodeposits contain alloy elements like nickel, cobalt or iron to improve wear resistance and other properties. These non-noble metals, however, can oxidize at soldering temperatures and reduce the integrity of the solder joint. For this reason, hard gold is not recommended for tin-lead soldering applications. In these cases, softer or ENIG gold is preferred. The AOI (Automated Optical Inspection) is a cost-effective and reliable way to test the quality of hard gold plating. It works by matching a 2D or 3D image of the plating with an ideal image. This allows you to quickly identify any areas of faulty plating and repair them.

Durability

The durability of hard gold is superior to that of soft gold because hard gold plating includes the addition of non-noble metal elements such as nickel, iron and cobalt. These metals help the gold deposit to harden into a finer grain structure that is more resistant to sliding wear.

This finer grain also makes hard gold deposits more lustrous and more resilient to burnishing. This can make hard gold more attractive for projects that are expected to see a lot of handling, such as visible interconnect projects. Soft gold, on the other hand, is better suited to projects that will not be handled much since it has a tendency to wear down and burnish over time.

Another advantage of hard gold is its resistance to corrosion. This is due to its lower rate of absorbing moisture and its high thermal conductivity. This means that it can withstand high temperatures without experiencing significant changes in its dielectric constant and loss tangent.

The final benefit of hard gold is that it is a more durable surface finish for PCBs than copper. This is because hard gold has a low coefficient of friction and can withstand many durability cycles. This is especially important for projects that require frequent insertion and removal of components, such as keyboards. This can be further improved with the use of lubricants.