Hard Gold Plating

Hard gold is a precious metal that requires solid process controls to maintain its quality. In hard gold plating, the gold electrodeposit is alloyed with non-noble elements like cobalt or nickel. This increases the hardness of the deposit and also improves its resistance to sliding wear.

However, these elements make the deposit difficult to solder. This is because they oxidize at high temperatures.

Strength

The most common reason to use hard gold is to provide a strong and durable coating for items that hard gold will experience frequent contact or friction. This is because hard gold has a much higher grain structure than soft gold, making it more resistant to sliding wear and damage.

In order to achieve its strength, hard gold is actually an alloy of gold with non-noble elements like nickel, cobalt and iron. This enables hard gold to hold up better in environments that require force friction, but these additional metals also make it difficult to solder, as they oxidize at high temperatures and reduce the strength of the resulting joint.

For this reason, hard gold is usually plated on top of a nickel underplate, which helps bear the load of contacts and reduces cracking. This plating method is recommended when the normal force of a contact is greater than 50 grams, but is not required in all situations.

Soft gold, on the other hand, is more suitable for sensitive joining applications such as ultrasonic wire bonding and thermosonic bonding. This is because it offers a much stronger and more pure form of gold, without the addition of non-noble elements that can cause oxidation or other compounds at high temperatures. Its luster and precise grain structure also make it attractive to those seeking cosmetically pleasing gold contacts, such as visible interconnect applications.

Durability

When considering which gold plating method is best for an application, several factors are important to consider. These include the item’s design and bonding characteristics, the item’s resistance to wear, the expected contact force and the temperature in which it will operate.

The durability of hard gold stems from the fact that it’s actually an alloy, composed of gold and another metal (typically nickel or cobalt). It’s an ideal choice for areas requiring high friction, such as edge connector fingers and keypads, where the material will see a lot of use.

In addition to being more durable, hard gold is less prone to corrosion. The coating is typically plated over with a Hard Gold PCB Supplier nickel undercoat, which provides an extra level of protection against chemical reactions. This is also important when reducing overall costs as it reduces the amount of material needed to protect the gold deposit.

The non-noble elements in hard gold deposits – like cobalt and nickel – change the grain structure of the deposit, providing a more durable surface that resists sliding wear better than soft gold. However, these non-noble elements also make hard gold deposits slightly more difficult to solder, and they can impact the ductility of the plate. For applications requiring good solderability, soft gold or ENIG is the better choice.

Corrosion resistance

Gold is one of the most corrosion resistant metals. It doesn’t oxidize easily, and it is also less reactive to other elements than many other metals. As a result, it can be used in environments that are hostile to other metals, such as those with high temperatures. Many metals will melt or degrade in high temperatures, but not gold. It is a vital part of electronics, as it facilitates electrical current through circuit boards and other devices.

Corrosion resistance is important when designing an electrical device, but it’s also important to choose the right kind of gold plating. Hard gold has many benefits for these applications, including its ability to withstand sliding wear and contact switching. Hard gold is an alloy of gold and other metals, making it suitable for places where force and friction are needed.

Unlike soft gold, hard gold has non-noble elements, such as nickel and cobalt, alloyed with it. These elements change the gold deposit’s grain structure, creating a much finer grain that resists sliding wear more effectively. However, these non-noble elements may corrode more easily in certain environments and reduce the longevity of hard gold deposits. Furthermore, these impurities can cause problems with soldering. Adding a barrier coat of nickel to the gold improves its corrosion resistance, but it can also lower the overall thickness of the layer, which can compromise durability.

Solderability

Unlike soft gold, hard gold contains non-noble elements such as nickel, iron and cobalt. These elements oxidize at soldering temperatures and reduce the strength of the bond. Therefore, hard gold is not suitable for soldering. On the other hand, soft gold does not contain any non-noble elements and performs well under normal contact forces.

A nickel underplate helps the hard gold deposit to bear the load of the contact surface and prevents cracking and wear. It also improves corrosion resistance and solderability. However, the thickness of the nickel underplate must be adequate to ensure proper solderability.

Sensitive components are arranged on the PCB automatically using a Surface Mounting Device (SMD). The solder paste is spread on the components. After that, the components are inserted into their respective positions on the circuit board by means of a pick and place machine. Once the components are inserted, the circuit board is reflowing.

When choosing between hard and soft gold for a printed circuit board, you should consider the application’s life cycle, the amount of sliding wear and on/off switching events, the temperature it will be exposed to, and the appearance you want the item to have. A harder finish is best for applications that require repeated sliding wear or on/off switching events. In contrast, soft gold/ENIG is more suited for sensitive joining processes such as ultrasonic wire bonding or thermostatic bonding.