Everything about Hard Gold Surface Finish in PCB Manufacturing
Are you familiar with hard gold surface finish in PCB manufacturing? If you’re in the electronics industry, this process is worth learning about.
Printed Circuit Boards (PCBs) are an essential component in modern electronics, and as such, manufacturers are always looking for ways to make them more durable and efficient. PCBs go through several stages during their production, and one of the most critical is the surface finish.
Hard gold surface finish is a popular choice for PCB manufacturers due to its durability and the ability to withstand multiple soldering reflows. If you’re a PCB enthusiast, it pays to understand what hard gold surface finish is and how it can benefit your projects. In this article, we’ll take an in-depth look at everything you need to know about hard gold surface finish in PCB manufacturing.
What Is a Hard Gold Surface Finish on PCB?
A hard gold surface finish is a type of plating applied to the surface of a PCB to protect the traces from damage. The layer of gold is deposited onto a nickel barrier that covers the copper traces and pads on the PCB.
Hard gold plating is thick, durable, and resistant to wear and corrosion. It is often used in situations where the PCB is likely to be exposed to excessive mechanical stress or exposure to harsh settings.
For example, hard gold plating often appears on the PCBs of home electronics, communication systems, and other equipment that needs to tolerate high heat.
Other names include hard gold electroplating and hard gold plating. However, instead of pure gold, the process often includes gold alloys made from gold and other metals, such as nickel.
Pros and Cons of Hard Gold PCB
Applying a hard gold finish to the surface of a PCB may provide the following benefits:
Hard gold plating increases the durability of PCBs. The gold protects the copper traces and pads from damage due to mechanical stress, frequent use, or rough environments.
Hard gold surfaces also tend to last longer compared to other types of plating, such as soft gold, tin surfaces, or silver surfaces.
Gold also provides good electric conductivity. It is a popular choice for maintaining a stable electrical connection between components and the PCB.
However, there also has a few drawbacks with hard gold finish.
- Takes longer
Applying a hard gold layer to the PCB increases the cost and timeframe for producing circuit boards. It is also more expensive compared to other finishes, making hard gold less cost-effective for low-volume products.
Repairing a PCB containing hard gold plating is also more difficult compared to working on a PCB with soft gold. The durability of the hard gold makes it more of a challenge to rework or repair.
Important Properties of Hard Gold Finish
A hard gold surface finish has unique properties. The bonding properties, appearance, corrosion protection, and wear resistance need to be considered before adding a hard gold finish.
- Bonding Considerations
Gold has poor solderability compared to nickel and copper, which can impact other bonding requirements. A different plating method may be needed if the PCB design requires the bonding of other components on top of the surface finish.
For example, immersion gold/electroless nickel (ENIG) may offer a better solution for bonding. The inclusion of nickel helps increase the solderability of the surface finish.
Hard gold is occasionally used in areas where the traces or pads remain highly visible. Gold has reflective properties that help it stand out compared to other metals. It can easily enhance the appearance of visible areas of the PCB.
Gold does not react with oxygen, which keeps it from corroding or rusting. However, the inclusion of other metals and alloys can lower the corrosion resistance of the surface finish. A hard gold finish can provide greater corrosion protection compared to a soft gold finish or tin finish.
Choosing hard gold can provide greater wear resistance compared to other types of surface finishes. If wear resistance is an important consideration, hard gold may be the best option.
Hard gold creates a smooth, glossy surface that helps components slide into place with less friction, such as when coating PCB fingers and other connection points.
PCB Hard Gold Plating Processes
PCB surface finishes can be applied using various techniques. The most common application processes include electroless tinning and electroplating.
Electroless tinning involves applying a thin layer of metal on the surface of the PCB. Unlike electroplating, this process does not require an electric current.
Electroless tinning requires the use of catalyst material. The material is deposited on the PCB in the areas that require hard gold plating. The PCB is then immersed in a solution that contains the intended finish, such as hard gold, and a reducing agent. The solution reacts with the catalyst material to affix the metal to the surface of the PCB.
Electroless tinning is often more affordable compared to electroplating and does not require the disposal of hazardous chemicals. However, it is not an efficient option for surface finishes that require a thick layer.
Electroplating involves applying an electric current to create an oxidation reaction and fuse metal to the surface of a PCB.
A solution containing the metal that needs to be deposited, such as gold or a gold/nickel alloy, is prepared. The PCB is immersed in the solution. An electric current is then applied to the solution, which causes the metal ions to deposit on the surface of the PCB.
Alternative Surface Finishes for PCBs
Instead of hard gold, a PCB may be coated with other alloys, including tin and silver. However, nickel gold electroplating (ENG) and electroless nickel/immersion gold (ENIG) offer greater durability and a more direct alternative to hard gold.
- Nickel Gold Electroplating (ENG)
Nickel gold electroplating (ENG) involves an extra step compared to the standard gold electroplating method. A separate solution containing nickel is prepared, along with a solution containing gold.
The PCB is immersed in a nickel solution, and an electric current is applied, which creates a thin layer of nickel on the surface of the PCB. The process is then repeated with the gold solution.
Using uniform layers of nickel and gold can provide greater electrical conductivity compared to using gold alone. However, the extra step in this process increases the cost of ENG compared to hard gold alone.
Immersion Gold/Electroless Nickel (ENIG)
Immersion gold/electroless nickel (ENIG) is another method that involves the application of a thin layer of nickel followed by a thin layer of gold. However, it relies on an electroless process instead of an electrolytic process.
First, the PCB is placed in a solution containing nickel and a reducing agent. The reducing agent reacts with the nickel to deposit a thin layer of the metal on the PCB. The PCB is then immersed in a solution containing gold. It does not require the use of an external power source.
What Is the Difference Between Soft and Hard Gold PCB?
Hard gold plating involves the use of gold and other alloys, such as nickel. The inclusion of nickel helps increase the hardness of the plating. Using pure gold without nickel or other alloys results in a softer finish that is often called “soft gold.”
Soft gold PCB finishes contain pure gold, while hard gold contains other alloys that contribute to the durability and longevity of the material.
Hard gold PCB finishes help protect copper traces and pads from damage, which is especially important for components that experience friction or exposure to harsh environments.
The plating may be applied across the full body of the PCB or select areas. There are also different methods of applying hard gold plating, including electroless tinning and electroplating.
Electroless tinning relies on solutions containing metals that react when exposed to oxygen. Electroplating involves the use of solutions that require an electric current to fuse the metals to the surface of the PCB.
Depending on the needs of your project, a hard gold PCB finish may be an appropriate option for increasing the durability and life of your PCB.
Need any help with PCB or PCBA manufacturing? Contact us now.