Hard Gold For PCB Edge Connectors
Hard Gold For PCB Edge Connectors
Hard gold is often used on PCB edge connectors due to its excellent electrical properties. However, this plating option should be carefully considered depending on end-use.
When metals come into contact with oxygen, they create oxide compounds that are electrically insulating. Since gold does not form these insulating layers, it can operate with lower normal contact forces and wipe distances.
Gold in its pure form is a soft metal, which makes it prone to removal from abrasion. When it is plated with a hard layer, the wear-resistance increases dramatically. This type of gold is commonly used in applications requiring contact forces and high durability. It is also often used for the edges of connectors (gold fingers).
When non-noble elements such as cobalt hard gold and nickel are alloyed with a gold deposit, the hardness increases over two times that of soft gold deposits. The reason for this is that the addition of these impurities alters the grain structure, which results in a finer particle size and better resistance to sliding wear.
While the increased hardness is beneficial in many situations, it can cause problems when soldering and other sensitive joining processes are required. In these cases, it is necessary to use a nickel underplate that will support the load, prevent cracking of the gold and improve surface finish. Mintek has developed a hard gold alloy that offers this underplate as well as superior wear and corrosion resistance, making it ideal for these types of applications. In fact, this new material is so good that it can be used as a replacement for conventional 22 carat gold in applications requiring hardness and solderability.
Hard gold is a good choice for items that will be exposed to the elements, like dental work placed in the mouth. It has excellent corrosion resistance, and is also resistant to wear due to its smooth surface. It is also an option for products that require a high number of cycles, such as telecommunication systems or automated machines.
The corrosion-resistant properties of hard gold are greatly enhanced by a low porosity level. Porous deposits, however, can still allow pollutants to penetrate and reach the base metal. Adding nickel or copper beneath the gold can reduce this vulnerability.
Another benefit of hard gold is its ability to tolerate temperature changes. This makes it an excellent choice for PCBs that are used in environments with varying temperatures. It is also less prone to thermal shock, which can damage the components on the board.
While hard gold has several advantages, it is not the best choice for sensitive joining applications. The high levels of contact force and wear can cause the plating to break down, and it is more prone to corrosion than soft gold. A better choice for these applications is ENIG, which offers a higher purity and a smoother plating surface. It also has a lower contact resistance, which is important for electronic devices.
Electrical Contact Resistance
Compared to other metals, hard gold has low contact resistance. This is important in electronic applications such as connectors and switches. Other metals such as nickel, cobalt and iron can have high contact resistance, especially in humid or corrosive environments. This can cause the formation of oxides and contamination films on the contacting surface. These can reduce the conductivity of the connection and cause failures.
The contact resistance of hard gold is also dependent on its Hard Gold PCB Supplier thickness. A thicker layer will offer more contact resistance than a thinner one. It is important to select the right thickness for the application.
Additionally, the choice of an underplate is crucial. A bright sulfamate nickel or medium phosphorous electroless nickel underplate can increase the life of hard gold and improve the functionality of your circuit boards. The coating will also help reduce corrosion and oxidation.
Whether you are working in electronics or aerospace, choosing the right PCB material can have a significant impact on your product’s quality and durability. The right materials will provide longevity and reduce maintenance and replacement costs. For more information on the best PCB materials for your application, contact a trusted manufacturer of hard gold PCBs today. They can provide expert guidance and technical support for your interconnection solutions, assisting you with component selection, surface finish, solder mask stack-up builds and more.
Typically, hard gold electroplating is used on PCBs that require a combination of wear resistance and corrosion resistance and a consistently low level of electrical contact resistance. The hardness of gold electroplating is actually an alloy of different metals so it is relatively hard and suitable for places that will have force friction; for example, in the electronics industry, hard gold is commonly used on PCB edge connector finger surfaces or more commonly referred to as “gold fingers”.
The smaller and more refined grain structure of hard gold plating provides a lustrous finish which is generally considered more visually appealing than soft gold. With a maximum hardness of 90 HK25 (which is similar to the hardness of human fingernails) hard gold is also more resistant to scratching and burnishing. Adding a nickel underplate to a hard gold deposit further increases the durability of the coating.
However, the presence of non-noble metals in hard gold deposits does limit their solderability and wire bonding capabilities as they are prone to oxidation at high temperatures. Because of this, it is advisable to use ENIG if your project requires solderability.