The Advantages of Hard Gold
Hard gold is used for edge connectors (gold fingers) and keypads, offering longer lifecycles based on the thickness of the plating. It is also able to resist sliding wear and high contact force.
It requires electroplating, which uses electric current to coat one metal over another. However, hard gold deposits contain impurities like nickel, cobalt and iron, which oxidize at soldering temperatures. This makes them unsuitable for ultrasonic wire bonding and thermostatic bonding.
Corrosion Resistance
Gold is highly resistant to corrosion and tarnishing, making it an excellent option for items that will be exposed to corrosive environments. Humid conditions like sulfur or chlorine gases can attack other metals, but they are less likely to affect gold. In fact, gold is often used for electrical contact components that must be protected from these corrosives in order to maintain their function.
Hard gold is also adept at preventing sliding wear. It can be plated to hard gold thicknesses that will allow it to withstand many thousands of life cycles. The number of life cycles is proportional to the thickness of the deposit, but typical functional hard gold deposits are able to withstand at least 100,000 life cycles.
In addition to corrosion resistance, hard gold is also highly durable. It can be plated to thicknesses allowing it to resist heavy amounts of force and wear, such as in applications that require edge connector fingers or keypads. The durability of hard gold can be further enhanced by adding a layer of nickel underplate, such as in an ENIG deposit, to provide additional mechanical support.
However, hard gold is not well suited to solderability and wire bonding applications. The added non-noble metals in hard gold deposits oxidize at the high temperatures required for these processes, reducing the strength of the resulting solder joint. Choosing the right type of gold plating for your item depends on a variety of factors, including its end-use, the environment in which it will be exposed and the desired appearance of the item.
Wear Resistance
Gold is a very hard metal. It resists the effects of corrosion and is also less sensitive to temperature fluctuations. This makes it ideal for use in circuit boards that must withstand harsh environmental conditions. This includes environments that are humid or contain corrosive substances, like sulfur or chlorine.
When used on printed circuit board contact points, hard gold provides exceptional wear resistance. It can be expected to last up to 1,000 cycles of abrasion under normal contact forces. This is significantly more than the 300 to 500 micro-inch wear-through thresholds for soft gold deposits.
However, a co-deposit of non-noble elements, including nickel, cobalt and iron, can affect the solderability of hard gold. This is because these elements oxidize at soldering temperatures, weakening the integrity of the solder joint. This makes it unsuitable for applications that require sensitive joining techniques like ultrasonic wire bonding and thermosonic bonding.
One solution is to use a duplex gold finish, which combines both hard and soft gold deposits to provide the best of both worlds. This is a common finish plated at Valence, and it is particularly useful for high-wear areas of a PCB like the edge connector contacts commonly called “gold fingers” or keypads. A duplex gold deposit is 30 to 50 micro-inch thick with a nickel underlayer and a hard gold layer on top.
High Temperature Resistance
Hard gold has excellent high-temperature resistance, making it a good choice for electronics that may be exposed to harsh environments. It does not oxidize or form other compounds when heated, even up to 200 degrees Celsius. This makes it an excellent electrical conductor at high temperatures, which is important for keeping signal loss low.
It is also extremely resistant Hard Gold PCB Supplier to corrosion, and it does not tarnish or rust. The best part is that it is completely recyclable, making it an environmentally friendly choice. Considering these characteristics, it is no wonder that most consumer electronic devices and computerized industrial machines feature hard gold plated circuit boards.
Another benefit of hard gold is its bright appearance. Due to its refined grain structure, hard gold plating has a more lustrous appearance than soft gold. It is a great option for applications that require cosmetically pleasing gold contacts, such as visible interconnect applications.
However, despite its good wear and corrosion resistance, hard gold has some disadvantages. For one, it is difficult to solder. The presence of non-noble elements like nickel and cobalt in the hard gold deposit causes it to oxidize at soldering temperatures, which weakens the solder joint. For this reason, it is not suitable for any kind of joining process. Fortunately, ENIG is an excellent alternative to hard gold, offering similar corrosion and oxidation resistance with a much more consistent and low contact resistance.
Electrical Conductivity
Gold is a natural conductor, with a higher conductivity than copper. However, the purity of hard gold plating is usually lower than silver, and it’s also alloyed with other elements to make it harder (usually nickel or cobalt). This reduces its conductivity compared to pure gold.
This makes hard gold PCBs useful for applications that require a combination of wear resistance, corrosion resistance, and a consistently low level of electrical contact resistance. It’s commonly used in high-wear areas like edge connector fingers and keypads. It’s also used to provide a conductive surface on PCBs when solderability is important.
When choosing a hard gold PCB manufacturer, look for one that has a strong track record of customer satisfaction and an ethical approach to business practices. They should follow RoHS guidelines and be able to offer advice on interconnection solutions, surface finish, solder mask stack-up builds, and other important factors.
Another thing to look for is a company that has the ability to perform quick and accurate prototyping to ensure that your product will work when you’re ready to start production. They should also be able to deliver your finished products on time. Also, remember to keep your hard gold PCBs clean to avoid corrosion & grime build-up, which can interfere with their functionality. If you need to clean your hard gold PCB, use a chemical solution that’s safe for the coating.
