There are two design alternatives accessible when working on an application that requires gold plating services: hard gold plating and ENIG plating. The hard plating method results in a refined grain surface and harder deposits that form when gold is alloyed with another metal, such as iron, nickel, or cobalt. ENIG plating, or “electroless nickel immersion gold” plating, is softer than hard plating since no additional elements are employed in the alloy.
A gold electrodeposit that has been alloyed with another element to change the grain structure of the gold is known as hard gold plating. Soft gold plating is the purest gold electrodeposit available; it is practically pure gold with no alloying components.
Which plating method is best for your project? Continue reading to learn more about the benefits and drawbacks of hard gold plating vs. ENIG.
Hard Gold plating
Hard gold plating usually has the lowest grain sizes conceivable, ranging from 20 to 30 nanometers, with a hardness of 130 to 200 HK25. Hard plating’s surface finish is significantly more glossy than ENIG plating because of these features. Hard plating is also effective in preventing slide wear. Hard plating can withstand applications with a contact force of 50 grammes or greater. Hard plating can also survive significantly more cycles than ENIG plating, with the exact number of cycles varying according to plating thickness.
The ability of hard plating to bind is a disadvantage. Soldering hard gold is substantially more difficult than ENIG plating since it contains nickel, iron, cobalt, and other non-noble metals. If you want to use ultrasonic wire bonding, thermostatic bonding, or any other delicate joining, hard plating will make the job much more difficult.
Chemical immersion gold is now commonly referred to as ENIG (Electroless Nickel Immersion Gold). ENIG plating has the advantage of attaching “nickel” and “gold” to copper without the need for sophisticated electroplating, and its surface is flatter than electroplated gold, which is ideal for finer and finer pitch. Because ENIG plating uses a chemical replacement process to create the effect of the surface gold layer, the gold layer’s maximal thickness cannot in theory match that of electroplated gold.
Because the ENIG plating layer is “pure gold” due to the replacement concept, it is frequently labelled as “soft gold,” and some people utilise it for aluminium wire bonding. However, a gold layer that is too thin will impact the adhesion of aluminium wire bonding, thus the thickness of the ENIG plating layer must be at least 3 ~ 5 micro-inches (μ “). ENIG plating typically has a thickness of 5″ or less, but electroplated gold plating can easily reach a thickness of 15″ or more, with the price increasing with the thickness of the gold layer.
ENIG plating is also preferable for the above-mentioned connecting applications. Though its softness makes it more likely to scratch, ENIG plating’s purity makes it significantly more resistant to corrosion over time than hard gold plating.
What Gold Plating Method Should You Use?
The following four aspects should be considered while choosing the correct gold plating method:
- Wear Resistance and Contact Force Absorption
Hard gold plating is more durable and resistant to wear. Hard gold plating should be specified for applications that demand frequent sliding wear or on-off switching.
Hard gold plating is more difficult to solder than soft gold plating/ENIG plating due to the presence of “non-precious metal” components. Only soft gold plating/ENIG plating should be considered for particularly sensitive joints, such as wire bonding, thermostatic bonding, or other sensitive connections.
- Biocompatibility/Corrosion Resistance
Other components in hard gold plating lower the overall corrosion resistance of the coating and are quickly oxidised at high temperatures, whereas soft gold plating/ENIG plating has a high purity and is superior in corrosion resistance. As a result, soft gold plating/ENIG plating is preferable for medical purposes.
- Resistance to Contact
Soft gold plating has a lower contact resistance than hard gold plating. Hard gold plating will increase contact resistance in high-temperature applications due to the increased production of oxides and other compounds; in this case, soft gold plating/ENIG plating is the best option.
Scratches are more likely to occur with soft gold plating/ENIG plating. In general, strong gold plating is suitable for applications that demand exquisite gold contacts (such as visible interconnect applications).
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