What Do You Know About Different Types of PCB Surface Finishing –II

Surface finishing is one of the last steps in the PCB manufacturing and assembly. Various types of surface finishing is available around. In the previous post, we have discussed some popular surface finishing treatments for printed circuit boards. In this post, we will introduce you to a few others.

Impact of Different Surface Finishes on the PCB

Following are some more types of the common surface finishing types available for printed circuit boards.

Gold Fingers: Gold fingers or hard gold surface finishing provides a planar surface, especially for wear applications such as edge connector fingers, and keypads. This surface finishing can be combined with other surface finishing treatments to provide a reliable solderable surface.

Advantages of Gold fingers

1. Gold finishing offers hard and durable surface finishing.
2. This surface finishing contains no lead, which makes it environmentally safe.

Disadvantage of Gold fingers

1. It requires extra processing, which makes it labor intensive and expensive.
2. The hard gold has poor solderability limit of 17 μin.

ENIG: ENIG (Electroless Nickel / Immersion Gold) surface finishing features a coating of silver applied over the nickel layer in the ratio of 2-8 μ and 120-240 μ. It offers double layer metallic coating, where nickel acts a barrier to copper in order to protect it from oxidation. Secondly, the layer of nickel is protected by gold, which prevents it from disintegration during the assembly.

Advantages of ENIG

1. It provides a planar surface plating on various circuit boards with a reliable solder joint.
2. It has a longer shelf life in most of the printed circuit boards.

Disadvantages of ENIG

1. It is one of the expensive surface finishing option available.
2. This surface finishing offers black pad failure in solder joints, due to the galvanic hyper corrosion. This happens due to the phosphorous buildup between the nickel and gold layers.

ENEPIG: ENEPIG or Nickel Palladium surface finishing is the advanced ENIG surface finishing with the addition of palladium layer. Palladium being harder than gold offers better solderability and antifriction properties. This type of surface finishing is good for semiconductors and various medical and military applications.

Advantages of ENEPIG

1. This surface treatment process helps in reducing the severity of black pads (nickel corrosion) in the circuit boards.
2. It is suitable for gold and aluminium wire bonding.

Disadvantages of ENEPIG

1. The surface finishing is complex and its solderability performance diminishes due to thick palladium layer.
2. This type of surface finishing is expensive.

As seen, all the above-mentioned surface finishing have their own pros and cons. Hence, choosing the right surface finishing for a particular application may get tricky. In such situation, it is always better to approach an industry expert with a vast experience. Creative Hi-Tech is one of the reputed PCB assembly and manufacturing services offering PCBs in various surface finishing options.