Advantages and Disadvantages of PCB Surface Finishes
Surface finishes can be classified in many different ways. This article discusses the main attributes of PCB surface finishes and the requirements of various types of PCB products. The benefits and disadvantages of each type are discussed. To determine the right surface finish for your PCB project, you can refer to the following table.
Among the most widely used surface finishes in the PCB industry is ENEPIG. It is a two-layer metallic coating consisting of 2-8 min Au over 120-240 min Ni. The nickel acts as a barrier for the copper on the PCB surface. Gold protects the nickel from corrosion during storage and provides a low contact resistance. ENIG is often a cost-effective choice for PCBs, but it is important to use proper application procedures.
The advantages and disadvantages of electroplated gold over electrolytic nickel (ESN) are primarily cost-effectiveness and ease of plating. Electroplated gold over electrolytic nickel is very durable and has a long shelf life. However, electroplated gold over nickel has a higher price tag than other finishes. In addition, electroplated gold over nickel interferes with etching and must be handled with care to avoid damage.
PCB surface finishes come in two major classifications: ENEPIG and ENIG. This article explores the differences between the two finishes and provides a comparison of their benefits and drawbacks. It also discusses when to use each.
The ENIG surface finish is a three-layer, bonded metallic finish. In the past, this material was mainly used on PCB boards with functional surface connections and high shelf-life requirements. However, the high cost of palladium and the requirement for a separate manufacturing line led to the failure of the material. In recent years, however, the material has made a comeback. Its high-frequency properties make it an excellent choice for high-frequency applications.
In comparison to ENIG, ENEPIG uses an additional layer of palladium between the gold and the nickel layers. This protects the nickel layer from oxidation and helps prevent the black pad problem. Because palladium prices have dropped recently, ENEPIG is now widely available. It offers the same benefits as ENIG but is more compatible with wire bonding. However, the process is more complex, requires additional labor, and can be expensive.
The HASL classification of PCB surface finish provides excellent solderability and is able to accommodate multiple thermal cycles. This surface finish was previously the industry standard, but the introduction of RoHS standards has forced it out of compliance. The alternative to HASL is lead-free HASL, which is more environmentally-friendly, safer, and better aligned with the directive.
Surface finish on PCBs is critical for reliability and compatibility. An appropriate surface finish can prevent the copper layer from oxidizing, which decreases the solderability of the PCB. However, the quality of the surface finish is only one part of the picture. Other aspects must be considered, such as the cost of board fabrication.
There are many classifications of PCB surface finishes, including the hard gold and soft gold finishes. Hard gold is a gold alloy that includes nickel and cobalt complexes. This type is used for edge connectors and PCB contacts and typically has a higher purity than soft gold. Soft gold, on the other hand, is typically used for wire bonding applications. It is also suitable for lead-free soldering.
Hard gold is generally used for components that have a high wear resistance. This is the type of plating that is used for RAM chips. Hard gold is also used on connectors, but the gold fingers must be 150 mm apart. Also, it is not recommended to place plated holes too close to gold fingers.
PCB surface finishes are a critical process between PCB board manufacturing and circuit card assembly. They play an important role in maintaining the exposed copper circuitry and providing a smooth surface for soldering. Usually, the PCB surface finish is located at the outermost layer of the PCB, above the copper. This layer acts as a “coat” for the copper, which will ensure proper solderability. There are two types of PCB surface finishes: metallic and organic.
Immersion tin is a metallic finish that covers the copper on the PCB. It has the advantage of being able to be reworked easily in case of soldering errors. However, it has some disadvantages. For one, it can tarnish easily, and it has a short shelf life. As a result, it’s recommended that you use immersion tin PCB surface finishes only if you’re confident that your soldering processes are accurate.