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A printed circuit board (PCB) surface finish has two main functions: To prevent the copper from oxidizing and to provide a solderable surface.
Some PCB surface finishes, however, are more popular and versatile than others. As you review your options, you&#;ll likely consider durability, cost, and the materials used within the finish, such as tin-lead, lead-free, various gold finishes, and silver. Additionally, you may have concerns about the finish compatibility with the subsequent termination process &#; such as wire bonding or welding. But how do you know which surface finish is best for your next PCB project?
We&#;ve compiled a comprehensive list of the nine different surface finishes. In this article, we&#;ll explain the purpose and common uses of each surface &#; plus the advantages and disadvantages &#; so you can find the best option for your next project.
The 9 Different PCB Finishes
How to Choose the Best PCB Finish for Your Project
ENIG is the most popular option and is used on about 80% of all PWBs. This finish provides a thin, gold, solderable layer that protects the copper traces with a nickel barrier between it and the copper. ENIG is a good lead-free option that results in a durable, long-lasting finish.
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With HASL, the printed circuit board is held vertically by clamps and dipped into a flux bath and then a molten solder hot vat. The finish, which contains tin/lead, is leveled off with hot air knives and the printed circuit board panel is raised out of the molten solder vat. This ensures a homogenous thickness over the entire board. It was once one of the most popular finishes but is now mainly used only on military and aerospace applications.
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The properties and uses of this finish are the same as HASL &#; except there is virtually no lead in the alloy. Instead, the alloy is a tin and copper, tin and nickel, or tin, copper, nickel and germanium alloy. This finish is not widely used.
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With this finish, a layer of tin is deposited onto the copper surface using a chemical process. This is frequently used in high-speed circuits. Immersion tin works well to protect underlying copper from oxidization, but copper and tin in such close proximity can create diffusion from one metal into the other, resulting in challenges.
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A thin layer of material is applied over the copper to protect it prior to soldering. Though this water-based organic surface finish was once very popular, it is not widely used today.
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Hard gold is plated over the nickel, which holds up well and doesn&#;t break down easily compared to other finishes. Because of its durability, this type of PCB plating is used in applications that involve mechanical contact, such as buttons and keypads.
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Similar to tin, this PCB finish is used in high-speed signals that don&#;t contain any nickel. Immersion silver, however, does require unique storage as it will tarnish if exposed to air.
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This three-layer metallic finish is used for printed circuit boards that also require wire bonding. The electroless nickel protects the copper and prevents it from coming into contact with the other metals. Palladium provides another anti-oxidation insurance layer and prevents the nickel from corroding, and the final gold layers adds more of a barrier against oxidation &#; plus it completely covers the PCB.
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This PCB finish has been used for a long time and has the same wire bonding process as ENEPIG. The pad is a crowned surface, which means there is less area to land wires.
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It&#;s important to pick the right PCB plating for your product. While there are a lot of available options, you want to consider the size and scope of your project &#; and budget.
For a solid overall option, ENIG offers a high quality finish and low-cost option with good solderability. You may, however, have to choose a finish based on a particular technology or requirement &#; such as HASL, which is military, aerospace, and space approved.
Selecting the right PCB surface finish can be a challenge, but we are here to help. Cirexx is your best-in-class solution for PCB layout, fabrication, and assembly. With more than four decades of experience, we have manufactured PCBs for almost every leading technology company &#; and we&#;ve worked with industries all over the world. Contact us today to learn more about what PCB surface finish you should choose for your next project or to connect with our experienced sales team.
Printed circuit boards are a maze of intricate interconnections terminating at exterior metal pads or in holes designed to accommodate component leads soldered onto or into them. However, the plated copper pads and holes need an interface to facilitate the soldering process and protection against oxidation and contamination. To provide this protective interface, PCB manufacturers rely on surface finishes applied to the board during fabrication. Two of the most common choices of surface finishes are hot air solder leveling (HASL) and electroless nickel immersion gold (ENIG). Consider the following highlights:
Beyond the surface, there are additional considerations between hot air solder leveling and electroless nickel immersion gold and how they compare. With a better understanding of these two surface finishes, electronics manufacturers can make the right choice between HASL vs. ENIG for their products.
A circuit board undergoing hot air solder leveling will proceed through the following steps:
Due to its thickness, HASL doesn&#;t give the best uniformity in its application on a circuit board. However, passing PCBs through a horizontal process rather than a vertical one produces a smoother surface finish due to the natural effects of gravity. Smaller components and fine-pitch parts are also not recommended for HASL-finished boards due to the thickness of the surface finish. Equipment manufacturers also need to be aware that due to the heat involved during the HASL application, circuit boards may experience delamination and other thermal stress-related issues.
HASL is a common choice thanks to its simplicity and low cost, making it a dependable surface finish. However, with the industry moving away from lead-based solder, the HASL process has lost popularity to other RoHS-compliant processes such as ENIG. This trend contrasts with the development of lead-free hot air solder leveling (LF-HASL), which is swiftly gaining popularity among manufacturers.
The process for applying an ENIG surface finish to a printed circuit board is much more complex and involved than the HASL process:
ENIG provides a flat finish of uniform thickness, excellent corrosion protection, and great solderability to the circuit board. This surface finish is perfect for small devices, fine-pitch parts, and wire-bonded parts and can go through multiple reflow cycles for assembly steps requiring repeated passes.
However, due to the nickel and gold and the multiple processes, ENIG is a more expensive process than other surface finishes like HASL. Electroless nickel immersion gold is also difficult to inspect visually during manufacturing due to the nickel and is not suitable for high-temperature applications. Additionally, ENIG is susceptible to &#;black pad,&#; a defect that can occur during its application that will hinder the solderability of the finished circuit board.
Hot air solder leveling surface finish has been in use for a long time, and it is a proven and reliable process. It is widely available, reworkable, and less expensive than ENIG. However, with its lead-based solder, HASL is not RoHS compliant. The lead-free version of HASL is necessary to avoid this limitation, but it may not be as readily available from all circuit board fabricators. HASL is also not recommended for fine-pitch components.
Electroless nickel immersion gold, on the other hand, is extensively used in aerospace, medical, and other industries that require high-reliability circuit boards. It is lead-free, making it an obvious choice for environmental concerns and RoHS requirements, and components of any size and pin-pitch are solderable to it. However, ENIG has a higher cost.
There are many other considerations to remember when selecting the best surface finish for a circuit board. The engineering team at VSE is ready to answer your questions and help you decide between HASL vs. ENIG surface finishes.
If you are looking for a CM that prides itself on its care and attention to detail to ensure that each PCB assembly is built to the highest standards highest standards , look no further than VSE. Contact us today to learn more about partnering with us for your next project.
Contact us to discuss your requirements of Industrial Control PCB Wholesale. Our experienced sales team can help you identify the options that best suit your needs.