Applying a surface finish is essential in the PCB fabrication process to ensure performance and reliability. Without the right PCB surface finish, board components and copper traces risk oxidative exposure to conditions that cause corrosion, tarnishing, or damage to the board.
Therefore, with structural integrity and component longevity at stake, it is essential to match the right surface finish with the PCB project. Unfortunately, finding the right finish isn’t always straightforward, with several factors playing a critical role in the selection process.
But it is possible to cut through the confusion for better PCB function and lifespan with a read of our guide to PCB surface finishes.
From standard finishes suitable for low-cost, less demanding applications to high-grade finishes for military and aerospace projects, we cover everything you need to know for the perfect printed circuit board.
What Determines the PCB Surface Finish You Use?
Every material used in the design and fabrication of PCBs is chosen based on its intended application, and PCB surface finish is no exception. With environmental, production, and cost factors all playing roles in the selection process, PCB designers and engineers need to consider the following for the right PCB surface finish.
Budget & Cost
Various aspects of PCB design may have higher cost thresholds than others. For this reason, choosing a surface finish that doesn’t overwhelm other essential parts of the budget is necessary.
Conversely, PCB projects requiring a high-performance surface finish – such as military and aerospace applications – may need to splurge a bit more to ensure optimal protection and performance.
Due to the chemical reaction of PCB finishes with copper traces, selecting the correct surface finish will also depend on manufacturing volume.
Because commonly used, highly affordable finishes such as immersion tin tarnish rapidly (within 30 days) after contact with copper, they are not viable when producing small batches of PCBs.
So, even though the lower price is tempting, designers must consider other options to avoid costly, time-consuming maintenance and rework, usually immersion silver or gold.
Many people don’t realize that the sleek futuristic look of a PCB is actually a well throughout part of the design process.
With options for matte finishes to prevent light reflection, shiny finishes to minimize the risk of whiskers, and even clear finishes to support electrical and environmental protection, the appearance of a PCB is anything but an afterthought.
So, when selecting a PCB surface finish, ensuring the look it provides matches the required characteristics for optimal performance is vital for success.
Hot Air Solder Leveling (HASL)
Hot air solder leveling (HASL) involves coating the printed circuit board with molten solder and then using hot compressed air to level the topology of the board.
This standard PCB surface finish for commercial and hobbyist projects is considered an economical yet reliable choice for mounting components, providing good protection against oxidation, and ensuring minimal electrical resistance with a uniform finish.
However, this method often results in flux residue or solder balls that will damage the PCB if not cleaned off the board post-etching.
To get the most out of HASL PCB finishes, it’s best to use them in applications or processes such as electrical testing, hand soldering, and high-performance electronics. These applications require stronger solder joints, reduced oxidation, and minimized electrical resistance that comes with the HASL process.
Depending on the specific requirements of the PCB application, lead-free HASL may offer a better fit than leaded HASL. Lead-free HASL finishes provide better reliability and performance in the long run, meet RoHS compliance, and often have an elevated melting point, making them better for high-temperature use.
Organic Solderability Preservatives (OSP)
Surface mount technology (SMT), server boards, and fine-pitch devices all benefit from the use of organic solderability preservatives (OSP). A water-based, lead-free finish, OSP creates a thin coating of organic molecules that protects the copper traces from oxidation while maintaining excellent solderability.
The absence of lead and other toxic materials makes OSP an ideal choice for commercial products and consumer electronics, where reliability, performance, and safety are top priorities.
OSP is also highly recommended for its low cost, ease of use (no cleaning required), and ability to be reworked — all of which can save time and money in the PCB fabrication process.
With a simple application process, OSP is often the go-to choice for reducing production time and cost. Additionally, because OSP reduces electrical resistance compared to other PCB surface finishes, it’s a popular option for high-speed boards requiring excellent signal integrity.
The drawbacks to OSP are its limited shelf life and susceptibility to harsh cleaning agents. Also, this finishing process isn’t as common as other finishes and may require a specialized PCB fabricator that can provide it, so be sure to check supply availability with your chosen supplier before investing in OSP.
Electroless Nickel Immersion (ENIG)
Electroless nickel immersion gold (ENIG) plating is a tried-and-true surface finish for high-reliability PCBs. From high-end consumer products to medical devices to aerospace electronics, ENIG is the go-to finish for its unbeatable combination of solderability, uniformity, corrosion protection, and durability.
It’s also perfect for complex boards when areas need full coverage in fine detail, wire bonding, and applications where durability is paramount — something other PCB surface finishes don’t do as well.
The multistep process combines a thin layer of nickel with a thicker gold coating, producing extraordinary results that achieve flat surfaces, minimal scrap and rework, and reliable electrical connections.
Overall, pricing for this finish is higher than other PCB soldering options. Still, its longevity makes it a cost-effective choice in the long run, especially when dealing with high-reliability applications or products that require flawless performance.
Find A Reliable PCB Manufacturer
Choosing the right PCB surface finish for your application means understanding its benefits, limitations, and associated costs. With the many PCB finishes on the market, it pays to find a reliable partner who can guide and execute your PCB fabrication needs.
And with the right supplier, you can get top-notch results that meet all your requirements for reliability, performance, and cost.
Learn more about why partnering with a reliable USA PCB manufacturer vs. an offshore manufacturer is essential to get the best finishes, quality control, and quick turn time for your upcoming PCB project.