10 Types of PCB Surface Finishes: All You Need to Know

The surface finish on any printed circuit board is a critical factor that needs to be considered while designing a PCB. Everyone wants to ensure the long-life product, and its surface finish ensures PCB’s long life. Surface finish is applied for two important reasons that are,

1. To prevent oxidation at the surface of copper
2. To ensure ease in the soldering

The surface of a PCB has the utmost importance. If the PCB has no surface finish, the copper on the surface will oxidize quickly. The oxidation will deteriorate the copper and affect the electrical performance of the PCB. At last, the PCB will be of no use. Thus, it’s important to have a surface finish on the PCB to give a long life to the exposed copper. Moreover, it offers a surface to solder the components easily.

There are different types of surface finishes, and you need to understand them before you select anyone. They have different pros and cons, and you must select the best one for your project. Today, we will discuss different types of surface finishes in detail. So, stay with us.

The types of surface finish are,

1) Hot Air Solder Level (HASL)

HASL is the most common and inexpensive type of surface finish. The process of HASL is quite simple; the bare PCB board is dipped into the molten solder. The solder covers the area over the copper and removes it from the tank. After that, the surface of the PCB is leveled using hot-air knives. It offers an excellent surface for soldering.

HASL is excellent for large components and SMTs. But if the SMT is smaller, it will not work as desired. It’s not suitable for Fine Pitch Technology (FTP). Furthermore, the processing temperature is in the range of 260-270˚C, which is quite high. Due to high thermal stress, there are chances of defects in the board.

Keep in mind that it contains lead. It’s usually dipped in Tin-Lead alloy, and the lead is a carcinogen. Thus, it’s not RoHS compliant. If you need a lead-free circuit board, then it’s not for you.

Hot Air Solder Level (HASL) PCB Double-sided Hot Air Solder Level (HASL)PCB Hot Air Solder Level (HASL) Machine

2) Lead-free HASL (LF HASL)

Lead-free HASL is similar to HASL, but it does not contain lead. Thus, it can be used for many purposes without any worries. It’s according to RoHS standards.

As far as the functions, pros, and cons are concerned, they are similar to HASL.

FR4 4 Layer Lead-Free HASL PCB Board FR4 4 Layer LF-HASL PCB Circuit Board FR4 Black Oil 4-layer Lead-free HASL PCB Circuit Board Automatic Lead-free Spray Tin Machine

3) Plated Gold

Plated Gold surface finish is also known as Hard Gold surface finish. It’s an expensive surface finish that uses a layer of gold on the PCB. It’s done through electroplating, and a hard layer of gold is attached to the surface of the copper. The adhesion between the PCB and the layer is firm, which increases the board’s durability. Since gold is an excellent conductor, it’s excellent for electrical performance. Moreover, its oxidation resistance is commendable. The surface finish is excellent for the PCB area, where high wear and tear is expected. It can last for a long time.

The problems associated with this type of surface finish are price and extra processing. It isn’t easy to process. Due to the high price, it’s rarely used, but it’s an excellent surface finish that can last longer. Moreover, the solderability of hard gold is poor.

FR4 ARLON Double Layer Gold-plated High-Frequency PCB Board

4) Organic Solderability Preservatives (OSP)

OSP is a process for the surface finish of copper foil of printed circuit board, which meets the requirements of the RoHS directive. OSP is the abbreviation of organic solvency preserves.

OSP has the characteristics of oxidation resistance, heat shock resistance, and moisture resistance. It protects the copper surface from further rusting (oxidation or vulcanization, etc.) in a typical environment. However, in the high-temperature welding process, the protective film must be easily and quickly removed by the flux so that the exposed clean copper surface can be immediately combined with the molten solder to form a strong solder joint quickly.

In this type of surface finish, a water-based coating protects the copper until it’s soldered. It prevents the oxidation of copper and increases its life. But remember that it’s only on an organic surface coating that is not durable enough; it’s quite sensitive. It has a short life span.

OSP is an inexpensive surface finish that can save money. It requires less time, and the process is also straightforward. If there are holes in the PCB, their size is not affected by the coating. It offers an excellent flat surface, and it’s environmentally friendly.

It can be used in areas where the PCB is handled carefully, and there are fewer chances of wear and tear.

OSP PCB Board OSP PCB 1.2mm 6 Layer OSP PCB Circuit Board

Learn more about What PCB OSP Surface Finish is.

5) Immersion Silver

Immersion silver is a flat surface finish that has a reasonable cost. Silver plating is done over the copper surface to protect it from oxidation in this type. The layer of silver is quite thin, but it offers excellent conductivity. It’s good for Fine Pitch Technology (FTP) because the layer is very thin, and it does not affect the size of the holes.

The problem with this type of surface finish is tarnishing. The silver plating tarnishes when exposed to air. Therefore, it’s packed as soon as possible in anti-tarnish packaging to prevent tarnishing. It is very sensitive, so you need to solder the board after taking it out of the package.

The life of immersion silver is moderate. It has a low cost, and it’s according to RoHS standards.

The immersion silver process is between OSP and electroless nickel/immersion gold. The process is relatively fast and straightforward; even if the PCB is exposed to heat, humidity, and pollution, the silver can still maintain good solderability, but it will lose its luster. Immersion silver does not have the good physical strength of electroless nickel/immersion gold because there is no nickel under the silver layer.

FR4 4-layer Immersed Silver Circuit Board

6) Immersion Tin

Immersion tin is a lead-free surface finish, which is excellent for small components. It is very thin and flat, perfect for Fine Pitch Technology (FTP).

The cost of this surface finish is reasonable, but it has some drawbacks. Tin can react with the copper on the PCB, which reduces the shelf life. Moreover, it’s also prone to tarnish, so it must be used as soon as possible. It’s very sensitive. After a few months, you will notice tin whiskers on the PCB.

Since all current solders are based on tin, the tin layer can be matched with any solder.

Immersion Tin PCB

7) Electroless Nickel Immersion Gold (ENIG)

ENIG is the most used type of surface finish because of its features and RoHS compliance. In simple words, there is a thick layer of nickel over copper and a thin layer of gold over the nickel layer. The components are soldered on the nickel, and the gold coating protects the nickel until it’s not soldered.

ENIG has a long shelf life; it is durable enough. But it’s expensive due to using two layers, especially gold. It has all the features, including a flat surface and a thin finish, to work with smaller components.

The only problem with ENIG is black pad syndrome, which is the building of phosphorus between the gold and the nickel layer.

6 Layer Electroless Nickel Immersion Gold (ENIG) PCB 4 Layer Electroless Nickel Immersion Gold (ENIG) Half-Cut/Castellated Holes/Half Hole PCBC

Learn what PCB Immersion Gold ENIG Surface Finish is.

8) Electrolytic Nickel Gold (ENEG)

ENEG is also an expensive lead-free finish. It contains a layer of hard gold or soft gold over electrolytic nickel. Gold prevents the oxidation of copper. Gold plating in ENEG has excellent adhesion; therefore, electrolytic nickel gold lasts for a long time and never rusts.

The surface of ENEG is flat, where you can easily work with small components. It has excellent conductivity and great performance.

Electrolytic Nickel Gold (ENEG) PCB

9) Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG)

ENEPIG is the best surface finish that resists corrosion and reaction with air. It has a longer shelf life, making it the best.

It is a three-layered surface finish that contains nickel, palladium, and gold. All these materials perform together to offer long life. Unlike ENIG, there is no risk of black pad syndrome in ENEPIG.

It’s RoHS-compliant, and there is no lead in it. The problems with ENEPIG are high cost and complex processing.

ENEPIG PCB ENEPIG PCB Board ENEPIG Surface Finished PCB

10) Mixed Surface Finish

A mixed surface finish is a mixture of more than two surface finishes to get the optimum performance. A single PCB has more than one finish surface finish as required. The most commonly used mixed surface finishes are ENIG +OSP, ENEG + ENIG, ENEG + HASL, and ENIG+ HASL.

FR4 Double-sided Immersion Gold + Gold-plated PCB Circuit Board FR4 Double-sided Immersion Gold + Gold-plated PCB

Final Thoughts

There are various types of surface finishes with distinct properties, pros, and cons. You need to select the best one according to your requirements. You need to develop a surface finish that can complete all your requirements at the minimum cost. We have explained all types of surface finish in detail. We hope you have a complete idea of the different types of surface finishes.

Surface Finish at JHYPCB

JHYPCB is a well-known PCB manufacturer in China. We have been providing high-quality PCB for more than a decade. We have strict quality control, which is compliant with RoHS and ISO 9001:2008. For the ease of our customers, we offer all types of surface finishes. You can get the desired PCB, prototype, or PCBA at a reasonable cost. We can handle small-medium volume PCB manufacturing and fabrication. For more information, feel free to contact us.

Advanced Learning:

 

Introduction

 

PCB surface finishes include two major categories: organic and metallic.

When comparing these two categories and considering all available options, it becomes clear that each has its benefits and drawbacks.

The choice of the most suitable finish is typically determined by factors such as the intended application, the assembly process, and the PCB design itself.

If you’re unsure about the most appropriate surface finish for your project, it’s advisable to consult with MorePCB before making a final decision. Our expertise will ensure that the chosen combination of surface finish and material yields a cost-effective design with optimal performance.

This article will help readers to have a brief understanding of PCB surfaces, their types use cases, etc. 

 

What is PCB Surface Finish?

A printed circuit board’s (PCB) copper traces and pads receive a final coating or treatment known as a PCB surface finish. It is a crucial stage in the manufacture of PCBs and serves a variety of functions, including protection, solderability, and general reliability.

To avoid oxidation, which can impair the PCB’s electrical conductivity and solderability, the surface finish is applied to the exposed copper surfaces. Between the copper and the environment, it serves as a barrier. As a result, it guards against corrosion and guarantees the PCB’s long-term functioning.

Additionally, the surface finish plays a crucial role in facilitating soldering during the assembly process. It provides a flat, solderable surface on the copper pads, by enabling the secure attachment of electronic components to the PCB. The choice of surface finish affects the wetting and adhesion properties of the solder. Therefore it impacts the quality of solder joints and the overall reliability of the PCB assembly.

There are several types of surface finishes commonly used in PCB manufacturing. These include Hot Air Solder Leveling (HASL), Electroless Nickel Immersion Gold (ENIG), Organic Solderability Preservative (OSP), Immersion Tin, and Immersion Silver. Each surface finish has its advantages, limitations, and suitability for specific applications.

The selection of the appropriate surface finish depends on various factors, including the desired electrical performance, budget, assembly processes, component types, and environmental conditions. Manufacturers carefully consider these factors to ensure the best possible surface finish is chosen to meet the specific requirements of the PCB design.

 

The Importance of Choosing the Right PCB Surface Finishes

 

Protection Against Oxidation

Selecting the correct Printed Circuit Board (PCB) surface finish is crucial. It’s not just aesthetics; it’s about practicality. Most importantly, the right finish shields your PCB against oxidation. Picture this: the critical copper traces on your board are exposed, and unprotected. Oxidation creeps in, compromising functionality. It’s grim, isn’t it? That’s where a surface finish steps in. Acting as a barrier, it wards off oxidation, enhancing your board’s lifespan. Your PCB, armored and robust, can now face harsh environments. Every PCB deserves such protection, and the correct surface finish offers precisely that.

 

Enhancing Solderability

Transitioning to another significant facet, enhancing solderability. Let’s decode this. A PCB without a surface finish is like a car without fuel; it’s not going anywhere. Surface finishes boost solderability, making your PCB more conductive. It’s simple: the better the solderability, the better the electronic connections. The result? A high-performing PCB. Plus, it’s a blessing for assemblers, making their job easy, and smooth. So, choose the right surface finish, enhance your PCB’s solderability, and gear up for unmatched performance. 

 

Prolonging Shelf Life

Lastly, the right surface finish prolongs your PCB’s shelf life. Think of it as a protective layer. This layer safeguards your PCB against wear and tear, maintaining its integrity. The result? Your PCB stays fresh, and usable, even after sitting on the shelf for a long. The importance of this cannot be overstressed. Why? Because a longer shelf life equals lesser wastage, saving you time, money, and resources. So, don’t just settle for any finish. Choose the right one. Your PCB deserves a long, healthy life. Let the correct surface finish make that happen. 

Types of PCB Surface Finishes

 

 

 

1. Hot Air Solder Leveling (HASL)

In the vast expanse of the electronics manufacturing industry, PCB surface finishes hold an essential role. They provide a solderable surface for component assembly while protecting the copper from oxidation. Among these surface finishes, Hot Air Solder Leveling (HASL) stands as one of the most common and efficient choices. This type of surface finish applies a molten tin-lead coating to a PCB via hot air knives. Let’s dive into the specifics of HASL, including its advantages, disadvantages, and common applications.

 

Pros

• Cost-effective: HASL is among the least expensive surface finishes.

• Widespread availability: Due to its popularity, HASL services are easy to find.

• Reworkable: Mistakes can be corrected and revised.

Cons

• Lead usage: For some applications, the use of lead might be restricted due to environmental regulations.

• Uneven surfaces: The application of HASL may result in uneven surfaces, problematic for smaller components.

• Thermal shock: PCBs, especially thinner ones, might suffer from thermal shock during the HASL process.

Use Cases

• General Electronics: HASL is suitable for general-purpose electronics where cost-effectiveness is vital.

• Prototyping: Its ease of rework makes HASL a perfect choice for prototypes, where changes are often needed.

• Non-fine pitch applications: HASL is suitable where surface planarity isn’t as critical, such as non-fine pitch applications.

 

2. Immersion Tin

Immersion Tin, also known as immersion tinimmersion tin plating or white tin, is a surface finish used in printed circuit boards (PCBs). It involves immersing the PCB in a chemical bath containing tin compounds, resulting in the deposition of a thin layer of tin onto the exposed copper surfaces. The immersion tin process is typically performed after undergoing PCB fabrication and before solder mask application.

 

Pros

• Excellent solderability: Immersion tin provides a flat, uniform surface that enables excellent solderability, particularly for fine-pitch components. 

• Cost-effective: Immersion tin is generally more affordable compared to other surface finishes like ENIG or Immersion Silver.

• Suitable for multiple reflows: Immersion tin can withstand multiple reflow soldering processes without significant degradation.

Cons

• Shelf life and storage conditions: Immersion tin has a limited shelf life compared to some other surface finishes. It is sensitive to oxidation, and if not stored properly, the tin layer can oxidize, affecting solderability.

• Reliability concerns: The immersion tin is not as durable as some other finishes. 

Use Cases

Immersion tin is widely used in various applications, including:

• Consumer electronics: It is commonly found in devices such as smartphones, tablets, and home appliances, where cost-effectiveness and fine-pitch component solderability are crucial.

• Communication equipment: The immersion tin is suitable for applications in telecommunications devices, routers, network switches, and other communication equipment.

• Automotive electronics: Certain automotive PCBs utilize immersion tin due to its cost-effectiveness and compatibility with reflow processes.

• Industrial and medical electronics: Immersion tin finds application in industrial control systems, medical devices, and equipment where reliable solderability is essential.

 

3. Immersion Silver

 

Immersion tin is an eco-friendly surface finish for PCBs that applies a thin tin layer to copper pads. Known for its uniform, flat surface, it’s well-suited for fine-pitch components and diverse assembly processes, such as surface mount technology. The process requires dipping the PCB into a tin salt solution, which reacts with the copper surface, forming a protective layer against oxidation and ensuring solderability.

Its compatibility with lead-free soldering and resistance to high temperatures make it a preferred choice. Besides, the uniform tin surface enhances accuracy in component placement, reducing defects. Immersion tin also strengthens solder joints due to the formation of intermetallic compounds with copper, thereby improving the PCB’s overall reliability.

 

Pros

• Flat surfaces are ideal for fine-pitch components, boosting assembly yields.

• Provides a robust and reliable solder joint.

• Offers middle-ground longevity compared to other finishes.

Cons

• Tin whiskers can develop, causing potential short circuits.

• Limited shelf life as oxidation occurs after a period.

• Not suitable for multiple reflow or assembly processes.

Use Cases

• This is mainly applied in the automotive industry due to its robustness.

• Used in telecommunication devices where fine pitch components are involved.

• Appropriate for products requiring medium-term protection from oxidation.

 

4. Electroless Nickel Immersion Gold (ENIG)

 

The exploration of electroless nickel immersion gold (ENIG) takes us deep into the heart of PCB finishing. A marvel of modern technology, ENIG is a technique that gives us reliable, top-quality circuit boards. Without the use of an electric current, a nickel layer is plated on the PCB, followed by a thin coating of gold. It’s a chemical reaction that plays out like an elegant ballet, ensuring precision and perfection.

 

Pros

• Superior Contact Resistance: ENIG promises excellent contact resistance, paving the way for smooth electronic flow.

• Robust Shelf Life: Its durability ensures a long shelf life, standing strong against the test of time.

• Ideal for PTH: The process is perfect for Plated Through Hole (PTH) technology.

Cons

• High Cost: The high quality comes with a price tag, making it an expensive choice.

• Black Pad Syndrome: This is a risk. It’s an uninvited guest that can cause a barrier in the connection between the gold and the nickel.

• Complex Process: It’s not a simple task. It requires strict control over the processing conditions.

Use Cases

• High-Density Interconnects ( HDI ): ENIG is the star of the HDI show, being commonly used due to its reliability.

• Fine Pitch Assemblies: With its good coplanarity, it is often chosen for fine pitch assemblies.

• Wire Bonding: In the field of wire bonding, the ENIG process makes its mark due to the gold’s intrinsic properties.

 

5. Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG)

 

Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG) stands as a three-layer coating applied on printed circuit boards (PCBs). An initial nickel layer to create a barrier, a palladium layer to aid wire bonding, and finally, an immersion gold layer for solderability.

 

Pros

• ENEPIG provides a universal surface finish, compatible with almost all types of assembly processes.

• It offers superior wire bonding and soldering capabilities.

• It has an excellent shelf-life and does not tarnish easily.

• ENEPIG is lead-free, making it an environmentally friendly choice.

Cons

• It is costlier than most other surface finishes due to its multi-layered process.

• The complex process requires skilled technicians and specialized machinery.

• The gold layer is extremely thin, making it susceptible to wear.

Use Cases

• It is widely used in the manufacture of complex PCBs where multiple assembly processes are involved.

• High-reliability applications like aerospace, medical, and military extensively use ENEPIG.

• In the realm of electronics manufacturing services (EMS), ENEPIG finds use due to its lead-free nature.

 

6. Organic Solderability Preservatives (OSP)

 

Emerging as a silent game-changer in the electronics industry, Organic Solderability Preservatives, abbreviated as OSP. They’re thin layers applied to bare copper for preserving solderability. Simplifying assembly processes, they offer an economical solution. Yet, they also invite a set of challenges. This write-up will delve into the ins and outs of OSP.

 

Pros

• Economical: Cost-effectiveness is a standout trait. OSP coats are less expensive than traditional methods.

• Simplified Assembly Process: OSP involves a simpler, smoother assembly process compared to other surface finishes.

• Flat Surfaces: OSP provides flatter surfaces for superior electrical performance.

Cons

• Limited Shelf Life: OSP layers have a shorter shelf life, demanding rigorous inventory control.

• Limited Handling: OSP-coated PCBs can’t withstand multiple reflows and extensive handling.

• Less Visual Inspection : It’s tough to ascertain the quality of OSP visually, leading to potential quality issues.

Use Cases

• High-Speed Circuit Boards: OSP’s flat surfaces make them an ideal choice for high-speed circuit boards.

• Fine-Pitch Technology: OSP coats are suitable for advanced technology like fine-pitch components due to their thinness.

• Surface Mount Assemblies: OSP is commonly used in surface mount assemblies where clean, flat surfaces are crucial.

 

7. Hard Gold Plating

 

The hard gold plating technique crafts a fine, grainy surface, and tougher layers by blending gold with another element, such as iron, nickel, or cobalt. Like above Gold fingers PCB.

 

Pros

• Unyielding Durability: Hard gold stands tall against the onslaught of time. It laughs in the face of corrosion and tarnish. Its high wear resistance offers years of service, making it a reliable ally.

• Excellent Conductivity: The golden conductor ensures your electrical signals take the most efficient route. A dependable steed, galloping through the circuits without a falter.

• Smooth Surface: The silky landscape of hard gold eliminates friction. Connectors slide home with elegant ease, ballroom dance in an electronic world.

• Aesthetic Appeal: There’s a charm to hard gold. It glows with an irresistible sheen, lending your board a touch of allure. It’s a beauty that’s more than skin deep.

Cons

• Thickness: The coat of hard gold is thin. It is but a sheet, leaving your copper bare if worn away.

• Selective Coverage: The hard gold finish is not all-encompassing. It chooses its territories wisely, usually connector points. The rest, it leaves bare.

• Complex Process: The creation of hard gold is a craft. It requires precision, a careful hand, and time. A complex ballet of chemicals and electrical currents.

Uses Cases

• Edge Connectors: Hard gold finds a home at edge connectors. It slides in, forming a bond, a connection that lasts.

• Keypads: Keypads, are the medium of man and machine. Hard gold embraces the constant touch, enduring the daily dialogues.

• Control Panels: Control panels, are the brain of a device. Hard gold weaves itself into the circuits, creating seamless pathways.

• Switches and Sliders: The versatile gold lends its service to switches and sliders, ensuring their operation is smooth and reliable.

 

8. Immersion Nickel Gold (IMG)

 

IMG is a surface finish, born from a two-step process. It starts with the deposition of nickel onto the copper surface. Then, a layer of gold follows. This finish aims to protect the copper from oxidation.

 

Pros

• High corrosion resistance, safeguarding your circuit boards.

• Good for fine-pitch components.

Cons

• Costly, due to the gold involved.

• Nickel corrosion might be an issue.

Use cases

• Works well for soldering.

• Suitable for applications demanding longevity, like in aerospace or medical devices.

 

9. Directly Plated Copper (DPC)

 

 

DPC involves the electrochemical deposition of copper directly onto the surface. This method is a part of the PCB manufacturing process.

 

Pros

• Good for thermal management.

• High electrical conductivity.

Cons

• Can have poor adhesion with some materials.

• Susceptible to corrosion if not protected.

Use cases

• Used in high-frequency applications.

• Effective in LED lighting systems, due to excellent thermal properties.

 

10. Electroless Nickel Electroless Palladium (ENEP)

 

 

ENEP is a process where nickel is deposited onto a surface, followed by palladium. Unlike other methods, this doesn’t involve electricity.

 

Pros

• High resistance to wear and corrosion.

• Good for fine-pitch applications.

Cons

• More costly than other finishes.

• This may be subject to the “black pad” phenomenon.

Use cases

• Ideal for high-reliability applications.

• Used in harsh environments like automotive and industrial electronics.

 

Comparison of Surface Finishes

 

Surface Finish Type Process Advantages Disadvantages

Hot Air Solder Leveling (HASL-Lead Free)

Uses molten solder and hot air knives.

Inexpensive, widely available, and good for hole plating.

Not suitable for fine-pitch components, can cause uneven surfaces.

Immersion Tin(ISn)

PCB is immersed in a tin bath.

Flat surfaces, good for press-fit pin insertion.

Potential for tin whiskers, sensitive to handling.

Immersion Silver(IAg)

PCB immersed in a silver bath.

Flat surfaces, good solderability.

Sensitive to handling, tarnishing, and limited shelf life.

Electroless Nickel Immersion Gold (ENIG)

Nickel is plated onto the PCB, followed by a layer of immersion gold.

Flat surfaces, good for fine pitch components, long shelf life.

Expensive, potential for black pad syndrome.

Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG)

Nickel is plated onto the PCB, followed by a layer of palladium and then immersion gold.

Excellent solderability and wire bonding capabilities.

Expensive, complex process.

Organic Solderability Preservatives (OSP)

A thin layer of organic material is placed over bare copper.

Inexpensive, flat surfaces.

Limited reworkability, sensitivity to handling, and limited shelf life.

Hard Gold Plating

A hard, durable gold layer is plated onto the PCB.

Durable, excellent conductivity, ideal for mating surfaces.

Expensive, and not suitable for soldering.

Immersion Nickel Gold (IMG)

Similar to ENIG but involves immersion of gold over nickel.

Good solderability, flat surfaces.

Expensive, potential for black pad syndrome.

Directly Plated Copper (DPC)

A layer of copper is plated directly onto the PCB.

Good for signal integrity, suitable for high frequencies.

More complex processes may require special handling.

Electroless Nickel Electroless Palladium (ENEP)

Similar to ENEPIG, but without the final immersion gold layer.

Good solderability and wire bonding capabilities.

Expensive, complex process.

 

Factors to Consider When Selecting a PCB Surface Finishes

 

Deciding on a Printed Circuit Board (PCB) surface finish is not to be taken lightly. It’s an intricate process. It demands a comprehensive understanding of your specific needs. Also, the environmental factors the PCB will face and the budget for the project. Let’s delve into some key considerations that will guide this decision.

1. Cost

Expense is often the first factor we consider. Remember, the cost isn’t solely about the upfront payment for the surface finish. Consider long-term implications too. For instance, HASL is an economical choice. Yet, it’s not suitable for high-density or fine-pitch components. ENIG might cost more initially but could save money in the long run by reducing manufacturing defects.

2. Application Requirements

Knowing how your PCB will be used is crucial. This guides the selection of an appropriate finish. For example, a PCB used in a device requiring high-frequency signals could benefit from Directly Plated Copper (DPC). This is due to its excellent signal integrity.

3. Function of the PCB

The function of the PCB is equally important. Is your PCB part of a device that needs strong conductivity? You might consider Hard Gold Plating. This finish boasts excellent conductivity. Yet, it’s not suitable for soldering. Always match the finish to the function.

4. Environment

Consider the environment where your PCB will operate. An outdoor environment with high humidity might require a robust finish like ENIG. It offers long shelf life and resists corrosion.

5. Shelf Life

If your PCBs are stored for extended periods, surface finish matters. Some finishes, like OSP, have a limited shelf life. Conversely, ENIG offers a longer shelf life.

6. Reliability Requirements

In applications where reliability is paramount, the choice of surface finish is vital. For high-reliability applications, consider ENEPIG or ENEP. These finishes offer excellent solderability and wire bonding capabilities.

7. Working with Your PCB Manufacturer

Finally, involve your PCB manufacturer in the decision-making process. They have the expertise to help navigate these complex considerations. MorePCB as one professional PCB manufacturer is able to supply you with correct suggestions for all your PCBs. 

Conclusion

When choosing a surface finish for your PCB, it is crucial to consider the available options while taking into account performance requirements and material costs. Let’s consider an example: if cost is a primary concern and RoHS compliance is not required, Tin-Lead HASL might initially seem like a good choice. However, it’s important to note that this finish is not suitable for RoHS-compliant products. In that case, you could consider lead-free HASL. However, if your design includes fine-pitch components, HASL-LF may not provide a perfectly flat surface. 

In situations where both RoHS compliance and fine pitch components are involved, you’ll need to opt for a flat, lead-free finish like Immersion Silver or ENIG. Keep in mind that using these finishes may require the use of more expensive high-temperature laminate.

If you’re unsure about the most appropriate surface finishes for your project, it’s advisable to consult with MorePCB before making a final decision. Our expertise will ensure that the chosen combination of surface finish and material yields a cost-effective design with optimal performance.

 

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Contact MorePCB today and experience top-quality manufacturing,

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Contact us and request a quote and start your next project!

1. To prevent oxidation at the surface of copper
2. To ensure ease in the soldering

The surface of a PCB has the utmost importance. If the PCB has no surface finish, the copper on the surface will oxidize quickly. The oxidation will deteriorate the copper and affect the electrical performance of the PCB. At last, the PCB will be of no use. Thus, it’s important to have a surface finish on the PCB to give a long life to the exposed copper. Moreover, it offers a surface to solder the components easily.

There are different types of surface finishes, and you need to understand them before you select anyone. They have different pros and cons, and you must select the best one for your project. Today, we will discuss different types of surface finishes in detail. So, stay with us.

The types of surface finish are,

1) Hot Air Solder Level (HASL)

HASL is the most common and inexpensive type of surface finish. The process of HASL is quite simple; the bare PCB board is dipped into the molten solder. The solder covers the area over the copper and removes it from the tank. After that, the surface of the PCB is leveled using hot-air knives. It offers an excellent surface for soldering.

HASL is excellent for large components and SMTs. But if the SMT is smaller, it will not work as desired. It’s not suitable for Fine Pitch Technology (FTP). Furthermore, the processing temperature is in the range of 260-270˚C, which is quite high. Due to high thermal stress, there are chances of defects in the board.

Keep in mind that it contains lead. It’s usually dipped in Tin-Lead alloy, and the lead is a carcinogen. Thus, it’s not RoHS compliant. If you need a lead-free circuit board, then it’s not for you.

Hot Air Solder Level (HASL) PCB Double-sided Hot Air Solder Level (HASL)PCB Hot Air Solder Level (HASL) Machine

2) Lead-free HASL (LF HASL)

Lead-free HASL is similar to HASL, but it does not contain lead. Thus, it can be used for many purposes without any worries. It’s according to RoHS standards.

As far as the functions, pros, and cons are concerned, they are similar to HASL.

FR4 4 Layer Lead-Free HASL PCB Board FR4 4 Layer LF-HASL PCB Circuit Board FR4 Black Oil 4-layer Lead-free HASL PCB Circuit Board Automatic Lead-free Spray Tin Machine

3) Plated Gold

Plated Gold surface finish is also known as Hard Gold surface finish. It’s an expensive surface finish that uses a layer of gold on the PCB. It’s done through electroplating, and a hard layer of gold is attached to the surface of the copper. The adhesion between the PCB and the layer is firm, which increases the board’s durability. Since gold is an excellent conductor, it’s excellent for electrical performance. Moreover, its oxidation resistance is commendable. The surface finish is excellent for the PCB area, where high wear and tear is expected. It can last for a long time.

The problems associated with this type of surface finish are price and extra processing. It isn’t easy to process. Due to the high price, it’s rarely used, but it’s an excellent surface finish that can last longer. Moreover, the solderability of hard gold is poor.

FR4 ARLON Double Layer Gold-plated High-Frequency PCB Board

4) Organic Solderability Preservatives (OSP)

OSP is a process for the surface finish of copper foil of printed circuit board, which meets the requirements of the RoHS directive. OSP is the abbreviation of organic solvency preserves.

OSP has the characteristics of oxidation resistance, heat shock resistance, and moisture resistance. It protects the copper surface from further rusting (oxidation or vulcanization, etc.) in a typical environment. However, in the high-temperature welding process, the protective film must be easily and quickly removed by the flux so that the exposed clean copper surface can be immediately combined with the molten solder to form a strong solder joint quickly.

In this type of surface finish, a water-based coating protects the copper until it’s soldered. It prevents the oxidation of copper and increases its life. But remember that it’s only on an organic surface coating that is not durable enough; it’s quite sensitive. It has a short life span.

OSP is an inexpensive surface finish that can save money. It requires less time, and the process is also straightforward. If there are holes in the PCB, their size is not affected by the coating. It offers an excellent flat surface, and it’s environmentally friendly.

It can be used in areas where the PCB is handled carefully, and there are fewer chances of wear and tear.

OSP PCB Board OSP PCB 1.2mm 6 Layer OSP PCB Circuit Board

Learn more about What PCB OSP Surface Finish is.

5) Immersion Silver

Immersion silver is a flat surface finish that has a reasonable cost. Silver plating is done over the copper surface to protect it from oxidation in this type. The layer of silver is quite thin, but it offers excellent conductivity. It’s good for Fine Pitch Technology (FTP) because the layer is very thin, and it does not affect the size of the holes.

The problem with this type of surface finish is tarnishing. The silver plating tarnishes when exposed to air. Therefore, it’s packed as soon as possible in anti-tarnish packaging to prevent tarnishing. It is very sensitive, so you need to solder the board after taking it out of the package.

The life of immersion silver is moderate. It has a low cost, and it’s according to RoHS standards.

The immersion silver process is between OSP and electroless nickel/immersion gold. The process is relatively fast and straightforward; even if the PCB is exposed to heat, humidity, and pollution, the silver can still maintain good solderability, but it will lose its luster. Immersion silver does not have the good physical strength of electroless nickel/immersion gold because there is no nickel under the silver layer.

FR4 4-layer Immersed Silver Circuit Board

6) Immersion Tin

Immersion tin is a lead-free surface finish, which is excellent for small components. It is very thin and flat, perfect for Fine Pitch Technology (FTP).

The cost of this surface finish is reasonable, but it has some drawbacks. Tin can react with the copper on the PCB, which reduces the shelf life. Moreover, it’s also prone to tarnish, so it must be used as soon as possible. It’s very sensitive. After a few months, you will notice tin whiskers on the PCB.

Since all current solders are based on tin, the tin layer can be matched with any solder.

Immersion Tin PCB

7) Electroless Nickel Immersion Gold (ENIG)

ENIG is the most used type of surface finish because of its features and RoHS compliance. In simple words, there is a thick layer of nickel over copper and a thin layer of gold over the nickel layer. The components are soldered on the nickel, and the gold coating protects the nickel until it’s not soldered.

ENIG has a long shelf life; it is durable enough. But it’s expensive due to using two layers, especially gold. It has all the features, including a flat surface and a thin finish, to work with smaller components.

The only problem with ENIG is black pad syndrome, which is the building of phosphorus between the gold and the nickel layer.

6 Layer Electroless Nickel Immersion Gold (ENIG) PCB 4 Layer Electroless Nickel Immersion Gold (ENIG) Half-Cut/Castellated Holes/Half Hole PCBC

Learn what PCB Immersion Gold ENIG Surface Finish is.

8) Electrolytic Nickel Gold (ENEG)

ENEG is also an expensive lead-free finish. It contains a layer of hard gold or soft gold over electrolytic nickel. Gold prevents the oxidation of copper. Gold plating in ENEG has excellent adhesion; therefore, electrolytic nickel gold lasts for a long time and never rusts.

The surface of ENEG is flat, where you can easily work with small components. It has excellent conductivity and great performance.

Electrolytic Nickel Gold (ENEG) PCB

9) Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG)

ENEPIG is the best surface finish that resists corrosion and reaction with air. It has a longer shelf life, making it the best.

It is a three-layered surface finish that contains nickel, palladium, and gold. All these materials perform together to offer long life. Unlike ENIG, there is no risk of black pad syndrome in ENEPIG.

It’s RoHS-compliant, and there is no lead in it. The problems with ENEPIG are high cost and complex processing.

ENEPIG PCB ENEPIG PCB Board ENEPIG Surface Finished PCB

10) Mixed Surface Finish

A mixed surface finish is a mixture of more than two surface finishes to get the optimum performance. A single PCB has more than one finish surface finish as required. The most commonly used mixed surface finishes are ENIG +OSP, ENEG + ENIG, ENEG + HASL, and ENIG+ HASL.

FR4 Double-sided Immersion Gold + Gold-plated PCB Circuit Board FR4 Double-sided Immersion Gold + Gold-plated PCB

Final Thoughts

There are various types of surface finishes with distinct properties, pros, and cons. You need to select the best one according to your requirements. You need to develop a surface finish that can complete all your requirements at the minimum cost. We have explained all types of surface finish in detail. We hope you have a complete idea of the different types of surface finishes.

Surface Finish at JHYPCB

JHYPCB is a well-known PCB manufacturer in China. We have been providing high-quality PCB for more than a decade. We have strict quality control, which is compliant with RoHS and ISO 9001:2008. For the ease of our customers, we offer all types of surface finishes. You can get the desired PCB, prototype, or PCBA at a reasonable cost. We can handle small-medium volume PCB manufacturing and fabrication. For more information, feel free to contact us.

Advanced Learning:

 

Introduction

 

PCB surface finishes include two major categories: organic and metallic.

When comparing these two categories and considering all available options, it becomes clear that each has its benefits and drawbacks.

The choice of the most suitable finish is typically determined by factors such as the intended application, the assembly process, and the PCB design itself.

If you’re unsure about the most appropriate surface finish for your project, it’s advisable to consult with MorePCB before making a final decision. Our expertise will ensure that the chosen combination of surface finish and material yields a cost-effective design with optimal performance.

This article will help readers to have a brief understanding of PCB surfaces, their types use cases, etc. 

 

What is PCB Surface Finish?

A printed circuit board’s (PCB) copper traces and pads receive a final coating or treatment known as a PCB surface finish. It is a crucial stage in the manufacture of PCBs and serves a variety of functions, including protection, solderability, and general reliability.

To avoid oxidation, which can impair the PCB’s electrical conductivity and solderability, the surface finish is applied to the exposed copper surfaces. Between the copper and the environment, it serves as a barrier. As a result, it guards against corrosion and guarantees the PCB’s long-term functioning.

Additionally, the surface finish plays a crucial role in facilitating soldering during the assembly process. It provides a flat, solderable surface on the copper pads, by enabling the secure attachment of electronic components to the PCB. The choice of surface finish affects the wetting and adhesion properties of the solder. Therefore it impacts the quality of solder joints and the overall reliability of the PCB assembly.

There are several types of surface finishes commonly used in PCB manufacturing. These include Hot Air Solder Leveling (HASL), Electroless Nickel Immersion Gold (ENIG), Organic Solderability Preservative (OSP), Immersion Tin, and Immersion Silver. Each surface finish has its advantages, limitations, and suitability for specific applications.

The selection of the appropriate surface finish depends on various factors, including the desired electrical performance, budget, assembly processes, component types, and environmental conditions. Manufacturers carefully consider these factors to ensure the best possible surface finish is chosen to meet the specific requirements of the PCB design.

 

The Importance of Choosing the Right PCB Surface Finishes

 

Protection Against Oxidation

Selecting the correct Printed Circuit Board (PCB) surface finish is crucial. It’s not just aesthetics; it’s about practicality. Most importantly, the right finish shields your PCB against oxidation. Picture this: the critical copper traces on your board are exposed, and unprotected. Oxidation creeps in, compromising functionality. It’s grim, isn’t it? That’s where a surface finish steps in. Acting as a barrier, it wards off oxidation, enhancing your board’s lifespan. Your PCB, armored and robust, can now face harsh environments. Every PCB deserves such protection, and the correct surface finish offers precisely that.

 

Enhancing Solderability

Transitioning to another significant facet, enhancing solderability. Let’s decode this. A PCB without a surface finish is like a car without fuel; it’s not going anywhere. Surface finishes boost solderability, making your PCB more conductive. It’s simple: the better the solderability, the better the electronic connections. The result? A high-performing PCB. Plus, it’s a blessing for assemblers, making their job easy, and smooth. So, choose the right surface finish, enhance your PCB’s solderability, and gear up for unmatched performance. 

 

Prolonging Shelf Life

Lastly, the right surface finish prolongs your PCB’s shelf life. Think of it as a protective layer. This layer safeguards your PCB against wear and tear, maintaining its integrity. The result? Your PCB stays fresh, and usable, even after sitting on the shelf for a long. The importance of this cannot be overstressed. Why? Because a longer shelf life equals lesser wastage, saving you time, money, and resources. So, don’t just settle for any finish. Choose the right one. Your PCB deserves a long, healthy life. Let the correct surface finish make that happen. 

Types of PCB Surface Finishes

 

 

 

1. Hot Air Solder Leveling (HASL)

In the vast expanse of the electronics manufacturing industry, PCB surface finishes hold an essential role. They provide a solderable surface for component assembly while protecting the copper from oxidation. Among these surface finishes, Hot Air Solder Leveling (HASL) stands as one of the most common and efficient choices. This type of surface finish applies a molten tin-lead coating to a PCB via hot air knives. Let’s dive into the specifics of HASL, including its advantages, disadvantages, and common applications.

 

Pros

• Cost-effective: HASL is among the least expensive surface finishes.

• Widespread availability: Due to its popularity, HASL services are easy to find.

• Reworkable: Mistakes can be corrected and revised.

Cons

• Lead usage: For some applications, the use of lead might be restricted due to environmental regulations.

• Uneven surfaces: The application of HASL may result in uneven surfaces, problematic for smaller components.

• Thermal shock: PCBs, especially thinner ones, might suffer from thermal shock during the HASL process.

Use Cases

• General Electronics: HASL is suitable for general-purpose electronics where cost-effectiveness is vital.

• Prototyping: Its ease of rework makes HASL a perfect choice for prototypes, where changes are often needed.

• Non-fine pitch applications: HASL is suitable where surface planarity isn’t as critical, such as non-fine pitch applications.

 

2. Immersion Tin

Immersion Tin, also known as immersion tin plating or white tin, is a surface finish used in printed circuit boards (PCBs). It involves immersing the PCB in a chemical bath containing tin compounds, resulting in the deposition of a thin layer of tin onto the exposed copper surfaces. The immersion tin process is typically performed after undergoing PCB fabrication and before solder mask application.

 

Pros

• Excellent solderability: Immersion tin provides a flat, uniform surface that enables excellent solderability, particularly for fine-pitch components. 

• Cost-effective: Immersion tin is generally more affordable compared to other surface finishes like ENIG or Immersion Silver.

• Suitable for multiple reflows: Immersion tin can withstand multiple reflow soldering processes without significant degradation.

Cons

• Shelf life and storage conditions: Immersion tin has a limited shelf life compared to some other surface finishes. It is sensitive to oxidation, and if not stored properly, the tin layer can oxidize, affecting solderability.

• Reliability concerns: The immersion tin is not as durable as some other finishes. 

Use Cases

Immersion tin is widely used in various applications, including:

• Consumer electronics: It is commonly found in devices such as smartphones, tablets, and home appliances, where cost-effectiveness and fine-pitch component solderability are crucial.

• Communication equipment: The immersion tin is suitable for applications in telecommunications devices, routers, network switches, and other communication equipment.

• Automotive electronics: Certain automotive PCBs utilize immersion tin due to its cost-effectiveness and compatibility with reflow processes.

• Industrial and medical electronics: Immersion tin finds application in industrial control systems, medical devices, and equipment where reliable solderability is essential.

 

3. Immersion Silver

 

Immersion tin is an eco-friendly surface finish for PCBs that applies a thin tin layer to copper pads. Known for its uniform, flat surface, it’s well-suited for fine-pitch components and diverse assembly processes, such as surface mount technology. The process requires dipping the PCB into a tin salt solution, which reacts with the copper surface, forming a protective layer against oxidation and ensuring solderability.

Its compatibility with lead-free soldering and resistance to high temperatures make it a preferred choice. Besides, the uniform tin surface enhances accuracy in component placement, reducing defects. Immersion tin also strengthens solder joints due to the formation of intermetallic compounds with copper, thereby improving the PCB’s overall reliability.

 

Pros

• Flat surfaces are ideal for fine-pitch components, boosting assembly yields.

• Provides a robust and reliable solder joint.

• Offers middle-ground longevity compared to other finishes.

Cons

• Tin whiskers can develop, causing potential short circuits.

• Limited shelf life as oxidation occurs after a period.

• Not suitable for multiple reflow or assembly processes.

Use Cases

• This is mainly applied in the automotive industry due to its robustness.

• Used in telecommunication devices where fine pitch components are involved.

• Appropriate for products requiring medium-term protection from oxidation.

 

4. Electroless Nickel Immersion Gold (ENIG)

 

The exploration of electroless nickel immersion gold (ENIG) takes us deep into the heart of PCB finishing. A marvel of modern technology, ENIG is a technique that gives us reliable, top-quality circuit boards. Without the use of an electric current, a nickel layer is plated on the PCB, followed by a thin coating of gold. It’s a chemical reaction that plays out like an elegant ballet, ensuring precision and perfection.

 

Pros

• Superior Contact Resistance: ENIG promises excellent contact resistance, paving the way for smooth electronic flow.

• Robust Shelf Life: Its durability ensures a long shelf life, standing strong against the test of time.

• Ideal for PTH: The process is perfect for Plated Through Hole (PTH) technology.

Cons

• High Cost: The high quality comes with a price tag, making it an expensive choice.

• Black Pad Syndrome: This is a risk. It’s an uninvited guest that can cause a barrier in the connection between the gold and the nickel.

• Complex Process: It’s not a simple task. It requires strict control over the processing conditions.

Use Cases

• High-Density Interconnects ( HDI ): ENIG is the star of the HDI show, being commonly used due to its reliability.

• Fine Pitch Assemblies: With its good coplanarity, it is often chosen for fine pitch assemblies.

• Wire Bonding: In the field of wire bonding, the ENIG process makes its mark due to the gold’s intrinsic properties.

 

5. Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG)

 

Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG) stands as a three-layer coating applied on printed circuit boards (PCBs). An initial nickel layer to create a barrier, a palladium layer to aid wire bonding, and finally, an immersion gold layer for solderability.

 

Pros

• ENEPIG provides a universal surface finish, compatible with almost all types of assembly processes.

• It offers superior wire bonding and soldering capabilities.

• It has an excellent shelf-life and does not tarnish easily.

• ENEPIG is lead-free, making it an environmentally friendly choice.

Cons

• It is costlier than most other surface finishes due to its multi-layered process.

• The complex process requires skilled technicians and specialized machinery.

• The gold layer is extremely thin, making it susceptible to wear.

Use Cases

• It is widely used in the manufacture of complex PCBs where multiple assembly processes are involved.

• High-reliability applications like aerospace, medical, and military extensively use ENEPIG.

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• In the realm of electronics manufacturing services (EMS), ENEPIG finds use due to its lead-free nature.

 

6. Organic Solderability Preservatives (OSP)

 

Emerging as a silent game-changer in the electronics industry, Organic Solderability Preservatives, abbreviated as OSP. They’re thin layers applied to bare copper for preserving solderability. Simplifying assembly processes, they offer an economical solution. Yet, they also invite a set of challenges. This write-up will delve into the ins and outs of OSP.

 

Pros

• Economical: Cost-effectiveness is a standout trait. OSP coats are less expensive than traditional methods.

• Simplified Assembly Process: OSP involves a simpler, smoother assembly process compared to other surface finishes.

• Flat Surfaces: OSP provides flatter surfaces for superior electrical performance.

Cons

• Limited Shelf Life: OSP layers have a shorter shelf life, demanding rigorous inventory control.

• Limited Handling: OSP-coated PCBs can’t withstand multiple reflows and extensive handling.

• Less Visual Inspection : It’s tough to ascertain the quality of OSP visually, leading to potential quality issues.

Use Cases

• High-Speed Circuit Boards: OSP’s flat surfaces make them an ideal choice for high-speed circuit boards.

• Fine-Pitch Technology: OSP coats are suitable for advanced technology like fine-pitch components due to their thinness.

• Surface Mount Assemblies: OSP is commonly used in surface mount assemblies where clean, flat surfaces are crucial.

 

7. Hard Gold Plating

 

The hard gold plating technique crafts a fine, grainy surface, and tougher layers by blending gold with another element, such as iron, nickel, or cobalt. Like above Gold fingers PCB.

 

Pros

• Unyielding Durability: Hard gold stands tall against the onslaught of time. It laughs in the face of corrosion and tarnish. Its high wear resistance offers years of service, making it a reliable ally.

• Excellent Conductivity: The golden conductor ensures your electrical signals take the most efficient route. A dependable steed, galloping through the circuits without a falter.

• Smooth Surface: The silky landscape of hard gold eliminates friction. Connectors slide home with elegant ease, ballroom dance in an electronic world.

• Aesthetic Appeal: There’s a charm to hard gold. It glows with an irresistible sheen, lending your board a touch of allure. It’s a beauty that’s more than skin deep.

Cons

• Thickness: The coat of hard gold is thin. It is but a sheet, leaving your copper bare if worn away.

• Selective Coverage: The hard gold finish is not all-encompassing. It chooses its territories wisely, usually connector points. The rest, it leaves bare.

• Complex Process: The creation of hard gold is a craft. It requires precision, a careful hand, and time. A complex ballet of chemicals and electrical currents.

Uses Cases

• Edge Connectors: Hard gold finds a home at edge connectors. It slides in, forming a bond, a connection that lasts.

• Keypads: Keypads, are the medium of man and machine. Hard gold embraces the constant touch, enduring the daily dialogues.

• Control Panels: Control panels, are the brain of a device. Hard gold weaves itself into the circuits, creating seamless pathways.

• Switches and Sliders: The versatile gold lends its service to switches and sliders, ensuring their operation is smooth and reliable.

 

8. Immersion Nickel Gold (IMG)

 

IMG is a surface finish, born from a two-step process. It starts with the deposition of nickel onto the copper surface. Then, a layer of gold follows. This finish aims to protect the copper from oxidation.

 

Pros

• High corrosion resistance, safeguarding your circuit boards.

• Good for fine-pitch components.

Cons

• Costly, due to the gold involved.

• Nickel corrosion might be an issue.

Use cases

• Works well for soldering.

• Suitable for applications demanding longevity, like in aerospace or medical devices.

 

9. Directly Plated Copper (DPC)

 

 

DPC involves the electrochemical deposition of copper directly onto the surface. This method is a part of the PCB manufacturing process.

 

Pros

• Good for thermal management.

• High electrical conductivity.

Cons

• Can have poor adhesion with some materials.

• Susceptible to corrosion if not protected.

Use cases

• Used in high-frequency applications.

• Effective in LED lighting systems, due to excellent thermal properties.

 

10. Electroless Nickel Electroless Palladium (ENEP)

 

 

ENEP is a process where nickel is deposited onto a surface, followed by palladium. Unlike other methods, this doesn’t involve electricity.

 

Pros

• High resistance to wear and corrosion.

• Good for fine-pitch applications.

Cons

• More costly than other finishes.

• This may be subject to the “black pad” phenomenon.

Use cases

• Ideal for high-reliability applications.

• Used in harsh environments like automotive and industrial electronics.

 

Comparison of Surface Finishes

 

Surface Finish Type Process Advantages Disadvantages

Hot Air Solder Leveling (HASL-Lead Free)

Uses molten solder and hot air knives.

Inexpensive, widely available, and good for hole plating.

Not suitable for fine-pitch components, can cause uneven surfaces.

Immersion Tin(ISn)

PCB is immersed in a tin bath.

Flat surfaces, good for press-fit pin insertion.

Potential for tin whiskers, sensitive to handling.

Immersion Silver(IAg)

PCB immersed in a silver bath.

Flat surfaces, good solderability.

Sensitive to handling, tarnishing, and limited shelf life.

Electroless Nickel Immersion Gold (ENIG)

Nickel is plated onto the PCB, followed by a layer of immersion gold.

Flat surfaces, good for fine pitch components, long shelf life.

Expensive, potential for black pad syndrome.

Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG)

Nickel is plated onto the PCB, followed by a layer of palladium and then immersion gold.

Excellent solderability and wire bonding capabilities.

Expensive, complex process.

Organic Solderability Preservatives (OSP)

A thin layer of organic material is placed over bare copper.

Inexpensive, flat surfaces.

Limited reworkability, sensitivity to handling, and limited shelf life.

Hard Gold Plating

A hard, durable gold layer is plated onto the PCB.

Durable, excellent conductivity, ideal for mating surfaces.

Expensive, and not suitable for soldering.

Immersion Nickel Gold (IMG)

Similar to ENIG but involves immersion of gold over nickel.

Good solderability, flat surfaces.

Expensive, potential for black pad syndrome.

Directly Plated Copper (DPC)

A layer of copper is plated directly onto the PCB.

Good for signal integrity, suitable for high frequencies.

More complex processes may require special handling.

Electroless Nickel Electroless Palladium (ENEP)

Similar to ENEPIG, but without the final immersion gold layer.

Good solderability and wire bonding capabilities.

Expensive, complex process.

 

Factors to Consider When Selecting a PCB Surface Finishes

 

Deciding on a Printed Circuit Board (PCB) surface finish is not to be taken lightly. It’s an intricate process. It demands a comprehensive understanding of your specific needs. Also, the environmental factors the PCB will face and the budget for the project. Let’s delve into some key considerations that will guide this decision.

1. Cost

Expense is often the first factor we consider. Remember, the cost isn’t solely about the upfront payment for the surface finish. Consider long-term implications too. For instance, HASL is an economical choice. Yet, it’s not suitable for high-density or fine-pitch components. ENIG might cost more initially but could save money in the long run by reducing manufacturing defects.

2. Application Requirements

Knowing how your PCB will be used is crucial. This guides the selection of an appropriate finish. For example, a PCB used in a device requiring high-frequency signals could benefit from Directly Plated Copper (DPC). This is due to its excellent signal integrity.

3. Function of the PCB

The function of the PCB is equally important. Is your PCB part of a device that needs strong conductivity? You might consider Hard Gold Plating. This finish boasts excellent conductivity. Yet, it’s not suitable for soldering. Always match the finish to the function.

4. Environment

Consider the environment where your PCB will operate. An outdoor environment with high humidity might require a robust finish like ENIG. It offers long shelf life and resists corrosion.

5. Shelf Life

If your PCBs are stored for extended periods, surface finish matters. Some finishes, like OSP, have a limited shelf life. Conversely, ENIG offers a longer shelf life.

6. Reliability Requirements

In applications where reliability is paramount, the choice of surface finish is vital. For high-reliability applications, consider ENEPIG or ENEP. These finishes offer excellent solderability and wire bonding capabilities.

7. Working with Your PCB Manufacturer

Finally, involve your PCB manufacturer in the decision-making process. They have the expertise to help navigate these complex considerations. MorePCB as one professional PCB manufacturer is able to supply you with correct suggestions for all your PCBs. 

Conclusion

When choosing a surface finish for your PCB, it is crucial to consider the available options while taking into account performance requirements and material costs. Let’s consider an example: if cost is a primary concern and RoHS compliance is not required, Tin-Lead HASL might initially seem like a good choice. However, it’s important to note that this finish is not suitable for RoHS-compliant products. In that case, you could consider lead-free HASL. However, if your design includes fine-pitch components, HASL-LF may not provide a perfectly flat surface. 

In situations where both RoHS compliance and fine pitch components are involved, you’ll need to opt for a flat, lead-free finish like Immersion Silver or ENIG. Keep in mind that using these finishes may require the use of more expensive high-temperature laminate.

If you’re unsure about the most appropriate surface finishes for your project, it’s advisable to consult with MorePCB before making a final decision. Our expertise will ensure that the chosen combination of surface finish and material yields a cost-effective design with optimal performance.

 

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