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PCB/PCBA knowledge
PCB-surface-finish-what-are-the-types-and-how-to-distinguish

In order to guarantee proper operation, the PCB surface finish must be thought about during both the design and manufacturing processes of electronic products. The electrical performance, reliability, and lifespan of an electronic component are all affected by the PCB surface finish. If you’re worried about PCB surface finish, we have the answers you need.

Table of Contents

What is a PCB surface finish?

The substance that is used to coat the copper traces of a printed circuit board is referred to as a “PCB surface finish.” This coating is done to reduce oxidation and to increase solderability. The objective of this component is to protect the circuit board from dirt and moisture while also maintaining a consistently low contact resistance over the board’s lifetime. PCB surface treatments can come in a wide variety, including hot air solder levelling, electroless nickel immersion gold, immersion silver, and organic solderability.

Why PCB surface finish is important?

Why-PCB-surface-finish-is-important

PCB surface finish is important because if the printed circuit board (PCB) has not been adequately finished, it is more susceptible to damage from moisture and contaminants, which can result in failed connections and poor performance. In addition to all of that, it helps to improve the solderability of the printed circuit board while simultaneously reducing current leakage, all of which lead to a higher level of reliability and efficiency.

What are the types of PCB surface finishes?

Hot Air Solder Leveling (HASL)

1.1 What is Hot Air Solder Leveling?
Printed circuit boards can be given a smooth, solderable finish with the help of a surface-mount technology procedure called hot air solder levelling (HASL). First, the entire printed circuit board is heated with a hot air nozzle. The solder melts during this heating process and is then dispersed uniformly across the board. Solder is solidified and correctly adhered to the board’s surface by cooling it in an oven after it has been heated.

1.2 Advantages and disadvantages
The use of hot air solder levelling has a number of important benefits (HASL).
• HASL can assist in the removal of cold solder connections, bridging, and surface finishes, and it is both cost-effective and efficient.
• HASL ensures that the solder thickness is uniform and that the coverage is consistent on both sides of printed circuit boards.
• HASL makes a material more resistant to the effects of thermal shock and moisture, it can be applied to printed circuit boards in order to decrease corrosion, which in turn boosts the boards’ performance and makes them more reliable.

When it comes to solder levelling, employing hot air presents a number of key challenges that need to be overcome.
• It’s possible that assembly yields will decrease because of misaligned components and inadequate wetting caused by hot air solder levelling.
• In addition, due to the tremendous heat that is generated, the process of hot air solder levelling has the potential to cause damage to sensitive components and potentially physically bend printed circuit boards.

Lead-Free HASL

HASL

1.1 What is Lead-Free HASL?
Lead-Free HASL is a technique for completing printed circuit boards that makes use of lead-free solder rather than the more common tin-lead alloy. This technique is also known as “Lead-Free HASL.” Lead-free HASL is a dependable process that offers protection against corrosion as well as electrical shorts. Lead-free HASL is a highly desired commodity in the printed circuit board industry because it satisfies the RoHS (Restriction of Hazardous Substances) compliance standards for lead-free solder. RoHS stands for the Restriction of Hazardous Substances.

1.2 Advantages and disadvantages
Lead-free HASL has various benefits.
• In addition to lowering lead concentrations in landfills, air, and water, lead-free HASL also benefits human health. The workers benefit from lead-free HASL as well because they do not need to wear protective gear like masks and gloves.
• On top of that, lead-free HASL has superior adhesion and solderability compared to its lead-containing counterpart.

Lead-free HASL is not without its drawbacks.
• Due to potential production cost increases brought on by lead-free compliance, lead-free HASL may be more expensive than alternative finishes.
• Lead-free HASL also requires more precise temperature control during the process and might result in surface flaws if not controlled properly, making it more challenging to manage.

Organic Solderability Preservative (OSP)

1.1 What is OSP?
Organic Solderability Preservative, often known as OSP, is a coating that is applied to electronic components in order to protect them from oxidation while they are being stored and handled before being soldered. The application of OSP is accomplished through the process of electroless copper plating, which entails the deposition of a very thin coating of copper onto the surface of the component. This procedure creates a barrier that stops the components from oxidising, but it does not make it difficult to solder them later on when they are ready to be assembled.

1.2 Advantages and disadvantages
Organic Solderability Preservative has many benefits (OSP).
• Because it is non-toxic and free of dangerous compounds, OSP has a minimal effect on the environment.
• OSP also helps to prevent components from oxidation and other forms of corrosion thanks to its corrosion-resistant qualities.
• OSP also has the ability to provide excellent adhesion to all metals, including copper, silver, and gold.

The use of organic solderability preservative (OSP) isn’t without its downsides.
• The performance of OSP coatings can degrade due to exposure to environmental risks like humidity, temperature, and air pollution. This is often a major issue in densely inhabited areas or places with a significant concentration of industry. And abrasion can wear away OSP coatings, revealing the metal underneath.

Immersion Silver (IAg)

1.1 What is Immersion Silver?
Electronic components can have a layer of silver electroplated onto their exteriors via a process called “immersion silver.” Electronic components are protected from corrosion and short circuits thanks to the silver layer, which also works as a barrier against oxidation. Excellent electrical conductivity, solderability, and thermal stability may all be achieved through the use of the immersion silver processing method, which is also dependable.

1.2 Advantages and disadvantages
Using Immersion Silver has a number of benefits.
• Immersion silver has superior solderability, high temperature performance, and contact dependability. It’s perfect for use in electronics because it won’t rust or corrode.
• Immersion silver is an excellent alternative for those who want to lessen their negative effects on the environment because it is both non-conductive and environmentally friendly.

Immersion Tin (ISn)

immersion-tin

1.1 What is Immersion Tin?
A form of electroplating known as immersion tin involves applying a very thin layer of tin to the surface of an object in order to give it a metallic appearance. Immersion tin plating is a process that is frequently utilised in industries such as electronics and aerospace, where it is utilised to produce a robust and corrosion-resistant protective coating on components. In addition to this, it offers a surface that can be soldered to, which facilitates subsequent assembly and serves to prevent electrical arcing in electrical components.

1.2 Advantages and disadvantages
Immersion tin has many benefits.
• Immersion tin produces a uniformly shiny surface that is corrosion-resistant, highly solderable, delivers reliable contacts, and needs just minimal upkeep.
• As an added bonus, it saves time and money because it doesn’t need to be pre-plated or fluxed before being used in industrial settings. The recycling potential of the bath chemistry used in immersion tin plating means that it has a low impact on the environment.

While Immersion Tin has several advantages, it also has a few drawbacks.
• Solder joints can fail due to the production of intermetallic compounds when tin is immersed in water. This brittleness is the result of the intermetallic compounds formed when tin reacts with copper, nickel, and other metals.
• In addition, printed circuit boards’ surface topographical flaws might cause Immersion Tin to be non-uniform.

Electroless Nickel Immersion Gold (ENIG)

1.1 What is ENIG surface finish?
The cutting-edge plating technology known as electroless nickel immersion gold (ENIG) is used to apply a uniform coating of nickel that is resistant to corrosion. Following this step, a layer of gold is added to prevent oxidation and maintain the surface polish. The precision of ENIG has found widespread application in fields as diverse as medicine and aerospace. Because of its low contact resistance and great dependability, this coating is perfect for high-density interconnects (HDI) and similar components.

1.2 Advantages and disadvantages?
Electroless Nickel Immersion Gold has a number of advantages.
• Electroless Nickel Immersion Gold’s ability to provide a good electrical contact with low-resistance plating is one of its main benefits. As a result of its low-resistance coating, Electroless Nickel Immersion Gold is ideal for use in components of computers and telephones, which rely on stable connections.
• Electroless nickel immersion gold has a long lifespan and resists corrosion well.

Electroless Nickel Immersion Gold is not without its drawbacks.
• Electroless nickel immersion gold has the disadvantage of being easily scratched, which can reduce the finish’s useful life and quality. Due to the complexity of the process and the use of many chemicals, this method of gold plating is also more expensive than others.

Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG)

ENEPIG

1.1 What is ENEPIG?
Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG) is a combination of electroless nickel plating, electroless palladium plating and immersion gold. The combination of the three plating techniques provides superior electrical and mechanical performance over traditional plating techniques. ENEPIG is widely used in the electronic industry for circuit boards and connectors due to its superior electrical and mechanical properties.

1.2 Advantages and disadvantages?
Electroless Nickel, Electroless Palladium, and Immersion Gold each have their own set of benefits.
• ENEPIG, or electroless nickel electroless palladium immersion gold, has great adhesion to a wide variety of substrates, including aluminium, steel, stainless steel, and copper alloys.
• Furthermore, ENEPIG has great solderability and wire bondability qualities without the need for any further pre-treatments.

• Electroless Nickel Electroless Palladium Immersion Gold also has some drawbacks. Consistently requiring several hours to allow for complete plating deposition onto the substrate is a major drawback.

• Given this timeframe, the price of manufacturing these plated components can be high. As this plating method is not selective, it will cover all exposed areas, so complex geometries are out of the question.

Electrolytic Wire Bondable Gold

1.1 What is Electrolytic Wire Bondable Gold?
Gold alloyed in a way that makes it suitable for electrolytic wire bonding is known as “electrolytic wire bondable gold.” It’s a type of gold that’s been engineered to be more pliable and ductile than pure gold, making it suitable for use in the fabrication of incredibly fine and precise electrical connections. Because of its malleability, ductility, and ability to form strong electrical connections, electrolytic wire bondable gold is widely used in the production of electronic devices.

1.2 Advantages and disadvantages
Electrolytic Wire Bondable Gold has a number of benefits.
• Gold that can be bonded with electrolytic wire is durable, resistant to corrosion, and easy to maintain without breaking the bank.
• Because of its high thermal and electrical conductivity, Electrolytic Wire Bondable Gold is a solid option for permanent uses. Electrolytic Wire Bondable Gold is also a very ductile and malleable material, making it suitable for a wide range of applications.

The use of Electrolytic Wire Bondable Gold is not without its drawbacks.
• Since its conductivity drops off dramatically at higher temperatures, Electrolytic Wire Bondable Gold is not ideal for use in high-temperature applications.
• Second, because of its high melting point, Electrolytic Wire Bondable Gold is significantly more expensive than alternative materials.

Electrolytic Hard Gold

Electrolytic-Hard-Gold

1.1 What is Electrolytiv Hard Gold?
Electrolytiv Hard Gold is a type of electroplating technique which utilizes a gold-based alloy to create an extremely durable layer of gold. This type of electroplating is used to protect items from corrosion and wear, due to the hard gold alloy’s superior resistance to abrasion and tarnishing. It is an ideal choice for items that require a long-term protective finish, such as jewelry and industrial components

1.2 Advantages and disadvantages

Advantages

• High electrical conductivity, good corrosion resistance, and minimal contact resistance are just a few of the many benefits of Electrolytiv Hard Gold. Applications that need reliability in a wide range of environmental conditions would benefit from its ability to keep working even when subjected to high temperatures and humidity.
• In addition, Electrolytiv Hard Gold’s high resistance to oxidation makes it a good fit for uses where it will be subjected to high temperatures or chemicals.

Disadvantages
• Electrolytiv Hard Gold’s surface must be re-plated if it ever becomes damaged, which is a tedious and time-consuming process.
• As it is a sophisticated process involving electrolytes and electrical currents, it is also quite costly in comparison to other surface treatments.

Considerations when processing PCB surface finish

• Selecting a surface finish compatible with PCB manufacture is the first step.
• If soldering or wave soldering is going to be done, then you shouldn’t use immersion silver because it can corrode the pads.
• Third, the surface finish must be nonconductive, permit easy removal of flux residues, and offer sufficient adhesion to components.

How to choose a PCB surface finish services supplier?

How-to-choose-a-PCB-surface-finish-services-supplier

Several considerations should be taken into account while deciding on a PCB surface finish services provider.
• The supplier’s familiarity with relevant materials, procedures, and laws is a crucial qualification.
• Other considerations include the supplier’s standing in the industry, the excellence of their offerings, and their dedication to satisfying their clients. Make sure the PCB surface finish services provider you choose offers reasonable rates and meets your deadlines reliably.

Conclusion

To assure the printed circuit boards’ dependability, efficiency, and best possible protection, it is crucial to understand the process of PCB surface finish. There are several types of PCB surface treatment technologies, each with its own advantages and disadvantages. Because of the rapid evolution of PCB surface finish technology, it is crucial to keep abreast of the most recent advancements in the field to guarantee that your printed circuit boards are always of the highest quality.

FAQ

The substance that is used to coat the copper traces of a printed circuit board is referred to as a “PCB surface finish.” This coating is done to reduce oxidation and to increase solderability.

Hot Air Solder Leveling (HASL)
Lead-Free HASL
Organic Solderability Preservative (OSP)
Immersion Silver (IAg)
Immersion Tin (ISn)
Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG)
Electrolytic Wire Bondable Gold
Electrolytic Hard Gold

Printed circuit boards can be given a smooth, solderable finish with the help of a surface-mount technology procedure called hot air solder levelling (HASL).

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