PCB SURFACE FINISH TYPES
IMMERSION GOLD (ENIG)Also known as Electroless nickel immersion gold (ENIG) is a type of surface finish used on printed circuit boards (PCBs). In this process, a thin layer of nickel is first deposited on the copper traces of the PCB, and then a thin layer of gold is deposited on the nickel layer, using an electroless plating process.
- Provides a flat, uniform, and solderable surface finish.
- Offers excellent corrosion and tarnish resistance.
- Provides high reliability and signal integrity due to reduced surface oxidation and increased conductivity.
- Allows for fine-pitch surface mounting technology.
- ENIG is more expensive than other surface finishes due to the additional processing steps and materials required.
- If overused, the process can cause reduced adhesion of solder mask on PCB.
- The gold layer is relatively thin, and it is not suitable for applications where repeated wire-bonding is required
IMMERSION SILVERImmersion Silver is a surface finish used for printed circuit boards (PCBs) that provides a thin layer of silver over copper. Here are some key points regarding Immersion Silver is a type of surface finish for PCBs that involves immersing the PCB in a solution containing silver ions. The resulting thin layer of silver provides a protective coating that resists corrosion and oxidation. Advantages: Immersion Silver offers several advantages over other types of PCB finishes, including:
- Good solderability: Immersion Silver provides a good surface for soldering, which helps in the production of reliable PCBs.
- High conductivity: Silver is a highly conductive material, which makes it a good choice for PCBs that require high current capabilities.
- Anti-tarnish properties: The silver layer on the PCB is resistant to tarnishing, which helps to maintain a good electrical connection over time.
- Cost: Immersion Silver is more expensive than other types of PCB finishes, which can add to the overall cost of PCB production.
- Risk of surface contamination: The silver layer on the PCB can be vulnerable to surface contamination, which can affect its performance.
- Limited shelf life: Immersion Silver has a limited shelf life, meaning that the solution used in the process must be replaced regularly to maintain its effectiveness.
Immersion TinImmersion Tin, also known as chemical tin, refers to a process of depositing a thin layer of tin onto the surface of a printed circuit board (PCB) using a chemical reaction. The thickness of the tin layer deposited is typically between 1-2 microns. Advantages:
- Excellent surface finish- Immersion tin provides a flat, uniform finish on PCBs with very little surface topology effect.
- Simple process- The immersion tin process is relatively simple and does not require complex equipment or sophisticated technology.
- Good solderability- Immersion tin provides a good surface for soldering and provides a reliable solder joint.
- Low cost – Immersion tin is relatively inexpensive compared to other surface finish options.
- Limited shelf life- The immersion tin solution has a limited shelf life and becomes less effective with time, resulting in inconsistent tin thickness and non-uniformity on the PCB surface.
- Thermal stress- Immersion tin can be thermally stressed during subsequent processing, which can lead to undesirable growth of tin whiskers.
- Brittle – Tin is relatively brittle compared to other metals, which can cause cracking or flaking if the PCB is excessively flexed.
- Compatibility issues- Immersion tin is not compatible with lead-free soldering processes, which may limit its use in certain industries or applications.
HASLPCB HASL stands for “Hot Air Solder Leveling,” which is a surface finish technology used in the production of printed circuit boards (PCBs). In the HASL process, the board is coated with a layer of molten solder, which is then leveled off with hot air to produce a flat, uniform surface. Advantages:
- Cost-effective: HASL is a relatively low-cost surface finish technology.
- Good solderability: HASL provides good solderability and is suitable for most through-hole components.
- Robust: The thick layer of solder applied during the HASL process provides a durable surface finish that can withstand multiple reflow cycles.
- Uneven surface: The hot air leveling process can produce an uneven surface, which can cause problems with component placement and solder joint formation.
- Potential for thermal shock: The thick layer of solder applied during the HASL process can cause thermal shock to components during the reflow process, which can lead to failures.
- Not suitable for fine pitch components: HASL is not suitable for fine pitch components or PCBs with high-density surface mount components.
OSPA PCB surface finish comparison based on green appeal leaves no questions. The Organic Solderability Preservative (OSP) doesn’t introduce any toxins into the process. Instead, an organic compound is used that bonds naturally with copper, creating an organometallic layer that protects against corrosion. Advantages:
- Cost-effective: OSP is less expensive compared to other types of surface finishes like gold plating or electroless nickel immersion gold (ENIG).
- Environmentally friendly: OSP is a water-based surface finish and does not require harsh chemicals, making it environmentally friendly.
- Good surface planarity: The surface of OSP-coated PCBs is relatively smooth and flat, making it easy to solder components onto them.
- Suitable for fine-pitch devices: OSP coating ensures high-quality solderability and coplanarity of fine-pitch devices.
- Limited shelf life: The shelf life of OSP is limited, and it degrades over time. Therefore, PCB manufacturers need to use it within a specific time frame.
- Susceptible to oxidation: OSP is susceptible to oxidation; hence, it requires proper storage and handling to avoid any contamination.
- Limited solderability: The solderability of OSP-coated PCBs may deteriorate after multiple assembly cycles or prolonged periods of storage.
- Inconsistent results: The quality of OSP may vary due to its process sensitivity, which can lead to inconsistent results.
HARD GOLDAmong the most expensive PCB surface finish, hard gold applications are extremely durable and enjoy a long shelf life. They’re commonly reserved for components that expect to get a substantial amount of use, with normal thickness rates ranging from 30 μin gold over 100 μin nickel to 50 μin gold over 100 μin nickel. It’s not often used for soldering points, due to poor solderability. Hard gold is typically used for edge connectors, battery contacts, and some test boards.
- Hard gold OSP provides superior electrical conductivity compared to traditional OSP.
- It has excellent solderability, ensuring that components can be easily soldered to the PCB.
- Hard gold OSP has a longer shelf life and is more chemically resistant compared to other OSP coatings.
- It is a cost-effective alternative to conventional electroplating.
- Hard gold OSP eliminates the need for a nickel barrier layer, which reduces the complexity of the PCB manufacturing process.
- The thickness of hard gold OSP is limited and may not work for certain applications where thicker plating is required.
- The process may require additional process steps in order to achieve the desired thickness, which can drive up production costs.
- It may be more challenging to achieve consistent gold thickness across the PCB.
- Some suppliers may not offer hard gold OSP as an option, limiting service options for certain projects.