PCB Surface Finish

The surface finish on a PCB protects the copper pattern from oxidation and deterioration. The surface finishes must provide perfect solderability when the assembly components are placed and welded on the board.
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With more than 20 years in the PCB industry, ICAPE Group has developed a solid knowledge of the different types of surface finishes. With our 35 partner factories in Asia, ICAPE Group can fully manage and control all the stages of the PCB manufacturing process, which guarantees complete satisfaction for our 3000+ customers worldwide.

Lead Free Hot Air Solder Leveling - LF HASL

The panels are immersed in a bath of molten tin and the excess is removed with high-pressurized hot air (air knives) through the panels. Immersing the board in such a hot bath will help identify defects or damage before assembling the components. Due to high-density boards, this process leaves uneven surfaces, can create electrical short circuits and is not suitable for fine-pitch components.

Pros

. Excellent solderability
. Cost-efficient
. Widely available technology

Cons

. Possible thickness difference on the surface
. Not suitable for fine-pitch components
. Abrasive with copper, depending on the alloy
. Thermal stress on the board

Immersion Tin

Immersion Tin or ISn, is a chemically deposited metallic finish, applied to the metal base of the PCB. The typical thickness of 1µm gives this finish a perfect flatness but also makes it very delicate. Copper and Tin can create an intermetallic layer which reduces the shelf life to 6 months. Generally, this finish ensures high reliability and is suitable for fine pitch and small components.

Pros

. Perfect flatness
. No Lead used
. Possible rework
. Top choice for press fit

Cons

. Sensitive, possible damage during handling
. Environmental problems with Thiourea used in the process

Immersion Silver Ag

Immersion Silver is a chemical process that ensures excellent surface flatness. The thickness of the finish varies from 0.12 to 0.40 µm and the shelf life is 6 months. This technology is weldable with aluminum wire, but it also brings constraints such as sensitivity to handling, the requirement for special packaging, and the reduced supply chain options to support this finish.

Pros

. Excellent Flatness
. Perfect for fine pitch and small components
. Competitive price
. No lead
. Rework possible
. Aluminium wire bondable

Cons

. Sensitive to handling
. Reduced supply chain options
. Short window between operations

ENIG – Electroless Nickel Immersion Gold

ENIG is a double-layer metallic coating with nickel and gold. It is a barrier for copper and a surface where the components are soldered. Then, 0.05 microns of pure gold is applied to the boards to protect the nickel during storage time. It is a lead-free process that offers a very flat surface and excellent solderability as well as reliability.

Pros

. Flat surfaces
. Strong solderability
. Bonding friendly

Cons

. Not cost-effective
. Electroless nickel/phosphorous can have undesirable magnetic properties
. Aluminum wire bondable, but not gold wire
. Oxidation of Nickel can cause a soldering failure

ENEPIG – Electroless Nickel Electroless Palladium Immersion Gold

The process is the same as for the ENIG finish. But despite being a high-quality finish, ENIG, due to nickel oxidation, can cause failure when it comes to soldering the components to the board. To eliminate this risk, it is possible to apply a layer of palladium between nickel and gold, which resists corrosion. However, the solderability could be affected if the palladium layer is too thick.

Pros

. Flat surfaces
. Strong solderability
. Bonding friendly
. The palladium layer eliminates potential corrosion from the immersion reaction

Cons

. Expensive technology
. Electroless nickel/phosphorous can have undesirable magnetic properties
. Solderability performance is reduced due to too thick palladium layer
. Slower to be wet

OSP - Organic Solderability Preservative

OSP is a water-based finish, applied in a bath, and generally used for copper pads. This organic solder mask bonds to copper and protects it from corrosion. However, this is not the most robust finish, and the shelf life is short. This process is environmentally friendly.

Pros

. Flatness
. Rework possible
. Clean and environmentally friendly
. Low cost

Cons

. Limited Shelf life
. Limited thermal cycles
. Difficult to inspect
. Request relatively aggressive flux at assembly

Any questions?

There is an ICAPE Group team close to you and your business. All around the world, our business units are staffed with native experts available to answer all your questions. Contact us today!

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