Top 4 PCB Surface Finishes – Pros and Cons

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PCB Surface Finish Solutions Pros & Cons

PCB Surface finish form the interface that is critical the board while the components. In modern times, their availability that is widespread has some electronic developers. This post hopes to shed some light regarding the benefits and drawbacks associated with four many PCB that is dominant finish solutions on the market: Organic Solderability Preservative (OSP), Electrolysis Nickel Immersion Gold (ENIG), Electroplated Nickel Gold and Immersion Tin or Silver. The post that is following to Rigid Printed Circuits Boards (PCB) and Flexible Printed Circuit (FPC).

Note: PCBs are generally made from rigid materials and certainly will perhaps not fold throughout their application. FPCs are often thin making of materials capable of bending and/or movement during application. Processing and application demands dictate perhaps the PCB surface finish is electroplated, electrolysis, immersion or deposited.

Conditions that influence PCB Surface Finish Selection:
Oxidation protection of PCBs metal traces (usually copper).
Surface solderability for electrical and component attachment that is mechanical.
Surface bondability for chip mounted components using gold and aluminum wire.
Any combinations of this above.
Technical applications (age.g. stress, strains etc.).
Environmental conditions (e.g. heat, relative moisture etc.).
Technical contacts abrasion that is requiring and oxidation security.
General Discussion of Available Surface finishes
Organic Solderability Preservative (OSP)
OSP has a shelf life that is limited. Its many use that is frequent soldering once the protectant is dissipated through the procedure, therefore no additional reduction procedures are needed.

Care: as soon as removed, the copper that is bare exposed and subject to oxidation. Whenever numerous finishes are essential in the same PCB, OSP are applied over other styles of area finish (age.g. cable bonding and soldering, mechanical contact areas and soldering, etc.).

Electrolysis Nickel Immersion Gold (ENIG)

ENIG is a widely utilized surface finish for soldering, aluminum cable wedge bonding and technical contact points (connector pads, test points, etc.). The copper surface has an electrolysis nickel layer deposited (150 inches that are micro) to seal the copper. A layer of gold will be deposited to protect the nickel from oxidation and offer a solderable area to the nickel. The gold is dispersed and absorbed to the solder. The silver is an immersion process and the thickness is self-limiting (2 to 3 inches that are micro).

The nickel layer is quite brittle and can not be exposed to stress or strains into the Z axis without breaking. Flexible PCBs are especially prone to this with all certain areas subject to prospective bending supported with rigidizing materials.

Caution: Improperly controlled ENIG processing can lead to weak solder connections which could never be visible and/or end in failure. An average sign of failure is an appartment copper that is black after the attached component has been forcibly eliminated.

Electroplated Nickel Gold

This surface finish is very limited because it requires that all surfaces to be plated have to be electrically connected (i.e. an electrical charge must be present for plating) in today’s complex circuits. These interconnections must be broken to then make the circuit functional. The plated nickel is quite solderable rather than subject to the solderability dilemmas of ENIG. The plated silver does not have any restrictions on depth and certainly will support processes that are wire-bonding Thermo Compression Bonding (i.e. ball bonding).

Care: Thicker gold can lead to solder bones being too brittle whenever using lead based solders.

Immersion Tin and Immersion Silver

These processes offer solderable areas but are apt to have oxidation and issues that are tarnish impact solderability. They are not widely available or used.