PCB Surface Finish Solutions Pros & Cons

PCB Surface finish form the interface that is critical the board while the components. In recent years, their availability that is widespread has some electronic developers. This post hopes to shed some light in the advantages and disadvantages associated with the 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 usually made of rigid materials and can perhaps not bend throughout their application. FPCs are often thin making of materials with the capacity of bending and/or motion during application. Processing and application requirements dictate if 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 utilizing gold and aluminum cable.
Any combinations associated with the above.
Technical applications (age.g. anxiety, strains etc.).
Environmental conditions (e.g. temperature, general moisture etc.).
Technical contacts abrasion that is requiring and oxidation protection.
General Discussion of Available Surface finishes
Organic Solderability Preservative (OSP)
OSP has a limited rack life. Its many regular usage is soldering when the protectant is dissipated through the procedure, hence no extra treatment procedures are expected.

Caution: as soon as removed, the bare copper is exposed and susceptible to oxidation. When numerous finishes are needed in the same PCB, OSP are used over other kinds of surface finish (age.g. wire bonding and soldering, mechanical contact surfaces and soldering, etc.).

Electrolysis Nickel Immersion Gold (ENIG)

ENIG is a widely used 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 guard the nickel from oxidation and supply a surface that is solderable the nickel. The silver is dispersed and absorbed into the solder. The gold is an immersion procedure as well as the depth is self-limiting (two to three inches that are micro).

The nickel layer is quite brittle and can’t be exposed to stress or strains in the Z axis without breaking. Flexible PCBs are specifically vunerable to this with all certain areas at the mercy of possible bending supported with rigidizing materials.

Caution: Improperly controlled ENIG processing can lead to weak solder connections that might not be noticeable and/or result in failure. A typical indication of failure is an appartment black copper pad following the connected 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 then be broken to make the circuit practical. The plated nickel is quite solderable and never susceptible to the solderability dilemmas of ENIG. The plated gold doesn’t have restrictions on thickness and can support wire-bonding procedures like Thermo Compression Bonding (in other words. ball bonding).

Care: Thicker silver may result in solder joints being too brittle whenever making use of lead based solders.

Immersion Tin and Immersion Silver

These processes offer solderable areas but tend to have oxidation and tarnish conditions that effect solderability. They’re not commonly available or used.