PCB Surface Finish Possibilities Pros & Cons
PCB Surface finish form the interface that is critical the board and the elements. In recent years, their availability that is widespread has some electronic designers. This post hopes to shed some light in the pros and cons for the four most principal PCB area finish solutions available on the market: Organic Solderability Preservative (OSP), Electrolysis Nickel Immersion Gold (ENIG), Electroplated Nickel Gold and Immersion Tin or Silver. The after post pertains to Rigid Printed Circuits Boards (PCB) and Flexible Printed Circuit (FPC).
Note: PCBs are often manufactured from rigid materials and can maybe not bend during their application. FPCs are thin making of materials with the capacity of bending movement that is and/or application. Processing and application demands dictate whether or not 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 technical component attachment.
Surface bondability for chip mounted components utilizing gold and aluminum cable.
Any combinations of the above.
Mechanical applications (age.g. anxiety, strains etc.).
Ecological conditions (age.g. heat, relative humidity etc.).
Mechanical contacts needing abrasion resistance and oxidation security.
General Discussion of Available Surface finishes
Organic Solderability Preservative (OSP)
OSP has a shelf life that is limited. Its many regular use is soldering when the protectant is dissipated throughout the procedure, therefore no extra elimination processes are essential.
Caution: when removed, the copper that is bare exposed and at the mercy of oxidation. When numerous finishes are needed on the same PCB, OSP may be applied over other forms of surface finish (e.g. wire bonding and soldering, mechanical contact surfaces and soldering, etc.).
Electrolysis Nickel Immersion Gold (ENIG)
ENIG is a commonly utilized surface finish for soldering, aluminum wire wedge bonding and contact that is mechanical (connector pads, test points, etc.). The copper area has an electrolysis nickel layer deposited (150 inches that are micro) to seal the copper. A layer of silver is then deposited to protect the nickel from oxidation and provide a solderable area to the nickel. The silver is dispersed and absorbed to the solder. The silver is an immersion procedure while the thickness is self-limiting (2 to 3 inches that are micro).
The nickel layer is very brittle and can not be subjected to stress or strains within the Z axis without cracking. Flexible PCBs are especially susceptible to this along with areas subject to potential bending supported with rigidizing materials.
Caution: Improperly controlled ENIG processing can result in weak solder connections which could not be visible and/or end in failure. A normal indication of failure is an appartment copper that is black following the attached component is forcibly removed.
Electroplated Nickel Gold
In today’s complex circuits, this surface finish is quite limited since it calls for that all surfaces become plated have to be electrically connected (in other words. an electric charge should be present for plating). These interconnections must be broken to then result in the circuit functional. The plated nickel is extremely solderable and never at the mercy of the solderability issues of ENIG. The plated gold has no limitations on thickness and may help processes that are wire-bonding Thermo Compression Bonding (in other words. ball bonding).
Care: Thicker silver may result in solder bones being too brittle when lead that is using solders.
Immersion Tin and Immersion Silver
These methods offer solderable surfaces but tend to have oxidation and tarnish conditions that impact solderability. They’re not widely available or used.