Top 4 PCB Surface Finishes - Pros and Cons

PCB Surface Finish Solutions Pros & Cons PCB Surface finish form the essential interface among the board and the components. In recent years, their full-size availability has crushed a few electronic designers. This post hopes to shed a few light on the professionals and cons of the four most dominant PCB floor end solutions on the market: Organic Solderability Preservative (OSP), Electrolysis Nickel Immersion Gold (ENIG), Electroplated Nickel Gold and Immersion Tin or Silver. The following post applies to Rigid Printed Circuits Boards (PCB) and Flexible Printed Circuit (FPC). Note: PCBs are normally manufactured from inflexible materials and will not bend at some point of their software. FPCs are typically skinny and fabricated from substances able to bending and/or motion throughout application. Processing and alertness requirements dictate whether the PCB floor end is electroplated, electrolysis, immersion or deposited. Conditions that affect PCB Surface Finish Selection: Oxidation protection of PCBs steel strains (typically copper). Surface solderability for electrical and mechanical element attachment. Surface bondability for chip hooked up additives the use of gold and aluminum twine. Any combos of the above. Mechanical applications (e.G. Strain, strains and so on.). Environmental situations (e.G. Temperature, relative humidity etc.). Mechanical contacts requiring abrasion resistance and oxidation protection. General Discussion of Available Surface finishes Organic Solderability Preservative (OSP) OSP has a constrained shelf life. Its most frequent use is soldering while the protectant is dissipated for the duration of the process, as a consequence no additional elimination strategies are needed.

Caution: as soon as removed, the naked copper is exposed and subject to oxidation. When multiple finishes are wanted on the equal PCB, OSP can be carried out over different varieties of floor end (e.G. Twine bonding and soldering, mechanical contact surfaces and soldering, and so forth.). Electrolysis Nickel Immersion Gold (ENIG) ENIG is a widely used floor finish for soldering, aluminum wire wedge bonding and mechanical contact factors (connector pads, test points, and so forth.). The copper floor has an electrolysis nickel layer deposited (one hundred fifty micro inches minimal) to seal the copper. A layer of gold is then deposited to defend the nickel from oxidation and provide a solderable surface to the nickel. The gold is absorbed and dispersed into the solder. The gold is an immersion technique and the thickness is self-restricting (2 to 3 micro inches max). The nickel layer may be very brittle and cannot be subjected to strain or strains in the Z axis without cracking. Flexible PCBs are specially at risk of this with all regions concern to ability bending supported with rigidizing materials. Caution: Improperly controlled ENIG processing can result in vulnerable solder connections which might not be visible and/or bring about failure. A typical signal of failure is a flat black copper pad after the attached component has been forcibly eliminated. Electroplated Nickel Gold In trendy complicated circuits, this surface end may be very limited as it requires that every one surfaces to be plated should be electrically related (i.E. An electrical rate ought to be present for plating). These interconnections ought to then be damaged to make the circuit functional. The plated nickel could be very solderable and not situation to the solderability problems of ENIG. The plated gold has no limits on thickness and can aid twine-bonding strategies like Thermo Compression Bonding (i.E. Ball bonding). Caution: Thicker gold can result in solder joints being too brittle whilst using lead based totally solders. Immersion Tin and Immersion Silver These strategies provide solderable surfaces however tend to have oxidation and tarnish issues that impact solderability. They are not broadly used or available.